20 Inches Motorcycle Magnesium Wheels 20 Inches Motorcycle Magnesium Wheels,Aluminum Wheels,Forged Wheel,Weld Off Road Wheels Shamora Material Industry , https://www.shamorawheels.com
Pressure relief valves are installed on the outlet pipe of fire pumps, typically in a closed position. They automatically open when the pressure in the fire water supply network exceeds the set value, preventing damage caused by overpressure. Overpressure in the system can occur due to several reasons: (1) When the pump flow is selected based on the design fire flow rate and has a steep head curve, overpressure may occur at low flow rates, such as during self-testing or initial fire conditions. If the pump stops due to power outages or other issues, water hammer from the sudden stop can also cause overpressure. The installation of the pressure relief valve should consider its location, size, pressure setting, and additional components.
â‘ The relief valve can be placed near the fire pump or fire water tank. According to the "Automatic Sprinkler System Design Code GBH84? 1985 Revised Draft Article 10.3.3," it states that each group of pumps should have a control valve on the outlet pipe, and if necessary, a pressure relief valve should be installed. Although the wording was later revised to "measures should be taken to control the pressure at the outlet of the water supply pump," relief valves are still considered an effective solution. When installed on the fire pump outlet pipe, the relief valve can be placed before or after the check valve. Installing it before the check valve helps prevent overpressure caused by small flows, while placing it after the check valve not only addresses overpressure from low flow operation but also mitigates pressure surges caused by pump shutdown. Even without additional measures like quick-closing or buffer tanks, this setup minimizes potential damage.
② There are two common practices for selecting the size of the pressure relief valve: one is matching the main fire water pipe diameter or slightly smaller, and the other is using a DN100 or DN150 valve. From a pressure relief perspective, a larger valve allows faster discharge, which improves performance. As shown in Figure 1, the larger the valve diameter, the higher the discharge capacity (Q), shifting the RBC curve to the right and lowering the pressure at the intersection point M. However, larger valves increase construction costs, so in practice, fixed sizes are often used. For example, if the main fire water pipe diameter is ≤150mm, a DN100 valve is used; if it’s >150mm, a DN150 valve is preferred.
③ The pressure setting of the relief valve must be higher than the main pump and booster pump settings. If a stabilizing pump is present, there are two pressure values for when the pump starts and stops. Stabilizing pump shutdown can cause water hammer, potentially triggering the relief valve. Therefore, for high-pressure fire water systems, reliable measures to prevent water hammer should be in place, and the residual pressure after the water hammer should be checked to ensure it doesn’t trigger the valve accidentally.
â‘£ The pressure relief valve should be installed on a branch pipe connected to the fire water supply line. To facilitate maintenance and avoid accidental closure, a signal valve or butterfly valve should be placed before the relief valve. A bypass pipe should also be included to maintain proper flow through the relief valve.
2. Emergency shut-off valve
The emergency shut-off valve is normally open and automatically closes when the pipe network pressure exceeds the set value, preventing the fire pump from sending water into the fire water tank during normal operations. It also prevents the fire pump from running unnecessarily. In China, the recommended life of the fire water supply system requires that when a fire occurs, the fire pump should not send water into the fire tank. To address this, an emergency shut-off valve should be installed on the pipe leading to the fire water tank. Additionally, a shut-off valve should be placed on the life water supply line to prevent overpressure during pump startup. The challenge lies in setting the correct pressure. If the pressure is too low, the valve may close prematurely; if too high, it may fail to close during a fire. Typically, the setting should be higher than the zero-pressure value of the life pump and lower than the design flow pressure. Reliable technical measures must also be in place to prevent water hammer in the main lines.
3. Emergency opening valve
Emergency opening valves are used in water spray fire suppression systems and are not yet widely implemented in projects. Normally closed, they open when the network pressure reaches a set value, preventing low-pressure water spray before the fire pump reaches its rated speed. These valves are usually kept open but are designed to open when the pump reaches its rated speed and the network pressure meets the design requirements. They function similarly to relief valves, opening when pressure is reached, but instead of discharging water back into the fire pool, they direct it into the sprinkler system to suppress fires. Both types are hydraulic control valves, with pilot needles and diaphragms that can become clogged or worn. To address these issues: â‘ Multi-stage filters should be installed before the needle valve, with progressively finer mesh to trap impurities. â‘¡ High-quality diaphragms made of durable materials should be used, along with springs to ensure reliable operation.
Currently, pressure relief valves, emergency shut-off valves, and emergency opening valves are treated as general-purpose valves, not classified as specialized fire-fighting equipment. They are not subject to testing by the Fire Product Quality Supervision and Inspection Center. This needs to change, as these valves are specifically used in fire water supply systems and should be recognized as essential fire products.