Latham_5_Accessories Controlling the Flow of Steam, Air, Oil and Water

8/7/2019 Latham_5_Accessories Controlling the Flow of Steam, Air, Oil and Water

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CHAPTER VACCESSORIES CONTROLLING T HE FLOW O F STEAM,AIR, OIL, AND WATER

6-1 . ACCESSORIES CONTROLLING THE FLOWOF STEAM.

Those accessories controlling the flow of s te amto be discussed ill this test are:

1. Maill Steam Stops coilt,rolling flow to themaill engines.

2. Auxiliary Ste am Strops controllillg flow t oauxiliary machinery.

3. TTalves controlling s team flow through th esuperheater and desuperheaters and to th e t,urbo-genera,tor.5-2. MAIN STEAM S TO P VALVE.

The main steam s top valve is located a t or nearthe stlearn outlet of the boiler d rum on sat ura tedsteam boilers, and a t or near t he superheateroutlet of boilers fitted with superheaters, to con-nect and disconilect the boiler and the main

stlearn sys tem. Since the stop valve closes againstboiler pressure, the resistance to closing increasesas the cross-sectional area of t,he valve opeiliilgdecreases, reaching a, maximum just a t t,he in-st an t of complete closure. This makes i t ex-tremely difficult to close a.n ordinary screw-down t ype of va lve on a high-pressure boiler.A mechanism, such as toggles or gears, to increaseth e mechallical advantage, may be used t o assistva,lve closure. A toggle operated globe valve de-signed for high pressure &earn servicz is shownin Fig. 5-1. With the toggle operating gear, t,hemechanical adva ntage between tjhe handwheeland the va.lve stem increases as the valve ap-proaches t he fully closed positmion, o th at th emaximum force is exerted on th e stem a t thesame ii~stal l tha t th e resistance reaches its maxi-mum value. For safety and for damage control

' OUTLET TO

DRAIN CONNECl'IONSFIG. 6-1.Main Steam Stop Valve.


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MARINE ENGINEERING

purposes, main steam stop valves are fitted withdis tant cont,rol gear, by means of which theycan be closed or opened from the deck above orfrom an adjacent compartmei~t.

The main steam stops are used either fullyopen or fully closed. The seating surfaces onth e valve disc an d seat of modern high pressuresteam valves usually are made of th e very hard,erosion-resisting alloy, stellite. The seat and discare mailufac,tured of steel and turned t,o approxi-mate size. A shallonr groove is cu t in each. Thesegrooves are filled with stellite by fusing stellitewelding rod met,al into the grooves. The meldmetal is turned down in a lathe, using a grindingattachment on the lathe to remove the excessstellite and attain a highly polished surface.

Many main steam stop valves have bypassconnections built in to the valve body (not showniu Fig. 5-1). The by-pass coilnectioil consists ofa small line and v a l ~ eeading f rom the low-er sideof the valve disc (inlet side) t o the upper or stemside of t he disc (outlet side). When the propul-sion plant is being warmed up this by-pass isopened, allo~ving team to warm t he steam lincslo~vly.f such a valve were not provided, t,hemain steam stop itself would have to be used, in-creasing th e danger of crodiilg the valve seat andthe possibility of warming the s tea m lines tooquickly, causing leaks resu lti i~g rom ullequal ex-pansion. A drain connection is provided t o drainwater which has condensed and collectcd in thevalve. Should water be carried by the steam tothe main engines when the valve is opened, it islikely t o damngc the tu rbine blading. Valves hav-ing drain connections a,re illstalled w;it,h t,he draincoilnections on the under side of the valve body.5-3. AUXILIARY ST EAM ST O P VALVE.

A11 auxiliary steam stop valve, of similar con-struction but smaller size than the main steamstop valve, is installed for the purpose of con-necting or discon~lecting he boilcr t o o r frornthe auxiliary steam line. In saturated steamboilers and in integral controlled superheatboilers, the auxiliary stearn stop is connected t othe auxiliary steam outle t of the boiler steamdrum. On integral uncoiltrolled superheaterboilers, the auxiliary steam stop is located at, thedesuperheater outlet connection. The auxiliary

steam stop, like the main steam stop, always iseither fully opened or fully closed.

Depending on thc size and desigil of t he boiler,the auxiliary steam stop may or may no t be tog-gle, gear, etc., operated and mag or may not beof the stellited valve seat construction. I n mostcases it is fitt,ed with distant co~l trol ear, per-mitting operation of t he valve from outside thefireroom space. Also, on most installations, thereis a guarding v a l ~ ell the ausiliary steam linewhich is placed adjacent tlo tlhe auxiliary st eamstop valve and is not distant operated. Thisarrangement allows the boiler to be cut off theauxiliary steam line from outside the fil.eroomspace hut does not allow it to be pu t on the lineunless the guarding valve is opened in the fire-room.6-4. O TH ER V A LVES C O N TR O LL IN G STEA MF L O W .

Boilers with uilcontrolled ttype superheaters,Fig. 5-2, require "cooling stea.mV for the pro-tection of t he superheate r tubes when lightingoff (no flow conditioils in the superheater). Whena boiler is lighted-off cold, for a period of time,no steam is available within the drum to passthrough the superheater and, therefore, there isno means of carrying off the heat absorbed by thesuperheater tubes from t,he gases of combustion.To provide a flow of "cooling1' steam through the~uperheat~erubes, prior to lighting fires underthe cold boiler, steam from another steamingboiler (from the shipyard or tender, if there isno other steaming boiler) sometimes is bled fromthe auxiliary steam line, through the superheaterprotection steam valve (S.P.S.), to the super-heater inlet. The steam passes through thesuperheater tubes (S.H.), out the superheateroutlet, through t he desuperheater (D.S.H.) and,thencc, into the auxiliary eshaust line via thesuperheater protection exhaust valve (S.P.E.).After steam has formed in the boiler drum andthe pressure has built u p t o about 100 psi, thesuperheater protection steam valve may beclosed. The boiler t hen furnishes its onrn protec-tion steam. After the boiler has been cut-in oilthe auxiliary steam line, the superheater protec-tion exhaust valve may be closed. Thc super-heater protection exhaust valve also is openedwhen a boiler is secured and remains open to


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AC CE SS O RI ES COATTROLLIATG FLO W

FIG. 6-2. Destroyer-Escort Boiler (Modified D-Type) with Uncontrolled, Integral, Interdeck, ConvectionType Superheater and Economizer.provide a cooling flow of steam throug h th e super-heater tubes as long as the furnace brick wallsradiate heat.

