HOW IT WORKS Water flows through the drive pipe into the pump and out through the waste gate. The buoyant ball will be pulled down by the flow of water and block the waste gate. See Picture to the Left.
In the first picture below, the ball has blocked the waste gate. The incoming water forces the spring-loaded check valve open, allowing water to fill the surge tank, compressing the air in the tank.
As shown in the last picture below, when the pressure in the surge tank equals the pressure in the drive pipe, the water from the drive pipe can lo longer flow into the pump and a bounce-back effect happens. The check valve shuts and the compressed air in the surge tank forces water in the tank up to where it is needed. The bounce-back causes the water to briefly flow back up the drive pipe, unseating the ball valve and letting the cycle begin again.
Gravi-Chek Pumps - How They Work 
HOW IT WORKS
