Accumulator safety tips and precautions

Hydraulic accumulators are able to store pressurized fluid, and for systems that are gas-charged, they store compressed nitrogen, which means they store energy even after the unit is removed from service and depressurized. Safe handling requires verifying zero pressure before service, never welding or drilling on a charged accumulator, using only nitrogen (never oxygen or compressed air) for gas pre-charge, installing a shut-off/bleed block valve, and following manufacturer-specified torque and inspection intervals. Since a damaged or ruptured accumulator could release energy violently, each worker who works near it should consider it an immediate danger until it is officially confirmed as safe.

Hydraulic accumulators differ from other components in a power system. A valve or cylinder loses its stored energy in a matter of minutes after the pump is shut off and the system is bled down. An accumulator does not. It was specifically designed to contain pressurized fluid and, in gas-charged models, compressed nitrogen ready to release at a moment's notice. This is precisely why it's ideal to absorb shock as well as emergency actuation and storage of energy. It is also why it is risky if not handled properly.

This article outlines the basic safety rules that must be followed by anyone who designs, installs, or maintains hydraulic accumulators, as well as the safeguards that lower the risk of injury or damage to equipment.

What makes accumulators a riskier investment?

The majority of safety instruction in hydraulics concentrates on high-pressure injection of fluid accidents and pinch points. Accumulators are a third type of risk: energy stored that is not affected by the other component systems. A machine could be shut off, the motor turned off, and the pressure gauges elsewhere read zero—but the accumulator may contain thousands of PSI internally.

These incidents generally are much more serious than the typical hydraulic failures. A ruptured or improperly removed valve could behave as an explosive release that propels parts, liquid, fragments, or other components that are powerful enough to cause serious injuries or even death. Each safety rule below is in place due to this fact: an accumulator first, and a hydraulic component later.

Pre-service security

Ensure that there is no pressure before any work.

Don't assume that an accumulator is under pressure due to the pump being off or the system being idle. Make use of the accumulator's shut-off valve or bleed-down valve, and verify zero pressure using an instrument calibrated prior to removing fittings and opening the shell or disconnecting the hoses. If the accumulator does not have an isolation valve, put one in place prior to starting the process—retrofitting this will be much less expensive than treating a laceration.

Do not touch before you isolate.

A valve for shut-off/bleed between the accumulator and the rest of the circuit must be included in all installations. It isolates the accumulator from pressure in the system and offers the ability to regulate the flow of stored energy in a safe manner. Lockout-tagout protocols should include this valve in the process in addition to an isolated disconnect from the pump.

Make sure to check the precharge for gas on its own.

For gas-charged (bladder piston or diaphragm) accumulators, the gas side stores its own energy stored in the system independent of the hydraulic part. When the hydraulic pressure is zero, the gas precharge can stay fully charged. It must be released via the gas valve in accordance with the instructions of the manufacturer, prior to any removal or removal of the chamber.

Charge and recharge safety security measures.

Use nitrogen only.

Gas-charged accumulators are pre-charged using dry nitrogen, never oxygen or compressed air, and no other gas. Air or oxygen combined with hydraulic fluid at pressure can cause the potential for a significant explosion or combustion danger since the compression of the oxygen-fluid combination can produce sufficient heat that ignites the liquid. Nitrogen is inert and removes this risk.

The charge is slow and stays within the limits of the rated limit.

Rapid charging produces temperatures that can cause damage to seals, and, in more extreme instances, it can cause damage to the shell. Charges should be conducted at the recommended rate of the manufacturer and shouldn't exceed the accumulator's max pre-charge capacity. The bladder is stretched by the piston and increases the likelihood for premature breakdown.

Use a charger that is specifically designed for charging.

A suitable charging kit—regulator, hose, and gauge that are rated to the accumulator's specific pressure class—is required every time. Improper connections or improperly fitted fittings are the most common cause of blowouts and leaks in the charging process itself.

Mounting and installation precautions

Mount in accordance with the manufacturer's orientation.

