Basic information about

Plumbing, Carpentry, Welding, Basic machining, Centrifugal pump and Air conditioner

By:

Mr.B.Ramesh, M.E.,(Ph.D),

Research Scholar, CEG, Anna University, Chennai, Associate Professor of Mechanical Engineering,

St. Joseph’s College of Engineering, Jeppiaar Trust, Chennai-119

Plumbing:

* Vice : Bench vice, Pipe vice * Taps : Taper tap, Intermediate tap(plug tap) and Bottoming tap * Plumb bob : Used for checking vertical lines * GI pipe : galvanized iron pipe ; SWGP : Stoneware glazed pipe * Zinc is used for galvanizing. It protects ferrous metal from corrosion * Flexible pipe : Alvin pipes are used for water supply in hilly areas and storey

areas. Armer pipe is a rubber pipe mainly used for temporary water supply of large volume and it contains wiring over it.

* The entire supply pipe should be so installed that it should drain to one point. * Cast iron pipes of larger size are joined with flanges while small size pipes are

joined by sockets. * The water pressure does not become low by using bend. * The other name of tap is cock. * Nipple : It is a short piece of pipe (less than 300 mm in length). It consists of

three parts in that two parts will be screwed on to the two pipe ends and the third one which is a nut, draws the pipes together tightly.

* Plug : For closing internal threaded openings temporarily. Cap : For closing external threaded openings temporarily. * Socket reducer : Used to connect a big pipe to a small pipe face to face. * Piping diagram : single line and double line. *

1

* Pipe joints : Bell and spigot joints, flanged joints and threaded joints. * Bell and spigot joints : where it is necessary to insert a fitting into an existing

pipe line. * Water tight joints: Flanged joints – rubber gaskets are used for cold water pipe

and asbestos gaskets are used for hot water pipe. * Threaded joints : eg. Coupling, nipple, close nipple. * Plumbing is the art of design, installation and maintenance of pipe, pipe

fittings and other accessories in a building. * The plumber is mentioned according to his experience by the following three

grades as apprentice, journeyman and master. * An apprentice is a beginner and serves as a helper. The journey man performs

the task of plumbing installation and repair. The master being the skilled person doing the business of plumbing, with knowledge of laws and ordinances affecting plumbing.

* Laying pipe connection to the suction side of a pump – inlet : * Should be short and direct

* Liquid velocities of 8 feet per second in the suction are usually satisfactory.

* Flange should be used to connect the suction pipe to the pump. The diameter of flange should not be same as that of the suction pipe. Hence the eccentric reducer is used to connect the suction pipe and the flange.

* Slope the suction pipe up to the pump. In order to avoid the air bubbles inside the pipe, the suction pipe is laid at 20 downwards towards the well.

* Do not use check valve in the suction pipe. * Submerge the end of the suction line and the foot valve atleast three

feet below the lowest level of the liquid to be pumped. * The suction lift( distance from the water surface to the pump centre

line including all losses) should not exceed 20 feet of water.

2

* Avoid loops in the suction pipe which rise above the horizontal centre line of the pump. Instead turn the loop downward. This prevents the formation of air pockets in suction pipe.

* Suction pipe should be larger than the pump suction nozzle. * Laying pipe connection to the delivery side of a pump – outlet :

* A check valve and a gate valve should be installed in the discharge line. The check valve should be next to the pump. Use a nozzle between the pump and the check valve. * The size of the pipe on the discharge side of a pump should be increased in order to reduce the friction losses. * Close the gate valve in order to run the pump and to stop the pump. Open the gate valve during the running of the pump.

* Metal pipes are used as a suction pipe for pump for the purpose of taking the underground water and these pipes are used to supply water to the water tank.

* Plastic pipes are used for transferring water from the storage tank to the various rooms of a house.

* Flexible pipes are used in house hold appliances like washing machine and vacuum cleaner.

* In plastic pipes, thermoplastic material is used. Types of plastic pipes : Polyethylene, Polypropylene, PVC and Cross linked polyethylene.

* The ends of cast iron water pipe are of three types and these are standard ends: Bell and spigot, Flanged and Screwed.

* Bell and spigot ends are used mainly for underground work and in buildings where there is too much space for the fittings and for caulking operations.

* Flanged ends are used in those buildings where space is limited. In this, the pipes are held together by bolts having gaskets between the flanges to make it leak proof.

