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condensate pump vent line

As I read the new LAOSH revisited, I am struggling to think what would happen if the open vent in the top of a U piped (gooseneck)vent line was not installed.
As I understand it, the inverted U vent line acts as a safety to prevent the boiler from draining if the pump, LWCO and check valve on the condensate simultaneously falied. This of course will prevent the boiler from draining, provided it is piped above the boiler's water line.
I notice on the drawings in the book that there is a vent tee at the top horizontal piece before the last elbow and drop piece.
So my question is, will the vent line still work without that vent tee on top?


  • steamfitter
    steamfitter Member Posts: 161
    I failed to mention that the main reason for the open vent is to obviously vent the air out of a gravity return steam system.
    It is the secondary reason and the placement of that vent tee that I am questioning.
  • steamfitter
    steamfitter Member Posts: 161
    Can the condensate siphon out of both the tank and the boiler if the vent tee (above the water line) is not installed?
    Provided that all of the previously mentioned components failed at the same time.
  • aircooled81
    aircooled81 Member Posts: 197
    Siphon affect requires liquid in the down tube to create enough draw on the entering side of the tube (or U bend) to lift water from the vessel. So If you had 1 psig of pressure in the pump tank, filled the tube with water (u bend not vented) and had the end of the u bend with no vent pointed down with a solid column of water taller than 2.31', you could start a siphon affect. But at atmospheric pressure, which the condensate pump should be at, you would then have to pull vacuum on the vessel, otherwise start sucking water from a source downstream of the vessel.

    Picture how the vent tube gets flooded. If the check valve fails maybe. And the boiler has a water line higher than the top of the u-bend, well then yes, you could siphon the boiler after the water line has drained to the top of your u-bend. But you'd also need something on the boiler side to prevent vacuum, like a vacuum breaker, make-up water, or leak.

    So heaven forbid, this vent line ever fills up with water, the tee at the top would allow the vacuum to be broken as the water drains out and prevent the siphon affect
    EBEBRATT-Ed Member Posts: 8,467
    If the vent line is plugged the tank could explode, also all the air in the system comes out the vent

    the tee at the top prevents the tank from sylphoning empty if it floods. the tee in that case would let air in and act as a vacuum breaker
  • steamfitter
    steamfitter Member Posts: 161
    So the tee on top is a vent, but can act as a vacuum breaker as well.
    I have seen many, and piped out a few, condensate pump vent lines. Usually up a couple of feet above the boiler water line and then gooseneck with nipples and elbows. The last piece (downcomer) is usually a long nipple.
    Is this generally a safe and suitable piping practice?
    Or should there always be a vent tee on top with a longer downcomer piece that ends below the boiler water line?
    JUGHNE Member Posts: 8,132
    If you have any traps passing steam into the cond pump, I believe the top tee/vent will let you see that steam easier than it coming out of a vertical drop pipe which could condense it into unnoticed dripping on the floor or back into the cond pump tank. IMO
    EBEBRATT-Ed Member Posts: 8,467
    @steamfitter I agree I have seen them piped the same way without the vent tee.

    Don't think it's needed unless the tank and vent line gets flooded.
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