content_image/592847.jpg
## Accumulators 

The accumulator is a steel sphere divided into two chambers by a synthetic rubber diaphragm. The upper chamber contains fluid at system pressure, while the lower chamber is charged 

with nitrogen or air. Cylindrical types are also used in high- pressure hydraulic systems. Many aircraft have several accumulators in the hydraulic system. There may be a main system accumulator and an emergency system accumulator. There may also be auxiliary accumulators located in various sub-systems. 

The function of an accumulator is to: 

• Dampen pressure surges in the hydraulic system caused by actuation of a unit and the effort of the pump to maintain pressure at a preset level. 

• Aid or supplement the power pump when several units are operating at once by supplying extra power from its accumulated, or stored, power. 

• Store power for the limited operation of a hydraulic unit when the pump is not operating. 

• Supply fluid under pressure to compensate for small internal or external (not desired) leaks that would cause the system to cycle continuously by action of the pressure switches continually kicking in. 

## Types of Accumulators 

There are two general types of accumulators used in aircraft hydraulic systems: spherical and cylindrical. 

## Spherical 

The spherical-type accumulator is constructed in two halves that are fastened and threaded, or welded, together. Two threaded openings exist. The top port accepts fittings to connect to the pressurized hydraulic system to the accumulator. The bottom port is fitted with a gas servicing valve, such as a Schrader valve. A synthetic rubber diaphragm, or bladder, is installed in the sphere to create two chambers. Pressurized hydraulic fluid occupies the upper chamber and nitrogen or air charges the lower chamber. A screen at the fluid pressure port keeps the diaphragm, or bladder, from extruding through the port when the lower chamber is charged, and hydraulic fluid pressure is zero. A rigid button or disc may also be attached to the diaphragm, or bladder, for this purpose. [Figure 12-49]  The bladder is installed through a large opening in the bottom of the sphere and is secured with a threaded retainer plug. The gas servicing valve mounts into the retainer plug. 

## Cylindrical 

Cylindrical accumulators consist of a cylinder and piston assembly. End caps are attached to both ends of the cylinder. 

<img src='content_image/592847.jpg'>