Most naval boiler iilstallatioils have a sepa-rate system for supplying steam to the turbo-generators. Steam for the turbogenerators istaken from the main steam line just after thesuperheater and prior to the main steam stop.This arrangement allows th e use of superheatedsteam in th e turbogenerator, witho ut pressuriz-ing the larger main steam line. T he valve whichcoiltrols this steam flow is called the turbogener-ato r steam stop, and is of coilstrl~ctionsimilarto th e auxiliary steam stop .5-6. ACCESSORIES CONTROLLING THE FLOW OF

IRAir for combustion is drawn through ducts

leading from topside locatiolls protected from en-trance of sea water , in case of heavy seas. Air isdrawn into turbine driven fans, called forceddraft blowers, m~hichdischarge air through flaps(similar in construction t,o Veiletian blinds) lo-cated in th e du ct leading t o th e boiler double cas-

ing. These flaps allow air to pass in only one direc-tion a nd a re necessary, when two or more forceddraft blowers are provided for each boiler, toprevent air from flowing backwards from theboiler double casing through the idle blowers,when all blowers are not in opera tion.

Air enters the furnace through an air registerhaving doors capable of being operated from th eboiler front. The register doors permit the en-trance of air to th e operating burners an d ex-clude air from the unlighted burners. Close con-trol of t he air supply may be attain ed b y varyingth e speed of t he forced dra ft blowers thro ugh ma-~iipulationof th e blower thro ttle (valve whichcontrols steam to blower turbines). Each boilerhas one blower throttle valve which coiltrols allforced draft blowers for that boiler.

Motor-driven forced dra ft blowers, of small ca-pacity, are illstalled in some vessels and are in-tended for in-por t use or for lighting off purposes.These blowers can be operated from an emer-gency power system or diesel generators t o facili-ta te lighting off a cold plan t when the re is nosteam available t o run th e turbogenerators.


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MARINE ENGINEERING6-6. ACCESSORIES CONTROLLING THE FLOWOF OIL. (SEE FIG. 6-15 FOR DIAGRAMMATICDRAWING OF A FUEL OIL SYSTEM.) '

Oil for combustioil is pumped by the fuel oilservice pump from the fuel oil service tank tothe burners for consumption in t he furnace. Thefuel oil passes first through a fuel oil meter whichmeasures the amount of fuel oil used in theboilers. It is a positive displacemeilt type meter~vhich ecords, in gallons, the amouilt of oil pass-ing through the fuel line. This meter is muchlike those comnlonly used in the city matersystems. For proper atomization, the fuel firstmust be heated ill the fuel oil heater to the re-quired viscositj~.The fuel oil heater is a heatexchange uni t consistiilg of corlcentric tubesthrough which the fuel oil to be heated and theheating steam pass. Fuel oil flows through the an-nuhis between the outer and iililer tubes. Stea.mis passed through the inner tube in the oppositedirection from the oil flow and gives off its heatto the fuel oil.

The fuel oil a.lso must be strained to preveiltsolid particles from scoring or clogging the atom-izing elements. A basket type strainer in theline leading to the burners provides this service.It is constructed so tha.t there are two completeunits through which the oil may pass. This provi-sion allows for chail~lelinghe fuel oil through-oneunit while the other strainer is cleailsed a.nd read-ied for use.

Oil leaving the fuel oil strainer passes througha ga te valve capable of being closed quickly inan emergency. This valve is springloaded and toclose it, when the boiler fires must be shut downrapidly, one needs only to release the handle.The fuel oil manifold, located on the boilerfront, receives the oil and distributes it to thevarious burners via the root valves. Each burnerhas a root valve which must be opeiled prior tooperating that burner. The fuel oil atomizer as-sembly receives the oil and atomizes it for burn-ing in the furnace. (A special type of a tomizerfor smoke making is an accessory which is pecul-iar to naval boilers.) The various parts of theatomizer \?rill be studied in Chapter VI.

There are several stop valves to isolate sec-tions of th e fuel oil system. One valve, located inthe fuel oil service line just after the pump dis-charge, is a quick-closing valve which call be op-

erated remotely to shut down the fires and stopth e flow of fuel oil in emergencies ~1-henhe fire-room must be abandoned. Other valves are usedto isolate or by-pass t he fuel oil meter when thefuel oil is being recirculated and not being con-sumed in th e furnace, to by-pass portioils or all ofthe fuel oil heater in order to regulate properlythe temperature of the fuel oil, to recirculate oilback to the pump suction mrheil warming thefuel oil to proper lighting off temperature inpreparatioil for lighting off t he boiler, and toenable rapid clearing of coiltaminated oil fromthe fuel lines, when such coiltamiilated oil causesthe furnace fires to be extinguished.6-7. ACCESSORIES CONTROLLING T HE FLO WOF FEED WATER

The boiler feed system which supplies materto the boiler was described in Chapter I . Furtherst udy of th e feed pumps is beyond the scope ofthis text . Th e valves and coiltrols associated withfeeding the boiler ~vill e discussed in the follo\i--ing order :

1. Feed stop and check valve2. Single element feed mater regulators3. Two element feed water regulators4. Three element feed water regulators5 . Feed water regulator valves

6-8. FE ED ST OP AND CHECK VALVES.The feed stop and check valves coiltrol the

flow of feed nrate r to the boiler. Fig. 5-3 illus-trates a type of combiiled feed stop-a,nd-checkvalve installed on na.i~alboilers. The valve bodyconsists of either a single casting, housing boththe stop valve and t he check valve, or two sepa-rate, flanged castings bolted together. The com-bined valve body is secured to {;he steam drum(or economizer inlet line) so that the stop valvealways lies bet~i~eenhe check valve and thedrum . This permits closing th e stop valve shouldth e check valve fail to function, or if emergencyrepairs to th e check valve or ally part of the feedsystem are required while the boiler is underpressure or when the boiler is dead but is filledwith mater. When the boiler is steaming, the stopvalve of the feed system in use remains fullyopened a t all times, and the check valve is usedto regulate the feed mater supply to the boiler.Since the pressure in the boiler drum acts on the


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ACCESSORIES CONTROLLING FLOW

FIG. 6-3. Combined Fee d Stop and Check Valve.

top of th e checli valvc disc, the check valve willclose if feed line pressure drops below the d rumpressure. When feed line pressure rises abovedrum pressure, the valve opens, admitting waterto the drum. It is necessary t,o mahltain the pres-sure in the feed system above that in the hoiler111order to feed th e hoilcr. W ith t he feed pressureso maiatained, the rate of water flow illto theholler is controlled by regulating th e amourlt ofopei~illg f the check valve. This is accon~plishedby turning th e check valve h and ~vheel, t h l ~ smoviilg the valve stem in or out, so that theflanged end of the valve stem l imits th e distancethe valve call open.

in case of casualty t o either the valve or the feedwater system in use.

