Accumulators are pressurized vessels that hold fluid under pressure. This stored energy can be called upon to boost energy to a system when needed, then recharged to store it again. This stored energy can be dangerous; proper care should be taken to ensure pressure and temperatures are kept under control.
Several small yet critical accessories can be installed on accumulators to prevent the release of this stored energy and to ensure temperatures remain in their safe operating range. Burst discs, temperature fuse plugs and relief valves are all safety devices for use on gas-loaded accumulators.
Overseas, the European Pressure Equipment Directive (PED) offers statutory regulations to ensure safety in the workplace. Fundamental risks affecting hydraulic accumulators are:
• Excessive pressure and
• Temperature increase (e.g. in the event of an external fire).
When selecting safety equipment, consideration must be given to the material (elastomers and housing material) in terms of material compatibility in the application. This means that the safety equipment must not exceed the maximum permitted operating pressure of a hydraulic accumulator.
If pressure exceeds the maximum level on the gas side, a burst disc is designed to burst, permanently opening the port. This reduces the gas pressure by discharging the nitrogen completely. Burst discs are designed for different response pressures and are supplied with a declaration of conformity. Bursting discs are made either entirely of stainless steel, or from an alloy based on stainless steel and nickel.
Temperature fuse plugs are used to release the gas pressure by discharging the nitrogen completely when an increase in temperature reaches unacceptable levels (e.g. in the case of fire).
Gas safety valves protect the hydraulic accumulator by reducing the pressure in a controlled way if pressure exceeds the permitted level unexpectedly. They are pre-set on the pressure side and load-sealed by an authorized representative. Mounted on a hydraulic accumulator on the gas side, they can be fitted with various pressure devices, charging equipment, safety valves, and other safety components.
The fluid side of an accumulator must be protected from pressures exceeding the permitted operating pressures by installing approved and appropriate unloading valves.
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