Types of Accumulator

The Diaphragm Accumulator

The Diaphragm accumulator consists of two dome – shaped shells held together by threaded or bolted flanges. The diaphragm is clamped between them as shown in Fig. 4–12. The diaphragm has an even thickness and is molded with a single convolution (wave or roll) to allow it to move more easily. During operation, the diaphragm flexes instead of stretching like the air bladder. It is not, therefore, suitable for high – pressure applications.

The Gas-Charged Piston Accumulator

The Gas – Charged Piston accumulator, shown in Fig. 4–13, can be compared to a diaphragm accumulator. It consists of a free float piston, placed in a cylinder, which separates the gas and fluid. The cylinder is precision machined, honed, and capped, and the piston is equipped with suitable seals to ensure positive separation of the fluid and gas. The end caps of the cylinder are retained by various means, including threading, lock rings, tie rods, and welding. The accumulator is safety – locked to prevent it from being disassembled while it is pressurized. Also, a safety – burst disc is sometimes built into the gas end to protect the accumulator from excessive pressures and to prevent serous accidents.  

Although the fluid capacity of some gas – charged piston accumulators may reach 20 gallons, the response of the piston accumulator is fairly fast. However, the gas – charged accumulator is less effective than the bladder accumulator in eliminating pulsations because of the mass of the piston and the friction of the seals. Disadvantages include cost, limitations in size, maintenance, and frequent recharging of the gas side. One of their advantages is that they are suitable for both high and low temperature operation when the proper O – ring seals are used.

The Differential Piston Accumulator

The Differential Piston accumulator is similar to the gas – charged piston accumulator. As shown in Fig. 4–14, it consists of a large – diameter air piston in an upper cylinder, which bears against a small – diameter fluid piston in a lower cylinder. This accumulator allows a smaller amount of air pressure to control a higher fluid pressure. It is also used as a pressure booster or fluid intensifier. 

The gain in pressure is offset by a smaller amount of fluid flow. The ratios of volume and pressure can be obtained by the following formula:

Ratio = Area of the air piston / Area of the fluid piston

For instance, if the gas piston has twice the area of the fluid piston, the fluid has twice the pressure of the gas and one-half of the actual volume.

Gas-charged accumulators depend on the compression of a gas for their fluid capacity and pressure level. If the gas temperature increases slightly, the gas volume also increases, and the fluid volume decreases. If the temperature of the gas cools, the opposite occurs. When selecting a differential piston accumulator, make sure that the selection is based on the volume of the fluid piston.