Pump question

Discussion in 'Irrigation' started by FIMCO-MEISTER, Jul 17, 2011.

  1. I have this pump for circulating the water in a fountain. The pond/fountain designer told me to get the pressure up to 20 psi and to keep running/shutting down/bleeding from a faucet above the pump until every bit of air is removed and then it will go up to 20psi. So i do this for what seemed like 20 times. Finally the pump went up to 20psi and stayed there. Why do small amounts of air get trapped and never leave? It seems to me they eventually would circulate out of the system through the fountain.
  2. mitchgo

    mitchgo LawnSite Silver Member
    Posts: 2,789

    I could be wrong, but my answer to that would be Air is much lighter then water- like water - it's entire goal is to reach atmospheric pressure- thus getting trapped trying to reach this
  3. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,031

    It may have to do with air being compressable, and altering the pump performance
  4. The pump is at the lowest point in the circulation and the fountain is at the highest but air seems to get trapped in the pump until it is all bled off after shutting the pump down and flushing water from a boiler drain right above it.
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  5. mitchgo

    mitchgo LawnSite Silver Member
    Posts: 2,789

    I have to do that for the pool I have to clean the filter

    Turn it off, bleed off all the air and then turn it on

    Rather funny, reading a review regarding the pool I bought.. Someone bought it- set it up, took it down and threw it away because the pump wasn't working right.. All it needed was to be primed correctly
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,031

    maybe the pump is a more-efficient sort that can't power out the air as easily as a jet pump might
  7. txgrassguy

    txgrassguy LawnSite Gold Member
    Posts: 3,083

    The impellers on low flow low pressure pumps common to fountains trap air on the inside of the impeller vane at the hub.
    The vane doesn't rotate very fast and from start up a certain amount of cavitation exists which the pump cannot displace due to low volume/pressure - requiring the process you went through.
    Believe it or not but if you get a quart of non-ionic surfactant from a chemical house and add eight ounces or so to start you'll find the pump will prime much easier.
    However, if you have fish or other aquatic non-plant material in the pond the surfactant may cause some off-target effect.
  8. Thanks. That clears up a lot of stuff for me on this setup.

    Another issue I have is the auto-fill runs all the time. i can get the three pools and fountain filled and as soon as I crank the pump on the auto-fill starts and does not stop. I've figured on some serious evaporation loss due to the dryness here and accounting for circulation but not to this extent.
  9. txgrassguy

    txgrassguy LawnSite Gold Member
    Posts: 3,083

    Your auto fill runs all of the time probably due to several issues.
    First your static set height is to high.
    Secondly the fill line lacks the capacity to fill the pond reservoir so when the pump starts and the water level lowers the fill valve stays open.
    In order for a separate fill line to work with a captive pond reservoir it needs to be in a separate part of the basin as far as possible from the pump. This way will the water level lowers and the fill valve float drops it is noticing only the water contained in the separate basin.
    The problem with low capacity pond reservoirs is the static level is adversely effected by pump start-up. A needed part of the reserve capacity of the reservoir is the volume calculation in order to off-set the loss of volume when the pump initializes. The separate basin helps to avoid an "over full" or overflow condition since it monitors only a small part of the reservoir instead of the entire reservoir.
    Try this if you can't re-establish the fill point and you have a float type fill valve - bend the float arm up, not down so the travel needed to activate the float is delayed while the pump displaces the amount of water through the fountain. This way when the pump is turned off the water returning will de-activate the float valve prior to over filling the reservoir.
  10. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,672

    air is compressible peter and steve is right on about the impeller issue. as far as the auto fill goes, they are floats exactly like the floats in toilets, when the pump starts the water is displaced and the auto fill does its job of filling the void. evap can be measured by doing a bucket test for 24 hrs. this will also tell you if you should be looking for a leak.

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