Air in Sand Filter and Air in Pump skimmer

[Eamonn]

Thanks for the tips advice

Can you help on this point, I don’t fully understand why no air is getting in when the water is circulating only. As noted when the water is by-passing the sand filter, no air gets into the pump skimmer and I am 100% certain of this as I have left it run for hours. The water turns perfectly though the pool. Then when I switch to filter mode air starts getting in immediately into the sand filter and pump skimmer. Is this because the filter mode increases the pressure on the suction side i.e. causing a draw of air into the system. i.e the filter mode puts the whole system under higher pressure exposing leaks. Is this assumption correct?

Replys to your questions:-
When you switch to filter mode, do you see any air in the pump basket?
Yes air builds up inside the pump skimmer, after running for a long time its gets to about 3/4 full of water, it never goes below this level.

Have you check the skimmer weir door to make sure it isn't stuck?
The skimmer weir is not stuck

Also, check the skimmer to make sure it is not sucking in air (i.e. a vortex).
No Vortex, water is circulating normally

When you have air in the basket and filter does the circulation stop, that is no flow from the return eyeballs?
The water continues to flow! I am just worried that it is not filtering correctly as there is not enough water in the sand filter.

Also air collecting in the filter should purge out into the return flow and discharge into the pool.
Doesn’t seem to as I don’t see air bubbles in the return water going into the pool,

One other thing to try, put a lot of soap bubbles round all the suction side of the pump and see if any gets sucked in.
Thanks for the tip, I tried with washing up liquid but the bubbles were too small to see much going on I will try to find some kids bubble mix to do it properly.

[Denniswiseman]

If when you are filtering the returns are flowing OK. Then you have filterd circulation into the pool
The water goes into the filter at the top, through the sand and out through the laterals to the pool.
You may think that the filter is full of air but their may be air according to the design of the filter in the top of the filter and the flow of water through may be causing turbulence
You say the skimmer basket is 3/4 full with water so it never empties completely, which is OK
I doubt that the filter mode would increase more suction in fact it would be less because of the resistance through the filter. Fitting a vacuum tube to the pool suction side will increase the pump suction resistance thus making the air intake more possible.
That may be an idea try vacuuming and see if the circulation stops

[mas985]

Is this because the filter mode increases the pressure on the suction side i.e. causing a draw of air into the system. i.e the filter mode puts the whole system under higher pressure exposing leaks. Is this assumption correct?

Not quite. When you put the filter in re-circulation mode, the return pressure will drop, flow rates will increase and the suction head will also increase usually making air leaks worse. However, the higher suction could also help seal the air leak while the lower suction in filter mode may not. That really sounds like a pump lid gasket problem.

Have you removed the gasket and inspected it for cracks?

Have you done the same to the pump drain plugs?

[Eamonn]

Hi..Thanks for all your help.

I found the problem. It was on the suction side alright. The joint connecting the pump to the pool pipework, is a union joint. The union joint was not tight. I could not see any water drops when it was circulating water, but when the pump was turned off I found a very small leak. I tightened up the joint and solved the problem.

Note 1: I still have a small leak on the discharge side of the pump but that does not cause air to get into the system
Note 2: Be careful not to over tighten plastic as it can break