Types of Accumulators Spherical Accumulators Cylindrical 12-31 Figure 12-49.  A spherical accumulator with diaphragm (left) and bladder (right). The dotted lines in the right drawing depict the bladder  when the accumulator is charged with both hydraulic system fluid and nitrogen preload. •  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.  •  Store power for the limited operation of a hydraulic  unit when the pump is not operating. •  Aid or supplement the power pump when several units  are operating at once by supplying extra power from  its accumulated, or stored, power. •  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. The function of an accumulator is to: 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 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 There are two general types of accumulators used in aircraft  hydraulic systems: spherical and cylindrical.  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 accumulators consist of a cylinder and piston  assembly. End caps are attached to both ends of the cylinder.  Bladder Diaphragm Screen to prevent extrusion Rigid button or  disc to prevent  extrusion Retaining plug Gas servicing valve Hydraulic system pressure Hydraulic system pressure Hydraulic fluid Nitrogen or air