Suggestions for check-valve on vertical line?

[jadog]

I'm installing a water recirculating pump which is a grundfos and supposedly already has a check-valve, but I figured I should install another check valve between the pump and where the line returns into the cold water inlet of the water heater. The water line is in a vertical position with the flow of water moving down. My light reading suggests that swing type valves are not recommended for this, so I'm left with the spring type option. Are there any suggestions here to indicate otherwise?

Also, does the PSI cracking pressure matter much for the spring type? Some have as low as .5 PSI cracking pressure while others have 5-10 PSI or more. The first one below from Home Depot has a lower cracking pressure but doesn't indicate that it is safe for drinking water.

3/4 in. FIP x 3/4 in. FIP Lead Free Brass Spring Check Valve from Home Depot

EZ-FLO Brass In-Line Check Valve, 3/4 Inch from Amazon

What do you guys recommend?

 

[havasu]

Why? The system is pressurized. The water needs to be pushed in order to work. I thing you are overthinking this simplistic design.

 

[jadog]

So you are saying just pick one?

 

[havasu]

I figured I should install another check valve between the pump and where the line returns into the cold water inlet of the water heate

But why?

 

[MicEd69]

supposedly already has a check-valve, but I figured I should install another check valve

It either has one or it doesn't. If it has one, you figured wrong about adding another one. You only need one check valve. Like havasu said, "why"!

 

[jadog]

A few weeks ago I contacted Grundfos with a question and one of their techs suggested adding a check valve. When I told him the model I have already has a check-valve, he said he would add it anyway. But what you are saying makes sense. Here is the diagram that Grundfos provided. Based on this, I should still add a check valve on the cold water supply line (see highlighted below). This would presumably prevent warm water from the recirc line flowing back up the cold line when the cold water is called.


Any reason to suggest otherwise? I would prefer just doing it correct the first time.

 

[MicEd69]

Your hot water circulating system is a closed loop. Hot water is being circulated from the water heater hot outlet to water heater cold inlet. That pump cannot pump any hot water into the cold-water supply line.

For a moment, forget about the temperature differences, and examine what you have. You have a pressurized water line going into a water tank, a pump taking suction from that water tank and pumping water back into the same water tank. For the pump to force water back into the supply line, a new source of water would have to be introduced somewhere in the system. Actually, you could cut the cold-water inlet line where you show that check valve, leave that line open, and after a few splashes of water coming out, the pump would still just be circulating water around the loop.

That check valve is not needed. And it would be best to install your expansion tank, which is required, upstream of where the hot circulating line enters the cold-water inlet. The rubber bladder lasts longer when only subjected to cold water.

Are you going to be running your circulating loop 24-7, or on a timer at certain times a day, or on a manual switch?

 

[jadog]

So even when a fixture calls for cold water, it couldn't pull from the cold side between the "T" and the hot water loop (when the pump is running)? It would be on a timer to run for 5 minutes every 30 minutes. I am also considering bathroom presence sensors to automate the pump cycles.

 

[havasu]

Your cold water will come out slightly tepid for a minute or so once the pump has pushed water into the cold side. It is not hot water, but warmer than actually cold water.

 

[MicEd69]

So even when a fixture calls for cold water, it couldn't pull from the cold side between the "T" and the hot water loop (when the pump is running)? It would be on a timer to run for 5 minutes every 30 minutes. I am also considering bathroom presence sensors to automate the pump cycles.

"So even when a fixture calls for cold water, it couldn't pull from the cold side between the "T" and the hot water loop (when the pump is running)?

No, it couldn't. The pump is essentially taking suction from the hot water supply line and returning it to the cold-water inlet to the water heater. That is a closed loop.

The water heater is supplied by the single cold-water inlet. The pump is taking suction from a closed system. The pump cannot pump hot water out of the water heater back into the cold-water supply.

When a cold-water faucet is opened upstream of the water heater, water from the main supply line will flow to that faucet.

 

[GReynolds929]

It can happen, I've seen it happen. I've also seen cold flow down the recirc line turning it cold. I always install a check on the cold upstream of the recirc tie in, and on the recirc line upstream of the tie in.