Pressure decay after squeezing hydraulic pump handles

Pressure decay after squeezing hydraulic pump handles

Pressure decay is a natural effect of using a hydraulic pump and does not necessarily (always check) mean a leak in your system. Here's why: When you use a hydraulic pump to increase system pressure rapidly, the hydraulic fluid's temperature rises. Once you stop adding pressure with the hand pump, the system pressure will naturally decrease as the liquid cools until it reaches equilibrium, which is called the Adiabatic process.

The QTHP pump, at room temperature, with only a reference gauge attached pressurized to 5,000 psig, will exhibit a pressure decay of approximately 10-20 psi per minute for the first several minutes after pressurization. This is a natural thermodynamic process and does not necessarily mean a leak in your system.

Ralston Quick-Test hose is strong and flexible but will temporarily stretch due to the Adiabatic process. This hose-stretching will significantly affect the system pressure until it stabilizes. Flexing or moving the hose can also create temporary changes in system pressure. 

Ways to reduce the range of pressure decay

The rate of pressure decay and the time-to-stabilize will vary widely based on the size of the system, test conditions, and environmental factors. But there are a couple of things you can try to reduce the amount of time you have to wait for equilibrium:
  1. Once you reach your target pressure, turn the Fine Adjust valve knob on the hand pump slowly enough that it counteracts the pressure decay without reheating the hydraulic fluid.
  2. Use an entirely metal system or isolate the system from the flexible hosing with a block and bleed valve.



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