Check Valves

Gerry_5

Hi

I am replacing some return piping and notice there are check valves close to the end of the return piping.  See photos.  Two questions

What is the purpose of the check valves?

Can I configure piping as shown in the sketch to gain headroom in basement?

Steamhead

Is this

a setup where the radiator returns its condensate to the steam line thru the check valve? Is there an air vent on the radiator? Can you post a pic of the radiator so we can see how it's piped?

Gerry_5

Check Valves

Will post a pic later when I get home but attached a sketch which shows typical at radiators

Gerry_5

Check valve

Hi Steamhead

forgot to thank you for replying to post.  Appreciate your help

Steamhead

That's unusual

but workable- a single-main system with 2-pipe radiators. The check valve keeps steam from moving backwards in the return line. There was probably a local contractor who settled on that method back in the day.



You'd need to put the check valve AFTER the drop, right where the pipe goes into the 3-inch main. This will allow water to stack up in the drop and open the valve.



Where are you located? Have you seen other installations like this in your area?

Gerry_5

Check Valve

Replaced boiler couple of years ago.  None of the contractors could actually figure out the system.  One called a hybrid two pipe system.  Have not looked at other houses in neighbourhood.  I live in south Chicago in a historical neighbourhood.  Had valve as suggested however a friend said should not matter if before drop since they are all presently on horizontal with slight pitch to mains and water flows through valve.  Thanks for all your help. 

Also what is the reason copper piping is not recommended for steam?

Paul Fredricks_3

Frank

Would a trap be better in this type of system? Or maybe add thermostatic traps on the radiators and get rid of the check valves and radiator air vents? Maybe the returns could drop to the floor with main vents. I know it wouldn't be cheap and would sort of be reinventing what is there, but I'd think it would operate better.

Steamhead

Only if

you were planning on running a completely new set of return lines.



In this setup, the condensate is returned to the steam main as in a one-pipe system. The only difference is that there is a separate return pipe from the radiator for this. That's why the check valve has to be there, to keep the steam from going up the return line and shutting the air vent. The vertical height is needed so the weight of the water will open the check.



You could also do this with a water seal, but a thermostatic trap would not work. Since a trap is open when it's cold, steam would come up the return line and shut the trap. Also, for a trap to operate there must be a pressure differential across it. That differential does not exist if both the supply and return go to the steam main. With the same pressure on both sides of the closed trap, water would not flow back to the steam main when or if the trap opened.



I ran into a similar situation years ago, and solved it by rerouting the return. Go here:



http://www.heatinghelp.com/article/11/Hot-Tech-Tips/246/Steam-Stumper

JStar

It matters.

Every inch and dimension matters with steam. You need positive pressure on the return to push water through the check valve. Let's say your steam main is running 2 psi. The return line from the radiator right at the check valve is probably 1 1/2 psi. The check will never open. However, when the return line starts filling up with condensate and stacks up to a height of more than 14 inches, you'll create more than 1/2 psi of water column which adds to the existing pressure in the line to overcome the steam main pressure, allowing the condensate to flow back.



In other words, you can move the check valve wherever you want, as long as you have enough height above it so water doesn't back up into a radiator. If it's a short run to a nearby radiator, it might not be a huge issue (less pressure drop, and less water column needed). The problem might start if you're moving things around on a far, first floor radiator line.

Gerry_5

Thank you

To all you guys for your expert advice.