In boilers fitted with economizers, thc fcedstop-and-check valves discharge to the economiz-er inlet. In this case, a lift check valve usually isinstalled between the ecollomizer outlet line andthe internal feed pipe connection. This checkvalve permits water to flow in hut one direction;into the boiler. Should damag e occur to t he ecoll-omizer, the check valve closcs, preventing t lhewater and steam in the boiler from flowing backand out t,hrough the ruptured economizer.6-9. A U T O M A T I C F E E D W A T E R R E G U L A T O R S .

TM-o ombined feed stop-and-check valves ma y Durin g the era of moderate steam pressures,be installed on a boiler. When two cornbilled regulators actuated b y floats in the steam drumvalves are installed, each is connected t o a sepa- ur in the feed system hot-well were employed inrate feed line, one to t he main feed line, th e other a few merchan t vessels. With th e adven t of pres-t o th e auxiliary feed line. Both discharge to the sures over 400 psi, this type of regulator provedintenla1 feed pipc con~lection.Only one combined inadequate. Mod ern boiler design has resulteci infeed stop-and-check valve is in use a t ally given reducing the rat io of contained water to "ivatcrtime, the other being available fo r immediate use rate." (Wat er rate is similar in meaning to steam


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5-6 M A R I N E E N G I N E E R I N Gra te and refers to the amount of water fed to a 2. Thermo-expansionboiler to replace the amount evaporated per unit 3 . Marine rhomboidof time.) In a modern boiler, safety, as well asefficient operation, demands an accurate, rapidresponse in feedmater flow. To meet this demand,automatic feedwater regulators are being usedin increasing numbers.Automatic feedwater (boiler water level) regu-lators replace or supplement the feed checkvalves. Feed check valve opening is adjustedmanually by the water tender stationed a t thevalve in response to water level changes in thegage glass while automatic feedwater regulatorsare controlled by reactions of t he boiler t ochanges in steam demand, a s reflected by oneor more of the following:

Thermo-Hydraulic Feedwater Regulator.-The thermo-hydraulic feed water regulator con-sists of a generator and a regulator valve (Fig.5 4 ) . The generator is a tube within a tube.The inner tube is coilnected to the steam drumwith one end above and one end below the waterlevel, so that any change in water level in thedrum correspondi~lgly changes the water levelinside the tube. The outer tube forms an ailnulusbetween itself and the inner tube and, togetherwith the connecting copper tubing and t he metalbellows of the regulating valve, forms a closedsystem. Attached to the outer tube are fins toassist cooling by heat radiation, thereby i m ~ r o v -" - A1. Steam drum water level ing speed of response of th e system to temper-

2. Steam rate leaving the boiler ature changes.3 . Feed water rate entering the boiler The closed system is filled with water to theThere are three general types of automatic

feedwater regulators, which differ only in thenumber of co~ltrolling actors used t o regulatethe amount of water entering the boiler. Theseare :

T y p e Con troll ing factor ( s )1. Single Element Steam dru m water level2 . Two Elemen t Steam flow from boiler and steamdru m wate r level3. Three Element m7ater flow to boiler, steam flow

from boiler, and steam drumwater level

When properly maintained and operated,automatic feedwater regulators have the follow-ing advantages over manual operation, becauseof more even water level regulation :

1. Higher operating efficiencies2. Reduced wear on valves3 . Smoother control of steam pressure4. Less moisture carry-over5. Continued safe operation during battle in

event of personnel casualties.6-10. SINGLE ELEMENT FEEDWATER REGULA-TORS.

There are three types of single element feed-water regulators used in the Navy:

filling plug a t the top of the outer tube. Theinner tube, open to water and steam in thesteam drum, contains water and steam at amuch higher temperature than the water in theouter tube. Therefore, the inner tube continuallytransfers heat which is absorbed by the waterin the closed system. A portion of the water in theclosed system is vaporized, forming a vapor pres-sure which eserts a positive pressure on the closedsystem. The pressure in the closed system actsupon th e bellows of t he regulating valve which,in turn , operates the regulating valve itself. Thetemperature of the steam in the inner tube willbe equal to the steam temperature in the steamdrum, since all steam in the entire steam-watersystem is a t saturation temperature and any cool-ing would cause condeizsation in the piping lead-ing from the steam d rum t o the inner tube. Thewater temperature in th e inner tube is somewhatless tha n tha t of t he water and steam in the steamdrum because of the exposed run of piping andattached radiating fins.

Heat transfer from the steam in the inner tubeto the water in the closed system occurs at agreater rate than does heat transfer from thewater in the inner tube to the water in the closedsystem for three reasons. :

1. The steam is at a higher temperature thanthe water, as explained above.

2. Heat transfer is retarded in the lower por-tion of the inner tube, contailling water, because


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ACCESSORIES CONTROLLING FLOW 5-7

STEAM IN CLOSED SYSTEM

WATER AT BOILER PRESS

Courtesy Ba i l e y Blrter Co.FIG. 6 4 . Thermo Hydraulic Feed Water Regulator.

f the presence of a stagnant film of water along

3. Heat transfer is accelerated in the upperion of the inner tube, containing steam,

f steam condensation trickling rap-nt film on one side of the inner tube mall, creat-

better heat transfer conditions.Changes in the water level in the steam drum

change the length of water and steam columnsin the inner tube, consequently changing the heattransfer area of each portion of the tube. There-fore, the total heat liberated from the inner tubedepends on the water level in the steam drum.The regulating elenlent (generator) is inclined atan angle of approximately 20' to increase thelength of t he tube so as to magnify the effect ofchanges in water level. The amount of hea t liber-ated from the inner tube controls the tempera-


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ture of the closed system and thus coiltrols th evapor pressure iir the closed system. The lowerthe water le ~ ~ e ln the iililer tube, t he greater willbe the heat transfer aiid the temperature andpressure in the closed system will increase. Thepressure is transmit ted through the copper tubingto the effective area of the bellows. The productof this pressure times the effective area of the bel-1 0 ~ ~ sxerts a force which opposes the regulatorvalve spriiig. Tihen the bellows and the valvespring orces are in equilib riun ~,he regulator valvehas a definite position, uncovering a certain valvearea through which the water under feed pumppressure can flow. The regulator valve is a bal-anced valve, so constructed that the pressureabove and below the double valve disc are thesame and very little force is required to changethe valve setting. A change in closed systempressure of 1 psi 15 ill move the regulating valve1/16 of an inch. This pressure change can occur~ ~ i t h i nwo or three secoilds as a result of a slightvaiia tion of boiler level. Wi th a higher waterlevel in the inner tube, the temperature in theclosed system decreases, some coildeilsatioil ofwater vapor occurs, and the vapor pressure de-creases. Th e bello~vs orce opposing th e valvespring decreases and th e regulator valve unco~lersa smaller valve area.

