How does steam pressure reducing valve work?

Steam reducing pressure valves are valves that precise control the downstream pressure of steam and automatically adjust the amount of valve opening to allow the pressure to remain unchanged even when the flow rate fluctuates by pistons, springs or diaphragms. The pressure reducing valve adopts the opening and closing parts in the valve body to adjust the flow of the medium, reduce the medium pressure and adjust the opening degree of the opening and closing parts with the help of the pressure behind the valve, so that the pressure behind the valve remains in a certain range, in the case of constant changes in the inlet pressure to keep the outlet pressure in the set range. It is important to choose the right type of steam relief valve. Do you know why steam needs pressure-reducing?

Steam sometimes causes condensation, and condensed water loses less energy at low pressure. The steam after decompression reduces the pressure of condensate and avoids the flash steam when it is discharged. The temperature of saturated steam is related to pressure. In the sterilization process and surface temperature control of paper dryer, pressure relief valves are needed to control the pressure and further control the temperature. Some systems are with high-pressure condensate water to produce low-pressure flash steam to achieve the purpose of energy-saving when the flash steam is insufficient or steam pressure exceeds the set value where needs a pressure reducing valve.
Steam has a higher enthalpy at low pressure. The enthalpy value at 2.5mpa is 1839kJ/kg, and that at 1.0mpa is 2014kJ/kg when the low-pressure steam valve is needed to reduce the steam load of the boiler. High-pressure steam can be transported by pipes of the same caliber, which are denser than low-pressure steam. For the same pipe diameter with different steam pressures, the steam flow is allowed to be different, for example, the steam flow in DN50 pipe at 0.5mpa is 709kg/h, while that in 0.6mpa is 815kg/h. In addition, it can reduce the occurrence of wet steam and improve the dryness of steam. High-pressure steam transportation will reduce the size of the pipeline and save costs, suitable for long-distance transport.

The types of steam pressure reducing valve

There are many types of steam pressure reducing valve, they can be divided into direct-acting pressure reducing valve, piston pressure reducing valve, pilot-operated pressure reducing valve and bellows pressure reducing valve according to their structure.
Direct-acting pressure reducing valve has a flat diaphragm or bellow and does not need to install external sensing lines downstream because it is independent. It is one of the smallest and most economical pressure reducing valves, designed for the medium with low flow and stable load. The accuracy of direct-acting relief valves is usually +/-10% of the downstream set point.

When the reducing valve size or output pressure is larger, with the pressure regulating spring directly adjust the pressure will inevitably increase the spring stiffness, flow changes when the output pressure fluctuation and valve size will increase. These disadvantages can be overcome by the use of pilot-operated pressure reducing valves, which are suitable for sizes of 20mm or more, for long distances (within 30m), dangerous places, high places or where pressure adjustment is difficult.
The use of piston as the main valve operating parts to ensure fluid pressure stability, piston pressure relief valve is suitable for frequent use of the piping system. From the above function and applications, the purpose of pressure reducing valves can be summarized as “pressure stabilization, dehumidification, cooling” in the steam system. Steam pressure reducing valve for decompression treatment, basically is determined by the characteristics of the steam itself, also by the medium needs.

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