Accumulator


An air charged accumulator can be added to a closed system to dissipate the energy released when a valve is closed abruptly.  An accumulator is a steel sphere which is divided in half by a diaphragm.  The top half of the diaphragm is sealed closed while the bottom half is open and attached to a water system. 

Let's attach an accumulator to the simple system shown below.  Now we have a reservoir, an intake pipe with a shut-off valve, and an accumulator. 

A simple system with an accumulator.

When the water is abruptly shut off in the intake pipe, the extra energy pushes water into the accumulator, as shown above. 

Water pushes the diaphragm in the accumulator up.

The water flowing into the accumulator pushes the diaphragm up.  Pressure builds up in the top of the accumulator.

The pressure in the top of the accumulator forces the diaphragm back down.

The pressure in the top of the accumulator forces the diaphragm back down.  As the diaphragm bounces back, water is pushed out of the accumulator and backwards through the system. 

The diaphragm in the accumulator continues to bounce back and forth for a while.  This causes water to move backwards through the system in a series of pulses known as a standing wave. 

The accumulator in this example acted as a shock absorber.  Inertia made the water keep moving even after the shut-off valve was closed.  By moving into the accumulator and then back into the reservoir, the water was able to dissipate the kinetic energy without causing damage to the system.