The volume of water in the closed system a tdifferent temperatures is proportioned so that,~~rhei lhe TT-aterevel in the steam drum is highand th e inner generator tube is entirely full ofwater, the regulator valve is in its extreme up-ward position and at miilimum opening. Theregulator valve is co~istruct ed o that an upwardmovement closes the openings in the ports of t he~ ~ a l v eage through which tlie water flows. Thevalve should never be allowed to close completelycausing a cessation of water flow which eildailgersthe economizer. When the water level is so lorn.that the entire iiliier tube is filled with steam,the regulator valve rill be opened wide.

Th e operation of th e system is as follonrs: As-sume a load that requires a partial regulator~ ~ a l v epening. If the steam rate being drawn offis increased, the water level in the boiler is low-ered. (Neglect the effect of STT-ell nd shrinkwhich will be discussed i11 a later art icle.) As th ewater level falls in the drum and the inner tube,a rise in pressure in the closed system follo~vs,as discussed above. Equilibrium is not reached

until the regulator valve is opened sufficieiltlyto replace the water being evaporated in theboiler. Equilibrium ill be reached a t a lowerwater level than existed previously since moresteam is being used and to replace the waterevaporated, a larger quant ity of feed water isneeded. This requires th at the regulator ~ ~ a l v ereach equilibrium a t a wider opening to provideth e proper amouilt of water . I11 order for it tJoreach equilibrium a t a wider opening, the vaporpressure in the closed system must be higher th anit was previously to couilteract the spring pres-sure tending t o close the valve. This, in turn , re-quires a lower water level in the steam drum andthe inner tube t o provide sufficient heat transfer,from a longer columil of s team, to produce thehigher vapor pressure in the closed system.

Now assume a full load condition. The waterlevel drops still further a s a larger quantity ofsteam is m~ithdra~vnrom the boiler (again neg-lecting t he effect of wvell) and t he increasedpressure in the closed syst>einopens the valve stillfur ther until equilibrium again is reached. Opera-tion of this system depends on a variable waterlevel, each level correspoildiilg t o a definite poweroutput and a definite valve opening. I11 otherT T T O ~ ~ S ,or each steam generation rate, a different,water level is mailltailled by the regulator. Thedifference bet~veen o load a nd full load is about4 inches in th e boiler drum.

When this ty pe of regulator first was used formarine service, trouble was ellcountered as aresult of t he rolling and pitching of the ship.Rolling caused a consta.nt surging of water andsteam in th e iililer tube of t he generator and thesteam touched a larger, bu t coilstantly changing,percentage of t he tube. This surging raised th etemperature of the closed system and had t hesame effect oil the regulator valve as did I O TV wa-ter. This condition was improved greatly by theinsertion of a smal l orifice in the steam line lead-ing t o th e generator, restricting the surging andaiding in maintenance of a more stab le waterlevel in the inner t ube during heavy seas.

Thermo-Expansion Feed Water Regulator.-The therino-expansion feed water regulator firstmrill be described i n it s simplest form, the straighttube thermostat (Fig. 5-5). I11 this system, athermostat, consisting of a steel tube about fourfeet long is placed aloilgside the drum. Th e top isopen t o the steam space and th e bottom is open


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ACCESSORIES CONTROLLING FLOW 5-0

Cour tesy Northern Equifimct: t Co .FIG. 6-6.Thermo-Expansion Feed Water Regulator with Straight Tube Thermostat.

to the water space. The upper end of the thermo-stat is connected mechanically by linkages to aregulating valve in the feed line. The water levelin the tube approximates the level of the water inthe boiler.

The tube, being filled with water and steamwhich is much hotter th an the surrounding at-mosphere, coiltinually radiates heat. The trans-fer of heat is as described for the thermo-hy-draulic regulator and t he upper end of the tube,which is exposed to the steam, is a t a higher tem-perature than the lower part, which is exposedto the water. By virtue of its coefficient of ex-pansion, the thermostat length varies with itstemperature, xvhich increases as the water levelis lowered and decreases as the water level israised. The tuhe is fixed at the lower end andelongatioil of t he tube causes a bell crank a t theupper end t,o turn counterclockwise. As the bellcrank arm rotates, it turns the valve arm andopens the regulating valve, permittillg morewater to flow into the boiler. As the water levelrises, the steam space in the tube decreases, lessheat is given off, and the tuhe contracts. Thevalve opening is reduced and less water flows

illto the boiler. The water level-steaming ratecharacteristics of the thermo-expansion typefeed water regulator are similar to those of thethermo-hydraulic type. Both depend on a vari-able water level, each level corresponding to adefinite power output and a definite valve open-ing. Provision is made for adjusting the waterlevel for any firing rate by means of an adjust-ment nut a t the fixed end of the thermostat tube.Turning this nut has t he same effect as elongat-ing or shortening the thermostat tube.

Marine Rhomboid Feed Water Regulator.-Th e thermo-expansion type of regulator describedabove is unsatisfactory when coilsidered from thestandpoiilt of pitching and rolling. Its principleof operation has been discussed to provide abackground for the esplailation of the marillerhomboid feed water regulator, which takes itsname from the shape of the linkage which trans-mit,~ otion to the regulator valve. The marinerhomboid thermostat, Fig. 5-6, is mounted infront of the hoiler drum and co~isist sf txvo stain-less steel tuhes inclined a t 45' angles and mount-ed in a rigid triangular shaped channel frame.The upper ends are connected to the steam space


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and the lower ends to the water space. For a boil-er drum located in a fore-and-aft direction, thethermostat is installed with its center line on thevertical center line of the drum. The thermosta tis set a t an elevation such t ha t, for normal boilerwater level, the upper halves of the expansiontubes are filled with steam and the lower halveswith water.

