How a Pressure Relief Controller Works

The pressure relief controller maintains a stable water pressure at the output, i.e., downstream in the flow direction. The pressure before the regulator may fluctuate, but the pressure after it will remain constant and will equal the set value. The pressure setting range is determined by the compression force of the included spring.

If the water pressure at the valve inlet is lower than the set value, the regulator is in the closed position. That’s why they are also called “normally closed.”

When the water pressure at the regulator inlet exceeds the set pressure, the valve opens. The higher the pressure at the regulator inlet over the set pressure, the more the valve’s shutter opens.

Principle of operation of the pressure relief controller is demonstrated using a diaphragm regulator with a spring-loaded setpoint and a single-seat valve.

The design of the regulator includes a sealed chamber divided by a diaphragm into two cavities. The central part of the diaphragm is rigidly connected to the valve stem, and the periphery is connected to the body of the chamber. The elasticity of the diaphragm allows it to move, shifting the stem and valve shutter.

One part of the diaphragm chamber is filled with water through the impulse line from the inlet pipe to the regulator, and the other part of the diaphragm chamber is under atmospheric pressure.

Water flows into the diaphragm chamber through the impulse line. The water presses on the diaphragm and tries to open the valve. The water pressure is above atmospheric pressure, so the diaphragm attempts to bend and shift the stem, but it is resisted by the compressed spring force, which is directed in the opposite direction. The spring tries to close the valve. The position of the shutter is determined by the balance of forces on the stem.

If the force created by the spring is greater than the water pressure force on the diaphragm, the valve is in the closed position. As soon as the water pressure exceeds the spring pressure on the diaphragm, the valve opens.

These water pressure regulators are also called proportional because the speed of opening the shutter is proportional to the deviation of the water pressure from the set value.

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