* Threaded or screwed ends are used in small pipes in general practice, although these are available in bigger diameter pipes also.

* Rubber is used in tubing and pipes either as hard or soft rubber to convey liquids to which it is corrosion resistant.

* Soft rubber is used in hose for conveying water and other fluids such as steam where flexibility is required.

* Separate set of pipe threading dies are required for each pipe size. * Taps are used for cutting internal threads on a pipe or fitting. Three types of

tap are necessary to cut threads. Taper tap is used first and cuts light threads. Then plug tap is used and finally bottoming tap is used which cut the threads to the required depth.

* The various pipe fittings used in plumbing are Socket, Elbow, Bend, T, Four way cross, Valves, Cock, Pipe union and Socket reducer.

* Joints used in pipe are : 1) Bell and spigot joints 2) Flanged joints and 3) Threaded joints.

* Slope the suction pipe up to the pump. In order to avoid the air bubbles inside the pipe, the suction pipe is laid at 20 downwards towards the well.

* Bell or Hub: That portion of a pipe which, for a short distance, is sufficiently enlarged to receive the end of another pipe of the same diameter for the purpose of making a joint.

* Plumber’s soil: A mixture of lampblack and glue used in lead work.

3

Carpentry: * Carpentry is the process of working with wood for applications such as floor

works, roofs and partitions in a building. Preparation of other wood works such as windows, stairs, cupboards etc is called as joinery.

* Wood seasoning is the process of removing the excess moisture present in the timber by evaporation. After seasoning of the wood the moisture content is reduced to 9- 25 percentage.

* Advantages of seasoning : Strength and durability is increased, wood becomes resilient and lighter, workability is increased, surface finish is improved and distortion is minimized.

* Types of seasoning : water seasoning, natural seasoning, chemical seasoning and kiln seasoning.

* Types of wood : Soft wood, Hard wood and Ply wood. * Soft wood: It has straight fibers and is comparatively weaker. Easy to work.

Weight and durability are less. Compared to hard wood, soft wood catches fire soon. Eg. Deodar, Kail and Chir.

* Hard wood: Hard wood has closed structure, heavy in weight, dark in colour, more durable. Difficult to work. It has proper bonds inside. So it is very strong. Eg. Teak, Shirham, Sal, Mango, Maple and Oak.

* Ply wood : It consists of three layers: 1) Top face plys layer 2) Core layer 3) Bottom face plys layer. The face plys layers are bonded to the centre core, which is thick and not of good quality.

* Annual rings are added to the timber every year. * Try square is used for testing squareness(900) and marking of joints. The blade

lengths available are 150, 225 and 300 mm. * Mitre square is used for marking and measuring an angle of 450. Length of

blade is between 200 to 300 mm. They are made up of steel blade with rose wood stock.

* Bevel square is used for measuring the angle from 00 to 1800. The shape of the bevel square is like a try square.

* The type of gauges used in carpentry are: 1). Marking gauge 2) Mortise gauge and 3). Cutting gauge.

* Gauges are used to mark lines parallel to the edge of a piece of wood. Marking gauge has one marking point. Mortise gauge has two marking points. Divider is used for dividing the centres.

* Front end of a blade along the teeth is called ‘point’. The back end is called ‘red’. The teeth of a saw are bent slightly to the left and right consecutively(a small zig zag).

* Types of saw: * Rip saw : Length of the blade is 650 – 710 mm. No. of teeth per 25

mm is either 4 or 5 .Suitable for sawing down the grain. * Cross cut saw: Length of the blade is 600 – 650 mm. No. of teeth per

25 mm is 8 to 10. Suitable for cutting across the grain in thick wood. * Back saw : Reinforced with a steel back. Length of the blade is 250 –

400 mm. No. of teeth per 25 mm is 13. Used for cross cutting when a fine finish is required.

* Compass saw : Length of the blade is 250 – 400 mm. Used for sawing small curves in confined spaces and has a narrow tapering blade.

4

* Coping saw : Approximately 10 teeth per cm. Used for cutting quick or sharp curves either internal or external.

* Key hole saw / Pad saw : Used for cutting thick internal curves where it is impossible to use other saws.

* Bow saw : A saw with two handles. Used to produce curved surfaces with quick turns.

