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.



    • Related Articles

    • Operation Instructions 5000 psi Hand Pump (Model QTHP)

      Add Fluid 1. Remove the Vent Plug at the top of the Fluid Chamber 2. Add fluid to the Fluid Chamber Acceptable fluids: Ralston Calibration Oil, mineral oil, transmission fluid, water, or alcohol. Remove the vent plug and add around 2 inches of fluid, ...

    • Operation Instructions 10,000 psi Hand Pump (Model XTHP)

      Add Fluid 1. Remove the vent plug 2. Add fluid to the Fluid Chamber Acceptable fluids: Ralston Calibration Oil, mineral oil, transmission fluid, water, or alcohol. Add around 2 inches of fluid, or enough fluid to keep the bottom of the fluid ...

    • Recent Articles

    • Set the logging interval for a test

      Applies to FieldLab Mobile versions 2.0 and later 1. Add the pressure and/or temperature readings you need to your test. Learn how to Add Readings to a Test. 2. Tap Test 3. Tap Interval 4. Select your desired interval 5. Select Back The interval you ...

    • Max logging durations based on interval: Quick reference table

      Applies to: All Bluetooth-enabled models of Field Gauge LC20, Process Meter LC30 Ralston Field Gauge and Process Meter gauges log data to on-board memory when you start logging from the Fieldlab Mobile app. The logging interval you select determines ...

    • Add Readings to a Test

      Applies to FieldLab Mobile versions 2.0 and later. This walkthrough demonstrates how to add one pressure reading. You can add as many readings to a test as needed by repeating the steps below. 1. Connect the included Bluetooth antenna(s) to the ...

    • Delete a Reading from the Test screen

      Applies to FieldLab Mobile versions 2.0 and later 1. Tap the Reading Card 2. Tap Reading 3. Tap Delete Reading 3a. Confirm that you wish to delete.

    • Getting Started: Run Your First Test with FieldLab Mobile

      This guide walks you through connecting a gauge, logging data, and retrieving a completed test run. This walkthrough uses a single gauge, but FieldLab Mobile supports multiple gauges and readings in a single test. The following guide applies to ...