Material delivered to the supply channel lifts up the valve
with its pressure and presses it against the seat on the
discharge side. While the valve is blocking material flow to
the discharge port, Chamber A (metering chamber) becomes
filled with material.
At the same time, material, under pressure from a supply
pump, is constantly being delivered to Chamber B (pressing
chamber) at the back of the metering piston through a bypass
groove around the valve.
At this time, when the same pressure is applied over both
Chamber A and B, the force acting on Chamber A is stronger
due to a difference of pressure receiving area.
Thus, the metering piston is pushed to Chamber B and
comes to a stop against the head of adjustment screw.