Single Chamber Pilot-Operated Pressure Reducing Valves

Design Features

The single chamber (SC) pilot-operated pressure reducing valve is a hydraulic control valve that reduces higher upstream pressure to lower downstream pressure regardless of downstream flow fluctuation or variations in upstream pressure. These control valves are widely used in water distribution and fire protection systems featuring:

• Single-Chamber Design: The single chamber control valve has only one control chamber formed between the bonnet and the diaphragm. It offers a straightforward, reliable design with fewer moving parts and no extra seals, which minimizes wear and leakage. This results in lower friction, reduced energy losses, and a more efficient valve operation at lower pressures. Additionally, their simplified construction makes them cost effective by reducing manufacturing complexity, spare parts, and maintenance expenses.

Single chamber pilot-operated pressure reducing valves (PRV) for waterworks.

• Pilot-Operated: The pilot-operated design uses a small, dedicated pilot valve to modulate the main valve’s operation. This setup enables more precise downstream pressure control by isolating the control function from the high-pressure process fluid, thereby enhancing accuracy, stability, and responsiveness while efficiently handling variable flow conditions.
• Lower Flow Capacity: Since the motion direction of the valve stem/ closure member is perpendicular to the pipeline flow direction, the flow capacity is relatively low compared to the Y-pattern dual chamber pressure reducing valve. The probability of forming water hammer or cavitation turbulence is a bit higher.

Working Principles

The single chamber (SC) pilot-operated pressure reducing valve consists of a single-chamber flanged main valve, a pilot valve, an upstream pressure gauge, a downstream pressure gauge, ball valves, a built-in strainer, manifold tubing, and a needle valve.

At the initial stage, the pressure-reducing valve is closed. The upstream pressure gauge indicates a high pressure, while the downstream gauge shows that the consumer supply line is empty. At this point, first open the needle valve and all ball valves, then gradually rotate the pilot valve’s adjustment bolt clockwise to open the pilot valve. Water flows from the main valve’s upper control chamber through the pilot valve to the main valve’s downstream outlet, which lowers the pressure in the upper control chamber. This pressure drop causes the main valve to gradually open, filling the consumer line. As water continues to flow in, the downstream pressure of the main valve gradually rises to the preset value. At that moment, the pressure below the pilot valve diaphragm balances with the spring pressure, maintaining a constant flow through the main valve.

Illustration of working principles of single chamber pilot-operated PRVs.

When water demand decreases, the downstream pressure suddenly increases, and the pilot valve responds immediately. The pressure beneath the pilot valve diaphragm pushes the pilot plunger slightly upward, tending to close the valve. This causes the pressure in the main valve’s upper control chamber to rise, which in turn pushes the its stem downward, partially closing the main valve. Despite the reduction in flow, the downstream pressure remains stable at the preset value. When water demand further declines to zero, the main valve closes completely. At this point, with no flow and a very high upstream pressure, the downstream pressure still remains stable at its designated set point.

When downstream water demand increases again, the main valve’s instantaneous downstream pressure drops, prompting the pilot valve to gradually open. This opening reduces the pressure in the main valve’s upper control chamber, causing the main valve to progressively open and allowing the downstream pressure to return to its preset value. During this stage, the upstream pressure decreases and the flow slightly reduces, yet the downstream pressure remains stable. If the upstream pressure drops significantly, the main valve will fully open to supply the maximum possible pressure to the consumer line, ensuring a continuous water supply even when the pressure falls below the desired level.

Typical drawing of single chamber pilot-operated PRV.

Specifically, adjusting the needle valve opening can change the response speed of the main valve. A strainer should be installed in front of the main valve to prevent impurities from clogging the tubing and needle valve. Additionally, closing the ball valve in series on the pilot valve line can immediately shut off the main valve in an emergency.

Technical Specifications

Single chamber pilot-operated pressure reducing valves shall be manufactured in accordance with AWWA C530, EN 1567, CJ/T 219, CJ/T 256, JB/T 10674, AS 5081, and AS 4020. The flanged ends shall be furnished in accordance with EN 1092-2 or ASME B16.1 Class 125. Working pressures: PN 10, PN 16; 250 psi, 300 psi. Working temperatures: 0°C~80°C. Both interior and exterior surface shall be epoxy coated as per AWWA C550. For dimensions of the valve, please contact our sales team!