Why use and how it works - AVK International

What is a pressure reducing control valve and how does it work? 

A pressure reducing control valve automatically reduces a higher inlet pressure to a lower outlet pressure regardless of changes in flow rate or inlet pressure.

The pressure reducing pilot senses the outlet pressure through the connection on the valve outlet port. Under flowing conditions, the pressure reducing pilot reacts to small changes in the outlet pressure, controlling the valve position by modulating the pressure in the control chamber. When the outlet pressure changes according to the set-value of the pilot, the pilot modulates to ensure pressure control.

Example: The pressure is 7-8 bar, which is appropriate to supply the consumers in area A but too high for the consumers in area B. Therefore, a pressure reducing control valve is installed to reduce the pressure to 3 bar in area B.

What is a pressure sustaining/relief control valve and how does it work?

A pressure sustaining control valve automatically maintains a minimum preset inlet pressure by relieving excess pressure regardless of changes in flow rate.

The pressure sustaining pilot reacts to small changes in the inlet pressure, controlling the valve position. If the inlet pressure falls below the set point, the main valve closes or modulates to ensure a minimum inlet pressure. The sustaining valve holds a minimum back pressure on the inlet and normally allows flow. The relief valve normally remains closed and only opens when pressure exceeds a pre-determined set-point.

Example: When the water reservoir fills, the pressure drops, leaving the consumers without water. Therefore, a pressure sustaining control valve is installed to maintain the pressure  for the consumers.

What is a constant flow control valve and how does it work?

A constant flow control valve automatically monitors the flow and regulates if required, to secure that the flow does not exceed the maximum allowed flow regardless of changes in the supply pressure.

The pressure drop across an orifice plate is sensed by the constant flow pilot. When the flow is low and the pressure drop is below the pilot setpoint, the constant flow pilot and the main valve will be fully open. If the flow is high and the pressure drop becomes higher than the setpoint, the valve starts to regulate the maximum flow according to the setpoint, to secure that the flow does not exceed the maximum allowed flow.