German SED valves SED models SED prices

SED valves can automatically open and close based on the system's operating pressure. They are generally installed on equipment or pipelines in closed systems to protect system safety. When the pressure inside the equipment or pipeline exceeds the set pressure of the relief valve, it automatically opens to relieve pressure, ensuring that the medium pressure in the equipment and pipeline remains below the set pressure, thereby protecting the equipment and pipeline and preventing accidents.

SED valve working principle

It is a type of hydraulic control valve. The main valve is divided into upper and lower parts by a diaphragm. The lower chamber of the diaphragm is the water flow channel, and the upper chamber is the control room, which controls the opening and closing of the main valve disc. The pilot valve itself is a relief valve; it also has a control room and a water flow channel, and the opening and closing of the valve disc are controlled by the control room. The needle valve, i.e., the throttle valve, controls the water flow in the connecting pipe. During the operation of the fire water supply system, the main pipeline water flows from left to right. One path of control water enters the pilot valve control room. When the water pressure is less than the set relief value, the thrust of the pilot valve spring is greater than the water pressure, and the pilot valve disc is in the closed state. Another path of control water enters the upper chamber of the main valve through the throttling needle valve, generating a static pressure. The pressure in the upper chamber is equal to the pressure in the flow channel. Since the upper plane area of the main valve disc is larger than the lower plane area, the pressure from the upper chamber on the valve disc is greater than the thrust from the water in the main flow channel on the valve disc, keeping the main valve in the closed state. If the main pipeline water pressure rises and exceeds the set relief value, the water pressure entering the pilot control room via the control pipe increases. The water pressure becomes greater than the spring thrust, the pilot valve opens, and the upper chamber of the main valve begins to relieve pressure. Due to the restriction of the throttle valve, insufficient replenishment causes the pressure in the upper chamber of the main valve to decrease. The flow thrust under the main valve disc becomes greater than the pressure in the upper chamber, the valve disc rises, and the main valve opens to rapidly relieve pressure. Since this process occurs instantaneously, no harm is caused to the indoor fire water supply system during overpressure events. If the main pipeline water pressure continues to increase, the opening of the pilot valve also increases, resulting in a greater pressure difference between the upper and lower chambers of the main valve. The opening of the main valve also increases, and the system relieves pressure faster. Conversely, if the main pipeline water pressure decreases (e.g., when the number of indoor fire hydrants in use increases or the number of open sprinkler heads increases), the pressure in the pilot valve control room decreases, and the opening of the pilot valve becomes smaller. The pressure in the upper chamber of the main valve increases, causing the main valve disc to move downward and close slightly, stabilizing the main pipeline water pressure at the system design level.

SED valve classification

Relief valves mainly have two structural types: spring-loaded and lever-loaded. Spring-loaded means that the sealing between the valve disc and the valve seat relies on the force of the spring. Lever-loaded relies on the force of the lever and the weight. To meet the need for large capacity, there is also a pulse-type relief valve, also known as a pilot-operated relief valve, consisting of a main relief valve and an auxiliary valve. When the medium pressure in the pipeline exceeds the specified pressure value, the auxiliary valve opens first. The medium enters the main relief valve through the guide pipe and opens the main relief valve, reducing the increased medium pressure.

SED valve operating method

Adjustment of relief valve opening pressure. 1) Before leaving the factory, each relief valve should be adjusted individually to the user's required set value for opening pressure. If the user specifies a spring working pressure class, it is generally adjusted to the lower limit of the pressure class before shipment. 2) Before installing the relief valve on the protected equipment, or prior to installation, the user must readjust it at the installation site to ensure that the set pressure value of the relief valve meets requirements. 3) Within the spring working pressure class range indicated on the nameplate, the opening pressure can be adjusted by rotating the adjustment screw to change the spring compression amount. 4) Before rotating the adjustment screw, the inlet pressure of the valve should be reduced to below 90% of the opening pressure to prevent the valve disc from being driven to rotate while turning the adjustment screw, which could damage the sealing surface. 5) To ensure the accuracy of the opening pressure value, the medium conditions during adjustment, such as medium type and temperature, should be as close as possible to the actual operating conditions. Changes in medium type, especially when the aggregate state of the medium changes (e.g., from liquid phase to gas phase), often cause variations in opening pressure. When the operating temperature rises, the opening pressure generally decreases. Therefore, if adjusted at ambient temperature for use at high temperatures, the set pressure value at ambient temperature should be slightly higher than the required opening pressure value. The extent of this difference depends on the valve structure and material selection and should be based on the manufacturer's instructions. 6) Standard relief valves are used in applications with fixed additional back pressure. When adjusting the opening pressure after testing (where the back pressure is atmospheric pressure), the set value should be the required opening pressure value minus the additional back pressure value.

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