Low output from pump

Discussion in 'The Projects Forum' started by prasan_y2k, Jun 19, 2012.

  1. prasan_y2k

    Thread Starter New Member

    Jun 19, 2012
    I have a 12v DC (rotary vane type) pump that is connected to a 12v auxillary battery. The battery is 12vDC 70Ah and it charges itself with the truck's alternator, which is 12 volts, 35 amps. the pump is 1/4 hp, and it draws 20 amps max. The problem is, the discharge output of the pump is very low(8-10lpm), whereas the pump is designed to have a max discharge of upto 57lpm.
    What is the reason of low discharge?
    Is there any way to increase the speed of the pump so that the discharge rate is increased?
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
    a pump like this one? check the chart in that manual, it gives an idea what kind of flow rate to expect from adding different crap (hoses, elbows, smaller fittings, etc) in the line. You want your hose to be as short and as wide as possible, use as few bends as possible, and get the pump as low as possible to the surface of the fluid, or ideally below the surface of the fluid.
  3. #12


    Nov 30, 2010
    Trying to boost the pump into a speed range it wasn't built for is guaranteed to wreck the pump. Much better that you fix the cause of the low output. As mentioned above, friction caused by length of tubing, small diameter, and elbows, and the power required to lift the liquid against the force of gravity. That's the route for a new installation. If this pump worked well at some other time, you are looking for wear or obstructions.

    If you don't mind smoking the pump, just supply more voltage. That will cause the current to increase and the power to increase.

    If you merely found that you have too many pipes and elbows for that pump, buy the right pump.
  4. mlog


    Feb 11, 2012
    1. Check the voltage applied to the pump. Are you sure you have 12 volts? Is the ground return solid?

    2. Do you have an very high back pressure? Check the pump specs and measure your pressure. Does it have low flow when pumping into no restriction, say an open barrel?

    3. What is your inlet pressure, and how does it compare to the net positive suction head (NPSH) and the vapor pressure of your fluid? Is your fluid cavitating?

    4. Maybe you have a bad pump. The pump should give a relatively constant flow at rated speed and over its rated pressure range.