Best Type Check Valve for DHW Recirc System?

srhodeswv

Hello! It's my first post, and of course, I'm here with a problem. I appreciate any help that those with more knowledge and experience can offer. Here goes:

My basic question is what is the best type of check valve for a domestic hot water recirculation system? I'm having a problem with my check valve sticking open, and I'm not sure whether it's a defective valve or simply a poor choice for the application.

The details of my system are as follows. I have a heat pump water heater with a 3/4" PE recirc tubing loop (dedicated return line). The return line is tee'd into the drain tap of the water heater, per diagram from Taco and confirmed okay by Rheem technical support. Recirc pump is a Taco 006e3 with a swing check valve on the outflow end of the pump, just before the tee into the water heater. The pump is powered by an AC outlet that's controlled by a programmable logic board to turn on and off with motion sensors installed in bathrooms. The motion sensor and pump part of this system work great! When motion is detected, the AC outlet is turned on, allowing the pump to run for 15 seconds until the recirc loop is primed up to the fixture groups. It then is shut out for 15 minutes so it doesn't run excessively. I have near instantaneous hot water even in the farthest bathroom, and it's great.

The problem: Occasionally, but more often than not, the hot water seems to fade very quickly when in the shower—I mean 3 minutes or so, and the temp has dived toward lukewarm. I have confirmed water tank temp is right around 120, so I know that's not the problem. Turns out, the check valve is not always closing when the taps are opened. I can tap the check valve when water's cold in the shower, and I hear a light "thunk" followed by instant hot water again at the shower. Also, if I turn off all fixtures and shut off the isolation valve at the water tank's hot water outlet (keeping the isolation valves adjacent to the recirc pump ON), I still get full water flow at fixtures, though it's cool, not hot. That tells me water is coming out of the water tank from the bottom.

So, the check valve is either defective or not of the ideal type for this application. But which is it? I'd rather not replace the valve with an identical type just to find out that all swing valves will do the same thing. I also don't want to replace it with some fancy, more expensive version just to find out it was simply a faulty valve. I don't know enough about the different valves to know what's best here.

Any ideas? I really appreciate the help!

hot_rod

a couple missing components. A check on the cold supply, and a DHW thermal expansion tank. You may be pushing some hot up the cold line. With a check on the cold the expansion tank is required. Or if you have a backflow device on the main cold line?

The tank also acts as a water hammer arestor, eliminates the bang from a fast closing valve. The tank alone may cure the bang.

Is it a brass or soft seat check? I prefer a DHW rated spring check. Swing checks can bang due to the long travel distance of the gate. Spring checks have a conical gate, are friendly to flow, and only travel about 1/4”.

Spring checks are used in circulators, mixing valves, some backflow preventers, and as a stand alone check.

Caleffi, Watts, Apollo, most any valve manufacturer had soft seat, spring checks. NSF listed is required for potable water

A good explanation of swing vs spring at Red White valve

IMG_0877.png

Larry Weingarten

Hi, Yes to the spring check valve, and I'll add a few more thoughts. I'd put a pressure gauge on the drain valve and see what pressures you get. If you find one with the red pointer in addition to the usually black needle, it will show you the highest pressure it has experienced. Best if pressure never goes over 80 psi and good for it to live between 40 and 60 psi. Another thing is that there is no connector or bushing where the power line runs into the pump. I'd find a 1/2" romex connector and get that installed so you don't have an unpleasant experience letting the smoke out. 🙀

Yours, Larry

bjohnhy

Nice work on the diagnosis.

What setting are you running the 006e on? It's the infinitely adjustable?

I would start by just putting Taco IFC (integral flow check) in the circulator and see how that works for you.

Another thought, although may not work and is not a true fix, is to turn the circulator speed setting down (say low/med junction ) so the swing check doesn't fully open and won't ever reach that sticky position. You may have to change the logic to 30 seconds or whatever length you need.

srhodeswv

Thank you all for your comments on this!

Hot_Rod: I don't have a separate backflow device on the cold supply, so I understand your concern about hot water getting pushed up the cold supply from the tank. Also understood that adding a check would necessitate the expansion tank too. Side question—Would the expansion tank help with water hammer from my washing machine supply? I don't have arrestors right at the washing machine shutoff valves (wish I did) or anywhere else in the system, so that would be an additional plus if an expansion tank would help with that.

Also, thanks for your thoughts on spring check valves. I see why this is a better type for this application than the swing valve. Since I didn't install or specify this valve, all I really know is that it's a brass-body swing valve. Not sure about the seat material. I guess I'll see when I take it off!

srhodeswv

Larry, thanks for your comments. Just so I understand fully, are you suggesting the pressure gauge because of concern about possible pressure spikes from a fast-closing check valve? Or lack of expansion tank? Both? I suppose any pressure spikes would be related to water hammer and would also be resolved by an expansion tank.

