Pool loses prime immediately when vacuuming

PASTR6

New member
Jun 29, 2020
4
Ontario
Has anyone experienced these symptoms which have got me stumped. When we start vacuuming the pump strainer fills with air and the pump loses prime. I have checked all the inlet piping, and the hose etc. I even replaced the seals and gaskets in the pump. Without the hose on the pump runs fine. No bubbles at all at the strainer or jets. Something is happening when the inlet pressure is drawn down due to the throttling effect of the hose, we then get a slug of air. Where is it coming from? Help!
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,831
SW Indiana
Likely either a clog in the hose or a leak. Clog would be apparent when trying to fill the hose, leak may be harder to see.
 

PASTR6

New member
Jun 29, 2020
4
Ontario
We replaced the hose and did check it was clear. If it was a blockage how does the air get in the strainer, doesn’t that need a leak too?
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
23,882
San Dimas, CA (LA County)
I see two choices: air leak in the hose or the vacuum head has worn enough that it is sticking to the pool floor. If it's the head, you're not seeing air, you're seeing a vacuum in the pump basket. It will also make a huge racket. A pinhole in the hose is more likely. Try reversing the hose so the opposite end stays submerged.
 

PASTR6

New member
Jun 29, 2020
4
Ontario
Thanks for your suggestions. I inverted to vacuum head so it was facing upwards. It wasn’t sealing to the pool floor as I had the same issue. I swapped the hose ends and that didn’t help either. It sounds like a piping leak that is only noticeable when pump is drawing down the inlet pressure. If I throttle the isolation valve right next to the pump it creates the same symptoms
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,831
SW Indiana
We replaced the hose and did check it was clear. If it was a blockage how does the air get in the strainer, doesn’t that need a leak too?
If there is a blockage, water can’t get to the pump. If water can’t get there, some gas will fill the space.