Pump loses prime at shut off

Pool pumps, filters and the plumbing of swimming pools. Problems relating to the piping and pumping of the swimming pool water.

Pump loses prime at shut off

Postby chaotic1 » Wed 25 Mar, 2009 14:51

My pump is losing prime when the pool shuts off and water gushes from the skimmer. When I try to restart the pump, it will not prime. When I add water to the pump prior to restart, it works fine until it shuts off again. What is causing this?
chaotic1
 

Pump loses prime at shut off

Postby Pool User » Thu 26 Mar, 2009 00:56

Almost inevitably a faulty check valve. :(
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Pump loses prime at shut off

Postby poobs » Thu 26 Mar, 2009 14:21

chaotic1 wrote:My pump is losing prime when the pool shuts off and water gushes from the skimmer. When I try to restart the pump, it will not prime. When I add water to the pump prior to restart, it works fine until it shuts off again. What is causing this?


I have the same problem but it is on my shallow well :crazy:
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Pump loses prime at shut off

Postby Ray1031 » Sat 28 Mar, 2009 14:57

chaotic1 wrote:My pump is losing prime when the pool shuts off and water gushes from the skimmer. When I try to restart the pump, it will not prime. When I add water to the pump prior to restart, it works fine until it shuts off again. What is causing this?


I agree that a check valve may well be the problem ... especially if you have either an inline flapper/swing valve type (the plastic hayward and sta-rite type) "or" if you have a Hayward EC serice DE filter. These valves use a rubber flapper with a small brass or plastic weight mounted on them. The "flapper" is attached by stretching two tiny holes over pegs within the valve. Though they tend to last for years, I have seen many where the holes eventually stretch and the rubber flapper comes loose and floats free - then you have no check valve and the filter "back pressures" through the pump and blows back prime. The most sure fix in this case is to replace the check valve.

However: that is not the only thing that can cause this, since I have seen it many times in sand and cartridge filters that do not have check valves built in. In these cases, it can be simple plugging causing the problem. Both DE and Cartridge filters can become permanently plugged with debris/solids that do not clears with normaly backwashing/cleaning methods ... in these cases a simple acid cleaning of the filter/fingers/grids may cure the problem.

In the case of a sand filter there could be a garbage built up on/in the top inch of sand that is not backwashing out (for whatever reason) and is a permanent impediment/pressure increaser. or the center pipe inside of the filter may be brokem/split. A broken/split center pipe will normally allow some amount of sand to return to the pool during filtering as an indication - but not always.

Same result though - blowback of the prime at shutdown. The cure here is to open the filter and inspect things. Check the condition of the sand and the integrity of the "Center pipe" It sould be one solid unit from the multipart valve down to the laterals at the bottom of the filter. No, you do not need to remove the sand to check this. If the center pipe has snapped (which I have seen more times than I like) then part of it nurmally remains within the multipart valve when it is removed. If the sand seems excessively dirty - scrape away and remove the top couple of inches. if the sand below seems good (is granular, well defined and there is no clumping) then you can simply add enough "new" to make up for that which you removed. If the center shaft is broken or you locate a split in it, you can repair it easily by cutting it squarely below the break or crack - sliding a 1 1/2 " pvc coupler over it and cutting a piece of 1 1/2 pvc pipe to the length of center pipe removed. Slip it down into the coupler and the multiport valve will slide down onto it's "new" center pipe. This repair does not "have" to be glued in place - though I usually do. If not glued you may find it seperating at the coupler if the filter is ever opened again.

Ray
Ray10311 is an experienced pool professional with 25 years experience
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