The water level rises and falls correspondinglyin the expansion tubes as the level in the boilerdrum changes. The tubes contract or expand asthe water level rises or falls, because of thechanging average tube temperature. The reasonfor the change in length is similar to that ex-plained above for the straight tube thermostat.Levers A and B, shown in Fig 5-6, magnify themotion of the two expansion tubes. Their mo-tions are added and further multiplied by leverC which actuates the feed water control valve.To illustrate, using Fig. 5-6, should the waterlevel drop in the drum, the level in the expansiontubes falls a corresponding amount. This in-creases the average temperature of the expansiontubes an d tube expansion causes right-hand mo-tion of lever A an d left-hand motion of lever B.The resultant of these motions is a clock15 lse ordownwards rotation of lever C. The feed watercontrol valve is arranged to open as C movesdownward, thereby increasing feed water flow.When the ship rolls, the quantity of water in thedrum at that instant does not change but thelevel in each leg of tlle thermostat changes, asshown ill Fig. 5-6. As the sh ip rolls t o the right,the water level in the left-hand expansion tubedrops, while the level in the right-hand tuberises. This causes right-hand motion of leversA and B. Since both A and B move in the samedirection, there is no resul tant rotation of C;thus, the control valve opening and feed waterflow are not affected by rolling of the ship. .Single element feed water regulators are in-tended primarily for th e purpose of keeping theboilers supplied with water under battle condi-tions when manual feeding may become difficultor inlpossible. BuSh ipJ s Manual instructs all en-gineering officers that single element feed waterregulators :

1. Shall be cut in immediately when "generalC o u r te s y N o r t h ~ r r iEqzriprnmt Cu. quarters,' is sounded'

FIG. 5-6. Marine Rhomboid Thermo- 2. If the regulators are not employed con-Expansion Feed Water Regulator. stantly, they shall be operated in full control


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ACCESSORIES COXTROLLING FLOW 5-11

of the boilers for a reasonable period each da y than previously. Similarly, the water level willto insure that t,hey will be in operable condition momentarily fall when the firing rate is decreasedwhen cu t in. and then rise rapidly unless the ra te of feeding

3. Control elements shall be cut in a t all times is decreased.and shall be blown down regularly in accordancc When feeding t,he boiler by hand, i t is difficultwith illstructions in manufacturer's instruction to maintain the apparent water level constantbooks. under maneuvering collditiolls and a considerable

Single element feed watcr regulators may beused a t other times but, shall not b e relied u ponentirely. The feed check valve remains the chiefreliance in maintaining the proper wa,ter levelon boilers not equipped with multiple elementfeed water regulators. Howevcr, nonuse of t hesinglc element feed water regulator will result inaccumulations of scale in the feed water regu-lating control valves preventing proper func-tioning when required during "general quarters."

These regulators will not and should not beexpectcd to hold the wat,er level exactly at thedesign water level as they depend upon a differ-ence in level from the design level to operate thecontrol valve. Single element regulators tend tocarry an increasingly lo~~rerater level as thesteaming rate is increased. Generally, this vari-ation in water level is within acceptable limits.These regulators will maintain the water levelwithin reasonably close limits under s teadysteaming and under all but severc malleuvering~ondit~ioilst which times it may be necessary toresort t,o hand control.5-11. SWELL AND SHRINK.

To explain fully the water feeding of anyboiler, the phenomella called "swell" and "shrink"must be considered. These terms refer to achange in th e water level resulting from a changein steaming rate without a change in thc weightof water in .the boiler. Swell and shrink are re-sultants d th e larger volume occupied by steambubbles l)elow the water surface a t high evapora-tion rates as compared to low evaporation rates(Fig. 4 2) . When th e load is increased suddenly,more steam bubbles are formed in the boilertubes The steam bubbles increase the to talvolume of steam and water mixture in the gen-erating tubes and displace some water from thetubes forcing i t into the 1)oiler drum and causinga sudden rise in thc water level If th e feed is de-creased when swell occurs, the level may falldangerously low after t he momentary rise, sincesteam is leaving the boiler a t a much faster rate

-

amo un t of skill and attentior1 is recluired.Whcnfeeding by means of a single element aut,omaticfeed water regulator, swell, resulting from an in-crease I11 firing rate, is relayed to the feed waterregulatol, which will react to "high water." Thisreaction causes th e regulator t o close, which is inerror, since the higher firing rate recluires morewater, not less. Shrink also causes the regulatort,o react in th e wrong direction. If steam denlandchanges are not too large and not too frequent,the regulator valve reacts correctly before thclevel changes too much. If the rat ing changes arerapid an d large, the single elenlent feed water reg-ulat,or lags behind and a lorn water casualty orhigh water casual ty is likely. Because of th is pos-sibility, the Bureau of Ships il4anual requiresth at a qualified water tender be kept on watch a tthe feed checks a t all times while single elementfeed wat,er regulators are in operation in order t otake over the feeding of the boiler mailuallyshould the need occur.5-12. MULTI-ELEMENT REGULATORS.

The regulators previously described are single-element regulators, i.e. , they have only one con-trolling featu re, the level of t he water in thesteam d rum. hfulti-element (two or three control-ling features) feed water regulators provide waterlevel control superior t,o that possible withmanual operation of the feed check valves andth e single element regulator.

The three element regulators coiltrol materlevel by combining the iliflueiiccs of s team flow,feed water flow, and n~at~erevel. Measurementof steam flow gives an immediate and accurat,eil~dic ation f change in boiler steam demand andbegins positioning the regulating valve in thedirection desired regardless of t he act ion of smelland shrink. By measuring feed water flow, abalance can be maintained between stea,m takenout and water brought in. Any change in steamAow or feed water flomr upsets the balance andthe control system acts in thc direction requiredto restore thc balance. The measurement of water


12/20

5-12 JfARIATE ENGINEERINGlevel resets the water level in the steam drum a t lation. the water level ca.nnot be maintained, orthe design point and corrects any deficiencies in continually fluctuates , t he regulator shall bethe measurement of steam and feed water flow. s ~ t c h e drom automatic to remote manual and

The two element feed water regulator func- operated manually from the control panel. If,tions similarly to the three element regulator bu t the water level still cannot be maintained, thedoes not utilize feed water flow measurement. feed check stat ion shall be manned and the waterWith this type of regulator, the water level level controlled by manual operation of the feedmeasurement exerts a greater influence on the check valve.oweration of the r e ~ u l a t i n ~alve.uMost three element and many two elementfeed water regulators are pneumatically con-trolled systems. In such a system, as shown inFig. 5-7, three instruments, the steam flow in-dicator-transmitter, the feed water flow indi-cator-transmitter, and the drum water levelindicator-transmitter, measure their respectiverates of flow and water level. Air pressures, calledloading pressures, proportional to the measuredrates of flow and water level, are transmitted torelay sta tions which balance and compare incom-ing loading pressures and transmit corrected load-ing pressures, through a control station, to apneumatically operated feed water regulatingvalve (Fig. 5-8). The operator also may controlthe feed water regulating valve manually from aremote station (feed water selector valve) bycontrolling the air loading pressure transmittedto the regulating valve.

