German COEM valves COEM models COEM prices

COEM valves can automatically open and close based on the system's working 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.

COEM valve working principle

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 serves as the water flow passage, while the upper chamber acts as 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 chamber and a water flow passage, and the opening and closing of the valve disc are controlled by the control chamber. 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 chamber. 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 passage. Since the upper surface area of the main valve disc is larger than the lower surface area, the pressure exerted by the upper chamber on the valve disc is greater than the thrust exerted by the water in the main flow passage 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 chamber via the control pipe increases. When the water pressure exceeds the spring thrust, the pilot valve opens, and pressure relief begins in the upper chamber of the main valve. 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, causing the valve disc to rise and the main valve to open rapidly for pressure relief. 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 degree of the pilot valve also increases, resulting in a greater pressure difference between the upper and lower chambers of the main valve. Consequently, the opening degree of the main valve 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 more sprinkler heads are opened), the pressure in the pilot valve control chamber decreases, and the opening degree of the pilot valve reduces. The pressure in the upper chamber of the main valve increases, causing the main valve disc to move downward and close partially, stabilizing the main pipeline water pressure at the system design level.

COEM valve classification

Relief valves are mainly categorized into two types: spring-loaded and lever-operated. Spring-loaded types rely on the force of a spring for sealing between the valve disc and the valve seat. Lever-operated types rely on the force of a lever and a weight. To meet the demand for large capacities, there is also a pulse-type relief valve, also known as a pilot-operated relief valve, which consists 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 then enters the main relief valve through the guide pipe, opening the main relief valve and reducing the increased medium pressure.

COEM valve operating instructions

Adjustment of relief valve opening pressure. 1) Before leaving the factory, each relief valve should have its opening pressure adjusted individually to the user's required set value. If the user specifies a spring working pressure class, it is generally adjusted to the lower limit of that pressure class before shipment. 2) Before installing the relief valve on the protected equipment, or prior to installation, the user must readjust it on-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. 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 during adjustment, which could damage the sealing surface. 5) To ensure accurate opening pressure values, the medium conditions during adjustment, such as medium type and temperature, should be as close as possible to actual operating conditions. Changes in medium type, especially when the aggregate state changes (e.g., from liquid phase to gas phase), often cause variations in opening pressure. As the operating temperature rises, the opening pressure generally decreases. Therefore, when adjusting at ambient temperature for high-temperature applications, 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) For conventional relief valves 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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