Pump looses its prime, suspect air leak

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  #1  
Old 10-03-09, 01:08 AM
D
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Pump looses its prime, suspect air leak

Hello ,




Let me explain the scenario. I live in a building. We have a water pipe supplying water from the city mains running parallel to my building. This horizontal water pipe is shared between my neighbour and me. We both have water pumps that suck water and fill our overhead storage tanks.


Please refer to the key in the diagram to understand the shapes .

If the figure does not load, please click : Imageshack - dsc03434pb8.jpg


I have a check valve just about half an inch from the begining of the vertical pipe. Off late, whenever I start my pump,after say a gap of 20 hours, I get a very shrill sound from the pump for 2-4 seconds and I do not get any water. If I leave the pump on after this sound, about 4-7 minutes later, I will get a perfectly normal flow of water.

Alternatively, I can open the priming tap( which is connected to the suction line of the pump) and pour some water in the suction line, a shrill sound comes once again lasting about 2-4 seconds and then I get the normal flow of water.

Another thing, I've noticed is if we switch off the pump after its run for 30-45 minutes and after the water started flowing, then restart it after 15- 30-45-60 minutes ( never tried beyond 60 minutes), I would never have to do any of the things I have mentioned above. The water would just flow normally.

We have not had any problem with this setup all these years, however this problem started the day my neighbour extended the main pipe & took a seperate connection from the mains till his house. Earlier we had a mutual understanding where one pump ( placed in my house ) would supply water to both houses.

Now since we have seperate pumps, we start pumps one after the other, never together.

When my neighbour did this seperation I saw that I had a leaking check valve which was leaking like say 30 drops a minute or less. I did not bother changing it that day.

I did another test because I felt that even if it was leaking, since it was connected so close to the source it would not matter. I filled the suction line completely using the priming tap near the pump and then monitored it for 12 hours, I did not notice any noticeable drop in the level of water. Can this method be used to check for a leak in a check valve ?

I still have not replaced the check valve.

I feel its a air leak somewhere, but I cannot figure it out.

I hope I have explained the problem well enough and I hope we can find a solution to this daily priming activity.

Thanking you

Danny
 
  #2  
Old 10-03-09, 02:38 PM
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"I get a very shrill sound from the pump for 2-4 seconds and I do not get any water"

Bearings going bad.

"with this setup all these years"
You don't say how old the pump is. 15 years is about all you can expect and that's from pumps made 20 years ago. These days, they don't last as long. Magic of thinning the metal, cheapening the product, etc.

If the level of the water doesn't go down, then there is no leak in the check valve. Examine the joints, since that is where a leak would happen. If you suspect a suction leak, spread a thick layer of shaving cream around each joint and while the pump is running look for pinholes or dimples.

But I think the long squeek sound is a tip. The rest could be co-incidental or irrelevant.
 
 

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