Accumulators and their functions may be the least understood component of a hydraulic circuit.
Versatile, ruggedly built for durability, long life and simple in design, hydraulic accumulators are able to solve numerous problems or enhance your hydraulic system.
Some typical applications include clamping shaker heads, loggerís and chipperís self-loader grapples, softening hydraulic motor starts, and any situation where there are ìhigh-spikeî pressures or sudden impact and jolts in hydraulic systems. Addition of accumulators will significantly reduce repairs due to hose and seal failures and extend the life of the system.
Accumulators are fluid storage devices that stabilize pressure in a hydraulic system by means of weights, spring tension, or compressed gas. The accumulatorís purposes are to reduce pump fluid capacity requirements, speed up operation, reduce pressure surges, serve as a safety, provide stand-by power, and also act as shock absorbers. Accumulators actually store energy in the form of fluid under pressure. Hydraulic fluid is basically non-compressible, therefore the pressure is derived from weights, springs or gases.
Most hydraulic accumulators are hydropneumatic, that is, they use compressed gas, usually dry nitrogen, for storing energy. They have a port inlet for the hydraulic fluid, separated from the gas by an elastic bladder or diaphragm.
As hydraulic pressures rise above the gas pressure, hydraulic fluid rushes into the fluid side of the accumulator causing the gas to be compressed into a smaller area, thereby raising the pressure of the gas. As pressure in the hydraulic system decreases, the gas pressure forces the hydraulic fluid from the accumulator and back into the system.
Weight type accumulators are very large and bulky having no practical use in mobile hydraulic systems.
Spring loaded accumulators are usually small and light weight. However, they are usually are limited to 500 psi, and typically we need pressures above 1,200 psi for the mobile or stationary hydraulic systems in use today.
There are three styles of hydropneumatic accumulators: bladder, piston and diaphragm. There are two styles of bladder accumulators. In one style, the bladder may be removed and replaced if need be. The second style is permanently assembled and cannot be repaired. However, itís cost is about half of that the removable bladder. The bladder style pictured at the left is removable.
Bladder type accumulators are the most popular, and are very dependable if sized properly to the application. One manufacturer makes accumulators that hold up to 200 gallons!
To give some idea of accumulator costs; we have included the following:
A non-repairable, 3/4 gallon capacity accumulator rated at 3000 psi costs $413.00.
A one gallon repairable accumulator from the same company, also rated at 3000 psi, costs $756.00. Typical applications for this size would be for soft-starting hydraulic motors.
Piston type accumulators are usually incorporated into the hollow chrome shaft of the hydraulic cylinders. A typical application is on cement trucks where the stinger axle is hydraulically lowered to help carry the load. The axle needs to move independently of the truck and therefore must also be able to support the load even as the truck goes through the dips and over obstacles.
The hydraulic fluid, being non-compressible, is essentially rigid inside the cylinder. The piston inside the hollow shaft is sealed against the fluid and charged at itís backside with 1,200 psi of dry nitrogen; hydraulic fluid on one side of the piston and nitrogen on the other. When the load pressure exceeds the gas pressure the piston compresses the gas. As the ram is withdrawn from the cylinder tube, the nitrogen gas under pressure forces the piston to follow the hydraulic fluid out of the tube until its travel is mechanically checked, thus permitting movement without shock or excessive pressure. The system described here is really little more than a shock absorber.
If you have questions or need help selecting an accumulator for your hydraulic system, give us a call at 1-800-200-4685.