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Any well-built hydraulic power unit (HPU) includes a system pressure gauge on the high pressure side.  When this HPU gets paired with a hydraulically driven submersible pump, the readings on that gauge can both help the operator reach the best operating point (given current conditions) and assist in analyzing a problem situation when the submersible pump is not moving water.

Finding the Best Operating Point:

In many parts of life, more is better, but when it comes to operating an engine based hydraulic power unit, that is not the case.  By using the pressure reading it is easy to find the sweet spot for any particular pumping situation.  Specifically, the pressure shown on the gauge is an indication of the amount of work being done by the hydraulic motor on the pump head.  The higher the pressure, the harder the motor is working.  This working pressure profile can vary for different styles of pumps, but the one thing that is the same across the board is this… when adjusting engine rpm the operator will see system pressure rising until it stops.  When the needle stops moving, it means that given the current set up, the system is at its most efficient point.  Attempting to increase engine speed in an effort to get more submersible pump flow will only result in burning more fuel; it will not change the gpm output of the head.  Of course, as conditions change, that ideal point will change too, so further adjustments will be required to stay at the best spot.  By educating your customers and staff about this pressure point, it becomes a win, win, as fuel costs can be cut, wear and tear on engines is reduced and the environmental impact of the fuel burn is minimized.

Problem Analysis Using System Pressure

Because hydraulic systems are fairly simple, they tend to react in the same way when something goes wrong.  When using hydraulic power to drive a pump head, we look at three sides to the same problem to find the reason why the pump head is not moving water.  If the submersible is not moving water, the operator should first note the pressure reading shown on the gauge on the high pressure side of the system.

If the pressure is above 1000 psi and you can be sure that the pump impeller is turning, then the following conditions are likely preventing the pump from moving product:

  • Head conditions are too great for the pump to overcome and a different pump head/HPU should be employed
  • The discharge line is kinked, or somehow blocked downstream of the discharge or too much lay flat hose is choking off pump head discharge flow

If the pressure is above 1000 psi and the impeller is not spinning, then the following conditions are likely preventing the pump from moving product:

  • The bearings or hydraulic motor are seized and need to be repaired
  • The impeller is jammed and the top of the pump may need to be removed to clear the obstruction

If the pressure is below 1000 psi look at the following:

  • Dead head the hydraulic power unit and see if it alone is capable of developing 2000+ psi ( FAQ –Is there a quick way to determine if my power unit is providing sufficient flow/pressure?)
  • If the HPU is good, the next thing to check for is lack of water in the pump.  Is the suction opening and/or the strainer base clogged?
  • If the suction is not clogged, the pump may not be submerged enough to begin working.  Generally speaking the pump should be in water that reaches to the bottom of the hydraulic motor.
  • Once you know if the HPU is good, and the suction side is clear and the pump is submerged enough, it is possible that the pump is air bound.  This can even occur with a pump that is continually sitting in water.
    • To overcome this problem, check the vent bolt on vortex impeller pumps to see if it clear.  This vent bolt is an air escape;
      • Pull the pump from the water and before lowering it back down, lay it on its back with the discharge at 12 o’clock,
      • Then lower into water
      • Pull the pump back out, start the power unit and have the impeller turning when dropping it back in
    • If none of the above are true, then it is likely worn parts.  The hydraulic motor could be washed out and the oil when under pressure is blowing by instead of doing the work.  Or, there may be excessive wear at the impeller and internal parts which is greatly reducing the efficiency of the pump head.

While troubleshooting can sometimes be a headache with hydraulic pumping systems, going through the process detailed above usually uncovers the cause of the problem.  If it does not, feel free to call us, and a member of our staff will be happy to work through to a solution.

Check out the support tab on our website for other useful technical information about our pumps and hydraulic power units.