* Chisels : Chisels are the tools produced from forged steel or tool steel

blades. * Firmer chisel : Used for light and heavy work. * Paring chisel : Has a thinner blade. Used for light work. Also

used for shaving or paring plane surfaces. * Mortise chisel : Used to make mortises. Used for heavy cuts. Blade thickness varies from 5 mm – 12 mm. * Gauge chisel : Used to finish curved holes. Types : Inside and outside gauge chisels.

* Planing tools : * Wooden jack plane : Length varies from 355 – 380 mm.

Cutting iron width is between 50 – 62 mm. Cutting edge is very slight curve. Also used in oblique planning. Used for rough work.

* Iron jack plane : Used for better finish; costlier. * Trying plane : A wooden jack plane in larger size. Length of

the plane is 550 to 650 mm. Blade width is 90 mm. Used for planing large surfaces.

* Smoothing plane : Used for smoothing the surface of the wood after the jack plane and trying plane are used. Length of the plane is 200 to 250 mm.

* Rasp / Rasp file : It is a finishing tool. Used to make the wood surface, remove sharp edge, finishing fillets and other interior surface. Used in wood work only.

* Boring tools : Ratchet brace and wheel brace. * Bradawl and Gimlet : Used for boring of small holes. The holes

obtained from this tool may be used to hold a nail. * Striking tools : * Cross-peen hammer: most used for positioning small nails. * Claw hammer : used for removing and driving very large nails. * Mallet: Used to give light blows. * Holding tools : Bench vice * C-clamp : Opening capacity varies from 50 to 350 mm. Used for

clamping small work and angled work. * Pincer is used for pulling out nails. * The operation of smoothing a wooden surface with the help of a suitable plane is called planing/facing/edging. Planing should be done

the direction of wood grains. * Mortising is the operation of producing a rectangular (or) square hole

and tenoning is the operation of making a corresponding projection so that it fits into the mortise to form an assembly.

5

* Grooving is the process of making grooves and tonguing is the process of producing corresponding projection of wood to fit into grooves. This operation is applied in wood partitions and drawing boards.

* Moulding : It is the process of producing convex, concave and other complex types of curved surfaces on a piece of wood. It is done with the use of moulding plane. Moulding work may be done for preparing photo frames and for decorative purposes in doors and window frames.

* Rebating : It is the process of making a recess(rebate) taken out of the edge of a piece of wood. It is done with rebating plane. * Mortise → Rectangular hole. Tenon → Rectangular peg. Width of the mortise is about 1/3 of the thickness of the material to be mortised and length should not exceed six times the width. * Dove tail joint : strongest of all corner joints. An angle of 1 : 6 ratio is adopted. * Bridle joint : Reverse of mortise and tenon joint. Used for square section. * Chisel is normally made up of forged steel. * The other name of butt joint is rubbed joint. * Setting of saw teeth: The teeth are bent alternately to the right and left of the blade to enable it to pass through the cut being formed in the timber with the minimum of friction. * The cutting bevel angle in a chisel is 250 to 300. Cutting angle for cross cut saw is about 450. Cutting angle for rip saw is about 600. * TPI stands for Teeth Per Inch. i.e. the no. of teeth is 5, 6, 7 and 8 per inch. * Mortise and tenon joint is generally used for framing work. Bridle joint is often used where the members are of square section. * Calipers are used for measuring diameters of curved surfaces. * Centre punch : It will make a dent in wood or metal for starting a drill. * Marking gauge : It is used for marking lines at a uniform distance from the edge of a board or a piece of work. * Marking knives: They are used mainly for accurately marking shoulder lines before they are cut with a tenon saw. * Mortise gauge : The gauge simplifies two parallel lines to be marked. * Veeners: Veeners are thin sheet of wood that are peeled off and sliced from a log of wood. Thickness of these sheets varies from 0.4 mm to 6 mm. Welding :

* Welding is a metal joining process wherein localized coalescence is produced by heating the metal to a suitable temperature, with or without the use of filler metal and with or without the application of pressure. * Two types of welding are plastic welding(non-fusion) and fusion welding. * Plastic welding : Done under pressure without addition of filler material. Eg. : forge welding and resistance welding.

