One Pipe Return Check Valves
When the old times used check valves, on one-pipe system, in the end of main drops to wet return, confirming purpose was to not need as much dimension "A"?
Comments
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I think you still need the "A" dimension to get water back in the boiler.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
Yup. Plus enough extra to overcome the check valve.
The hope was to keep water from backing out of the boiler perhaps all the way up into the mains — but the physics of that doesn't work out either (see some of @ethicalpaul 's comments on equalizers!).
Check valves were used in some of the more complicated two pipe systems, though — you can find examples in The Lost Art — in conjunction with some remarkable gadgets to get water back to the boiler if the boiler pressure got too high — but that is a very different situation.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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Pumping traps require them. That's the only use that comes to mind.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
In my analysis
It's just a swing check valve. Pressure on the wet side should not cause the column of condensate to rise on the other side due to the check valve, until enough condensate stack's up to overcome the wet side pressure and opening the check valve flapper . Since the check is not a Y check it needs very little differential to pass thru.
In theory the amount for dimension "A" should be less.
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You would be incorrect.
If there is pressure on the boiler side of say 1 psi, it takes 28” of water in the pipe to overcome that and return to the boiler. If you add a check valve, you still need the 28” to overcome the pressure on the other side of the check valve, plus any possible resistance from the check valve. So in theory it could make things worse. It also adds an unnecessary component that could fail and stop the condensate from returning entirely. That last point is one reason they stopped installing them.
Simply put, on one pipe systems they are completely unnecessary.
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KC_Jones I just ran the numbers on paper using both theories. That would be correct. It doesn't actually solve anything but I can see it definitely can create a problem down the road. That may be a reason I can't find much information on them used other than some references.
Doesn't seem to make sense from a time construction standpoint. The edition with the check valves, was built later than the the one without. I guess adding the check valves was cheaper than the extra pipe.
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what extra pipe?
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
When I went back to look at the pics, I had originally thought they wetre getting creative on the EOM drips as original plans called for. But followed them thru and it's just a junction area for several drops from EOM runs. There are two identical areas of this piping arrangement. This is the older side which does not have check valves in any drop.
Included pic
The air vent has already been changed to a #75
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