Lose suction when vacuuming

[Juli]

I didn't know if I should post this in the vacuum or pump part but I am going this route.
We installed a new pump a couple weeks ago after the intex one finally crapped out. I cannot for the life of me get it to use the auto vacuum.
I have both the Hayward bug/penguin and a kreepy krauly (even crappy suction with the hand vac). .
When I do the suction test it won't even go to the minimum mark, it just stays at the top and around 18 psi.
But if I have it on backwash/waste it works beautifully, drops the psi to 10 and has great suction (goes past the max mark).
Why does it work so well when it goes straight to waste?
I have no air in my lines and no leaks...it just quits working eventually and gets air in the leaf basket.
Leaf basket is clean, the sand is brand new, got lube on the oring for the basket. Hoses are all new for the cleaners.
Halp

 

[foobert]

Re: Lose suction when vacuuming

Pumping to waste is an easier path for the water to flow through -- it by-passes the filter and all the return plumbing (as you've noted from the 18 to 10 PSI reduction), thus, you get more flow through the pump. Some reduction is normal.

If you need more flow, you have to do some or all of the following:
Keep filter clean
Increase size of plumbing
Increase number of returns
Get a larger filter
Get a "better" pump -- Pumps are designed for the amount of head pressure they have to work against. If you already have an optimal pump, then, you might need bigger...

 

[Juli]

Re: Lose suction when vacuuming

Well after a lot of choice words we hard plumbed the suction side (we were using game adapters with the intex hoses). We did it with 2" pipe and I do believe that fixed it. The kreepy has been going 30 minutes with no loss of suction. Fingers crossed it sticks because I've never wanted to pick up a 300 lb pump and throw it so bad. Lol. I had no idea that the size of pluming and actually having it hard plummed would make such a big difference.

Thank you SO much for your reply!

 

[foobert]

It's amazing how much difference it makes freeing up the suction side of the pump.

 

[Sfpat]

Pumping to waste doesn't change anything on the suction side. Working better when pumping to waste suggests a dirty filter. Backwash, clean the filter and see if it improves.

 

[foobert]

Pumping to waste doesn't change anything on the suction side. .

Flow is determined by the total head in the system. Part of the total head is friction due to flow. By reducing the friction losses, it reduces the total head, allowing the pump to move more water.

The absolute PSI drop from going to waste vs going back to the pool is only one part of the total head. With less friction on the intake side of the pump, that delta in PSI will actually be even greater now due to shifting more head to the outlet side of the pump.