6

* Fusion welding : Done without application of pressure but with the addition of filler material. Eg. : gas welding, electric arc welding and thermit welding. * Acetylene – oxygen → 3200 – 33000C * Thermit welding: Done by pouring super heated liquid thermit steel. * Oxygen in black cylinder; acetylene in maroon cylinder. * I C2H2 + O2 → 2Co + H2 + heat (small inner white cone flame close to the tip) II 2Co + O2 → 2Co2 ; 2H2 + O2 → 2H2O ( larger blue flame surrounding the small white cone flame) * Neutral flame → oxygen and acetylene in equal proportions. Oxidising flame → excess of oxygen Reducing flame (carburizing flame) → excess of acetylene * Neutral flame : Temperature is 32600 C. Used for welding mild steel, copper, aluminium, cast iron etc. oxygen : acetylene → 1.1 : 1 * Oxidising flame : Temperature is 34820c. used for welding copper- base metals and zinc-base metals. Will produce a hissing sound. * Reducing flame (carburizing flame) Temperature is 30380C. Much brighter in colour. Used to weld high carbon steel, non-ferrous alloys and zinc bearing alloys. Flame will burn quietly and have more length. * Gas cutting or flame cutting : Special oxy-acetylene torch is used to cut steel and iron. First the job will be pre-heated by producing a pre- heating flame. Oxygen and acetylene mixed in the mixing chamber to produce a pre-heating flame. The metal will be heated to its kindling(combustion) temperature. At this high temperature, the metal reacts with oxygen and iron oxides are formed. The metal will be bright red. The iron oxides will be very weak, now, a jet of pure oxygen will be supplied through the central hole of the torch by pressing the oxygen lever in the torch. This oxygen will cut through the pre-heated hot metal and the work piece will be cut. * Gas cutting (flame cutting) : Only those metals whose combustion/oxidizing/kindling temperature is below their melting point can be cut. So iron and steel(upto 1000 mm) can be cut by flame cutting. When combustion temperature is reached the metal reacts with oxygen and iron oxides are formed. * Gas welding techniques: i) Leftward technique/ Forehand welding method: welding is done from right to left direction. Suitable for upto 3 mm thick sheets. ii) Rightward technique/ Backhand welding method : welding is done from left to right direction. Suitable for large size jobs. * No flux → low strength welds, poor quality. * Flux prevents oxidation by preventing oxygen from contacting the weld zone. * No flux is used in the gas welding of steel. * Flux materials → boric acid, soda ash and sodium chloride. * The various types of gas welding are: i) Oxy-acetylene welding ii) Oxy-hydrogen welding iii) Air-acetylene welding and iv) Pressure gas welding.

7

* The types of flame in oxy-acetylene welding are : oxidizing flame, neutral flame and reducing flame. * Copper piping in the presence of acetylene forms copper acetylide. This is an unstable compound and disassociate violently at the slightest shock. So a copper piping is never used for acetylene gas. * LPG can be used in underwater cutting. * Oxidising flame is used for welding brass material. Arc welding: * Welding may be carried out in air or in an inert atmosphere. Filler material may or may not be used. * Temperature of the arc is of the order of 36000C. * Job/working table → -ve Electrode holder → +ve. D.C. supply. * Electric motor generator (or) transformer sets are used. * Transformer type welding machine produces A.C. Produces high current and low voltage to the welding. Least expensive. * Electric motor generator type welding machine produces D.C. * A high current arc with a smaller arc length produces a very intense heat. *

Sl.No. AC arc welding machine (Transformer )

DC arc welding machine (Electric motor generator)

1 Ferrous metals Both ferrous and non ferrous metals.

2 Only coated electrodes Both coated and bare electrodes 3 Less power 0.4 Consumes more power 0.7 4 Energy 4 Kwh/kg of metal

deposit Energy 6 to 10 Kwh/kg of metal deposit.

5 High efficiency 0.85 Low efficiency 0.6 6 Least expensive High expensive 7 50A – 400 A – AC 125 A – 600A - DC 8 Noiseless operation Gives noise 9 Suitable for welding thick

sections only Suitable for welding thin sections only

* Bare end for gripping in electrode holder is 20 mm. *

Sl.No. Consumable electrodes Non-consumable electrodes 1 These electrodes are made up

of copper, steel, brass etc. * Electrodes made up of carbon and graphite varieties are used in DC arc welding. * Tungsten electrodes used for both AC and DC welding.

