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2 Check Valves on Feeder Pump....Help or Hinder operation

JUGHNE
JUGHNE Member Posts: 8,954
Boiler water feeder controls operates the pedestal feed pump in pit. Poppet check in vertical riser from pump. Riser up 7' over 6-7' and drops about 3' into equalizer just below water line. There is a horizontal swing check valve where the equalizer is tapped. Boiler at 5-7 PSI.

I believe both checks leaking and short cycling pump. I am thinking syphoning plus the PSI reversing the water. Operator thinks things are normal.

Is it common practice to have the double check valves? One at pump and one at boiler connection? It seems like a good idea to me.....or is there something I am not realizing?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,098
    Shouldn't really hurt anything when the pump is running -- just a small amount of extra head loss. When the pump stops, if both of them close, great. If the one at the equalizer leaks, no big deal. If the one at the pump leaks, there will be a very slight vacuum where it goes up and over -- but again, in application like this, no big deal even if there were a little leakage and air got in.

    Problem is, of course, that you won't find out if one is leaking until both of them leak. Double checks - whether separated by a distance or close together -- are a built in recipe for a hidden failure, which can go on for a long time.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE
  • JUGHNE
    JUGHNE Member Posts: 8,954
    I only visit this place about 2 times a year and noticed that the poppet at the pump really hammers. Such a change from the minor click of 6 months ago. Operators consider it normal as it must have slowly got noisier, (like weight gain or grey hairs creep up on you :o ).

    So I think the swing check at the boiler is shot and the 5-7 PSI plus syphon is slamming the poppet that hard. The fairly new high dollar poppet is now leaking from the hammer and causing the short cycling. I do believe they should have changed both at the same time.

    Looking at the original shop drawings it shows both checks.
  • Jamie Hall
    Jamie Hall Member Posts: 17,098
    Surely does sound ( :) ) as though that swing check is shot to me!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,317
    Around here the boiler inspectors insist on two check valves, one at the pump and one at the boiler.
    JUGHNE
  • JUGHNE
    JUGHNE Member Posts: 8,954
    Ed, for your area does that double check apply to condensate pumps also......some that I have seen pump into the lower part of boiler so if the single check and the pump both failed this could drain the boiler and the float operated low water feeder would continue to fill the boiler and eventually the room.

    Would it be best to pipe a condensate pump up on the equalizer line just below the water line or would we risk shooting water up into the header? Have a minor repipe of equalizer and cond pump inlet coming up so could up grade if it were better. Header is probably 10' above lower boiler inlet.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,317
    Had a job we changed the boiler and the boiler feed tank remained. The water level in the feed tank and boiler matched There was no motorized feed valve between the pump and boiler. When the boiler needed water the pump control on the boiler started the pump. After we were done we realized the water level in the new boiler being lower than the old boiler (I know Dummy) the water was sylphoning into the boiler after the pump shut down.

    Not wanting to install a motorized valve we piped the feed water up above the boiler water line and then back down into the boiler. Installed a vacuum breaker on the feed water line above the boiler water line to break the sylphon. Worked like a charm. I would go into the boiler low and use two checks.