Also, duly noted on the lack of a bushing on the circulator power cord. That was an oversight on my part for sure. I'll get one put in there. But I sure hope there's no smoke to be holding back with that bushing! That might indicate a separate issue…😯

srhodeswv

bjohnny, thanks for your thoughts. I'm not familiar with the Taco IFC. Is that an add-on piece that I can use with the 006e circulator? Any advantage to that over a separate inline spring check valve?

The circulator is currently at high speed setting. It seems I remember running it and timing it to make sure it fully primes the system without pumping too long, and also at a speed that didn't exceed the max flow of my PE tubing, but I'm going to double check all that. May be up too fast. I definitely get what you're saying about lowering the speed to keep the swing check from opening all the way and sticking. If that does keep the valve from sticking open, it would at least be a great temporary solution until I can replace with a spring valve.

Well, I'm off to make some adjustments to the system. I'll report back soon!

SteveSan

https://forum.heatinghelp.com/discussion/comment/1825970#Comment_1825970

Unfortunately, our 006e3 doesn't accept an IFC. Would need one in-line.

Larry Weingarten

Hi @srhodeswv , Another thought came to me. Presently, I don't see a way for you to flush the recirc line. This could cause problems with air etc. If you added a ball valve at the tank drain, between tank and the T, that valve would allow you to use water pressure to flush the recirc line and even dislodge any sediment that might make its way into the new spring check.

Yours, Larry

bjohnhy

https://forum.heatinghelp.com/discussion/comment/1826033#Comment_1826033

Thank you Steve for clarifying this!

Kaos

Which swing check is that? Most need to be mounted in the vertical orientation to work. The other issue is your recirc line is very big, so if the check valve doesn't seal perfectly, it is a very low resistance path to your hot water fixutres. Recirc line can be 3/8" which would help with leaky check valves.

I haven't had good luck with check valves on recirc, at least not on chlorinated city water. Most just don't last. I'm trying a one with viton seats, it that doesn't last, I will end up machining something passive like a tesla valve.

hot_rod

ideally you want the water hammer arrestor at the device causing the hammer

Sioux Chief has them for wash machines, dishwashers, icemakers, and whole house size.

Generally water hammer is in high pressure systems, 70-80 psi. It,s caused by fast acting valves usually.

Loose and unsupported piping can bang easily, even shutting off a shower valve quickly.

the DHW expansion tank would be my first upgrade, then a spring checks

Run the recirc pump as slow as possible, look for about a 10 degree lower temperature at the return compared to the supply from the water heater.

The recirc pump moves just enough flow to overcome the heatloss of the recirc loop.

Of course insulating the entire loop reduces gpm needed, and operating cost.

Some swing checks are horizontal only, some can be either vertical or horizontal. Check the installation doc for the specific check.

Swing checks are great for high flow conditions, dirty water, sump pumps, sewer pumps, flowing solid particles, Not so good for hydronics

For a swing check to seal tightly it wants to see a delta P. Think sump pump. But that is not what you get in hydronics. When the pump is off, pressure is the same on intake and discharge.

srhodeswv

@Kaos I'm not sure exactly which swing check this is, as I didn't buy or install it personally. Really interesting idea with the Tesla valve, by the way. Never heard of one but looks really cool, and with no moving parts! Thanks for sharing. Not in my budget to custom fabricate one, unfortunately.

@hot_rod Thanks for the additional thoughts on water hammer and expansion tanks. On the note about recirc speed, I'm not running the pump continuously, or even on a timer. It runs only based on motion sensors when someone goes into a bathroom. If it's been more than 20 min since the pump has run, it runs for 10 seconds, just enough to "re-prime" the recirc loop full of hot water, then stops. I do have the hot lines, including recirc, insulated to cut down on heat loss in the loop.

That said, I went back to take a look at my pump settings and did some figuring, calculating, measuring temps, etc. I had the pump turned up WAY too high (was on high setting). Not sure what I was thinking (I bet I had been misreading the Taco flow/pressure chart). I found I was able to turn the pump down to LOW and still get the loop primed within a 10 second period. AND now my check valve is no longer sticking open when taps open. AND I have confidence I'm keeping the flow velocity under the safe limit for my pipes. My guess is that the pump was slamming that valve open to a "sticky" position as bjohnny suggested.

Been enjoying fully hot showers since I made the adjustments. Next time, I'll spec spring checks. I'll also look more into the expansion tank and water hammer arrestors for the washing machine. But for now, problem solved.

Thanks everyone for your help and great advice!

SteveSan

@srhodeswv I remember speaking with you on the phone, glad everything worked out for you.

srhodeswv

@SteveSan Yes, thanks. I appreciated our conversation. It turned me onto the right path!