* Chipping hammer is chisel-shaped one and it is used to remove the slag from the weld bead. * Hand screen → Fitter lens

8

* Chipping goggle are used to protect the eyes while chipping the slag. They are fitted with a plain glass to see the area to be cleaned. * Hand gloves are used to protect the hands from electrical shock, arc radiation and hot spatters. * Set the welding current as per the diameter of the electrode to be used. * Select the electrode as per true thickness of the metal to be welded. * Hold the electrode at an angle of 700 – 800 with the weld line and 900 with the adjoining plate surface. *

Plate thickness in mm

Electrode currentSize mm

Range (Ampere)

1.6 1.6 40 – 60 2.5 2.5 50 -80 4 3.2 90 -130 6 4 120 -170 8 5 180 -270 25 6 300 - 400

* Arc producing methods : scratching method and tapping method * Tapping method : In this method, the arc is produced by moving the electrode slowly and holding it approximately 6 mm from the surface for a few seconds and then lower it to approximately 4 mm from the surface. * Tack welded to maintain correct root gap during welding. * Length of each electrode varies between 50 – 70 mm. * Arc welding cannot be used to weld metal of thickness less than 1.6 mm. * Three basic types of joints common to arc welding and gas welding are Butt joint, Lap joint and T-fillet joint. * Flux: During the welding, if the metal is heated in air, the oxygen in the air reacts with the metal to form oxides which result in poor quality, low strength welds (or) in some cases may even make welding impossible. In order to avoid this problems, a flux is added during the welding. This prevents oxidation. * Filler material is the material added to the weld pool to assist in filling the gap(or groove). * Weaving implies giving a side-to-side motion to the welding arc during transferring the material to weld joint. A slight weaving (or) oscillating motion is preferred as this facilitates gas to escape from weld bead. Weaving also produces a wider bead with better penetration. * The materials used for coatings on electrodes are: copper, carbon, graphite etc. * Coating factor = [Diameter of the electrode/ Diameter of core wire] * Types of electrodes: Bare electrode, lightly coated electrode, medium coated electrode and heavily coated electrode. * Welding defects: lack of fusion, undercut, cracking, oxidized weld, incomplete penetration etc.

9

* Alternating current(AC) : An electrical current that reverses its direction at regular intervals, such as 60 cycles alternating current(AC) or 60 hertz. * Direct current (DC) : Flows in one direction and does not reverse its direction of flow as does alternating current. * Direct Current Electrode Positive (DCEP) : The specific direction of current flow through a welding circuit when the electrode lead is connected to a positive terminal and the work lead is connected to a negative terminal of a DC welding machine. Also called direct current reverse polarity(DCRP). * Inverter: Power source which increases the frequency of the incoming primary power. An inverter improves electrical characteristics of a smaller size welding machine such as faster response time and more control for pulse welding. * Power efficiency : How well an electrical machine uses the incoming electrical power. * Weld transfer: Method by which metal is transferred from the wire to the molten puddle. Eg. Short circuit transfer. Basic machining : * Machining is a process of converting the given work piece into the required shape and size with the help of a machine tool. * Types of head stock : belt driven head stock and geared head stock. * H shaped part fitted on lathe bed → saddle Cross slide is in the form of dove tail. * Lead screw → ACME threads. * The included angle in lathe centres is 600. * Face plate is used for mounting the type of jobs which cannot be held by chucks. There are no. of holes and slots on the face of the face plate. * Lathe carriers or dogs is used for transferring the motion from the rotating driving plate(catch plate) to the work held between the centres. * The types of dogs are : Bent tail, straight tail and clamp type. * Steady rest supports cylindrically long jobs when machined between the centres or by a chuck. Types : Fixed and traveling steady rest. * Mandrel is a hardened piece of round bar for holding bored or reamed jobs(i.e.hollow jobs). It has drill holes at both the ends. Work piece is mounted over the mandrel and the mandrel is rotated between the centres. * Follower rest is used for supporting long slender work pieces, against the cutting tool forces. * Types of tool: Facing tool, Rough turning tool, Finishing tool and Radius tool. The two types of radius tool are concave radius tool and convex radius tool. * Parting tool : Used for grooving and also to cut the job into two parts. * Form turning tool : Used for jobs which require both convex and concave turning.

