Why would THIS bypass be plumbed in?

[austin_puckhead]

Well, in Austin we lost power in the middle of the night with temps in the single digits, so my freeze protection (running the pumps 24/7) failed. Cracked a ball valve, an actuated valve, a check valve, and some other PVC & fittings (all 2" plumbing).

I'm trying to rebuild everything exactly as it was because a) everything worked, and b) the workmanship looked professional. The implication of the latter statement is that, I feel the plumbing was done in the fashion below on purpose, with a reason. (see picture)

But I don't understand the bypass around the gas heater. The water is unimpeded from the filter to the heater; nothing will stop it, no valve of any kind. But they plumbed in a bypass line that can be closed with a ball valve (the circle on the diagram).

Why would you plumb a closable bypass around the heater, but not close off the flow to the heater itself? Maybe to temper the water coming out of the heater, or to balance the pressures on the inbound and outbound side of the heater?

I checked the documentation on my heater and found nothing to explain a possible reason. Anyone have intelligent thoughts on this?

 

[Jimrahbe]

A,

Even though the by-pass you have does not allow you to remove the heater, when the valve is open most of the water will by-pass the heater as it is an easier flow path..

An example... I can run my pool at 1200 RPM and still turn on my SWCG, but if I had a heater, I'd have to run at 1600 or higher.

If this was my pool, I would either remove it, or make it so that the heater could be removed without any water leaking out of the plumbing.

Thanks,

Jim R.

 

[mknauss]

Heater Bypass - Further Reading

www.troublefreepool.com

Take a look at the above article.

 

[JamesW]

Possibly to allow the pump to be used at full speed to give good jet action without forcing all water through the heater.

The risk is that you could have too little water going through the heater and burn it up.

You would normally use a 5 psi check valve bypass to open only when the pressure differential reached 5 psi, which would ensure sufficient water flow through the heater.

What pump do you have?

 

[ajw22]

What model heater do you have?

 

[tgrinchy]

Mine has a similar bypass but the bypass goes from 2” input to 1” bypass back to the 2” output on the heater. My Jandy heater manual actually calls out having a bypass like this. My builder said it is for better flow to the IFCS for ones integrated to the main filter pump. My ifcs is actually on a separate pump so a moot point for me. I leave the bypass ball valve open at all times, fwiw

 

[austin_puckhead]

Thanks for the info folks.
@ajw22 I've updated my signature (finally) with my set up.
@JamesW see above. Also, I do have a check valve (not on diagram) on the outbound leg of the heater (before the T) to prevent chlorine from the puck dispenser (further down stream) from backing up into the heater.
@tgrinchy My Polaris 280 is on a separate booster pump also. Its water supply comes from the leg that has left the heater and is heading back to the pool walls.
@mknauss Nice article. It talks mostly about isolating the heater, not the "superfluous" bypass. But it will influence my approach see below.
@Jimrahbe Really useful info. Back in '05 this was built as a SWG pool. After some period of time, the previous owner took out the SWG and switched to trichlor pucks. Could be a residual from that original build.

Based on all of the replies, I'm thinking about replacing the T at the top-center of the diagram with a 3-way valve to isolate the heater.