A lot of accumulators are designed to be installed vertically with the gas end facing up to ensure the piston or bladder is functioning in a correct manner and prevent uneven wear. If you install one upside down or sideways, it can cause uneven wear. down in opposition to the manufacturer's instructions can reduce service life and, in certain designs, alter the way that the mechanism for safety works.

Secure using rated brackets and hardware.

A pressure accumulator has a real mass and stored forces behind it. Hardware and mounting brackets need to be designed to accommodate the weight of the accumulator and the shock or vibration load associated with the process. A mount that is not properly sized or tight can result in the accumulator being unusable in time, straining the pipe that is connected to it.

Access for isolation valves and valves to bleed

Plan the installation to ensure that you can ensure that the isolation valve, bleed valve, and pressure gauge are accessible without having to remove guards or disassemble other equipment. Safety devices that are difficult to reach are often ignored in the course of maintenance that does not serve their purpose.

In-continuous inspection and maintenance

Check shells for signs of corrosion, cracks, and deformation.

The shell of the accumulator is the pressure vessel. Damages, corrosion, or dents on the exterior or visible deformations can be a sign of the thinning of the wall or stress concentration, which reduces the pressure that is safe for working. Any of these indicators need to be a cause for a formal check against the criteria of fitness-for-service set by the manufacturer prior to returning the unit to service.

Monitor pre-charge pressures according to a set schedule.

The pre-charge for gas naturally decreases with time due to slow permeation even in a sealed unit. Checking the pre-charge is a necessary and essential part of the preventive maintenance routine and should not be done just when a problem is suspected. A significant pre-charge loss alters how the accumulator reacts to load, which can lead to an increase in seal or bladder wear.

Disruption valves and relief valves must be used with respect. disc ratings

Do not plug, bypass, or re-rate a relief valve or a rupture disc to protect a circuit of an accumulator. These devices are specifically designed for the accumulator's operating volumes and the pressure. If you replace one that has an alternative rating—perhaps "just to stop nuisance trips"—it is the final line of protection against pressure overpressure.

Be sure to follow the certification and testing requirements.

In several jurisdictions the hydraulic accumulators are categorized as pressure vessels and are subject to periodic certification, hydrostatic tests, or registration requirements comparable to air receivers or boilers. Check local regulations and make sure that the documentation is current. This isn't merely an obligation to comply; it's an organized method of catching wear and fatigue before it causes failure.

The creation of a culture of safety around accumulations

Controls for technical systems only function when the people who work around the equipment know the reason they are important. Anyone performing lockout-tagout or hydraulic maintenance troubleshooting around an accumulator needs to be educated specifically about stored energy hazards, not only general safety in hydraulics. A clear labeling system—including the rated pressure of the unit, types of fuel, and the isolation method—will help to keep this in mind every time anyone comes near the unit.

Thinking of an accumulation device to be "just another hydraulic component" is the main reason for serious accidents. Thinking of it as an accumulator that is part of a system of hydraulics is the way of thinking that keeps people safe.

How can I tell whether a hydraulic accumulator is still in pressure?

Do not rely on inspections or shutdowns by themselves. Utilize the accumulator's isolation as well as the bleeding valve to release tension in a controlled fashion and ensure that there is no pressure using a gauge that has been calibrated prior to performing any maintenance.

Do I have to utilize compressed air instead of nitrogen to charge an accumulator prior to charging?

No. The oxygen in compressed air may react with hydraulic fluids under compression, causing an explosion or fire risk. Dry nitrogen is the only type of nitrogen that should be used to pre-charge the gas.

When should the accumulator pre-charge pressure be monitored?

The charge should be inspected on an annual preventive maintenance plan because it naturally decreases in time due to the slow rate of gas permeation with no leak.

What happens if the accumulator's adsorption valve is not sized correctly or is bypassed?

The removal or under-rating of this valve, also known as the rupture disc, removes the system's defense against pressure overpressure, thereby increasing the chance of a ruptured shell.

Are hydraulic accumulations legally considered to be pressure vessels?

In some regions there are jurisdictions that allow it. In accordance with specific regulations in your area, the accumulator could require regular certification, hydrostatic testing, or registration, as with similar pressure vessel devices. Check the requirements specific to your area.