Requirements for the installation of pressure-reducing valves

Pressure-reducing valves are widely used in fire water supply and automatic sprinkler systems. Today, we will explore the working principle of pressure-reducing valves and their installation requirements.

I. Working Principle

1. Pilot-operated Pressure Reducing Valves
Pilot-operated pressure reducing valves achieve pressure reduction within the pipeline by altering the throttling area, thereby changing the flow velocity and kinetic energy of the fluid in the pipeline system. This results in varying degrees of pressure loss. Through precise control and adjustment, a balance is established between fluctuations in the internal valve pressure and the spring force, ultimately maintaining the pressure downstream of the valve within a specified tolerance range.

Pilot-operated pressure reducing valves utilise hydraulic principles to achieve control. Functioning as a component for localised pressure adjustment and throttling, they regulate the inlet pressure to reduce it to a predetermined outlet pressure range, and then rely on the energy of the medium itself to automatically maintain a stable outlet pressure.

2. Proportional Pressure Reducing Valves
Proportional pressure reducing valves are a type of pressure reducing valve that controls the downstream pressure according to a numerical ratio, with upstream-to-downstream pressure ratios such as 2:1 or 3:1. The downstream pressure varies in response to changes in the upstream pressure; it is not maintained at a constant level, but rather maintains a specific ratio with the upstream pressure. When the inlet pressure increases, the outlet pressure increases proportionally; when the inlet pressure decreases, the outlet pressure decreases proportionally, thereby maintaining a constant ratio between the inlet and outlet pressures of the pressure reducing valve.

II. Installation Requirements

1. The pressure-reducing valve shall be installed upstream of the inlet to the alarm valve assembly. Where two or more alarm valve assemblies are connected, a standby pressure-reducing valve shall be provided.
2. A strainer shall be installed at the inlet of the pressure-reducing valve. The mesh size of the strainer shall not be less than 4 mesh/cm² to 5 mesh/cm², and the flow area shall not be less than four times the cross-sectional area of the pipeline.
3. Pressure gauges shall be installed upstream and downstream of the filter and pressure-reducing valve; the dial diameter of the pressure gauge shall not be less than 100 mm, and the maximum range shall preferably be twice the design pressure.
4. Control valves shall be installed upstream of the filter and downstream of the pressure-reducing valve.
5. A pressure test drain valve shall be installed downstream of the pressure-reducing valve.
6. The pressure-reducing valve shall be fitted with a flow measurement test port or a flow meter.
7. For vertically installed pressure-reducing valves, the flow direction should be downwards.
8. Proportional pressure-reducing valves should be installed vertically, whilst adjustable pressure-reducing valves should be installed horizontally.
9. Pressure-reducing valves should be fitted with a device to protect or lock the adjustment mechanism.
10. The pipe section connected to the pressure-reducing valve shall be free of air locks or air pockets.

Note:
1) The performance of a pressure-reducing valve requires that the direction of water flow remains constant. In the case of a proportional pressure-reducing valve, if the direction of water flow is reversed, the valve will increase pressure rather than reduce it; in the case of an adjustable pressure-reducing valve, if the direction of water flow is reversed, the valve will cease to function and act as a check valve. Therefore, during installation, the valve must be fitted strictly in accordance with the direction indicated on the valve.

2) A strainer must be installed on the inlet side of the pressure-reducing valve, primarily to prevent debris from the pipework network entering the valve, which could block the pilot valve passage or accumulate on the moving parts inside the valve, impairing its operation and causing the valve to fail. Control valves should be installed upstream and downstream of the pressure-reducing valve, primarily to facilitate maintenance and replacement of the valve; this reduces the time required to drain the system and minimises the impact of water supply interruptions during maintenance or replacement.

3) The spool of a proportional pressure-reducing valve features a cylindrical piston design. During operation, the sealing is achieved by a rubber seal ring on the outer sleeve of the spool against the valve body. When installed vertically, the sealing contact surface between the spool and the valve body is subjected to more uniform force, which helps ensure reliable performance and extends the service life. If installed horizontally, the valve core and body are subject to gravity, which can cause tighter contact at the lower section, increasing frictional resistance and adversely affecting pressure-reducing performance and service life. When installed horizontally, the single vent hole should face downwards and the dual vent holes should be horizontal; this is primarily to prevent external debris from blocking the vent holes and compromising performance.

4) A pressure gauge is installed primarily to verify the pressure-reducing performance of the valve during commissioning. During operation, it allows for continuous monitoring of the supply pressure and the pressure downstream of the valve to ensure they meet design requirements, thereby confirming that the pressure-reducing valve is operating normally.

III. Commissioning of the Pressure-Reducing Valve
1. The static and dynamic pressures upstream and downstream of the pressure-reducing valve must meet design requirements.
2. The outlet flow rate of the pressure reducing valve must meet design requirements. When the outlet flow rate is 150% of the design flow rate, the dynamic pressure downstream of the valve must not be less than 65% of the rated design working pressure.
3. The pressure reducing valve must not exhibit a significant increase in noise at low flow rates, the design flow rate, or 150% of the design flow rate.
4. The dynamic and static pressure differentials downstream of the pressure reducing valve must comply with design requirements.

IV. Maintenance of Pressure Reducing Valves
1. A drain test shall be carried out on the pressure reducing valve assembly once a month, and the pressures upstream and downstream of the valve shall be measured and recorded. Should the values not comply with the design specifications, measures such as commissioning and maintenance shall be taken to ensure the system requirements are met.
2. The flow rate and pressure of the pressure reducing valve shall be tested once a year.