Swing Check as Vacuum Breaker

Question

Swing Check as Vacuum Breaker

sajego (Mechanical)

(OP)

14 Apr 03 09:45

Hello.  I have two questions here...

Firstly, we are experiencing a "leak" from a "vacuum breaker" when our pump system is shut off.  There is a plumbers loop that goes up from the main return line... then it dips down and has the "vacuum breaker" at the end. When the pumps are shut off a gallon or so of water pours out the end of this section.  Apparently on other installations they do not have this problem, but I cannot get find data about what is different in this installation.

I have been putting "vacuum breaker" in quotations because after looking into this situation the part number is actually for a Swing Check valve.  So I am also searching for find information about swing check valves being used as vacuum breakers.

For what it is worth, we are not worried about preventing fluid backflow since only air comes in through this valve and nothing is supposed to come out of it.

Thanks for your insight!
Sara

saxon (Chemical) · Answer 1 · 2003-04-15 17:44:46

sajeg, It sounds as if the valve seats are shot or have dirt on them and do not seat correctly, Try opening up the valve and cleaning or resurfacing the seat and flapper as required. Or better yet replace it. This should solve your problem if the swing check is installed correctly. Personnaly I would use a spring loaded vacuum breaker.

Hope this helps.
saxon

quark (Mechanical) · Answer 2 · 2003-04-16 00:22:48

It seems you have not installed the vacuum breaker at the highest point of the loop. (atleast your line which has the breaker, may not be taken from the highest point) Check positioning it at a better place.

Swing check valve should work in your case if the spring tension is not very high.

sajego (Mechanical) · Answer 3 · 2003-04-16 08:41:57

saxon - They claim to have replaced the valve several times... still as you said, it might not be seating properly...

quark - Correct, it isn't installed at the highest point in the loop... Am I right in thinking that shortening the loop so it ends at the highest portion and installing the breaker there would probably fix the problem?

quark (Mechanical) · Answer 4 · 2003-04-17 04:20:10

Just check that the pipe (where you are installing the vacuum breaker)height is more than that of any other point of the piping system. You won't have any draining problem.

Regards,

DLANDISSR (Mechanical) · Answer 5 · 2003-04-17 17:44:50

Sajego:
There has to be enough pressure on the valve to keep it closed during the normal operation of the system and the loop has to be high enough so that any compression the the gas in the loop does not allow the water to move up the loop and over the top. If this occurs there will be some fluid on the valve. When the system is shut down there is not enough pressure to keep the valve closed, or a vacuum occurs allowing the valve to open and air to enter. When the valve opens the water escapes.

Try raising the top of the loop sufficiently to not allow any fluid to rise up in the loop and go over the top. Calculate the volume of water and the volume of 1Ft of pipe and raise the loop high enough to contain that volume of water plus some extra.

Come Join Us!

Posting Guidelines

Swing Check as Vacuum Breaker