10

* Drawing slanting or square projecting lines on the surface of a job is known as knurling. * HSS → 18 : 4 : 1 → Tungsten : Chromium : Vanadium. 5 to 10 % cobalt is also added to improve the heat resisting properties of the tool. * Taper is defined as the uniform change in the diameter of a work piece measured along its length. Taper = (D – d) /L where D = large diameter, d = small diameter and L = length of taper. * Knurling is a process of making serrations on the work piece. Chamfering is a bevelling operation or turning a slope at the end of work piece to remove burrs. Usually performed on bolts and nuts. Tapping is a process of making internal threads in small jobs. * Power feed is given to the carriage through lead screw and for one rotation of the job, it covers the distance equal to the pitch. * Right hand thread: View the screwed part of the thread in a direction normal to its axis. If the threads found sloping downwards from top from left to right then it is right hand thread. * Left hand thread : If the threads found sloping downwards from top from right to left, then it is called left hand thread. * Calculation of change gears : [Pitch of thread to be cut/Pitch of lead screw] = [Driver teeth / driven teeth] = [speed of lead screw/speed of spindle] * Generally, centre lathes are provided with a set of gears ranging from 20 to 120 teeth in steps of 5 teeth. * Centre gauge : It is used for setting the thread cutting tool, square to the spindle axis. It is also used for checking the thread cutting tool angles, after grinding. * Cutting speed = πDN m/min. It is the peripheral speed of the work past the cutting tool. It is the speed at which metal is removed by the tool from the work piece. * Feed : It is the distance the tool advances for each revolution of the work piece. Unit is mm / revolution. * Depth of cut = [d1 – d2] / 2. d1 = diameter of the job before machining, d2 = diameter of the job after machining. * Different types of lathe machines are ; centre lathe, production lathe, capstan lathe, turret lathe and auto lathe. * Tail stock: It can be positioned anywhere in the bed. It is used for supporting lengthy jobs and also carries tool to carry out operations such as tapping, drilling and reaming. * Mandrel: It is a hardened piece of round bar for holding bored or reamed jobs. It has drill holes at both the ends. It is used for holding hollow jobs. * The cutting tools used in lathe are facing tool, rough turning tool, parting tool, form turning tool, thread cutting tool, drill tool and knurling tool. * Various operations done in lathe are facing, turning, step turning, taper turning, knurling, drilling and thread cutting. * Knurling is a process of making a serration on the work piece. It is a operation of creating a hand grip or roughened surface on a work piece.

11

* Cutting speed : It is the peripheral speed of the work past the cutting tool. It is the speed at which metal is removed by the tool from the work piece. It is expressed in meter/minute. * Feed: It is defined as the rate of tool travel across a surface cutting it. It is the distance the tool advances for each revolution of the work piece. It is expressed in mm/revolution. * Depth of cut: It is the perpendicular distance measured from the machined surface to the uncut surface of work. It is expressed in mm. Depth of cut = [d1 – d2]/2. In lathe if you rotate 10 divisions the tool will advance by 0.5 mm ,thereby 1 mm in diameter can be reduced. Machine assembly practice: Centrifugal pump : * The pump is a hydraulic machine which converts the mechanical energy into hydraulic energy in the form of pressure energy. The centrifugal pump is a hydraulic machine which converts the mechanical energy into pressure energy by means of centrifugal force. * The centrifugal pump works on the principle of forced vortex flow which means that when a certain mass of liquid is rotated by an external torque, the rise in pressure head of the rotating liquid takes place. The rise in pressure head at any point of the rotating liquid is proportional to the square of tangential velocity of the liquid at that point. (i.e. Rise in pressure head = [V2/2g] = [ω2r2/2g] ). Thus, at outlet of the impeller where radius(r) is more, the rise in pressure head will be more. Due to this pressure head, the liquid can be lifted to a high level. * The main parts of a centrifugal pump are : 1) Suction pipe 2) Impeller 3) Casing and 4) Delivery pipe. * Some of the points to remember regarding installation of suction pipe : 1) Length of the suction pipe should be as small as possible. 2) Try to avoid bending in the suction pipe, If it is unavoidable make the bend with maximum radius ( radius = five times of the diameter of the suction pipe). 3) Use an eccentric reducer to join the suction pipe with inlet of the pump. 4) Avoid the check valves in suction side of the pump. 5) Cross sectional area of the foot valve should be double the cross sectional area of the suction pipe. 6) If the suction pipe is in horizontal position, the suction pipe must be in 20 inclination with downwards. * Impeller : The rotating part of a centrifugal pump is known as impeller. It contains series of curved vanes. The impeller is mounted on a shaft which is connected to the shaft of an electric motor which runs the pump. * Casing : Casing is an air-tight passage surrounding the impeller and is designed such a way that the kinetic energy of the water discharged at outlet of the impeller is converted into pressure energy before the