The multi-element regulators have an emer-gency device similar to a single element regulatorwhich, in event of failure of t he control air sup-ply, provides a secondarjr control of the boilerwater level until such time as a supply of controlair is restored. The concept of secondary controlis pursued by the Navy in all shipboard systemsto insure reliability of equipment in times ofemergency.

Bureau of Ships Jfa?aualinstructs th at on boil-ers equipped with multi-element feed waterregulators personnel shall use these regulators a tall times. Prime reliance for control of \?laterlevel shall be placed in the automatic regulatorand no t in manual operation of the feed checkvalve. While the regulator is in service, a feedcheck operator need not be stationed at the feedcheck valve. All boilers equipped with multi-element feed water regulators have remote read-ing water level indicators installed a t the loweroperating level in vie\?. of t he man in charge ofthe steaming watch. If, while on automatic regu-

6-13. ACCESSORIES MEASURING BOILER OPER-ATING CONDITIONS.To provide operating personnel with informa-

tion required for intelligent boiler operation, ac-cessories which measure boiler operating condi-tions are a necessity. The following accessorieswill be discussed with respect to their basic usein anj r control system.

1. Pressure gages2. Water level gages

Courtesy J. J. Hemy Co , I v c Nrir~ ' o ~ f iFIG. 6-8. Feed Water Regulating Valve.


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S T E A M F LO WT R A N S M I T T E R

ACCESSORIES CONTROLLIATG F L O W 5- 13

F E E D W A T E R FLO W D R U M W A T E R L E V E LT R A N S M I T T E R I N D I C A T O R - C O N T R O L L E R

@ F E E D W A T E RS E L E C T O R

A I R +TO T H E R M O - H Y D R A U L I C SUPPLYG E N E RA T O R M O U N T E DON B O I L E R D R U Md .

?+@ C A I R SUPPLYD U A L C O N T R O L

F E E D W AT E Rd R E G U L A T I N G V A L V EBureau of Ships

F I G . 6-7. Control Diagram for Three -Ele ment Fee d Wa te r Cont ro l .


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MARINE ENGINEERING-143. Thermometers4. Temperature alarms5. Steam flow indicators6. Smoke indicators7. Automatic controls

6-14. PRESSURE GAGES.Pressure enters as a variable factor in a vast

number of physical phenomena, and the re isfrequent need for its measurement over a verywide range. For ordinary pressures, there aretwo chief types of gage; viz., the liquid man-ometer, of urhich the mercury barometer is a nexample, and the Bourdon type u~hich s widelyused because of i ts simplicity and rugged con-struction. As shown in Fig. 5-9, the Bourdontype gage collsists of a meta l tub e having an ovalcross section, bent t o form an arc of a circle andsealed a t one end. The o ther end i s connected t,othe region whose pressure is t o be measured. Ifthat pressure is above atmospheric, th e pressureexerted on the tube tends to change it from anoval to a circular cross-section, accompanied byan ullcurling action. The motion of the sealed endis amplified by a lever and gear mechanism, soth at the limited movement of t he tip of t he tubemay be converted into a full swing of t he indica t-ing needle. This type of gage is termed a second-ary illstrument in that it must be calibrated bycomparison t o a primary gage, such as a manom-eter which measures pressure directly by theheight of a liquid in a tube.

When properly calibrated and installed, pres-sure gages provide operating personnel withuseful information, provided that they under-stand wha t is being measured. For example, ifoil flow in the fuel oil manifold leading to theburners is sufficient to carry the load under whichthe boiler is operating, the operator knours that,with the same physical apparatus, he can dupli-cate tha t oil flow a t any time by carrying th esame oil pressure. A change in manifold pressurewill cause a change in t he oil flow rate. I n likemanner, when the feed check man adjusts thecheck valve for proper feeding of the boiler undercertain 1oa.d conditions, he knows th a t if th e feedwater pressure should drop , the boiler will not re-ceive the amount of water necessary and a casu-altmy ill occur if the situation is allowed to con-tinue. Similarly, the throttl eman a nd the burnerman kilom that fo r a given opening of the turbine

FIG. 6-9. Pressure Gage.

thrott le, a ny variation in boiler drum pressurewill change the ship's speed; hence, the burner-man tries t o hold th e drum pressure constant byadjusting the oil pressure and the throttlemanwill meet ally change in ma in steam line pressureby varying th e throttle opening.6-16. WATER GAGES.

Water gages are installed in pairs on the steamdrums of naval boilers to ind icate the height ofwater in the drum. Fig. 5-10 shows the con-struct ion of a steel water gage, consisting of th eframe and front and back covers. Thick glassstrips, ground true to flat, parallel faces, areheld between the frame and the front and backcovers, as shorn11 in the cross-sectional view. Theglass strips are backed by sheets of mica, whichserve as a gasket to prevent etching of the glassin operation and p revent sha tter ing of the glass incase of breakage. Usually, a light is placed be-hind this typ e of mater gage to facilitate observa-tion of th e water level. TTarious types of glassesare used, some of which have corrugatioils on theouter side. These are known as "refles" glasses,because they refract the light in such a way thatth e part covered by mrat,er, ~v it hi n he colunln,appears darke r than t he rest of the glass.

Th e handles of the top and bottom cut-outvalves consist of short levers connected by


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A CCESSORIES CONTROLLIATG FLOW 5-15

REGULATORCONN.

Bureau of N a n d PersonnelFIG. 6-10. Water Gage Column.

chains. The threads on the valve stein are quad-ruple threaded and have a steep pitch so thatless than a half turn gives the valve full travel.The ends of the levers are connected by chains.Also connected to the ends of the bottom lever isa long loop of chain mrhich reaches to the lowerfloor plates of the fireroom. In case the gageglass should break or leak, personnel on thelower grating can close both the top and bottomgage cut-out valves in one operation.

The steel water columil has a check valve inthe bottom connection. The check consists of ahall which rests on a holder just above the bottomvalve stem. With the pressure on each side of theball in equilibrium, the ball rests in the holder.In case of gage glass breakage, the sudden rushof water through the bottom coilnection forcesthe ball up onto its spherical seat, preventing theflow of hot water through the break. There is noprovision for preventiilg the escape of steamthrough the top coilnection because, if the glassbreaks, the relatively small volume of escapingsteam creates little hazard to personnel or dam-

age to material. Further, the chain operated cutout valves can be closed immediately from thelower level without danger from falling hot water.

