Trouble Shooting DC Hydraulic Power Unit

Q: Why does my pump lose prime?

A: The most common culprits of a pump losing prime is as follows:

1.      Suction tube not staying submerged due to pump mounted improperly

2.      Partially clogged suction filter

3.      Loose or poorly install suction line or pick-up tube

4.      Reservoir not being properly vented

5.      Oil has too low of viscosity for the operating temperature (too thick)

6.      Front pump seal failure; this is a fairly rare occurrence and all other possibilities should be eliminated first.

Q: What is the Volt/Amp requirements?

A: The Voltage requirement should be labeled on your system.  DC motors use high amperage and low volts to make the torque required to create flow and pressure.  Amperage requirements would be determined by the amount of load on the motor.  The load changes depending on the amount of pressure that your hydraulic system is required to perform.  How hard the motor has to work is also dependent on the displacement of the pump within the power unit.  When setting up a system it is a good rule of thumb is to limit the system to the 150-225 amp range.  This will allow a longer life expectancy to the motor.  It is necessary to size components of the electrical system to accommodate your maximum potential current draw to avoid shorts and potential fire dangers.  Please see the 12vdc charts below for reference.

Q: Why is my pump so slow?

A: DC power units are usually fairly limited in the amount of GPM they are able to produce.  However, if your power unit is slower than it has been in the past with the same amount of load, there are usually only a couple of causes.  Make sure that your power unit is receiving the full voltage required to operate.  Check to make sure the unit is properly grounded. 

A)      If the unit is receiving full electrical power and sounds like the motor is being “labored” your motor will need to be re-built or replaced.

B)      If the unit is receiving full electrical power and does not sound like the motor is being “labored” there is most likely fluid bypassing within the system.  This can be caused by relief valve not being fully seated, a worn pump, or even a faulty piston seal on a cylinder.  First eliminate the possibility of the piston seal bypassing by using standard cylinder trouble shooting procedures.  Once that is done, attach a gauge to the pressure port on the power unit.  By “Dead-heading” the pump you will we able read the relief valve setting. 

1.      If the pump slowly builds up to a steady pressure, either your relief valve is not seating properly or the Cartridge valve on the return circuit (if so equipped) is malfunctioning.

2.      If the pump quickly builds to a set pressure, try adjusting the relief pressure higher.  If it fails to raise the pressure regardless of adjustment, your pump is wearing out.

Q: Why is oil shooting out of the breather cap on my reservoir?

A: Clear oil coming out of the reservoir might indicate that the system is over-filled due to a cylinder not being fully retracted when the system was filled.  Foamy oil coming out might indicate air in the system.  Common causes to this can be a loose suction tube, or no down spout.  Other potential causes can be excessive return oil velocity.  This can be typically solved by slowing the return oil through a unidirectional flow control valve, or increasing reservoir capacity size.

Q: Do I need to replace the motor on my power unit?

A: If the motor fails to engage, the first step is to ensure that it is receiving sufficient volts/amperage.  Inspect the condition of all wires and connections for breaks and or corrosion.  Check to make sure that the trigger wire is engaging the start solenoid.  If the solenoid is engaging you should here an audible “clicking” coming from the solenoid.  No clicking, replace solenoid and continue diagnostics.  If you hear the solenoid engaging, check that there is power coming across the solenoid to the motor side.  Once you are positive that you have sufficient amperage reaching the motor and it still fails to engage the motor will need to be re-built or replaced.

DC motors do not always “catastrophically fail” rather most get weaker and slowly burn out over time.  It can be difficult to determine if it is your motor or the pump that is wearing out.  If the motor stalls out before making target pressure, the motor will need to be re-built or replaced.  If the motor continues to run, but the unit fails to make pressure, the failure is usually in a different component.