12

water leaves the casing and enters into the delivery pipe. Three common types of casing are : 1) Volute casing 2) Vortex casing and 3) Diffuser casing. 1) Volute casing : It is of spiral type in which area of flow increases gradually. The increase in area of flow causes decrease in velocity of the flow. The decrease in velocity, increase pressure of the water flowing through the casing. 2) Vortex casing : In vortex casing a circular chamber is introduced in between the casing and the impeller. The vortex casing reduces formation of eddies and this results reduction in loss of energy. Thus efficiency of the pump with vortex casing is more than the efficiency with volute casing. 3) Diffuser casing: Here, the impeller is surrounded by a diffuser. Both the diffuser and the outer casing are stationary parts. The diffuser has a series of guide vanes. The guide vanes are designed in such a way that the water from the impeller enters the guide vanes without stock. Increasing area of guide vanes reduces the velocity of flow which consequently increases the pressure. Also it reduces vibration of the pump. * Some of the points to consider regarding installation of the delivery pipe : 1) Use a check valve and gate valve in the delivery side of the pipe. Gate valve is used to regulate flow of the water. The check valve allows water from pump to the delivery side. But it will not allow the flow in the opposite direction. 2) The check valve must be placed in between the pump and the gate valve. * Multi stage centrifugal pump : If a centrifugal pump consists of two or more impellers, the pump is called multi stage centrifugal pump. A multi stage pump is used for two important purpose i.e. i) To produce high head and ii) To produce large amount of discharge. * Multi stage pump for high head : To get the high head, number of impellers are connected in series i.e. on the same shaft. Water discharged at the first impeller outlet with increased pressure enters into the inlet of second impeller with the help of a connecting pipe. Water from outlet of second impeller has more pressure than water from the outlet of first impeller. * Multi stage pump for high discharge: To get the high discharge, the pumps should be connected in parallel. The parallel pumps are connected to a common delivery pipe. Here, all the pumps are working for a same head. * Priming : Before starting the pump, air from suction pipe, casing and portion of delivery pipe i.e. up to the valve is replaced by water. The operation of replacing the air with water in the pump is called priming. If the priming is not taken place, the pump will not deliver the water. The head generated by the pump is independent of density of the fluid. * Applications of centrifugal pump: 1) In houses it is used to fill the overhead tank. 2). In agricultural sector centrifugal pump is used to

13

deliver the water from the well. 3). Centrifugal pumps are used to feed the water to boilers in industries.

Air Conditioner : * An air-conditioner is defined as an assembly of different parts of the system used to produce a specified condition of air within a required space or building below that of the atmosphere or surroundings. * Minimum capacity of air-conditioner is 0.5 ton. * An air-conditioning system works on vapour compression cycle. This cycle works in following four phases: 1) Compression 2) Condensation 3) Expansion and 4) Evaporation. * Boiling point of a refrigerant is very low. * Generally Freon 12 is used as a refrigerant in the domestic air- conditioner. It is observed that all the Chloro Fluoro Carbons (CFC) including Freon affects the ozone layer causing global warming. Since now-a-days the newly invented refrigerant Hydro-Fluoro-Carbon (HFC) is used as refrigerant. * Hermatic compressor is also called as sealed compressor. * In hermatic compressor, the rotary compressor and motor are assembled together and suspended inside a metal casing called “Dome”. * RSIR(Resistant Start Induction Run) or CSIR (Capacitor Start Induction Run) type motor is used to operate the compressor. * Function of the compressor is to provide the necessary pumping action to the refrigerant thereby maintaining a continuous flow of the refrigerant through the system. * Normally the condenser and evaporator are made by copper aluminium or iron pipe. * The function of the expansion valve is to supply proper amount of refrigerant to the evaporator after reducing its pressure considerably. Due to the expansion the high pressure is reduced very much to allow the vaporization of liquid at a very low temperature of about -100C. * If the selector switch is turned from any cool position to OFF position, do not turn again to cool position before five minutes. If we do so the compressor will not be able to start immediately after it is stopped. _____________________________________________________________________

14

15