What Is a Flow Control Valve? Working Principle, Setting and Applications

In water treatment, filtration and distribution systems, keeping the flow through a line at a defined value is important both for correct process operation and for avoiding water waste. A flow control valve is an automatic control valve that keeps the flow rate through the valve at its set value even when the inlet pressure or the system demand changes.

This article covers the working principle of line-pressure operated diaphragm flow control valves, how to set and install them, their technical data and their applications.

What Is a Flow Control Valve?

A flow control valve limits the flow in a line to a preset value and holds it there. Diaphragm-type valves are operated by the pressure of the water in the line itself and need no external energy source such as electricity or compressed air. This is particularly important in critical applications such as preventing excessive flow during backwashing in filtration systems, which protects the filter bed.

Working Principle

A diaphragm flow control valve consists of a main valve, a control (pilot) circuit and an orifice plate installed in the line:

1. Sensing the flow: A differential pressure that depends on the flow rate develops across the orifice plate. These pressures are transmitted to the control circuit through signal tubes.
2. Comparison: The control circuit compares the sensed differential pressure with the set value.
3. Diaphragm movement: If the flow exceeds the set value, water is admitted to the diaphragm chamber of the main valve and the valve throttles; if the flow drops, the chamber is relieved and the valve opens.
4. Constant flow: Through this continuous correction, the flow is held at the set value despite changes in inlet pressure.

Technical Data

Key technical data of the Ayvaz flow control valve supplied by ORFA:

Key Advantages

• No external energy: Operates on line pressure, so no electrical or compressed air connection is needed.
• Easy, precise setting: The required flow rate can be set easily and accurately.
• Water savings: Prevents excessive water use in processes such as backwashing.
• Easy maintenance: Simple construction; parts such as the diaphragm can be replaced without removing the body from the line.

Setting and Installation

• The flow rate is set with the orifice plate and signal tubes connected. After the 3-way ball valve in the control circuit is turned to “Auto”, the required flow is reached using the adjuster on the valve.
• The valve can be installed horizontally or vertically, which makes it adaptable to different piping layouts.
• The flow direction must match the arrow on the body.
• A strainer upstream of the valve is recommended to keep the control circuit from clogging.

Applications

• Backwash lines of water treatment and filtration systems
• Closed-loop water distribution networks
• Heating, ventilation and air conditioning installations
• Agricultural irrigation systems

Frequently Asked Questions

Conclusion

Flow control valves keep the line flow constant without external energy, ensuring that filtration and distribution systems work correctly and preventing water waste. Correct setting and installation result in long, trouble-free operation. Explore our flow measurement and control solutions on the Flow Measurement and Control Equipment page.