Heater Valve Question

[bradgray]

Putting the CV on a 3 way will only work if the valve has one input with two outputs.
The CV flapper is positioned over the input port and will prevent backflow to the input pipe. It will not prevent siphoning or backflow between the output ports.

If a 3 way is installed to select between two inputs for one output the CV will not work as it would be of little value on one inout and not the other.

Overall a CV inserted in a 3-way diverter can be very confusing as to what the CV is actually doing.

I understand what you're saying. And perhaps I'm visualizing this wrong. But hear me out:

- When the first 3-way is in bypass mode, the flow will continue in a straight path and will close the new CV to the heater return.

- When the first 3-way is sending water into the heater, it will open the CV and will indeed exit both straight and left, but the left will just become a pressurized dead-end.

I'll attach a diagram of what I'm describing in OPs case. Red is CV behavior, orange is first 3-way diverter position, and green is flow.

Help me find the fatal flaw?
This would an ideal solution for the OP because it eliminates the potential to deadhead his pump.

 

[ajw22]

I was commenting theoretically without looking at the OP situation.

I question if the CV spring will overcome the water flow through the L and allow the flapper to fully seal.

I think there are too many variables to say the CV will work reliably in that setup under all conditions.

 

[228newbie]

I think you guys jinxed me, I just got back from the property after the renter told me there was in issue with the pool heater. I arrived to find this:



@bradgray looking at the check valve and the arrangement, I agree, if you could get the check valve to operate in the 3 way valve body, it would indeed do the trick and eliminate the need for the 3 way on the outlet.

 

[ajw22]

@bradgray looking at the check valve and the arrangement, I agree, if you could get the check valve to operate in the 3 way valve body, it would indeed do the trick and eliminate the need for the 3 way on the outlet.

Lets take a step back.

What do you plan to use those valves for?

Why are they needed?

 

[228newbie]

Lets take a step back.

What do you plan to use those valves for?

Why are they needed?

To bypass the heater in the case of an issue like what just happened.

 

[bradgray]

I question if the CV spring will overcome the water flow through the L and allow the flapper to fully seal.

I guess I don't see the difference between the bottom two setups.

I drew the most typical bypass we install on homes. Then the OPs.

The only real difference is the actual location of the CV, but I can't imagine why behavior would be different given the flow patterns being the same.

Not an engineer though. Happy to be proven wrong!

 

[ajw22]

I guess I don't see the difference between the bottom two setups.

Big difference in the fluid pressures at the flapper interface point between the OP drawing and your typical drawing.

If the spring becomes weak the fluid flow can create a low pressure at the flap causing the flap to open.

Like I said, too many variables to know if it will work reliably and consistently.

 

[ajw22]

To bypass the heater in the case of an issue like what just happened.

Yeah, that is unfortunate and where the two valves are helpful.

I would table the valve discussion until you see what the heater needs. The heater repair may give the opportunity to redo the valve setup with one 3way and a CV at the heater output.

 

[bradgray]

Big difference in the fluid pressures at the flapper interface point between the OP drawing and your typical drawing.

If the spring becomes weak the fluid flow can create a low pressure at the flap causing the flap to open.

I'm fully willing to concede I don't have the fluid dynamics background to argue this with and accept this.
Let's say this does occur, what is worst case for a heat pump if water flows in reverse? Our area is 100% gas heaters, so this is an honest question.

I'm not advocating for a hokey setup, but given the circumstances, I wonder if this could this be an acceptable method to try short of a complete replumb. Unless OP invested in the pipe-saver, he would have to trash at least one heater union, one 3-way, a CV and what appears to be a SWG union. That's a lot of waste if it can be reasonably accomplished by moving the CV he already owns and a clear valve lid for $20.

Maybe I'm too optimistic!

 

[ajw22]

I'm fully willing to concede I don't have the fluid dynamics background to argue this with and accept this.
Let's say this does occur, what is worst case for a heat pump if water flows in reverse? Our area is 100% gas heaters, so this is an honest question.

That is why I was asking what the purpose of the valves are.

