Water Entrance

• A pressure water valve is constructed of both an upper and lower chamber. Between these two chambers is a round diaphragm and a relief valve. The water makes it way to the upper chamber through a bypass valve located in the diaphragm. The pressure of the water holds the diaphragm and the relief valve in place over the valve barrel's opening.
  
  

Plunger Activation

• Depressing the handle activates a plunger. This plunger in turn shifts the stem of the relief valve, which causes it to tilt. This tilting allows water to exit the upper chamber through the valve barrel.
  
  

Flush Cycle Completion

• The final phase is the completion of the flush cycle. Pressure in the lower chamber of the flush valve is caused by water emptying from the upper chamber. This pressure forces the diaphragm and the relief valve to rise up from the barrel opening, thereby letting water flow from the barrel's inlet pipe into the toilet bowl without needing to go through the upper chamber. A small amount of water will get into the upper chamber via the bypass valve so that pressure can build up to depress the diaphragm and close the opening of the barrel.
  
  

Piston Flush Valve

• In a piston flush valve, the upper and lower chambers are separated by a rubber cup. This cup is extended inside a hollow piston and the bypass valve can be found on the piston side. The relief valve is used for sealing the upper chamber from the lower chamber. Pressing the handle causes the plunger to push against the relief valve, causing it to tilt and release water from the upper chamber. This causes a reduction in the water pressure above the relief valve. The high pressure of the water coming from above the inlet pipe causes the piston assembly to rise up from the lower chamber. Water continues to flow from the inlet pipe to the lower chamber until a smaller stream of water that is flowing through the bypass valve restores the pressure within the piston. This creates enough force to push the piston assembly back down.