Air in Sand Filter and Air in Pump skimmer

[Eamonn]

http://tinypic.com/r/atloa8/5
I have a below ground pool. All the pool equiment sits at a lower level

I have air in my sand filter and in the pump skimmer and I cant solve what is causing it.

If I run the pump for a period of 2 hours it fills the sand filter with air at I guess about 3/4 of the sand filter. The pump skimmer also fills with air about 3/4 the way.

I have small water leak on the discharge side of the pump, just at the first joint to the pump. see photo the joint is now white as covered in mastic which is not stopping the water leak. This is my priimary suspect however I read that a leak on the discharge side should not cause air to enter the system.
Question 1. Is this correct?

Checks done
(a) I have checked the water level in the pool - Its Ok the water is drawing well and not sucking in air. (b) I have checked the pump skimmer, the rubber ring and applied magic lube and put the lid back on tightly all looks ok. (c) Sand changed earlier this year in the sand filter

Question 2: Would a blockage in the pipes caused by debris, leaves etc cause a restriction in the water flow and cause air to enter the system as the pump is pumping too fast?

Question 3: any other suggestions as to what may cause the problem would be of great assistance.

Thanks alot
Eamonn

[mas985]

Question 2: Yes, a blockage can cause very high suction that can make any pump lid leak air.

Is your filter pressure lower than normal? If so, check for a suction side blockage.

[Eamonn]

Hi

Thanks million for your advice.

I am not sure if the pressure is lower as I haven't been monitoring the pressure. But I think a blockage on the suction side could be causing my problem, combined with a quite a strong pump for only 1 return pipe.

Before I get someone out with the equipment to rod the line. Is it safe to assume that the small water leak (1 drop a minute) on the discharge side would not cause air to leak into the sand filter system ?

Thanks

Eamonn

[mas985]

A leak on the return side (discharge) would only leak out when the pump is on. However, the same leak can leak air in while the pump is off and if it is near the filter, the filter can accumulate air. If this is the case you would normally hear the air bubble up into the filter while the pump is off.

[Denniswiseman]

If your equipment is at a lower level than the pool level then that small discharge leak won't draw in any air as it will be under the static water pressure

Most air problems occur in the suction side of the pump
Generally when your pump skimmer basket fills with air it stops your circulation.
When it pumps water any air should be purged from the skimmer and filter and show as bubbles from the return eyeballs

Does the pool lose water? If so you may have a leak from the skimmer to the pump
Do the return eyeballs have a good flow when working, that would eliminate a blockage

[Eamonn]

Hi

Thanks for your replies, I appreciate it.

The equipment is below the water level and no air leaks into the system when the pump is off. So I assume that the problem must be on the suction side

My pool does not loose water and the return eyeball have a what appears to be a normal flow.

I think my opinions are now

(i) a blockage reducing the flow, causing high suction making the pump lid leak air
From reading message boards I assume the best way to investigate this is to pump water in the opposite direction with a water hose and bladder?

(ii) an air leak at one of the junctions. If so this is going to be very hard to rectify if its below ground.
Any suggestions?


Thanks alot

[Denniswiseman]

On checking for a blockage on the suction side
Block the skimmer
Disconnect the suction pipe from the pump
Unblock the skimmer and check the water flow coming from the disconnected pipe
Although I don't think that is your problem as you say the return eyeballs have a good flow
You say that the pool doesn't lose water so the suction line should be intact
I would suspect that air is being sucked in from the suction side of the pump. Have you tried a new "O" ring on your pump skimmer lid with silicon grease

I had a new pump that sucked in air only when vacuuming, a new "O" ring and silicon grease cured it

[Eamonn]

Hi

Thanks alot again for your replies.

I have changed the o ring and put plenty of magic lube around the joint , no change air is still getting in, when I switch the filter on.

I put the pump on recirculation mode only, ie by-passing the sand filter. I left it run for 4 hours. No air got into the pump skimmer. The water is circulating nicely into and out of the pool, So am I correct in assuming that there is no blockage on the suction side?. Also as no air is getting in either when it is on recirculation mode does that mean I have no leak in my underground pipes (which is my biggest worry) ?

When I switch it back to filter the sand filter starts to fill with air ie it would take about 4 hours to substantially lower the water level in the sand filter. Therefore am I correct in assuming the air must be comming into the system from the sand filter or discharge side?

Any suggestions or advise would be welcome!

[mas985]

No that's not possible. Air can only enter the plumbing system when the air pressure is higher than the water pressure and that can only happen on the suction side of the pump especially when the pump is below water level. If there were a leak on the pressure side of the pump, you would see water coming out, not air going in.

When you switch to filter mode, do you see any air in the pump basket?

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

Also, check the skimmer to make sure it is not sucking in air (i.e. a vortex).

[Denniswiseman]

One other thing

When you have air in the basket and filter does the circulation stop, that is no flow from the return eyeballs
Also air collecting in the filter should purge out into the return flow and discharge 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.

[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