MAIN SEAWATER PUMP OVERHAUL REPORT

MAIN SEAWATER PUMP OVERHAUL REPORTIntroduction

Over the past few week, it was noticed that the forward port bilge have been filling up with water very fast. After tracing the source of the leak, it was realised that the main seawater pump No. 2 was leaking badly from the mechanical seal cover. It was imminent that a repair should be carried out. This report will note the step by step procedures of carrying out the above-mentioned repairs.

Preparatory Work

Before any work on machinery can begin, it is important that the machinery be isolated first. This is done by first putting off the main breaker for the pump located in the engine control room and putting up a Man at Work sign on the panel. Apart from that, we locally isolate the pump by engaging the twist lock stop button located next to the pump. All this is done to prevent the pump from being accidentally started while working on it.

Next, we asses the problem and conclude the probable cause of the leak. Upon inspection, it was concluded that the mechanical seal had given way and water was leaking from the shaft.

The work area was cleared and appropriate tools were selected and brought down to avoid the inconvenience of looking for tools at the last minute. Chain blocks are put in place to aid in the lifting of parts. Wooden planks and boards were also made available for the dissembled parts to be laid on so as not to damage it.

Appropriate manuals and diagrams were studied and made ready and also checks were done to see whether spare parts were available on board. After which, a permit to work was issued.Once all this was done, orders were given to commence work.

Actual work-The first thing that was done was to shut off the suction and discharge valves. Next, the pump was drained of all water and pressure by removing the drain plug.

-The pump had to be un-coupled from the motor and this was done by loosening the coupling bolts. The coupling used is a flexible coupling made of ductile cast iron. The coupling bolts are tightened by the bush wish will be compressed at the bolts are tightened and thus securing both couplings.

- The bolts on the mechanical seal cover are removed so that the shaft can be freed from the casing.

- Once un-coupled, the front pump casing is taken out by removing the bolts. It is then lifted out of the work area and placed on a wooden plank. The casing which has been taken out is now cleaned with a wire brush and secured safely aside.-Now that the whole shafting is clearly visible and freed, it is removed by lifting it out with the aid of a chain block. Before doing so, the area of which the sling is put around must be protected by tying a piece of cloth around it so as not to damage the shaft.

- The shaft comes with the impeller, wear rings, mechanical seal, bearings and coupling as a single unit and it is carried up to the engine room where the mechanical seal will be replaced.

- Once the shaft arrangement is safely resting on a wooden board, the coupling and bearings are removed by means of a puller. - The mechanical seal now can be slowly eased out and checked for damage.

Condition of the Mechanical SealAfter checking, we noticed that the o-ring at point No. 1 was damaged and therefore was the sole reason for the leak. Because the o-ring is designed as a sealing element, it is the most important unit which prevents water from leaking. A break in the seal would produce such leak.

As the pump was already opened, it was also decided to inspect the condition of the other components.

A clearance test was taken between the wear rings and the impeller and we noticed that the clearance was far greater than recommended by the manuals. It was also decided to be change with new ones.

All the spare parts were made ready and the pump was now ready to be assembled again.

Assembly

Assembling the parts proved to be more of a challenge than dismantling.

- The new mechanical seal is first fitted on the shaft.

- The mechanical seal cover follows after.

- Next, the bearings had to be put back onto the shaft. Bearings are designed to sit flushed on the shaft and therefore, the clearance between the shaft and the bearing is almost negligible. To slide the bearing in place, it was necessary to expand the bearings first. A can of oil with the bearings inside was heated until boiling temperature. Using a pair of thongs, it is then removed and put back on the shaft.- The final part of the shaft was the coupling and it was hammered onto the shaft with the key in place.

- Now that the shaft assembly is ready, it is brought back down to the work area.

- Again, with a chain block, the shaft is lowered into place and the pump casing is boxed back.

- All bolts on the casing are tightened.

- The mechanical seal cover is also bolted into place.

- Finally, the pump coupling is put in line with the motor coupling and the bolts are tightened.

TestingBefore testing the pump, final checks are done to make sure that no part is missing and that everything is properly tightened. All the switches are put back to normal.

The breaker in the engine room is also put back on. The suction and discharge valves are opened up with the drain plug still opened so as to allow the pump to be purged of air first.

When water is seen coming and no more air is present, the drain plug is screwed back on and the pump is now ready to be tested. All tools are cleared from the area first and the pump is switched on intermittently. This is to ensure that any loose connections do not give way when the pump is running fully.

Once it is seen that the pump is holding and that all is good, the green light is given and the pump is started and left to run for sometime.

The original source of the leak is examined and it is noted that it has been rectified.

Conclusion

It was concluded that the reason for the faulting is largely due to the fact that the mechanical seal was old and the o-ring had hardened. This contributes largely to the cause of the breakage of the o-ring.

Wear rings on the other hand are put in place as a sacrificial piece for the impeller. To avoid the impeller from coming in contact with the casing, wear rings are put in place to take the wear and tear of normal operations. Wear rings are periodically changed and the system was updated as to when the next change should take place.

REPAIR & MAINTAINENCE