Conversion to hard plumbing for AGP: Plumbing design question regarding filter GPM

[MITBeta]

Hi All,

Before starting up my AGP this season I want to get rid of the flexible tubing and hard plumb everything.

I am planning to use 2" Sch 40 PVC with the equipment in my signature.

My question is regarding the flow rating of my filter. The manual says that it has a "design flow rate" of 50gpm.

Does this mean that the pressure drop of this filter will yield 50gpm at some semi-standard nominal head output from a typical pump?

Or does it mean that I have to be careful to design my plumbing to ensure that flow stays below 50gpm so that I don't cause damage to the filter internals?

If the latter is true, then maybe I'd be better off with 1.5" piping instead of 2", and may still need an additional flow restriction to limit the flowrate on the high setting.

95% of the time my pump will run at low speed, which makes this question irrelevant, but when I vacuum or need some extra skimming, I will need the high setting.

Thanks in advance for the advice.

 

[mas985]

It means this:

Or does it mean that I have to be careful to design my plumbing to ensure that flow stays below 50gpm so that I don't cause damage to the filter internals?

In most cases, upsizing the pipe size doesn't really benefit you much and as you pointed out, has a negative consequence as well. Note too that larger pipe results in higher flow rates and also higher energy use. The efficiency is higher (GPM/Watt) but the energy use is higher too. So if you are upsizing the pipe for energy conservation, don't bother.

 

[MITBeta]

Thanks for the reply. How can I determine the pressure drop the filter will produce? I can't find specs on that anywhere. The filter pressure gauge reading with fresh DE on it will be the sum of all downstream restriction, right? I think I might need to add some restriction to reduce the flow accordingly at high speed. The filter notes an optional flow restrictor device that can be installed at the inlet, but the manual gives no guidance whatsoever on what conditions this would apply to or how to test for that.

 

[mas985]

Pressure loss in plumbing is dependent on flow rate. Some manufactures publish head loss curves for filters others don't. If it isn't in the manual, it probably doesn't exist.

Why are you changing the plumbing to 2"? What is the objective?

 

[MITBeta]

The objective is to convert from flexible tubing and hose clamps because I'm afraid of them falling off or apart to hard pipe. I don't have an issue with using a smaller pipe size, I just don't know how to evaluate whether MORE flow restriction, even at 1.5" PVC is necessary.

 

[mas985]

Is it necessary? No!

If fact, in some cases, it can be counter productive. Some think it will save in energy costs but with single/two speed pumps, the opposite is true. For a two speed pump, both speeds will have more flow rate, but energy use will also go up. So if you need more flow rate for the pump, then it might be worthwhile.

As for worrying about the pipe coming apart, hose clamps are pretty secure. A lot of AG pools use hose clamps and flex without any issues and upsizing the pipe is a lot of work without much benefit. If it were me, I wouldn't bother unless there is a problem. If it ain't broke, don't fix it.