Enquire Now
Slide Form

How to Charge HYDAC Hydro-pneumatic Diaphragm Accumulator

This video has been prepared in order to explain the process of charging the Nitrogen pre-charge pressure of a diaphragm type accumulator.

Hydraulic accumulators are specifically designed to store and then discharge pressurized fluid as needed. They are classified as pressure vessels. Hydro-pneumatic accumulators are charged with nitrogen, which is separated from the fluid by a piston, bladder or diaphragm. There are risks involved when working with high-pressure gasses and fluids. On no account must any welding, soldering or any mechanical work be carried out on the accumulator shell. Work on systems employing hydraulic accumulators must only be carried out once the pressure in the fluid and/or the gas have been released. This tutorial video has been prepared in order to explain the process of testing the nitrogen pre-charge pressure of a diaphragm type accumulator.


Hydro-pneumatic accumulators need to be pre-charged with an inert gas in order to work at all. Selection of the correct gas pressure is vital, as it defines the stored hydraulic fluid volume and pressure, which are important for the safe and correct operation of any machine. It is important that the correct gas pressure is maintained, and periodic inspection is therefore necessary.

This gas used is hydro-pneumatic accumulators is almost always industrial grade nitrogen. The use of other gasses in these applications is dangerous, and should not be considered.

The nitrogen pre-charge pressure of an accumulator can only be assessed when it has been fully de-pressurised of hydraulic fluid. This means that the accumulator must be positively isolated from a live system and released of all hydraulic energy, or that the entire system has been completely shut-down and fully de-pressurised, or that the accumulator is not currently connected to a system, for example, it is on a workbench.

The HYDAC FPU-1 Universal charging and testing unit can be fitted directly to HYDAC diaphragm and piston accumulators.

The accumulator gas valve will be opened and re-sealed by operating a hex key in a socket head cap screw, and during the charging process, it will be operated by the main spindle of the charge head. Use only the correct equipment, that is the universal charging and testing unit, and follow this process:

  • Remove the plastic protective cap.
  • Use a hex key to break the torque on the sealing screw. Close the sealing screw lightly, so that it may be operated by the charging head spindle.
  • Before fitting the universal charging and testing unit to the gas valve, first ensure that the surfaces are clean and that the sealing O-ring has been correctly fitted.
  • Align the spring-loaded hex drive to the screw, and screw the unit to the accumulator gas valve, hand-tight.
  • Ensure that the gas release valve on the side of the charge head has been closed firmly. It closes clock-wise, like a tap.
  • Slowly turn the main spindle counter-clockwise, until the nitrogen gas pressure is displayed on the gauge.
  • If the pressure is below the anticipated correct level, then gas re-charging is necessary. If there is in-fact no pressure seen on the gauge, then the diaphragm has possibly ruptured, and unit replacement may be necessary.
  • If the pressure is at the correct level, you can begin disconnection by winding the main spindle clockwise to re-close the gas valve.
  • Release the gas from the charge head by opening the gas release valve in a counter-clockwise direction.
  • Once de-pressurised , you can remove the charge head from the accumulator gas valve.
  • Use a leak detection fluid to ensure that no gas is escaping from the accumulator.
  • Re-torque the gas valve sealing screw to 20Nm.
  • Finally, replace the plastic protective cap.

We recommend that the gas pre-charge pressure is re-checked the following week. If there is no gas loss observed, check again after four months. Again, if there are no losses observed, a six monthly inspection cycle should be sufficient.

HYDAC host regular training courses on hydraulic accumulator technology, and many other topics in Melbourne, Australia. For more information, please visit our website, hydac.com.au

AUSTRALIA 1300 449 322

AU au-flag NZ nz-flag