Need help with this one

[JesseFrank]

My set up is as follows.

Skimmer pool with Hayward 1.5Hp pump with 28" Hayward filter with 6 way valve and a saltwater chlorinator which commands the pump.

There is a check valve between pump and filter, which has been checked and is working properly, and a manual tap on the main drain from the filter which is closed.

Pump is almost at water level and next to the pool.

All has been working properly for the past 3 years.

Now for the past week when a filter cycle ends a large air bubble sucks into the chlorinator cell, leaving the cell almost without water.The water level in the leaf basket of the pump also goes down at the same time.

I have checked all connections on the pipes, pump filter and wherever but can't find a leak.The air bubble happens right when the filter cycle stops and there isn't any more air sucked in the system after that.

Now if I after the cycle is ended, and the air bubble is in the system, I let the pump run for a minute the air bubble is gone and will not return .

Any suggestions as where to look are welcome.

I want to add that about a week ago I have removed the debris basket from the skimmer since it was broken, but I would be surprised if this could be the reason.

[SwimmingPoolsThailand]

Without knowing more, the quick answer is that the missing strainer basket in the skimmer shouldn't be too much of an issue as long as the pipe is not now blocked - usually the strainer basket in the pump will catch most oversized debris. This basket is however important because it prevents the impeller from getting damaged;

The check valve between the pump and filter may not be a strictly necessary accessory - check it again because the cone (or ball inside) are known to stick, especially in cheaper spring-type cone check valves. A check valve just before the pump's intake port may assist slow self priming pumps to prime quicker. If the chlorinator cell runs dry, most quality chlorinators have a 'no flow' protection feature which will shut off the pump preventing damage to both chlorinator cell and the pump.

You should really also be drawing water from the maindrain as well as from the skimmer.

Check all the O-rings in the unions on the suction side - you'd be surprised how these can get leaky. Check also that the large O-ring on the clear plastic strainer lid is not drawing air.

In worse case scenarios, the mechanical seal on the motor shaft may need replacing especially if the pump has run dry often. The seal between the motor housing and the pump body housing may also need to be replaced.

Air leaks in any underground pipes on the suction side are of course more difficult to locate and repair.

After thought: is this a top mount or side mount filter? Side mount filters occasionally need to have any accumulated air bled off through the air release valve in the lid. Also, are you sure that the spider gasket in the MPV is seating correctly?

[JesseFrank]

Without knowing more, the quick answer is that the missing strainer basket in the skimmer shouldn't be too much of an issue as long as the pipe is not now blocked - usually the strainer basket in the pump will catch most oversized debris. This basket is however important because it prevents the impeller from getting damaged;

The check valve between the pump and filter may not be a strictly necessary accessory - check it again because the cone (or ball inside) are known to stick, especially in cheaper spring-type cone check valves. A check valve just before the pump's intake port may assist slow self priming pumps to prime quicker. If the chlorinator cell runs dry, most quality chlorinators have a 'no flow' protection feature which will shut off the pump preventing damage to both chlorinator cell and the pump.

You should really also be drawing water from the maindrain as well as from the skimmer.

Check all the O-rings in the unions on the suction side - you'd be surprised how these can get leaky. Check also that the large O-ring on the clear plastic strainer lid is not drawing air.

In worse case scenarios, the mechanical seal on the motor shaft may need replacing especially if the pump has run dry often. The seal between the motor housing and the pump body housing may also need to be replaced.

Air leaks in any underground pipes on the suction side are of course more difficult to locate and repair.

After thought: is this a top mount or side mount filter? Side mount filters occasionally need to have any accumulated air bled off through the air release valve in the lid. Also, are you sure that the spider gasket in the MPV is seating correctly?

Thanks for your comprehensive reply. The filter is top mount, and there are actually no unions on the suction side, only ball valves.

The check valve was checked a few days ago, and since it is such spring cone type, there was indeed something stuck between, but is has been cleared and is functioning properly now.

I have a feeling that I see some airbubbles under the transparent cover of the pump, but this can be normal behavior. How do I check if that seal leaks ? I have checked everywhere and everything is powder dry.

The strange thing is that if I let the pump run for a minute after the cycle there is no air bubble anymore. I would think that if there was an airleak in the suction side the air would sipping in slowly over the hours when the pump is inactive, but this is clearly not happening.

The seal from the MPV is sitting correctly, but since I previously had a leak to the maindrain I placed a ball valve on the drain. Is there another place in the MPV where it can suck air ?

As for your suggestion that I should draw water from the floor drain as well, would you think that the reason is that the pump doesn't get fed enough water through the skimmer ?

[PoolDoctor]

Sounds like water is reversing itself in the system and returning back to the pool once the pump shuts off. This is like taking your finger off a straw and releasing the water trapped inside the straw. When you turn off the pump, stand quietly and try to hear if there is any air leaking into the system. If you hear water rushing past the check valve also, that might be the problem. also. Sometimes, the return line valves (especially the ones with red handles or twin union valves) are not fully tightened down. They won't leak water, but they will allow just enough air to enter to let the water reverse itself.

Does the pool have air bubbles when running the pump? If so, that's usually a suction side leak. As you said though, that the air disappears after you turn on the pump, sounds like you do not have a suction side leak

Seperately, as mentioned, you should also circulate water via the main drain. A skimmer is often not enough flow to achieve a good turnover time.

[JesseFrank]

When the pump is inactive there is no sucking sound on the MPV, I know that one from when the exit to the drain was leaking, but now with my ear on the valve there is no sound.

I just noticed however that there is a movement in the water in the debris basket of the pump every 30 seconds or so. I don't see a bubble coming up but I see some movement.

[PoolDoctor]

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When the pump is inactive there is no sucking sound on the MPV, I know that one from when the exit to the drain was leaking, but now with my ear on the valve there is no sound.

I just noticed however that there is a movement in the water in the debris basket of the pump every 30 seconds or so. I don't see a bubble coming up but I see some movement.

Yes, that's likely water returning to the skimmer backwards if you know what I mean. Is there a check valve on that line?

[JesseFrank]

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When the pump is inactive there is no sucking sound on the MPV, I know that one from when the exit to the drain was leaking, but now with my ear on the valve there is no sound.

I just noticed however that there is a movement in the water in the debris basket of the pump every 30 seconds or so. I don't see a bubble coming up but I see some movement.

Yes, that's likely water returning to the skimmer backwards if you know what I mean. Is there a check valve on that line?

Think you misread my comment. There is NO sound in the MPV. I think rather that the movement in the water are water drops that fall of the pump cover.

There is a check valve right before the pump intake, and that has been checked.

[JesseFrank]

Thanks for the tip of drawing water from the main drain guys. That seems to have done the trick.