Using a side-vacuum port as a return

[Provencal Pool Jay]

My return lines are too small (50mm, needs 75mm) for the flow from the pump, so the pressure builds up in the filter. Since it's an in-ground pool, the cost is prohibitive to replace them. Can I use a valve to use the vacuum-side port as a return for the 90% of the time I'm not vacuuming or using the Polaris?

 

[Darin]

What speed is your pump running?
What is the filter pressure?
Who told you your lines are too small?

 

[1poolman1]

My return lines are too small (50mm, needs 75mm) for the flow from the pump, so the pressure builds up in the filter. Since it's an in-ground pool, the cost is prohibitive to replace them. Can I use a valve to use the vacuum-side port as a return for the 90% of the time I'm not vacuuming or using the Polaris?

If you have a 280, it is, essentially a return line. Just remove the fitting from the wall. Water is always going through that line when the main pump is running. What pump do you have? 50mm = 2", usually a very adequate size, especially if you have a variable-speed pump. Your return fittings at the wall are probably all 1.5" (38mm?) anyway.

 

[Provencal Pool Jay]

What speed is your pump running?
What is the filter pressure?
Who told you your lines are too small?

The pump is a 3-phase Pentair Ultraflow running a constant 32m³. It's a new exact replacement for the old one that had been dying a slow death since we acquired the house and pool 2 years ago.
The filter pressure is now 1.4+bar/21 psi. The filter itself has 75mm intake and discharge ports.
Two different pool guys said that lines on both sides are too small (also too many 90° elbows). The skimmers have 3-50mm lines that come together into a single 50mm line. The 4 returns are fed though a single 50mm line.

My thought was that opening up another 50mm line would literally take the pressure off them. Reduce by half, even.

Yes, with the Polaris, it's essentially a return line, but the secondary pump has a much smaller line in and out, so it only takes significant pressure off when that pump is running.

The nozzles on the 4 returns are maybe 25mm each, so they're not the problem with the 50mm feed for all 4. (19.6 cm² vs. 19.63 cm²)

I did check if removing the nozzles helped at all. Maybe brought it down .5 psi. ti 1.4 bar/20 psi.
What did help getting it into the yellow was allowing a bit to bypass the saltwater converter, which is fed with 50mm pipes (it branches off a 75mm main), taking me to 1.3 bar/19 psi.

 

[Darin]

I do not know what 32 m2 is equal to in RPM.
Is your motor a VS? If so, slow it down so that your skimmers/SWG still work properly. If you are running your motor wide open, that is not necessary if you can slow it down so that your skimmers/SWG work. That alone will reduce your pressure. 21 psi will not hurt anything on your filter.
If you have a single speed motor you can throttle back on your pump discharge side with a valve to reduce pressure as well.
Good Luck.

 

[Provencal Pool Jay]

It's 2850 RPM. The 32m³ is the amount of water it moves each hour in cubic meters.
It's not variable speed.
The skimmers have always been somewhat feeble, so we were planning on opening up the line into which they converge into a 75mm now that the pump runs properly.

I've read that 21 psi isn't worrisome, but the filter does bulge and groan when the pump starts. That's a bit disconcerting.
Though I gave it a backwashing yesterday (and collected 5 giant storage bins of water for the plants in the process), I'll probably do it again once it's finished playing 24hr/day catch-up and that may help. At least with the returns and skimmers moving water along better, the pool is clearing faster.

 

[Darin]

Since you are 3 phase you could put a cheap VFD on it to reduce hz from 50 to 25. This will cut your flow to half. Then monitor your skimmers. and make sure they are working as well as your SWG. Your pressure will also drop to around 10 psi. Your pool is not much bigger than mine and my 38 mm returns are just fine.

 

[Provencal Pool Jay]

After 2nd backwash in 2 days (during a draught, yet) and diverting some flow around the saltwater converter, it's settling at 15 or so with the side port free-flowing out (without the Polaris pump boosting it). The output of the side port is more than I would expect, seeing it's working its way through a non-activated pump and using smaller pipes.