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pump losing / hard to prime

Posted by newtothepool (My Page) on
Sat, May 16, 09 at 22:27

Hi all,

I just bought a new home with a pool and I am trying to get as much info as possible on some problems I am having. My pool is approx. 13.5K gallons with a Sta-Rite 1hp pump and a Hayward DE filter. I have been told that the Sta-Rite models are notorious for leaking causing problems with suction. I have trouble trying to prime the pump each time I open it to clean the basket. I try and try with a garden hose filling the basket and eventually am able to get it to prime. And each time I turn the pump off a small amount of water squirts out from under the lid. I have been told this is normal, but I am looking for advice. The lid does go on tight and the seal or o-ring seems to be in good shape. Once primed it seems to be ok, but I just installed a Hayward Navigator cleaner and realized that my pump is not staying primed each time it turns off. I'm worried that I am going to run my pump when dry (set to run from 10 pm to 1 am) and eventually burn it out. Any help or suggestions would be greatly appreciated.


Follow-Up Postings:

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RE: pump losing / hard to prime

there should be no water squirting out from under the lid
i need a new o ring.
is the water level where it should be?
suction air leak ?

replace lid o ring


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RE: pump losing / hard to prime

If water is squirting out from the lid, then air can get in, thus you will lose, or not be able to prime the pump.

Need to lube the o-ring with a pool lube, or replace and lube the o-ring.


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RE: pump losing / hard to prime

I just put in a new filter, re-plumbed it and ran into a little problem - the pump would not prime when it fired up. I found out why there was a check valve in there, that I had removed. I put the check valve back in between the pump and filter and the pump primed every time. The valve stopped the water from leaving the filter, going thru the pump and thru the skimmer when the system shut off.

Dont know if this applies to your situation, just an idea


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RE: pump losing / hard to prime

Pump lids will seal differently under suction and pressure conditions. When the pump is turned off, a fairly large pressure wave hits the pump basket and some pumps are designed to allow that pressure to be released through the lid. Under suction, the lid seals and should not allow any air into the basket.

The water coming out of the pump lid after the pump is turned off is fairly common in pumps and should not be of any concern. In fact, that is better than allowing the pressure wave to flex the pump housing which might actually damage it over time.

However, if you are getting air in the pump basket, then that should be fixed since that can affect the performance of the pump.


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RE: pump losing / hard to prime

Mas,
Please tell us all which of the manufacturers make a pool pump that is designed to "release pressure through the lid"
I am just dying to know.


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RE: pump losing / hard to prime

Mas is right. I believe Whisperflows are designed to do this.


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RE: pump losing / hard to prime

Interesting,
I have had Whisperflo pumps on my pool since they came out with the things. I have never had water squirt from the lid.
I have also installed these pumps 10 to 12' below water level. If the pump lid was designed to "release pressure", wouldnt it just leak all the time?


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RE: pump losing / hard to prime

pb, It was a few years ago when I first noticed it, was alarmed the first time and was told they were designed that way to release the pressure spike. Its not much water.


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RE: pump losing / hard to prime

Quote: "wouldnt it just leak all the time?"

No, it requires a fairly high pressure in order for seal to leak but a pressure wave can have more than enough pressure to do this. Also, this is dependent on the design of the plumbing system and the size of pump. The higher the velocity of the water, the longer the pipe and the shorter the transition from full flow to zero flow, the more likely this is to happen.

Any positive or negative pressure seal has its limits. It is hard to design a seal which will seal well under both suction and high pressure. Pump lids are primarily designed to seal well in suction and because of this, do not seal very well for high pressure. However, they will seal enough to prevent leaks for reasonable pressures including below water level installations. Even a pump installed 10 ft below the surface of the water has only 4 PSI of pressure on the seal so this is easily sealed.

Also, pump lids have limits on the amount of suction that they will seal which is why they start to leak air when suction gets too high.

Moving water has a lot of momentum and cannot stop on a dime. When the pump shuts off, there is a lot of energy that needs to be dissipated. I have heard of cases where the pump lid blew off under certain conditions.

For example, in a 2" pipe with a flow rate of 100 GPM and the water stopping in 0.1 seconds will generate a pressure wave of over 200 PSI. However, the stopped impeller will allow some water to pass so the time to stop the water flow may be greater than 0.1 seconds and the pressure may not get this high but this illustrates the potential. Even if it takes a second for the water to stop, the pressure wave may still be over 40 PSI which may still break most pump lid seals fairly easily.

Owners of many different pump models have reported this happening so I do not believe that a particular pump is more inclined than another to exhibit this behavior.

But I do suspect that it is more dependent upon pumbing design. Lower head loss designs will have higher flow velocities and therefore more likely to experience this.

Here is a link that might be useful: Water Hammer


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RE: pump losing / hard to prime

Every one is so worried about the lid o-ring. How about a filter break down? The o.p. said he/she bought a new home not a new pool.


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