splitting flow for 4 returns (bullhead vs branch tees)

[Diver]

Mark,

My calculations do take into account the height of the filter gauge. I took the information from your famous "Hydraulics 101 - Have you lost your head?" topic.

I will take new readings with a new gauge and probably backwash and get clean numbers too. I will post them here to check if they make sense.

Thanks!

 

[Diver]

Return plumbing should always have more head loss than the suction and more than 2x is desirable. If it is too low, the pump could cavitate.

Mark, how do you calculate head loss for return vs suction? i have number for return pressure in psi and suction vacuum in inches, I assume I can't equate one to another directly...

 

[mas985]

Return Head (ft) = Filter PSI * 2.31 + 3 + Other

OR

Return Head (ft) = Pump PSI * 2.31

Suction Head (ft) = Pump Suction in-Hg * 1.13

Total Head (ft) = Return Head + Suction Head

Other is the piping and BW valve between the pump and filter. This is not easy to calculate which is why I created the SS.

 

[Diver]

For my systems curve, 47 GPM is about 44 feet of head. 3" of vacuum for 44 feet of head, I believe results in about 14 psi of filter pressure. Which is probably close to what I have now after opening the pool and not backwashing the filter afterwards.

The new filter gauge is in and it reads 13.5 psi, almost exactly what I calculated it should be. 3.5" of vacuum. I will backwash soon and get clean filter pressure.

 

[Diver]

backwashed and with the new gauge the filter pressure is 10.5 and vacuum is 5. seems a bit more restrictive than i anticipated. maybe i didn't backwashed it enough, maybe check valve creates more back pressure than i would like. maybe even with 2" fittings somehow new split is more restrictive as well

currently i don't have a flowmeter installed, but with 41 feet of head, the flow should be about 55 gpm.

 

[mas985]

currently i don't have a flowmeter installed, but with 41 feet of head, the flow should be about 55 gpm.

Plumbing curve is 0.0136. Better than Curve-A and worse than Curve-C so better than typical1.5" plumbing but not quite as good as typical 2" plumbing. Sounds pretty normal for your setup.