Hydraulic Accumulator ? How do they work ?

Introduction :

“Energy can neither be created nor be destroyed, but it can be transformed from one from to another.” This energy can also be stored in a device or equipment, so that they can be used in another form. For example, we know about the function of flywheel in a rotary machine. It gains energy from the prime mover, stores the gained energy, and, when required, releases the energy back into the same system. Another example of energy storage and conversion, which is the most recent development in the automobile industry or Kinetic Energy Recovery System. The system utilizes the kinetic energy when the car reduces its speed, and gives it back to the car itself for its acceleration. Thus energy is stored in some form and given back to the system in another form.” Have you ever wondered how energy is stored? Read here to know about one of the most widely used energy storage devices, the hydraulic accumulator.

What is Hydraulic Accumulator ?

The hydraulic accumulator is a device used for the storing the energy of liquid in the form of pressure energy, which may supplied for any sudden requirements. In case of hydraulic lift or hydraulic crane a large amount of energy is required when lift or crane moving upward. This energy is supplied from hydraulic accumulator. But when lift moves downward no energy is required and at that time the energy from the pump is stored in accumulator.

Let ,         Area of a sliding Ram = A
Stroke Or Lift of Ram = L
Intensity of water pressure = p
Weight placed on Ram = W
Now,
W = p x A
Work done in lifting = W x Lift of Ram
  = W x L
   = p x A x L     ( W = p x L )
Therefore,
Capacity of Accumulator = p x A x L
But,
A x L = Volume of Accumulator
Therefore,                              
Capacity of Accumulator = p x Volume    

Working of Hydraulic Accumulator :

An accumulator usually has a cylindrical chamber, which has a piston in it. This piston is either spring loaded or some calculated weight is kept on it or even pneumatically pressurized. The hydraulic pump pumps the fluid into the accumulator, which is nothing but a sealed container. The volume of the container is fixed and cannot be changed. But the quantity of hydraulic fluid being pumped inside the container is increasing continuously. So the pressure of the hydraulic fluid inside the container starts to increase. The figure  shows a hydraulic accumulator which consists of a fixed vertical cylinder containing a sliding ram. A heavy weight is placed on the ram. The inlet of the cylinder is connected to the pump, which continuously supplies water or the hydraulic fluid under pressure to the cylinder.

The outlet of the cylinder is connected to the machine (which may be a lift or a crane). The ram is at its lower most position in the beginning. The pump supplies hydraulic fluid under pressure continuously. If the hydraulic fluid under pressure is not required by the machine, it will be stored in the cylinder. This will raise the ram on which a heavy weight is placed. When the ram is at its upper most position, the cylinder is full of hydraulic fluid and the accumulator has stored the maximum amount of pressure energy. When the machine (the crane or the lift), requires a large amount of energy, the accumulator will supply this energy and the ram starts to move down.

Uses of Accumulator :

To supplement pump flow: As discussed earlier, the most common use for accumulators is to supplement pump flow. Certain machinery circuits require a high quantity of oil flow for a short time and then use little or no fluid for an extended period. So, generally when the circuit does not require oil flow, the pump keeps the accumulator pressurized for future use.

To absorb shock: At times, the sudden changing of valve positions or operations may cause a pressure wave which sets up a shock. The pressure of fast-moving hydraulic circuits can produce pressure spikes that cause shock when flow is stopped abruptly as well. When installed in shock prone areas of hydraulic circuits, accumulators serve as pressure shock dampening devices.

As an emergency power supply: Ships generally have emergency means of starting arrangements for life saving appliances. The life boat engines are either manually started or sometimes hydraulically started. These act as secondary means of starting in times of emergency.

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