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Summary of the installation of pressure relief valves, emergency shut-off valves, and emergency opening valves: Pressure relief valves, emergency shut-off valves, and emergency opening valves are valves that have been developed and put into use in recent years; they have attracted considerable attention in the fields of building and fire protection water supply. The author shares their views on the issues related to their installation. Keywords: pressure relief valve, emergency shut-off valve, emergency opening valve, hydraulic control valve, designed for fire protection. 1 Pressure relief valve: This valve is installed on the outlet pipe of the fire pump; it remains closed under normal conditions, but opens automatically when the pressure in the fire water supply network exceeds a set value, thereby preventing damage to the water supply system due to overpressure. The overpressure in the fire protection water supply network is mainly caused by the following reasons: ① The flow-head curve of the pumps selected based on the designed fire protection flow rate is steep; as a result, overpressure occurs at low flow rates (during self-checks or in the early stages of a fire) ； ②If the water pump stops operating suddenly due to some reason (such as a power outage), and no appropriate technical measures are taken for the outlet pipe, the water hammer effect resulting from the stopped pump can cause overpressure. When setting a pressure relief valve, attention should be paid to issues such as location, diameter selection, pressure setting, and the appropriate accessories required. ①The pressure relief valve can be installed near the fire pump or near the fire water tank. Article 10.3.3 of the draft revision of the «Design Code for Automatic Fire Extinguishing Systems» GBH84—1985 stipulates that: \"For each set of water pumps… a control valve should be installed on the outlet pipe… and, if necessary, a pressure relief valve should also be provided.\" ”In the draft for approval, this provision was changed to: “...if necessary, measures should be taken to control the outlet pressure of the water supply pump.” ”These measures include pressure relief valves. When the pressure relief valve is installed on the outlet pipe of the fire pump, it can be placed before or after the check valve. When installed in front of the check valve, it can eliminate the excess pressure caused by the pump operating at low flow rates; whereas when installed behind the check valve (in the direction of water flow), it can not only eliminate the excess pressure resulting from low-flow operation of the pump but also the excess pressure caused by water hammer due to pump shutdown. Even if no other measures are taken to address water hammer during pump shutdown (such as quick-closing check valves, slow-closing check valves, or buffer tanks), it will not cause any harm or damage. ②There are two approaches regarding the diameter of pressure relief valves: one is to use a diameter equal to that of the main fire water supply pipe or one size smaller, while the other option is to use pressure relief valves with a diameter of DN100 or DN150. From the perspective of pressure relief, the larger the diameter of the pressure relief valve, the faster the pressure is relieved and the better the effect. As shown in Figure 1, Q represents the flow rate of discharge. The larger the diameter of the pressure relief valve, the greater the value of Q; as a result, the RBC curve shifts to the right, and the intersection point M between the R curve and the H curve also moves to the right, leading to a decrease in the pressure value. From an economic perspective, however, the larger the diameter, the higher the price of the pressure relief valve, which inevitably increases the cost of project construction. Therefore, in practice, fixed-diameter pressure relief valves are preferred at present; even though the actual pressure during pressure release is slightly higher than that of larger-diameter pressure relief valves, the overall outcome remains satisfactory. Therefore, the diameter of the pressure relief valve can be specified as follows: if the diameter D of the main fire water supply pipe is ≤ 150 mm, a DN100 pressure relief valve shall be used ； If the diameter D of the main fire water supply pipe is >150 mm, a DN150 pressure relief valve shall be used. ③The pressure setting of the pressure relief valve should be higher than those of the main fire pump and the pressure stabilizing pump. When a pressure stabilizing pump is present, there are two pressure values associated with starting and stopping the pump (referring to the pressure levels when the pump is in operation). The water hammer pressure generated when a pressure-stabilizing pump stops operating can cause the pressure relief valve to open accidentally. Therefore, fire protection water supply systems with pressure stabilization must have effective technical measures to eliminate such water hammer effects. It is also necessary to check the residual pressure in the fire protection water supply network after water hammer occurs; only if this pressure is below the set value of the pressure relief valve can it be ensured that the valve will not open accidentally. ④The pressure relief valve should be installed on a branch pipe connected to the main fire water supply pipe. To facilitate the maintenance of the pressure relief valve and prevent the control valve from closing accidentally, a signal gate valve or signal butterfly valve should be installed in front of the pressure relief valve. A bypass pipe should be installed to maintain unobstructed water flow during the maintenance of the pressure relief valve. 2 Emergency shut-off valve: The emergency shut-off valve is normally open, and it closes automatically when the pressure in the pipeline system exceeds the set value. This prevents fire water from entering the tank while the fire pump is operating. It also safeguards against damage to the domestic water supply fixtures in the combined domestic and fire water supply system due to overpressure when the fire pump is in use. Our country recommends a water supply system for both domestic use and firefighting. In such systems, the pressure at which the domestic water pumps are started under normal conditions is low, while the pressure at which the fire pumps are started during a fire is much higher than that used to start the domestic water pumps. According to Article 8.6.3, Paragraph 4 of the Code for Fire Protection Design, \"After a fire breaks out, the fire-fighting water supplied by the fire pumps shall not enter the fire-fighting water tank.\" ”To address this issue, an emergency shut-off valve should be installed on the pipeline leading to the fire water tank (as shown in Figure 2). Meanwhile, to prevent overpressure in the domestic water supply fittings when the fire pump starts, an emergency shut-off valve should be installed on the main domestic water supply pipe. The problem with emergency shut-off valves is the pressure setting. If the pressure setting is too low, the emergency shut-off valve will also close when the domestic water pump starts ； If the pressure setting is too high, the emergency shut-off valve does not close when the fire pump starts. Generally, its pressure setting should be higher than the pressure at zero flow rate of the domestic water pump, and lower than the pressure at the design flow rate of the fire pump. At the same time, reliable technical measures must be taken on the main water supply pipe to prevent water hammer. 3 Emergency opening valve: The emergency opening valve is used in water spray fire extinguishing systems, but it has not yet been implemented in any projects. The emergency opening valve is normally closed; it opens automatically to allow water flow when the pressure in the pipeline system reaches the set value. This is done to prevent water spraying from occurring in the water spray fire extinguishing system due to low pressure, before the fire pump reaches its rated speed. The valves installed in fire water supply pipelines are mostly designed to be in the open position, while emergency release valves are required to be in the closed position; they open only after the fire pump reaches its rated speed and the pressure in the pipeline system reaches the specified design value. This requires that the valves operate properly and reliably. The emergency opening valve functions similarly to a pressure relief valve, both of which open when a certain pressure level is reached. The difference is that after the pressure relief valve opens, water is discharged or returned to the fire tank in order to relieve pressure