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FITTING SHOP2.1 INTRODUCTION
Fitting shop is one of the important workshops in the Sri Lanka Ports Authority. The all
maintenance equipment what are the use of port authority in every workshop has been repaired in
the fitting shop. Most common equipments are fans, various types of pumps... etc. In addition to
that, the tapping operation is most common operation in fitting shop. There are several work
benches, a drill machine, puller machine, tools & equipment store in the fitting shop. The fitting
shop is a good place to get a basic knowledge and good idea about the mechanical engineering.
2.2 GLOBE VALVE
A globe valve is a linear motion valve used to stop, start, and regulate fluid flow. A Z-body
globe valve is illustrated in the globe valve disk can be totally removed from the flow path or it
can completely close the flow path. The essential principle of globe valve operation is the
perpendicular movement of the disk away from the seat. This causes the annular space between
the disk and seat ring to gradually close as the valve is closed. This characteristic gives the globe
valve good throttling ability, which permits its use in regulating flow. Therefore, the globe valve
may be used for both stopping and starting fluid flow and for regulating flow. When compared to
a gate valve, a globe valve generally yields much less seat leakage. This is because the disk-to-
seat ring contact is more at right angles, which permits the force of closing to tightly seat the disk.
Globe valves can be arranged so that the disk closes against or in the same direction of fluid flow.
When the disk closes against the direction of flow, the kinetic energy of the fluid impedes closing
but aids opening of the valve. When the disk closes in the same direction of flow, the kinetic
energy of the fluid aids closing but impedes opening. This characteristic is preferable to other
designs when quick-acting stop valves are necessary. Globe valves also have drawbacks. The
most evident shortcoming of the simple globe valve is the high head loss from two or more right
angle turns of flowing fluid. Obstructions and discontinuities in the flow path lead to head loss. In
a large high pressure line, the fluid dynamic effects from pulsations, impacts, and pressure drops
can damage trim, stem packing, and actuators. In addition, large valve sizes require considerable
power to operate and are especially noisy in high pressure applications. Other drawbacks of globe
valves are the large openings necessary for disk assembly, heavier weight than other valves of the
same flow rating, and the cantilevered mounting of the disk to the stem.
Advantages of a globe valve
Good shut off capability
Moderate to good throttling capability
Shorter stroke(Compared to a gate valve)
Available in tee, wyes and angle patterns, each offering unique capabilities.
Easy to machine or resurface the seat
With disc not attached to the stem, valve can be used as a stop-check valve
Disadvantage of a globe valve
Higher-pressure drop(Compared to a gate valve)
Requires greater force or a larger actuator to seat the valve(With pressure under the
seat)
Throttling flow under the seat and shutoff flow over the seat.
2.2.1 FACING A GLOBE VALVE
First of all the valve was dismantled and cleaned all the parts, valve and valve seat were faced
by using lapping compound. When removing the valve firstly, we removed the locknut on the
hand wheel was removing. After removing the bonnet bolts and nuts, the bonnet was removed.
Then glands were removed. Then the entire components were cleaned using kerosene and water.
That valve dice was about 50 mm in inner diameter, hand wheel diameter was about 220mm,
body length was about 368 mm and open valve height was about 569mm.
Facing procedure was;
With the use of the scraper the valve was scraped. After that the compound
mixture was applied on the valve and vapid (to spread all over the required area.). Then the
spindle was turned clockwise and anti-clockwise continuously until the valve was seated well.
After that all the parameters were assembled also a gland packing is used for gland box. In this
globe valve, gaskets, packing were made of graphite stainless steel.
2.2.2 DIAGNOSIS AND SUGGESTED
1. Valve stem is improperly lubricated or damaged.
Disassemble the valve and inspect the stem. Acceptable deviation from theoretical
centreline created by joining centre points of the ends of the stem is 0.005"/ft of stem.
Inspect the threads for any visible signs of damage. Small grooves less than 0.005" can be
polished with an emery cloth. Contact Vela Field Engineering Service if run-out is
unacceptable or large grooves are discovered on the surface of the stem.
2. Valve packing compression is too tight.
Verify the packing bolt torque and adjust if necessary.
3. Foreign debris is trapped on threads and/or in the packing area. This is a common
problem when valves are installed outdoors in sandy areas and area not cleaned before
operating.
Always inspect threads and packing area for particle obstructions, even seemingly small
amounts of sand trapped on the drive can completely stop large valves from cycling. The
valve may stop abruptly when a cycle is attempted. With the line pressure removed from
the valve, disconnect the actuator, gear operator or hand wheel and inspect the drive nut,
stem, bearings and yoke bushing. Contaminated parts should be cleaned with a lint-free
cloth using alcohol, varsol or equivalent. All parts should be re-lubricated before re-
assemble. If the valves are installed outdoors in a sandy area, it may be desirable to cover
the valves with jackets.
