Air in filter tank when running low speed

[amati5]

I changed to Pentair variable speed and run 1200 rpm 14 hrs/day to save energy. Then as soon as I cleaned the cartridges I got a lot of ait in the filter tank every day. The gauge shows very low pressure like 2 or 3, with or without the air. Running with 2200 rpm has no problem. I know that when the filter get dirtier the problem will go away. Is my filter (Pentair 420 sq ft) too big to run 1200 rpm?

why would low rpm pull air into the system. Shouldn’t it be the other way around?

thx

 

[mas985]

There are a couple of possibilities.

Then as soon as I cleaned the cartridges

After you clean the cartridges, do you run the pump on higher speed and purge the air out of the filter tank using the valve on the top of the tank until water comes out?

Next, when running on low speed, if you open the air purge valve on the top of the cartridge tank, does water come out or does air get sucked in. If the later, then the pressure in the tank is below atmospheric so air can get drawn in if there is a leak somewhere.

Lastly, do you see any air in the pump basket? Sometimes on low speed, the pump lid does not fit as tight and air can get drawn into the pump basket. However, it usually stays there because the flow rate is too low to push it out towards the filter. This may not be the case for your setup and that air travels to the filter tank.

 

[amati5]

Thx for your response.

Yes, I always purge out the air after opening the system for any reason.
when running low speed, if I open the filter tank valve, either water or air come out.
I see bubbles in the pump basket with both low and high speed. At low speed (1200 rpm)water level stay below the lid and at high speed (2350 rpm) it raises up near the lid but still not as full as when I ran full speed (around 3200 ?)with my old pump.
Maybe I should check the pump basket after the pump is off for a while to see if water stay in the basket or drain back into the pool?

 

[mas985]

Sounds like you might have an air leak. Try lubing both the pump lid gasket and the drain plugs.

 

[amati5]

would higher speed pull even more air if there is a leak from the basket? Instead it stops the problem. I did lube the basket lid and will check the drain plug.

 

[mas985]

Maybe, maybe not. The way the lid is designed, at higher speeds, there is more suction in the pump basket so the lid can actually seal better.

Valve o-rings are another place where air can sneak in.

 

[amati5]

Maybe, maybe not. The way the lid is designed, at higher speeds, there is more suction in the pump basket so the lid can actually seal better.

Valve o-rings are another place where air can sneak in.

yes, that makes sense. I didn’t think of it. Actually, I always do a final turn to close the lid after turning on high speed and there’s always more room to turn.

Just went out and check to find the drain plug quite loose. This explains why dirty filters stop or reduce the problem, less suction.

your help is appreciated.
thx.

 

[amati5]

We’ll, that didn’t do much. It’s still sucks in air at low speed, and loses prime slowly at rest. I replaced the plug’s oring with one from HD, 11/16 od 1/2 id, added thread sealant but it still didn’t help. There is no water leak to outside anywhere while the pump is running so I assume it’s not the filter tank’s clamp ring, correct? I suspect it might be the cause because it‘s old and I didn’t lube it last time I cleaned the cartridges.

Also, what is the second (identical) plug that is more on the pump housing that sits toward the left of the basket’s plug?

thx

 

[mas985]

There is no water leak to outside anywhere while the pump is running so I assume it’s not the filter tank’s clamp ring, correct?

Leaks are not always bi-directional. Sometimes air can leak in but water not leak out. They are vastly different sized molecules not to mention o-rings can sometimes seal under pressure but not vacuum or visa versa. So any o-ring can be at fault.

However, if the pump is sucking in air when it is running, then the issue is more than likely on the suction side of the pump. Do you have any valves before the pump inlet?

 

[amati5]

leak from suction side can cause losing prime when not pumping too, right? strangely, it doesn’t suck in air at higher speed given the plug is tight, so is the lid with newer gasket.

I do a valve to divert water either from the pool or spa or both going to the pump. It’s set to pull 100% from the pool most of the time.

Should I check the second plug, or it’s just for draing the pump’s housing if needed?

 

[mas985]

There are two drain plugs. There is one that is at the bottom of the pump basket. That is on the suction side of the pump and would leak air into the pump if it was not sealing properly. The other plug is on the pressure side of the pump so would leak water out when the pump is running if it was not sealing properly.

If you have already lubed the pump basket drain plug, they you might look at the valve o-rings to see if they are in good condition or need replacement. If they look ok, try lubing them.

 

[amati5]

yeah, I should look at the diverter valve. I haven’t done any maintenance on it for 20+ yrs because it’s body seems to be submerged in the water and I am not sure how. It’s the Ortega valve
thx