Before overhauling centrifugal pump
As a thumb rule,
before dismantling or overhauling any onboard pumps, it's a good idea to check the standby pump's working condition.
and the availability of spares onboard. Like the gaskets and bearings.
The diagram below shows the cut section of the typical centrifugal pump.
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| Centrifugal Pump |
Here the pump bearing is oil-cooled (oil bath) and oil is filled through an opening - red cap.
and one more thing that you could notice is the mouth ring and wear ring.
and the sealing arrangement of the pumps. whether it's a mechanical seal or has got a gland packing.
The most important step on any Pump overhaul:
If you try to open any centrifugal pump without securing it or isolating it,
you could see the Big Raging eyeballs of your second engineer. Pointed right at you.!
Especially if its the high pressure fuel line.
This same goes for cleaning your filters.
YOU need to secure the valves. both inlet and outlet. And should lock it if needed.
and never ever forget the "MEN at WORK" tag in the ECR pannel
This is the most important step to do - for yourself, your juniors your friends, and for your family.
These are the safety measures related to the overhaul of a centrifugal pump.
Steps to overhaul a centrifugal pump:
1. Yes, as we discussed, isolate the pump Electrically and Mechanically.
Switch off, close, and lock suction and delivery valve, and tag it, MEN at WORK
2. CRACK OPEN.! Yes. it should not be opened fully. the flanges should be cracked open.
In case if the valves are not holding.
If it's a huge main seawater line or any high-pressure line. it would be uncontrollable.
A) Lifting the motor Away:
3. Ensure the SWL (safe working load) of the lifting block and check shackles.
Hang the chain block above the pump and hook into the i-bolt.
4. Make markings in the coupling so that the mating surfaces still MATES after boxing back.
5. Remove motor supply cables and apply insulation tapes.
6. using chain block, hook the motor, and keep it aside.
care should be taken to avoid any banging on mating surfaces.
7. Remove external fittings from pump casing like the pressure gauges and cooling pipes to sealings
B) Going Inside the Pump Casing:
8. Remove the top cover of the casing and scrap off the gasket
9. Check mating-surfaces. And replace the gasket.
C)Removing impeller and the shaft:
10. Now the pump shaft and impeller unit can be easily removed out.
11. Remove impeller nut which holds the impeller on to the shaft.
12. Pull off the impeller ( from the shaft )
13.Takeout the key which holds the impeller and the shaft together.
D) Removing the mechanical sealing arrangement
14. Remove the spring and the rotating part of the mechanical seal.
This is the easiest mechanical seal. This can be drawn easily if asked.
E) Bearing cover and bearing removal
15. Removing the bearing cover and Bearing Lock arrangement
16. Pull off that Stubborn - Bearing with the help of bearing puller.
6 Checks for your centrifugal pump:
It's nothing like a big boiler inspection. But a boiler inspection day can be beautiful too.
If you smile just after exiting from a carbon filled furnace.
Okay, It's easy.Pump overhauling and checks can be completed just before lunch if we have to.
1. Wear ring and Impeller ring
Have a look at this short video. A bit of information on WEAR RING.
Not to confused this wear ring and mouth ring;
Wear ring: It is fitted into the casing to protect the casing.
Some people may also call this as casing ring.
Mouth ring: Mouth ring is fitted on the impeller to protect the impeller.
And wear ring clearances are measured using feeler gauges
And speaking of these rings,
there is a beautiful term in our merchant navy called "Lantern Ring".
comment down if you know about this. Let them know.
2. Check the trueness of the shaft and threads on it.
How do you check the trueness of the shaft?
Keep the shaft of the lathe, and turn it
the deflection should not be more than 0.05 mm
3. No Pitting marks or corrosion in the shaft.
4. No Erosion or Pitting marks on Impeller or Impeller's seating surface.
5. Check the Keys, Mechanical seal. And casing.
keys should be snug fit on the shaft.
6. Replace sealing, bearings, and gaskets (consumables)
A beautiful infographic designed for you.
Enter parts renewed and date of the overhaul in the pump maintenance log.
Related read: 3 Onboard priming arrangements Of all time.
Procedure to start the pump after overhaul
1. Open inlet and outlet valves (centrifugal pumps can be also started with closed valves)
2. Open the air cock and purge out the air. And check for leakages
3. Turn the shaft by hand and check the freeness.
4. Reconnect motor. then remover men at work tags.
5. Reconnect cooling water.
6. Check for discharge pressure and amperage.
5 Common Problem and Answers for your pump
EEEh.!
Is your fitter trying to fix your bottom-most pump?
for the 7th time?
And if you are running up-and-down, consider scanning this.
Sure, life can be ups and downs.
but better to avoid running astronomical heights when you are onboard.
.
Inform these below reasons to your second engineer, for an easy appraisal.
Pumps not delivering any liquid
Primary Causes:
1. Pump not primed
2. Pump speed low
3. Chocked suction/discharge valve
4. Change in impeller direction
5. Leak in the suction line
6. Damage in Mechanical seal spring or sealing surface. Usually, The spring.
Reduced pumping rate or Lesser discharge pressure
Causes:
1. Suction line leaky
2. Low pump speed
3. Suction lift too high
4. Impeller dirty
5. Worn out mouth ring or casing ring (aka wear ring)
6. Stuffing box or mechanical seal is worn out.
Pump Fails to deliver after Running smoothly
Causes:
1. Suction line leaky
2. Leakage in sealing arrangement
3. High temperature in liquid or liquid getting heated up after a while
4. Suction side liquid gets empty
Pump overheated and draws too much power
Causes:
1. Misalignment of the pump and motor
2. Bend in Shaft
3. Stuffing box packing too tight or no cooling water for sealing arrangement
4. Too much clearance in wear rings
Excessive Vibration
Causes:
1. Loose foundation
2. Misalignment in any of the 3 axis
3. Unbalanced impeller or clogged impeller
4. Bearing Worn out
5. Bendy Shaft
If you are wondering about "misalignment in the axis" or new to pump alignment,
here is a video for you.
A simple video explaining Shaft alignment
Centrifugal pump on-a way to your bright future.
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Have a great day. Ciao for Now.!