If the heater is leaking and the water is flowing in reverse the water will leak out and having the valve setup is worthless.

If the water pH is low and you are looking to isolate the heater and protect it then having water backflow into the heater is not good.

If you are looking to bypass the heater to reduce the “head” then you just need one input diverter valve and the other valve or CV are not needed.

Or a bypass can be used to partially bypass water to not exceed the HP maximum flow rate.

Given these are the uses of the bypass you either want a reliable seal or you don’t need any seal on the output depending on the usage.

I'm not advocating for a hokey setup, but given the circumstances, I wonder if this could this be acceptable method to try short of a complete replumb. Unless OP invested in the pipe-saver, he would have to trash 2 heater unions, two 3-ways, a CV and what appears to be a pump union (upper left). That's a lot of waste if it can be reasonably accomplished by moving the CV he already owns and a clear valve lid for $20.

Maybe I'm too optimistic!

Depends what the bypass is used for. I don’t see any usage where putting the CV in that place will be useful. Especially when there will be no responsible homeowner to watch how that CV is operating.

 

[Ahultin]

Given the ops response in #25: "To bypass the heater in the case of an issue like what just happened."
Could they just flip the inlet on 3 way 2 to the outlet so that the outlet could never be blocked (short of a tenant unscrewing the 8 screws)?

For re-plumbing it correctly, it looks like there is already some funny business at the swg as there appears to be two reducers, 1 in the swg union amd 1 in the cv so it would be a ton of work

 

[bradgray]

If the heater is leaking and the water is flowing in reverse the water will leak out and having the valve setup is worthless.

Haha. Yes, but this wasn't a variable until an hour ago. The original discussion was how to make the bypass setup he had, work closer to the ideal setup.

If the water pH is low and you are looking to isolate the heater and protect it then having water backflow into the heater is not good.

Correct. The question though was more about damage to internal components from flow direction itself. Because the point you made was the CV may not close properly if the spring wears out. So assuming OP did no preventative, what was the worst that would occur. In a gas heater, the T-Reg and internal bypass would largely impede the water.

If you are looking to bypass the heater to reduce the “head” then you just need one input diverter valve and the other valve or CV are not needed.

Or a bypass can be used to partially bypass water to not exceed the HP maximum flow rate.

Given these are the uses of the bypass you either want a reliable seal or you don’t need any seal on the output depending on the usage.

Great point related to the above; if this is fine, then why are we adding a disclaimer about adding the CV into the 3-way? In the context of the goal, CV failure prevention isn't absolutely needed.

Depends what the bypass is used for. I don’t see any usage where putting the CV in that place will be useful. Especially when there will be no responsible homeowner to watch how that CV is operating.

I hear you.

So, I see us at this point.

We've established he doesn't need to be 100% certain water never flows backward by pool design or by system necessity. So a CV is not useful here.

He does need the bypass to work as close to typical as possible, without the risk of a renter closing the second 3-way on the return and deadheading the pump. This is where the CV is useful, and better than the 3-way he has.

I sort of feel like we're looking at the same car, but one person is saying it has headlights and one is saying it has taillights.

 

[bradgray]

@228newbie you could always rewind to the front of the discourse, and go back to manually moving the second 3-way and taking the handle away every time. And leave a note with a warning for fines if the equipment is adjusted.

Having seen even 2" tees expanded and distorted from the intense pressure of deadheaded pumps, and working in the STR space for so long, I'm just trying to invent some quick ways out of the liability of the way it sits now.

If you were my client, I'd make the suggestion and with your blessing, see how it worked. I may not have the right answers here though. I'll concede to others.

 

[ferretbone]

I appreciate all the feedback, but at this time I am not looking to replumb the piping, just wanting to verify the proper positions for the two valves.

How big is your heater? Does your heater fire up and run without cutting off because of low water flow? Noop. If not leave those valves alone. If the heater does not have enough flow through it then, turn the bottom valves off tab up a little and reroute some more water to your heater. All the water in your return line/system does not need to go through that heater all the time period. The heater will stop heating if you lose to much water flow, like needing a filter clean backwash etc....