User:Pdr415/sandbox/Accumulator (Energy)

Accumulator (Energy) act as energy storage devices in which the energy they store is in the form of pressurized hydraulic fluid. The fluid is pressurized by either a compressible gas, deadweight, or a spring. The casing (outer shell) of the accumulator is usually made of materials like steel, aluminum, titanium, and fiber-reinforced composites. Accumulators are attached to systems, or machinery, with the purpose of providing hydraulic energy to them whenever necessary, similar to how rechargeable batteries function in electrical systems. Examples of systems attached to accumulators include automotive suspension, landing gear mechanisms on airplanes, power brakes, etc. Accumulators control the power and flow of liquids and gases through the system to which they are attached.

Types of Accumulators
There are three main types of accumulators: weight-loaded, spring-loaded, and gas loaded. Gas loaded accumulators can be further subdivided into bladder accumulator type, piston accumulator type, and diaphragm accumulator type.

Weight-loaded Accumulators
Consists of a steel cylinder with a piston inside with deadweight attached to the top of it. The piston is specifically designed to perfectly fit the accumulator so as to reduce leakage of the hydraulic fluid. Pressure is exerted by the force of the deadweight pushing down on the piston and onto the hydraulic fluid. When the piston is at its highest point (when the hydraulic fluid is not being pushed down on), it is at its greatest potential energy.

Spring-loaded Accumulators
A spring-loaded accumulator is similar in design to that of a weight-loaded accumulator, but instead of the piston being pushed down by deadweight, it is being pushed by a preloaded (preset pressure) compression spring. When fluid enters the accumulator, the spring is compressed, thus increasing pressure in accumulator resulting in stored hydraulic energy.

Gas-loaded Accumulators
There is a non-separator gas accumulator and a separator type gas accumulator. Non-separator types consist of a fully enclosed shell with gas occupying the top of the accumulator and the hydraulic fluid occupying the bottom. There is no membrane or barrier separating the gas and fluid, hence the name. Separator type gas accumulators can be further divided into bladder type, piston type, and diaphragm type.

Bladder Type
An accumulator is fitted with an expandable bladder which the gas is located in. There is a charging valve (determines the pressure by controlling the gas entering the accumulator) connected to the bladder at the top of the accumulator. At the bottom is a spring-loaded poppet valve in open position before the accumulator is pre-charged. After it is pre-charged, the bladder is expanded to the volume of the accumulator which closes the poppet. The poppet also acts as a shield, preventing the bladder from being destroyed by extruding into the pipes connecting the accumulator to the system. When the hydraulic fluid fills the accumulator to its maximum capacity, the gas is compressed to the maximum pressure.

Piston Type
A cylindrical accumulator with a moving piston separating the gas and hydraulic fluid. Works similarly to the bladder type, with fluid filling the bottom of the accumulator pushing the piston upward thus compressing the gas at the top. This leads to increased pressure leading to hydraulic energy being built up and stored. Pre-charged at a pressure below the minimum hydraulic pressure so as to prevent the piston from bottoming out.

Diaphragm Type
In this type of accumulator, a diaphragm (rubber disc) separates the gas from the fluid. The gas fills the top portion of the spherical accumulator while the bottom portion is connected to the hydraulic circuit (where the fluid enters the accumulator). A poppet at the bottom of the accumulator prevents the diaphragm from protruding into the pipes, similar to the bladder type. Diaphragm types are not as serviceable as other types of accumulators because if the rubber disc ruptures or the pre-charge is lost, the entire accumulator has to be replaced.

Function of Accumulators
All accumulators have one of two functions: to add volume to the system it is attached to at a fast rate, or to absorb shock. An accumulator’s function depends on the pre-charge (pressure in accumulator before the hydraulic fluid is added) it has. For accumulators that add volume to the system, the pre-charge is well below the maximum system pressure (highest pressure possible) which allows for oil to enter. Accumulators that absorb shock have a pre-charge extremely close to the maximum system pressure so there is little to no oil present. Generally, it is best to set up accumulators in a vertical position as mounting it horizontally would cause rapid wear of the piston seals, or wear the bladder down in the case of bladder type accumulators. Diaphragm accumulators on the other hand, can be mounted in any position. A hydraulic accumulator performing its job can be seen through the power brakes of a car. Attached to the brake of the car is a spring-loaded accumulator in which the piston is depressed after pushing the brakes of a car. This causes the spring to compress and push the hydraulic fluid along the pipes and into cylinders at each wheel of the car resulting in pistons being forced out, stopping the car.

History
William Armstrong, English engineer and industrialist, created the very first hydraulic accumulator in 1846 at Newcastle, United Kingdom. It was a crane powered by water, later known as Grimsby Dock Tower. In 1852, Armstrong would use Dock Tower to provide consistent pressure for cranes, lock gates, and canals.