4. The hand wheel is too small.
Increasing the size of the hand wheel will reduce the amount of torque required to operate
the valve. If a larger hand wheel is installed, the person operating the valve must be
careful not to over-torque the valve when closing it.
2.3 REPAIRING A HAND DRINDER
There was a dismantled hand grinder to repair and replace. The fault was not working very well
according to the worn bearing. So we serviced all parts and assembled according to the above
figure. Then the rotor was tide and we had to remove a metal washer which we fitted unnecessary.
Used a jack puller to remove old bearing and replace new bearing. But the problem was still there.
Again dismantled it and thought about the problem a long time. But we had no idea. So we made
small changes in the mechanism. After re-assembled it and checked it by rotating the rotor end.
But the rotor is a bit tide too. So we didn’t plug the grinding wire to the electricity. When rotate
the rotor, we felt that some parts were touching each other. Finally we found the cooling fan
blades were touching the stator grinder. So we moved the fan forward. The cutting plate and fixed
it. Finally reassembled the hand grinder and checked. Then the problem had been solved.
2.4 INTERNAL THREAD CUTTING USING HAND TAPS.
I had to taper a steel pale so I drilled the hole and reamed, until the whole,
Tapping size = Outside diameter = 2*Depth of hole
Depth of thread = 0.64*Pitch of the thread
1. Clamped a steel plate (1) securely in a vice (2) Drill and ream a hole of desired size.
2. Selected tap (3) and secure in tape wrench (4)
3. Applied cutting oil to the tap and the hole
4. Placed point of the tap in hole (5) and rotateted clockwise for right hand threads or
rotate left handed tap counter-clockwise for left-hand threads.
5. Removed tap wrench and using a square (6), checked tap for squareness. Check at
least two different positions on the tap.
6. Replaced the tap wrench and continue tapping operation. It was not necessary to
apply pressure, as the threads would be pulled through at all times.
7. Removed tap by turning in the opposite direction, wipe excess oil and metal shavings
from metal plate. Checked newly-cut threads with screw pitch gauge before inserting
screw or stud.
Recommended Tap hole Size
2.5 GEAR PUMP
Gear pumps are external, internal, or lobe types.
(a)External Gear Pump
The operating principle of an external gear pump. It consists of a driving gear and a driven
gear enclosed in a closely fitted housing. The gears rotate in opposite directions and mesh at a
point in the housing between the inlet and outlet ports. Both sets of teeth project outward from the
centre of the gears. As the teeth of the two gears separate, a partial vacuum forms and draws
liquid through an inlet port into chamber A. Liquid in chamber A is trapped between the teeth of
the two gears and the housing so that it is carried through two separate paths around to chamber
B. As the teeth again mesh, they produce a force that drives a liquid through an outlet port.
(b) Internal Dear Pump
The teeth of one gear project outward, while the teeth of the other gear project inward toward
the centre of the pump. One gear wheel stands inside the other. This type of gear can rotate, or be
rotated by, a suitably constructed companion gear. An external gear is directly attached to the
drive shaft of a pump and is placed off-cantering relation to an internal gear. The two gears mesh
on one side of a pump chamber, between an inlet and the discharge. On the opposite side of the
chamber, a crescent shaped form stands in the space between the two gears to provide a close
tolerance. The rotation of the internal gear by a shaft causes the external gear to rotate, since the
two are in mesh. Everything in the chamber rotates except the crescent, causing a liquid to be
trapped in the gear spaces as they pass the crescent. Liquid is carried from an inlet to the
discharge, where it is forced out of a pump by the gears meshing. As liquid is carried away from
an inlet side of a pump, the pressurise diminished, and liquid is forced in from the supply source.
The size of the crescent that separates the internal and external gears determines the volume
delivery of this pump. A small crescent allows more volume of a liquid per revolution than a
larger crescent.
(c) Lobe Pump
It differs from other gear pumps because it uses lobed elements instead of gears. The element
drive also differs in a lobe pump. In a gear pump, one gear drives the other. In a lobe pump, both
elements are driven through suitable external gearing.
2.6 REPARING A SINGLE STAGE CENTRIFUGAL PUMP
1.5 HP, 1.1 KW, 7.4 A, ph 230V, 2850 rpm, 50 Hz centrifugal pump was being leaking, it was a fress
water pump of the Hansakawa dedger. So we disassembled the pump and cleaned all parts, using
kerocene and water. Specialy impeller was cleaned also using WD40. The applying with a new
grapertite glands-4, the pump was assembled.