Can I use a pressure relief valve to drain winter water line?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by tuckerdog, Feb 28, 2012.

  1. tuckerdog

    tuckerdog New Member

    Messages:
    5
    Location:
    Ontario
    I'm trying to find an easier way to drain a winterized water line so I don't need to continually run the heat-line. I have a shallow well jet pump bringing water in from the lake with polyehylene pipe probably 75psi.

    Could I put a pressure relief valve close to the foot valve where the water doesn't freeze and then pressurize the line (30-40psi dependent on the valve) with a compressor?

    There is a 10 ft drop in elevation which according to my math results in a 4-5 psi at the foot valve. If I attach a compressor and pressurize the line, could I evacuate the water in the line thru the pressure relief valve? Once the water is evacuated, I'd remove the pressure and the valve should close and there is no way for the water to re-enter the line.

    Could I use a hot water heater pressure valve or something similar? Would the foot valve survive 30-40 psi?

    Thank for any input
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,583
    Location:
    Lubbock, Texas
    I think a bleeder orifice above the foot valve would work better. But either way, unless you keep an air charge on the line, the footvalve will let water back in until it fills to the lake level again.
  3. tuckerdog

    tuckerdog New Member

    Messages:
    5
    Location:
    Ontario
    Would a bleeder orifice maintain prime when the pump is not in use? Does a bleeder orifice expel the water at a certain minimum pressure?

    Secondly, regarding the foot valve don't they close unless under the negative pressure from the pump. Or would the pressure from being under water be greater than the pressure from the spring in the foot valve?
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,583
    Location:
    Lubbock, Texas
    The bleeder just above the footvalve will act like a little footvalve itself. It will let water in but not out. When you want to drain the system you need to shut off power to the pump and open a faucet to drain the tank. When the pressure is out of the system the bleeder will open and drain the line to the lake water level.

    A footvalve will not let water go backwards, but the spring is not strong enough to keep water from coming in and filling to the lake level.
  5. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    If you want to drain all the way to the pump, I have a funny little valve made for draining air compressors that is actuated by a 1/16" wire rope. You could run that along the pipe and open it while blowing all the water with air out of the system. Then close your inlet air valve and release the rope and you have a line full of pressurized air to the pump for the season [hopefully]
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,185
    Location:
    NW Ontario, Canada
    Normally, a footvalve is and should be the only checkvalve in the system and so designed to hold full system pressure. A PRV next to footvalve would work to purge the line if the air pressure was raised above the relief trip pressure. I would keep the pipe pressurized with air, both to keep water from re-entering and also to provide a little bit of crush resistance. A would use a regular PRV, not a TPR for a HWT.
  7. tuckerdog

    tuckerdog New Member

    Messages:
    5
    Location:
    Ontario
    What would be better (I realize neither solution is ideal). Leaving the line pressurized to keep the water out of the line and the foot valve closed as described above or removing the foot valve and replacing it with a check valve at the pump and using a hand pump to pump air into the line evacuating the water from the line.

    I guess the question lies is what has the potential for more problems, having the line with positive pressure or negative pressure or is it equal.

    I appreciate the help so far.....thx
  8. valveman

    valveman Moderator Staff Member

    Messages:
    4,583
    Location:
    Lubbock, Texas
    I think a check valve would be better to keep from freezing, but a footvalve is always better than a check valve on a suction line as far as the pump is concerned. If you use the check valve idea, I would also add a low pressure cut off pressure switch so you don't nuke the pump if you loose prime.
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