Basic Check Valve Question

Discussion in 'Pumps and Tanks Well Forum & Blog' started by turkeyvulture, Apr 12, 2013.

  1. turkeyvulture

    turkeyvulture New Member

    Messages:
    25
    Location:
    California
    I think this is an easy one. Does the typical residential submersible pump have a check valve built into it? I have heard that this is so, but then I always see another one just before the pressure tank, so why is that one necessary if there's one in the pump?

    Thanks for the Wells 101 advice!
  2. craigpump

    craigpump Well-Known Member

    Messages:
    1,039
    Location:
    ct
    They are either part of the discharge or screwed into the discharge. Around here everyone puts a check on the tank as well, someplaces check valves on the tank are against code.
  3. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,444
    Location:
    Houston, TX
    Sometimes a Check Valve on the top side is used when the Check Valve in the well won't hold pressure.

    That is a half-fast fix that is cheaper and easier than pulling the pump out of the well.
  4. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,150
    Location:
    NW Ontario, Canada
    If the checkvalve in the pump doesn't hold, the line is no longer under pressure and could be under vacuum. If a leak develops, the vacuum can suck in surface water and contaminate your well, creating a health hazard.

    Sometimes a topside checkvalve is used with a snifter and a bleeder as an air maker for a hydro-pneumatic tank. Sometimes it is setup as a drainback for frost protection.
  5. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,444
    Location:
    Houston, TX

    I can see it under Vacuum, but how would it suck in surface water if it is on the output of the pump.


    What am I missing ? And where would the leak have to be for it to suck in surface water ?
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,150
    Location:
    NW Ontario, Canada
    Seriously, how would a vacuum suck? Is that a trick question? I don't know how to answer that in a way you'd understand. I don't know what you're missing.

    When you drink through a straw, that is a partial vacuum sucking.

    The leak would have to be underground where surface water is present.
  7. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,444
    Location:
    Houston, TX

    It is not a trick question. lol

    If the leak is underground then the water would be contaminated even if the check valve was working.

    The Venturi affect would suck in the contaminated water when the pump was running.

    What does the check valve have to do with it ? That is what I must have missed.
  8. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,150
    Location:
    NW Ontario, Canada
    If there is no topside checkvalve, the water stays under pressure all the time, so well water would exit the leak continually. There is no "venturi effect" in normal piping to suck in ground water. You need to take a look at how a micronizer is made to understand the forces it takes to create a vacuum through a venturi.

    It is possible for a fitting to leak under vacuum but not leak under pressure.
  9. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,444
    Location:
    Houston, TX

    I understated what you are saying.

    But I would not call a leak in a pipe "normal piping". If the pipe was leaking there could be no vacuum.


    Thanks for the clarification.
  10. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,150
    Location:
    NW Ontario, Canada
    I don't know if you are arguing semantics or just being belligerent. True, there cannot be a perfect vacuum since the water would turn to vapor and occupy some of the space.
    In the presence of a topside checkvalve, there most certainly can be a partial vacuum. The weight of the water falling back to the well would create it. It works on the same principle as a mercury barometer.

    Fill a garden hose with water. Leave one end open and put your thumb over the other end and climb a ladder or stairs, dragging that end of the hose with you so that the other end remains lower. When you release your thumb at the top of the stairs, you will experience the suction. This same suction can suck in contaminated ground water.
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