Pneumatic And Hydraulic Equipment Page 935

HYDRAULIC ACCUMULATORS 1. Accumulator 2. Bleed or automatic discharge valve 3. Check valve 4. Pump 5. Oil pressure gauge Applications Accumulators are devices used to store fluid power to do the following: 1. Store power for intermittent duty cycles thus economizing pump drive power 2. Provide emergency or standby power 3. Compensate for leakage loss 4. Dampen pulsations and shocks of a periodic nature Principals of Operation Most hydraulic systems require variable and intermittent flow rates. Energy can be saved by using the accumulator as a storage device to accept pump output flow when system demand is low and supplement output when demand is high. Most accumulator designs are based on the principle that gas is compressible and oil is nearly incompressible. Assume an inert gas, such as nitrogen, is contained under pressure in a vessel. If hydraulic fluid is pumped into that vessel at a higher pressure than that of the original gas, the nitrogen compresses as its pressure rises to that of the fluid being pumped. This increase in gas pressure is proportional to the decrease in volume. The vessel now contains energy in that the volume of hydraulic fluid, stored against the pressure of compressed nitrogen gas, if released, will quickly be forced out of the vessel under the pressure of the expanding gas. Hydro-pneumatic accumulators with the gas separated from the liquid by a piston, diaphragm or bladder are by far the most common type. To prevent auto ignition at high pressures, an inert gas such as dry nitrogen or helium should always be used. Diaphragm Type (Non-Repairable) Typical Accumulator Circuit Bladder Type (Repairable) R E X R O T H Rexroth Bosch JHF Catalog [ Volume 7 ] (314) 427-0600 800-444-0522 (FAX) 314-427-3502 www. j 935 Prices Subject to Change Without Notice John Henry Foster pneumatic and hydraulic equipment

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