Water gages are located so that the middle ofthe glass is a t the normal water level of theboiler. If either the top or bottom connection ofa water gage is closed or partially obstructed byscale or other solid matter entering from theboiler, a false indication of the water level results.Gage glasses, therefore, must be "blo\?-n down"before the boiler is connected to the steam lineat t he end of each watch and at frequent intervalsthereafter whenever there is any questioil as tothe correct water level in the steam drum.Blowing of gage glasses is acuoiuplished by firstdisconnecting the chains between the top andbottom valve handles, then closing the top shut-off valve and opening the drain valve at thebottom of t he gage glass assembly. This permitswater to flow through the bottom connection tothe drain, clearing it of ~bs t~ruct ions .he topshut-off valve then is slightly opened and thebottom shut-off is closed. This permits steam to


16/20

5-16 MARINE ENGINEERINGflow through the top connection, clearing it ofobstructions, thence through the glass to thedrain. The drain valve is then closed and thebot tom shut-off valve opened fully. After blow-ing, care must be taken to see that both valvesare opened wide, the chains between t he top andbot,tom valve handles are replaced and that thewater level indicated is accurate. If the returnof the mater level in the glass afte r blo ~vin g sat all sluggish, the cause should be determinedand correct,ed a t once.

Two direct reading water level gage glassesare installed on each boiler to insure correctknowledge of th e tr ue water level in case onegage fails or sh o~ vs false water level. Older con-structioil mounted one 10" gage and one 18"gage, the la tte r consistiilg of two stand ard 10"gage glasses overlapped so that the distancefrom the bottom of the lower glass to the top ofthe upper glass is 18". More recent design re-quires that two 18" gage glasses be installed oneach steam drum.I11 some cases, one of the two 18" gage glassesis a Bi-Color gage (Fig. 5-11). The Bi-Color gageis of simi lar construction t o th a t previouslydescribed with exception of the method of illumi-nation lo facilitate observation of the wate rlevel. Illumiiiatioii of the Bi-Color gage is based

upoil the optical principle th a t refraction of alight ray differs as it passes obliquely throughdifferent media (steam and wat,er in this case).Parallel s trips of red and green glass are placedbetween the illuminator lamps and the strip lensadjacent t o the gage. Th e windows of the gageare set at angles with each other to utilize thedifference in light refraction between water an dsteam. Beams of red and green light, projectedthrough t he entire length of t he strip lens, striketh e faces of th e gage windours at different angles,each color beam being refracted as indicated inFig. 5-11 shown when the gage is filled withsteam. When steam fills the space between thegage windows, the green light beam is bent outof t,he field of vision, and t he red light beam isben t in to the field of vision. Conversely, whenwater fills the space between the gage a~indows,the red light is bent out of and the green light isben t in to the field of vision. At intermediat,econditions, the water level is indicated by thebouildary line between the two colors.

Recent boiler designs equipped with multi-element feed water regulators also include aremote reading water level indicator. This instru-men t indicates the water level in the boiler dru mat a convenient location, as on an instrumentpanel. When installed on naval boilers, remote

WINDOWS

I \ / GR EEN GLASS STRI PTRIP LENS

' RED GLASS STR IP

STEAM IN GAGECouvtes y I . I . I lenvy Co . , Ilir., Nrzo I'ovk

FIG. 5-11. Bi-Color Water Gage.


17/20

ACCESSORIES CONTROT,LTNG FLOWreading water level indicators a.re also equipped At times, th e temperature measurement pointwith visual alarms and u~it11 rovisio~l or audio is a t an iilcoilvenient or rern0t.e location. I11 suchalarms for high and low water. cases, a distant reading thermometer is used, in

R.emot,e reading water level indicators are which th e nlercurjr is led through a length of cap-usually of th e manometer type actuated by the illary tubing to a distant reading thermometer.differential pressure head existing between a Some di stan t reading thermometers have a dialfixed water column and a variable water columil and are similar in construction to a pressure gage.dependent upoil nTater evel in the steam drum. Th e latte r typ e of thermometer f re q ~ en t~l ys usednaval boiler spccificatioils require that, remote to measure the steam temperature a t the super-water level indicators be independent of external heate r outlet for superheat control and the oilsources of energy so th at they may be safely used temperature for control of fuel oil heaters.in lieu of tl ie water gage glasses.

One ty pe of remote water level device has a 6-17.HIGH TEMPERATURE ALARMS.dial and pointer indicator showing steam drum A high temperature alarni is i~lst~alle do warnwater level and three colored warning lights when the stlearn temperature a t th e superheater(white, red and blue) moun ted adjacent to th e outlet exceeds a predetermined safe limit. I tindicator. The white light remains lighted at all esseiltially is a dis tan t reading thermometcr in-times as a signal of "Power On," and goes out if stalled at the superheater outlet. As the mercurythere is a power failure or if the indicator bulb expands with increase in temperature, it actua tesburns out. The red light is an indication of an electric switch which is adjusted to malie con-critically high drum water level, arid the blue ta ct whenever the temperat,lire exceeds a fixedlight is ail indication of critically low drum water limit. T he electric circuit which is controlled by

th e switch call be utilized to sound an alarm, suchevel.as a klaxon, and light a red danger light. I11 some

6-16. THERMOMETERS. installations, a solenoid-operated, quick-closingTemperature control is.one of the crit,eria most valve is energized by t he circuit, causing the fuel

important in determining plant efficiency. Ther- oil to be sh ut o f f instantly from all or nearly allmometers which measure t he te ~np era tur es of th e supe rheate r burners.water, steam, air, and oil keep the operator in -formed as to t he efficiency with which th e plant =-I8- STEAM INDrC*TORS-is operating. I11 double furnace, single uptake, coiltrolled

