pump basket turbulence on MD only

[Diver]

while troubleshooting this i noticed that i get a little bit of air in the pump strainer basket when running MD only.

i have 1.5" plumbing all around, skimmer & MD on intake and 3 returns. when i run both MD and skimmer, i have absolutely no air in the basket and it all seem transparent - no visible turbulence. the same on skimmer only.

when i change to MD only i hear a "ooosh" sound and immediately i can see air in the basket. it seems like it gets drawn into a basket very quick, almost like it comes from under the lid. which it might when the pressure drops when skimmer valve closes. the amount of air in the basket goes down, but some of it stays and i could see some turbulence. i don't see the column of water coming in and being thrown around, but i could see how the water moves.

filter pressure:

MD+skimmer: 11.3 psi
skimmer only: 10 psi
MD only: 9 psi

now i wonder if i do have an air leak in the MD line or maybe my pump (SFHP 1.1) is not powerful enough to draw enough water from MD fast enough? i hope it's the latter

 

[Bama Rambler]

The MD only definitely has more suction head and if there's a leak somewhere, the greater suction head would exacerbate the problem. I'd try looking for a leak at all the above ground fittings and even the pump strainer basket lid. Clean and lube everything good and if there are valves try running water over them when in MD only and see if it helps the problem.

 

[Diver]

Dave, I will clean the seal on the basket and try the garden hose trick. i hope it's just extra suction head and not the leak and the air comes initially from under the lid and then it seals again.

 

[JohnT]

It may be just a lack of sufficient flow from the MD to keep up with the pump.

 

[Diver]

It may be just a lack of sufficient flow from the MD to keep up with the pump.

that's what i'm thinking too

 

[Bama Rambler]

I should have added, that if you don't find a leak, don't be too concerned about it. AS JT said, it may just be the greater suction head through the MD lines and nothing wrong at all.

 

[Diver]

well, there must be at least a temporary leak when the pressure drops - the air has to come from somewhere. i'm not very concerned about it - i don't run MD only so i just wanted to check that there is a possibility of this occurring without a prominent air leak in the line... and look like there is.

 

[marty]

Any luck?

 

[Diver]

i was a bit surprised to get a notification for update on this thread to only find out it was a thread started by me!

i actually have an opposite problem right now - i have some air in the basket when using skimmer only. two things changed since last year that made me uncover that - i changed the motor to 2 speed and i polished the cover for the pump basket. so now i can see with a skimmer only on high speed there is air coming to the basket but it gets all sucked into the filter. on slow speed there is a bubble or two floating on top of the water under the cover. that's on skimmer only. MD only seems to be doing ok.

there is a very slow leak in skimmer line that i can detect with a dye. it's very small, but i think it's what causes the air in the basket. i plan on digging and following the skimmer line as far as i can to see if i can spot the problem area. we didn't have rain all summer, but got tons in a last week and today, so digging will have to wait...