Williams pumps are pneumatically actuated injection pumps that consist of an Oscillamatic controller (timer) which generates pulses of air that are introduced into the pneumatic portion of the pump. The air from the Controller pushes down on the piston of the pump, which moves the plunger down into the fluid cylinder, this is called the “power stroke”.
This displaces chemical in the fluid chamber, seats the suction check valve, and generates pressure to exit chemical out the discharge check valve. Then the Oscillamatic Controller enters the exhaust cycle and the air is removed from the top of the piston/plunger assembly and the pump returns to what is referred to as the “suction stroke”.
Then the whole process continues again and again until the air is shut off to the Oscillamatic Controller.