Pressure Sustaining and Reducing Control Valve: Two Functions in One Body

On downhill water transmission lines with large elevation differences, two needs arise at once: pressure at the higher points must not collapse because of consumption in lower zones, and the pressure of water reaching the lower zones must be reduced to a safe value. A pressure sustaining and reducing control valve combines both tasks on a single main valve: it keeps the inlet pressure at a set minimum while reducing the outlet pressure to the required value.

This article explains how the dual-function valve works, its advantages and applications, and how the two pilots are set.

What Is a Pressure Sustaining and Reducing Control Valve?

It is a hydraulic control valve with two separate pilots on the main valve: a pressure sustaining pilot connected to the inlet and a pressure reducing pilot connected to the outlet. The valve works on line pressure and needs no external energy. Both functions are active at the same time; the valve opening is determined by whichever pilot calls for more throttling.

How Does It Work?

• Pressure sustaining function: When the inlet pressure falls toward the set minimum, the valve throttles to maintain upstream pressure. For example, consumers in the upper zone are not left without pressure because of high demand in the lower zone.
• Pressure reducing function: When the outlet pressure tends to rise above its set point, the valve throttles to hold downstream pressure at that value.

In normal operation the valve acts as a pressure reducing valve; when the inlet pressure approaches its minimum limit, the sustaining function takes priority.

Advantages

• Two functions in one valve: Removes the need for separate sustaining and reducing valves, saving space and installation cost.
• No energy required: Operates on line pressure.
• Independent settings: Inlet and outlet pressures are adjusted independently on separate pilots.
• Control on sloping lines: Limits excessive pressure, and the resulting excessive flow, in downhill systems.
• Controlled line filling: Helps fill sloping lines in a controlled way.
• Easy maintenance and flexible installation: Simple design for easy maintenance; can be installed in horizontal or vertical lines.

Applications

• Water transmission networks: Delivering water at the correct pressure to settlements at different elevations.
• Irrigation systems: Sustaining head-end pressure on sloping land while reducing pressure in lower sections.
• Industrial plants: Pressure management in process lines at different heights.
• Pump and reservoir outlets: Lines that need a minimum upstream pressure and a limited downstream pressure.

Installation and Setting

Installation

• Install the valve in a horizontal or vertical line following the flow arrow.
• A strainer upstream and isolation valves at the inlet and outlet are recommended.
• Pressure gauges on both the inlet and outlet are needed to make both settings.

Setting the Pilots

1. Inlet (sustaining) pressure: Turning the adjusting screw of the inlet pilot clockwise raises the sustained inlet pressure; turning it anticlockwise lowers it.
2. Outlet (reducing) pressure: Turning the adjusting screw of the outlet pilot clockwise raises the outlet pressure; turning it anticlockwise lowers it.
3. After each adjustment, lock the screw with its lock nut.

Frequently Asked Questions

Conclusion

A pressure sustaining and reducing control valve performs two critical pressure control tasks in one body, without consuming energy, on downhill and multi-level systems. Correct positioning and careful setting of both pilots ensure balanced, safe operation in both upper and lower zones. You can explore valves with other functions in our hydraulic control valves product group.