Many of these thermometers are similar in supe rheat boilers, to avoid damage to th e super-principle to the ordiilarg household liquid column heate r tubes through overheating, a certain mini-thermometer but var y in regard to rigidity of mum flow of steam mus t be established beforeconstruction and typ e of inaterial used. Use of th e supe rheate r furnace may be lit off. Th e tem-uilprotccted glass thermometers is restricted perature of th e steam a t th e superheater outletto laboratory or field research applications. docs not necessarily indicate the conditions exist-Thcrmorneters measuring high temperatures ing within the superheater especially ~ vh en hemust be made of material which can ~v iths ta nd steam flow is reduced or stopped entirely. There-such temperatures. Man y thermometers are fore, in order t o enable the operators to deter-installed in locations where t,he bulb is subjected mine when this minimum steam flow has beento high velocities of flow and where personnel established, th is t ype boiler is equipped withmight strike t he therm omete r while working steam flow indicators.~ ~ i t l ither equipment. Mercury filled glass Th e steam flow indicator, illus trated in Fig.thermometers are protected by a metal casing 5-12, measures the steam flow through t'he super-and the bulb is inserted in a thermometer well heater by measuring th e steam pressure drop be-fitted into the pipe or unit where the temperature tween superheater inlet and outlet. T he pressureis being measured. However, where quick re- drop across the superheater is indica'ted 011 asponse is required, such as at th e superheater transp arent scale graduated in inches of water.out,let, quick-readii~g bare-bulb the rmo n~ ete rs Rehind th e trans paren t scale, a movable red andare used without therm omete r wells. green st,rip is located so th at th e division line


18/20

5-18 MARINE ENGINEERING

B ~ L F ~ ~ If .S/Iu.Ublruntm

FIG. 6-13(a). Details of Lamp and Reflector Units.

presence of smoke in th e uptakes indicates in-complete combustion, dirty burners, or ot,herabnormal collditioils in the funlace. The mostcommon typ e of smoke indicator is illustrated inFig. 5-13(a) and (b). This indicator consists of alamp, installed in a cylindrical casing fitted overa hole in th e rear of th e uptake , with a lens infron t of t he lamp. A second casing fits over a holein the front of th e uptake , exactly opposite thelamp unit. The second casing coiltains a mirror,which reflects the light beam from the lampdownward through a vertical tube, a t th e bottomof which a second mirror is positioned to reflectthe beam horizontally through an eyepiece. By

combustion is taking place in the furnace. The FIG. 6-13(b). Periscope Smo ke Indicator Installation.


19/20

ACCESSOR IE S CONTROLLING FLOTV 5-19looking int,o th e eyepiece, operating persoi~nelcall see any smoke preseiit as it passes in front,of the lamp, and, from the amo unt and densityof the smoke, determine whether or not furnacecoilditiolls are normal. Each naval boiler has twoor more smoke indicators to determine collditiollsin different areas of t he gas pa,th.Recent boiler accessory developmellts havebrought forth an automatic smoke density indi-cator suitable for naval use. This instrument isdesigned for use on boilers with remote auto maticcoiltrols in order to furnish informat,ion about,the conditi o~l f the stack gases a t th e remotecontrol st,at,ion. The automatic smoke indicatoroperates with a photo-electric cell which respondsmrhen th e density of tlhe smoke present betweenthe light source and the photo-electric cathodereceiver becomes a certain density.6-20. AUTOMATIC CONTROLS.

Automatic colltrols for steam generating unitsare operat'ional accessories which enable person-1x1 t,o operate boiler uni ts over long periods a thigh efficiencies, regardless of var iat ions in loadand ot,her operating factors.

The N avy has employed autlomatic controls tosome degree for many years. Feed water regula-tors have been conlmon since the first years ofWorld War 11. The increased pressures and t,emperatures, higher combustion rat,es, smaller size,and lighter coilstructio~lof modern boiler unitscause load changes and casualties to be reflectedin boiler operat,ing characteristics with utmostrapidity. In many i~~st,an ces,t is extremely dif-ficult for the operator t o mailually co~l tro l oilersof recent design. Even with manual control possi-ble, such control would not be sufficiently re-sponsive to boiler needs and efficiency lossesmould result).-41~0,he single furnace boilers nowemployed lend themselves more readily to suchregulatioil than do the douhle furnace, superheatcontrol units. He i~ ce he present t'rend in boileroperation is t,omrard automatic controls.

Th e use of au tomatic cont,rols offers five dis-tinct advantages as compared with manual con-trol:

1. Ability to colltiilue steaming the boilerwhen the fireroom becomes untenable.

2. A decreased numher of operating personnel.3. More efficient operat ion of t he boiler during

all conditions of operations.

Co ur t e sy The Babcock 6.W i l c o x Co . , a nd Ba i l ry M c t e r C o .FIG. 6-14. Automatic Recorder.

4. Bette r regulation of steam pressure.5. Less likelihood of overheating superheater

tubes and producing excessive superheatedsteam temperatures bccause of too high ex-cess air.

Operationally, automatic co~ltrol s erve threeprincipal purposes :

1. To regulate steam pressure and tempera-ture.

2. To control smoke by regulating oil-airratios.

3. To maintain wat,er level.The automatic feed water regulators which

have already becn discussed are considered partof a st,eam ge11erat)ing automatic control system.The combustion controls to regulate steam pres-sure and temperature and to control fuel-airratios will be discussed in Chapter VI along withmanual combustion control.

Several types of flow ~ne le rs re used t o meas-ure fluid flow on the basis of volume or weightper unit of t ime to provide illfo rmatio~l or usein automa tic boiler controls. Flow meters measure


20/20

the pressure drop across calibrated orifices andflow nozzles in a pipe line. They normally areemployed in automatic control sj ~s tem s nd insystems where automatic recorders for pressures,temperatures, arid fluid flow rates are illstalled(Fig. 5-14). Such iilstrumcilts give the operatoriils ta~l tail eous readings of all illformation re-quired fo r a thorough ullderstaildiilg of boileroperating conditions. These instruments aremounted on control panels or coilsoles located at

I-Io~vever,wit11 automat,ic coiltrol devices, itis highly desirable, if not imperative, th at allwatchstanders know at least the rudiments ofwhat takes place in boilers and where the majorautomatic coiltrol overides are and how to usethem . For example, the operator must k no ~vhatthe water level will va ry on a large steaming rat echange atld that by observiilg the iildicators onthe feed control panel, he can tell ~ vlie ther lhedevice is respondiilg correctly. I11 this way he

the main coiltrol s tation for the particular need not wait for th e low or high water levelmachinery space \vhich the boiler units service. alarm signal to ring. If the indicator does notAlso a t this station are t he thr ott le coiltrols respoild correctly for the steam rate change, heand coiltrol instrumellts for operating th e maill may introduce a bias upon the coritrol system a tengines. Thus , close liaison between maill engines the remote control sta tion an d prevent the ab-an d the boiler uni t is possible. iiormal ~ va te r ondition.

Documents

Latham_5_Accessories Controlling the Flow of Steam, Air, Oil and Water