Accumulators

Accumulators

In most hydraulic systems, the demand for hydraulic fluid and pump work varies greatly during an operating cycle f the system as shown in Fig. 4 – 7. Starting at zero, the system requires 8 gallons per minute (gpm) of fluid for one minute, 2 gpm for 2 minutes, 6 gpm for 3 minutes, 3 gpm for 3 minutes, and no flow for 1 minute. In a period of 10 minutes the pump supplies 36 gallons of fluid or 3,6 gpm. If the system requires no additional fluid for another, then the average flow would be 1.8 gpm.

One way to provide sufficient hydraulic fluid to meet the needs of this system is to use a pump that can supply a minimum of 8 gpm whenever it is needed, and a smaller amount at other times. On this basis much of the pump’s capacity is not used during the greater portion of the cycle. If the system can store fluid, a smaller pump can b e used. For instance, if a pump supplies a minimum of 3 gpm to the system continuously, and the system accumulates excess fluid until it is needed, the installation, operating and servicing costs of the pump are greatly reduced. This is the function of an accumulator. The accumulator stores hydraulic fluid under pressure until the system needs it. At the same time, the accumulator helps cushion or absorb hydraulic shocks that occur during the operation of the system. Selection of the accumulator is based on total system requirements and not just a partial sampling

Accumulators are made in many different types. Although each type is different in design and construction, the all operate in the same manner. Some of the more common types of accumulators used in hydraulic systems are:  

Weight – loaded or gravity

Spring – loaded piston

Air bottle or non separated gas

Bladder or bag

Diaphragm

Gas – charged piston

            Differential piston

The performance ranges for some of these accumulators are shown in Table 4-2. Different manufacturers have slightly different ranges than those shown.