The non-bleed relay is a type of direct acting relay, it consists of two bellows connected to the force beam
It also consists of a rod, and plugs are connected to the both ends of the rod.
The spring is connected to plug at the downward side.
The air supply is given from the bottom side of the non bleed type of relay.
In direct acting relays, the input is directly proportional to the output. So when the input increases,the output also increases. And when the input decreases, the output also decreases.
When the nozzle back pressure increases, there is a movement of bellows. The bellows move towards the downward direction.Then the air supply is from the bottom side of relay, so there is a restriction to the air supply, because the nozzle back pressure increases.
Hence the output also increases.The air bleed stops when equilibrium condition is obtained, no loss of pressurized air at steady state position. When the nozzle back pressure decreases , the bellows starts moving to upward direction.
The air supply is given to the spring from the downward direction, hence the spring moves in upward direction. There is no restriction to the air, because the nozzle back pressure decreases.
Hence the output also decreases. The air bleed stops when equilibrium condition is obtained, no loss of pressurized air at steady state position.
Author: Laxmi Omprakash Singh