Pool plumbing anomaly — why does pool plumbing setup return some water to pool without filtering it?

[gpilcher]

I wonder whether anyone can explain an anomaly in my pool plumbing. The line from the pump to the filter has a T Union that returns some of the water directly to the pool return without first running it through the filter. I can’t think of any reason for returning water to the pool without first filtering it. What am I missing? Here’s a picture of the plumbing setup. I circled in red the return line I don’t understand.

 

[Oly]

A bad solution to controlling a big increase in pump pressure?

 

[IceShadow]

There's a red handle on that line that looks like it can open or close the water. Maybe it's just a way to bypass filter, heater, chlorinator, etc. to return water to the pool, probably during initial prime or when those items need servicing?

 

[gpilcher]

The red handle is a valve that can open or shut the water flow through that line, but I don’t know why. I made the mistake one year of shutting that valve, thinking it made no sense for the pump to do the work of pumping water from the pool only to return that same water without first treating it. But the act of closing the valve left standing water in the line that froze and burst the pipe. The red handle is the replacement valve that I now keep slightly open to avoid a repeat of the frozen water/burst pipe problem. At the time, I wondered whether I should remove and plug that entire section rather than replacing the burst pipe and valve. And that remains my question today. Although shutting that valve does stop water from returning untreated (and then that water freezes if I forget to reopen it in the winter), opening it does not prevent water from running through the filter (i.e., the valve does not isolate any equipment while equipment is being serviced).

 

[IceShadow]

I can't see the filter well - does it have a MPV on it that you can close? If so, closing that valve and opening the red handle one would bypass the equipment after the pump.

It might be a convenience you don't need or that causes more problems than it solves, given your frozen pipe issue. If you do want to keep it, just be sure to drain it out with the rest of the system when closing for the winter.

 

[gpilcher]

IceShadow — I was wrong, and you are correct. There is an MPV on the filter that would enable closing off water from the pump before it gets to the filter and forcing that water to be returned directly to the pool through the red-handled valve. You knew that might be a possibility. I can’t imagine why I would want to run the pump only to return the water directly to the pool without treating it. Why would someone want to do that? You may be interested — here’s a pic of the MPV you guessed I had. FYI I run my pool year round. I have a spa with a spillover.

 

[TX2OBX]

wild guess I am by no means an expert, but in all the research I did for my pool build I read over every option for pool/spa combos. Im guessing by the looks of the automatic actuators you have a spa? If so my guess would be that's a bypass to increase the jet action without pressure loss going through all the equipment.

 

[sktn77a]

I don't think that's an MPV on the filter - its simply a 2 way valve to allow pumping to waste. The line you are asking about would appear to serve no useful purpose. I would get rid of it.

 

[gpilcher]

Correct, sktn77a — it’s a 3-way diverter valve, and that’s a regular system 3 cartridge filter. I’ve used that diverter valve only for draining the pool. I think the diverter valve could be turned like I think IceShadow was suggesting to stop the water from going through the filter and simply returning it to the pool instead of to waste. But I don’t know why anyone would want to do that. I agree that the T union and return line seem to have no useful purpose. But some installer must have thought it was useful for something.

 

[gpilcher]

The original installation included a single speed 2 hp WhisperFlo pump that ran at 3400 rpm. I replaced that pump with a 2-speed pump and later with a variable speed pump that I run at about 1,500 rpm. Maybe the original installer thought 3400 rpm was potentially too much and built this silly return to bleed off some pressure. I can’t think of any other reason.

 

[Jimrahbe]

G,

There is just no logical reason for that line to be there. I suggest that you remove it.

Thanks,

Jim R.