Pressure Relief & Sustaining Valves

What’re Pressure Relief & Sustaining Valves?

Various pressure relief & sustaining valves supplied for waterworks by Metalsin Tech.

The pressure relief and sustaining valve is a diaphragm-type hydraulic control valve that is actuated by the hydraulic pressure within its own pipeline. Its key advantage is its dual functionality—it can serve as either a pressure relief valve or a pressure sustaining valve. When operating as a pressure relief valve, it automatically releases any upstream pressure that exceeds a preset limit, thereby protecting the pipeline and associated equipment from damage caused by high or sudden pressure surges. Conversely, when used as a pressure sustaining valve, it maintains the upstream water supply pressure at a predetermined value to ensure that the upstream area receives prioritized water supply.

Working Principles

The pressure relief & sustaining valve supplied by Metalsin is a diaphragm-type, pilot-operated hydraulic control valve. It is equipped with an adjustable pilot valve, needle valve, compact strainer, ball valve, and other components.

• When used as a pressure relief valve: In this configuration, the valve is connected to a bypass branch that leads to a low-pressure area or drainage ditch. Under normal conditions, water continuously flows from the main valve inlet through needle valve 1 into the upper control chamber (labeled 2). The pilot valve (labeled 3) is set to a predetermined pressure value (A). If the upstream pressure is below the set value A, the pilot valve remains closed. The incoming water builds pressure in the upper control chamber, which forces the diaphragm to drive the valve disc downward, keeping the main valve closed. When the upstream pressure exceeds the set value A, the pilot valve senses the increase and opens. This allows the upper control chamber to release pressure, causing the main valve disc to lift and discharge water. As a result, the pipeline pressure is maintained below the safety limit A.

The illustration of working principles of pressure relief & sustaining valves (PRSV) in water systems.

• When used as a pressure sustaining valve: In this mode, the valve is installed in series along the main pipeline to ensure that the upstream water supply maintains a predetermined pressure (B). Again, water continuously flows from the inlet through needle valve 1 into the upper control chamber, and the pilot valve (3) is set to pressure value B. If the upstream pressure is lower than the set value B, the pilot valve remains closed. The water entering the upper control chamber builds pressure, causing the diaphragm to force the valve disc downward and close the main valve. This “stores” pressure until the upstream pressure reaches the desired value B. When the upstream pressure exceeds B, the pilot valve opens, releasing pressure from the upper control chamber. This causes the main valve disc to open and discharge water, thereby maintaining the upstream pressure at the set safety level B.

Design Features & Technical Specifications

The pressure relief & sustaining valve supplied by Metalsin features a spherical, Y-shaped body with a full-diameter design that delivers strong flow capacity, low head loss, and an optimized flow channel to minimize turbulence and cavitation hazards. Its integrated, easy-to-assemble diaphragm functions as a soft piston for smooth, sensitive, and precise control, while the dual-chamber main valve protects the diaphragm from high-pressure impacts and debris, ensuring a service life of over one million cycles. Additionally, the external connecting pipe is equipped with a self-cleaning strainer to reduce maintenance, and the valve operates automatically without external power, saving energy and enabling unmanned operation. A throttling hole linking the lower chamber to the back outlet further guarantees gentle response, stable pressure, and reduced pipeline vibration and noise.

Typical drawing of pressure relief & sustaining valves for water systems.

Design standards: AWWA C530, CJ/T 219，JB/T 10674，BS EN 558 serial 10. Flanged connection shall be made to ASME B16.1 Class 125 or EN 1092-2. Working pressures: PN 10, PN 16; 175 psi, 200 psi, 250 psi, 300 psi. Working temperature: 0~80°C in waterworks systems. Both interior and exterior surfaces should be epoxy coated in RAL 5005 or  5015 color as per AWWA C550. Click to view the dimensions and flow characteristics for pressure relief & sustaining valves designed to ASME/AWWA waterworks systems and EN BS/DIN waterworks systems.