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Piping diameter

Posted by camisdad (My Page) on
Thu, May 26, 11 at 15:36

I recently had a large pool built after doing some deep research on past posts in this forum. I am facing an unexpected issue:

I spec'ed the manifold at 4" diameter, along with 2" returns, and oversize filter, and put in a Pentair variable speed pump. The outcome is great. I can circulate my 30K gal pool on 125W usage for the pump, with 0 psi measured pressure at the filter, and I am very pleased with this great result.

The bypass for the heat pump and salt cell, however, is only 2", because that is what the heat pump requires. The outcome is that, in order to insure enough water flow through the bypass, I end up having to tighten the manifold exhaust valve (main valve) to "almost" closed, thereby losing the advantage of my 4" manifold.

I understand, of course, that the 4" manifold also benefits me due to less friction. But I would really like to be able to leave the main valve open to take the full benefit of my 4" manifold. What is wrong in the design? Is there any way, short of an accessory pump for the heat pump bypass, to allow me to open that valve? I did some calculations about adding a pump for the bypass, and figured I would lose a lot of my power savings by doing so.

Any thoughts? I can't think of any solution.

Follow-Up Postings:

RE: Piping diameter

If you are running a pump with 125W output I doubt you will see a massive performance gain with 4" over, 3", or even 2" piping.

There just isnt enough flow through the pipe to create a lot of friction. Most of your friction loss will be through the equipment itself.

With that being said, If you have a controller you can run a valve that shuts off the bypass while the heat pump is running.

RE: Piping diameter

camisdad...sounds like you might be handy with this sort of stuff...our setup is like yours.

We have a 2" bypass on the heater with a 2 speed pump. On low speed, I use a 2" 24V irrigation valve to close the bypass circuit directing all flow through the heater. On high speed, the valve opens allowing efficient flow of water through both the 2" heater line and and 2" bypass line.

Of course, for all this to work, you must have a pool controller or ,depending on how handy your are, make provisions for the 24V bypass valve to close when the VS pump is set to lower speeds. I only mention the latter option if the cost of a controller is not attractive and you like to tinker with this kind of stuff.

Hope this helps.

RE: Piping diameter

Thanks for the suggestions! My heat pump circuit is 2" in diameter (because the heat pump cannot take anything larger) but my "bypass" is really the manifold, which is 4" in diameter. I was looking for a 4" variable valve (which is very hard to find and expensive to set up) but I am now realizing that I can just have an on/off electric valve, which would work if I can find one in 4".

Does anybody know of one, by any chance?

RE: Piping diameter

camisdad...we're using two of the Hunter 2" PGV irrigation valves with adjustable flow.

Hunter also makes a 3" brass valve with adjustable flow.

Four of the 2" valves or two of the 3" valves will flow as much as a single 4" pipe.

If you're looking for a pool industry solution, Jandy makes a 3" manual valve that can be fitted with a valve actuator for electronic control.

Below are links to the valves I mention above.

Hope this helps provide more options/ideas to accomplish what you need.

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