英文及譯文翻譯英文原文：AccumulatorsAn accumulator is found in many hydraulic systems. As the name suggests, it is a storage device. The various types of accumulators are studied in this chapter. A simple accumulator is sometimes used in household water system. It may consist of a tee with a side branch pipe that is capped. The air that is trapped in the side branch pipe is compressed, and then acts like a compressed spring. As a faucet is either opened or closed quickly, a sudden change in pressure and flow occurs. The trapped air acts as cushion, or shock absorber, to prevent water hammering in the piping system. The storage batter in a car is a typical example of an electrical or chemical accumulator. Chemical energy is stored in the batter is not in use. The stored chemical energy is converted into electricity that is used to start the engine. Hydraulic Accumulators A hydraulic accumulator may be used for a variety of purposes. Some of its uses are: ( 1 ) as a shock absorber; (2) to provide oil makeup in a closed system; (3) to compensate for leakage in a system; (4) to provide a source of emergency power in event of failure of the normal power supply;(5 ) to maintain steady delivery pressure over a period of time without keeping the pump operating continuously; and (6) as a transfer barrier device to separate the oil from some other fluid in the system. Types Of Accumulators Accumulators may be divided into three general types: ( 1 ) weight-loaded, (2) spring-load, and (3) air-or gas-type accumulators. The air-or gas-type Accumulators can be subdivided further into the separator and non-separator types. Weight Loaded or Gravity TypesThe weight-loaded or gravity-type accumulator consists of a cylinder, a movable position, a ram or plunger, and a weight. The dead weight ( which may be placed in a container) may be concrete, iron, steel, water, or other heavy material. The position should have a precision fit inside the cylinder in order to reduce leakage. The inner cylinder wall should have a honed or ground finish in order to reduce friction and wear. As hydraulic oil is pumped into the cylinder, the piston pushes the weight to a higher level. Thus the potential or stored energy of the weight is increased. The energy stored in the weight is released in the downward motion as it is required by the demands of the system. An accumulator of this type may be custom-built for a particular installation. The weight is adjusted so that the ram rises when the fluid pressure reaches a set level. The travel of the ram can be controlled by an arrangement of a cam on the plunger and limit switches. The gravity force of the piston on the oil provides a nearly constant oil pressure level forthe full stroke of the piston. By providing adequate piston area and ample length of piston stroke, a large volume of fluid can be supplied at high pressure. A single large accumulator may provide service for a number of different machines.Spring-loaded TypeA spring-loaded type of accumulator is illustrated. This device consists of a cylinder, a piston, and a spring. One or more springs may be used. The springs may be arranged to provide various adjustments by means of bolts. As the oil is pumped into the accumulator, the piston or plunger compresses the spring; The energy stored in the spring is released as it is required by the demands of the system. The pressure on the oil is not constant for all the positions of the piston, because the spring force depends on the movement of the spring. Usually, this type of accumulator delivers only a small amount of oil at low pressure. Air or Gas Type Hydraulic fluid or oil is nearly incompressible. This means that a large increase in oil pressure results in only a small, or negligible, decrease in the volume of oil. ~ On the other hand, a large increase in air or gas pressure results in a large decrease in the volume of the air or gas. Relatively speaking, hydraulic oil is less elastic or spring-like than air. Oil cannot be used effectively to store energy by compressing it, whereas air or gas can be compressed to store energy. Thus, one general type of accumulator used gas or air, rather than a mechanical spring or a weight, to provide the spring-like action. Air or gas types of accumulators can be divided into two subdivisions: (1) the non-separator type, and (2) the separator type. In the non-separator type of accumulator, the oil is in direct contact with the air or gas. In the separator types of accumulator, either a solid or a flexible barrier is placed between the oil and the gas to separate the two different types of fluids. Non-separator Type A non-separator type of air or gas accumulator consists of a fully enclosed cylinder, adequate ports, and a charging valve. A portion of oil must be trapped in the bottom of the cylinder before this type of accumulator can be placed in operator. Air, nitrogen, or an inert gas is then 。