DHW Check valves

Servicewiz_3 · March 13

I have (2) check valves on the discharge side of a hot water re-circ. pump. they are serving (2)

Raypak DWH's. Line is horizontal. Should these checks be swing or spring loaded? Why?

Thanks in advance for any help!!

J. Scheel Jr.

EBEBRATT-Ed · March 13

Usually only one on the discharge is used. Some pumps contain check valves factory installed. I would use spring loaded. You have to make sure the circ pump can open the check.

hot_rod · March 13

swing checks need a pressure differential to close tightly, spring checks do not

Swing checks have a long travel distance which can lead to chatter or banging

All checks should be sized by the Cv number not the pipe size.

If a check is oversized it may not be opening fully

Horizontal, 6” or more from a pump discharge is best. Some brands can be vertical.

Any check used for DHW needs to be low lead.

Are you having trouble with the checks?

Mad Dog_2 · March 13

Spring checks usually hold tighter than brass swing checks. Mad Dog

retiredguy · March 13

I have had a few spring loaded checks hum or become noisy due to a low flow condition where the pressure or flow did not hold the check totally open.

Kaos · March 13

I've had long term durability issues with checks on recirc loops. Some are sensitive to chlorine and will deteriorate over time, when this happens fixtures will draw cold water in through the recirc line. Having a much smaller diameter recirc line like 3/8" helps but not 100% fix.

Definately not a swing check, they are nosy and don't seal well enough. Install the smallest spring check that you can still get reasonable recirc flow rate though and in a way that is easaly replacable. I've given up on proper connection, mine are now sharkbite.

I'm half tempted to replace the check valve with a conical restrictor, this will mostly limit flow in one direction without any moving parts.

Intplm. · March 13

"Swing checks" in my humble opinion have a tendency to allow fluid to pass. "Spring checks" do not have that happen as often if at all.

hot_rod · March 13

Lets see exactly what you are trying to accomplish or protect with the check. It could be mis-sized, or mis applied.

You will find Neoperl brand spring checks in IFC circulators, BFDs, balance valves, 3 way mix valves, check valves, boiler fill valves, etc, etc.

These checks have an excellent track record in most any water condition.They build aerators, restrictors for kitchen faucets, all sorts of flow regulation innards, domestic water, hydronics, and high temperature for solar work.

Spring checks are considered a "bubble free" shut off. It would be a special engineered swing check that could provide a bubble free seal.

I'm always envious of the Neoperl booth at trade shows :)

Alan (California Radiant) Forbes · March 13

I had to install a swing check on my system because it’s gravity flow and I get a “clunk” when I open a hot water tap. I hear it and think about it and see it “in my mind’s eye”……..and then I think about something else.
“Now, Alan: Do you realize that your 24-hr. thermosiphon system gives off heat and is grossly inefficient?” In my little, soon-to-end, unimportant life, convenience outweighs cost.

JUGHNE · March 13

I too, have a gravity flow recir DHW system, 24/7 365, (My first transgression).

It has a swing check that allows the small trickle of return water to go into the bottom of the tank. An almost closed ball valve throttles the flow (another sin).

Instant hot water in the farthest bath. Insulated supply and return lines.

No pump, no controls, no electricity……I tell myself the cost of the previous items would offset the added NG cost…….❓️

Larry Weingarten · March 13

Hi, Old trick was to drill a small hole through the disc to allow slow gravity flow, and just be happy. The amount of leakage through it on a hot water draw is not noticeable. But @Alan (California Radiant) Forbes , you have too many people relying on you, so you have to live forever, even if not with absolute efficiency. 😇

Yours, Larry

JUGHNE · March 13

I drilled the hole on two other installs but not on my own, thinking that if I needed more flow I would then do it later. But years later it is still working with the swing check.

The return is about 65' long (sloping downward to the tank with a 6' drop at the tank). I think this induces more gravity flow to just barely lift the swing check.

hot_rod · March 13

Swing checks sometimes get used as an over-heat protection valve on wood boilers. In this example the check is intended to stop reverse thermosiphoning.

Also if power goes out the hotter, higher buoyancy water will crack open the swing check enough to allow thermosiphoning. Same concept as a gravity hydronic heating system, movement caused by ∆T

So a swing check on an application with a thermal differential, may in fact not be checking.

Not an easy thing to calculate when a swing check cannot do it's job, really. A swing check really likes to see higher pressure on the downstream side to close and seal. A sewage lift pump is a good application for a swing check. High flow rate, can handle small solids.

If positive, bubble free check protection is what you want or need, go with a spring assist type check.

So that is why you want to know specifically what the check is expected to do.

DHW Check valves

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