The bleed type of relay is consists of a main diaphragm on which the nozzle back pressure acts.
The diaphragm is connected to the metal rod.
At the both ends of metal rods the plugs are connected.
The plugs are connected to the spring.
The air supply is given to the spring from the bottom side of the relay.
Bleed Relay
WORKING
The bleed type of relay is a type of direct acting relay. In this relay, the output is directly proportional to the input. Means if the input increases,the output also increases. And if the input decreases, the output also decreases.
When the nozzle back pressure increases, this back pressure acts on the metal diaphragm. The metal diaphragm moves in downward direction because of increase in pressure. As the diaphragm is connected to the rod, the metal rod and plugs are also moves in downward direction.
Then the air supply is given to the spring from the bottom side of the relay. But the air is restricted by the nozzle back pressure, therefore spring also moves in downward direction. so the output also increases.
When the nozzle back pressure is decreases, that back pressure acts on the metal diaphragm. The metal diaphragm moves in up direction because the pressure is decreases. The air supply is given to the spring from the bottom side of the relay.
Because of decrease in pressure, the spring moves in up direction. Therefore the plugs and rods are also moves in up direction. so the output gets decreases. In all position of valve excepts the position of shut off the air supply, air continues to bleed in atmosphere even after equilibrium condition is obtained between nozzle back pressure & control pressure.
Author: Laxmi Omprakash Singh