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Thread: pump control valves

  1. #1

    Default pump control valves

    I'm looking for someone who has experence with "cycle stop valves".
    Company literature claims " as pressure on a pump increases, the power required decreases. So if you have a stop valve on the discharge of a pump
    and begin to close it, restricting the flow, the power required by the motor will decrease. I`m talking about a pump with centrifugal impellers.
    Is this true? Has anyone actually proven this?

  2. #2
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    It's true and it has been proven.

    I'm not sure what you mean by centrifugal impellers though. Are you referring to a centrifugal pump, jet pump or submersible pump?

    bob...

  3. #3
    Rancher
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    Quote Originally Posted by speedbump
    I'm not sure what you mean by centrifugal impellers though. Are you referring to a centrifugal pump, jet pump or submersible pump?
    bob...
    I think all 3 of these use cntrifugal impellers... even the jet pump.

    Rancher

  4. #4
    DIY Senior Member Phil H2's Avatar
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    Paulie,
    It is very true that the energy consumption decreases as the pressure increases. When a centrifugal pump operates at higher pressure, less GPMs are being pumped. The energy savings comes from the reduced flowrate. It does require more energy to pump higher pressures, but it requires even more energy to pump the higher flow rates with lower pressure.

    I have seen this many time on an ammeter with different centrifugal pumps. Most will consume the most electricty when they are pumping the maximum GPM with no head. At this point, the motor heats up because of the high amperage.

    While pumping at an increased head with a lower flowrate reduces energy use, it does not neccessarily increase efficiency (often the opposite). Centrifugal pumps have a best efficiency point (BEP) where you get the biggest bang for your buck.

  5. #5
    vaplumber
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    I would think that for single family use the power savings would be insig. Around here, separately metered pumps for multi family use usually measures less that $20/month anyway. Dont know if youd notice much in a single family bill per month. The savings will come in pump life. The basic motor design has remained unchanged. Mechanical couplings (the splines shaft and impeller hex openings) are basic and can not be improved on. A pump cycling on and off is like pointing your car up the street every morning and flooring the gas as you pull out. Its fine for a while, but the shock loads will eventually destroy mechanical links in the system. Turn that pump on when you open the faucet, and turn it off when you close the faucet. Dont let it start 3 or 4 times during a shower or a load of wash. Of all the pumps Ive replaced over the years, very few actually had a bad motor or worn down impellers. Most had the splined shaft destroyed, or the hubs of the impellers wallowed out from starting and stopping. Which is better? Spending an extra dollar or two per month even if it should use a little extra elecric? Or $1500 to replace a bad pump every 5 to 8 years, not counting newtons law that says it will usually fail late at night or on a holiday weekend?

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    Not to get off topic, but since paulie has not come back in here, maybe I can sneak this question in.

    What kind of pump are you using? And what kind of system do you have? Pump, well, cistern etc. Inquiring minds want to know.

    bob...

  7. #7

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    Just a regular deep well pump, 1 hp. set at 400 ft. plentful supply of water.
    supplies water for a farm including a home, 250 head of dairy cows, etc.
    Thanks for all the replies. A very useful and educational site. Again THANKS.

  8. #8
    DIY Senior Member Phil H2's Avatar
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    The initial question is reasonable and legitimate. Many people will intuitively think that is you restrict the flow to a fan, vacuum, or centrifugal pump, that the machine will need to do more work and require more energy. This is not the case. The two previous comments concerning Leonardo and cloverfields might be construed to be insults.

    On the other hand, try throttling the flow on a positive displacement pump and watch the amps. Many lay people do not know the difference. Much the same, many people think centrifugal pumps create pressure when the pump's actual mechanics impart velocity on the fluid.

  9. #9
    vaplumber
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    Quote Originally Posted by Phil H2
    On the other hand, try throttling the flow on a positive displacement pump and watch the amps. Many lay people do not know the difference. Much the same, many people think centrifugal pumps create pressure when the pump's actual mechanics impart velocity on the fluid.
    But a positive displacement pump is designed to make working pressure. A hydraulic pump for example. The steer pump in your car. A centrigugal impeller (even your jet pump or well pump uses centrifugal impellers) is not designed to make pressure. They will, but pressure damages them. The volume pumped and the force of the flow is what gives us useful pressure (exactly as your saying here phil). This is why we use ballons in our tanks, or air cushions in the case of our galvanized tanks. I dont qute know the wording to explain this, but comparing positive displacement pumps to our water systems is like comparing an air compressor to our fans and vaccuums. Block a fan, the amps go down. Block a compressor they go up. Positive displacement is going to move exactly the volume of the pumping chamber no matter what, even if something has to blow in the process. This is not a argument either. Just trying to give an example that any one can understand. What I would love to see is a long term bench test of 2 pumps pumping the same amount of water. 1 with the valve, running constantly, and 1 allowed to cycle on and off normally at say 12 to 15 gallon drawdown. I would like to see both torn down after pumping the same amounts of water over the same perios of time, and to examine the motor coupler and impeller hubs of both for wear. Many single families would never notice enough electrical useage to even matter, but what about wear on each style system after pumping the same amount of water over a simulated 5 year time frame? I still feel that pump life is the one great benefit.
    Last edited by vaplumber; 11-03-2006 at 11:58 PM.

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