25P英国斯派莎克导阀型蒸汽减压阀它是指用在蒸汽系统管道中，通过调节，将蒸汽管道的进口压力减至某一需要的出口压力，并依靠蒸汽介质本身的能量，使出口压力自动保持稳定的阀门，主阀出口压力不因进口压力变化而改变，并不因主阀出口流量的变化而改变其出口压力。适用于工业给水、消防供水及生活用水管网系统。
25P英国斯派莎克导阀型蒸汽减压阀通过对同一主阀、不同型号异阀的多元化组合，可有效的控制蒸汽温度和/或压力。 斯派莎克25系列调节阀的设计制造完全依据使用者的需求，其多元化的组合在工业界没有任何其他的调节阀可与之媲美。为了实现多目标控制设备的***性和经济性，可在同一个主阀上组合多种控制，无论是温度控制、压力调节还是二者在一起，都能做到反应迅速、控制***、安全可靠。
同时，25系列调节阀的所有零件均能够分解检查或***，而无需移动管路中的主阀体。正确的选型和安装***，更能保证其长期无故障的工作。
25P英国斯派莎克导阀型蒸汽减压阀工作原理：
启动前导阀弹簧处于自由状态时，主阀和导阀处于关闭状态。导阀有弹簧力作用打开，蒸汽经由导阀进入主隔膜室，一部分蒸汽则经由控制孔流出，当导阀流入的蒸汽大于由控制孔流出的蒸汽，主隔膜阀中的控制压力增大，打开主阀。随着蒸汽流过主阀，下游压力的增量经由感应管反馈，作用在导阀隔膜下，平衡隔膜上部的弹簧压力，使导阀组建关闭节流，维持主隔膜中的压力，控制主阀开度输送适量的蒸汽。调节导阀隔膜上的弹簧即可改变下游压力。
25P英国斯派莎克导阀型蒸汽减压阀主要特征：
导阀弹簧：三种颜色的弹簧，可提供从0.2-14bar g范围内不同压力的准确控制。
温度调节刻度盘：快速准确的设定所需温度。
温度感应器：在温控元件中有无需补偿的液体，感应瞬时温度的变化，提供准确的控制。
***的测试：每一个25P系列的减压阀在出厂前都经蒸汽测试，以确保无故障的操作。
Many reducing valve problems are caused by the presence of moisture or dirt. A steam separator and strainer with fine mesh screen, if fitted before the valve, will help to prevent such problems. The strainer is fitted on its side to prevent the body filling with water and to ensure that the full area of the screen is effective. Large isolation valves will also benefit from being installed on their side for the same reason.
All upstream and downstream pipework and fittings must be adequately sized to ensure that the only appreciable pressure drop occurs across the reducing valve itself. If the isolating valves are the same size as the reducing valve connecti***, they will incur a larger pressure drop than if they are sized to match the correctly sized, larger diameters of the upstream and downstream pipework.
If the downstream pipework or any connected plant is incapable of withstanding the maximum possible upstream pressure, then a safety valve or relief valve must be fitted on the downstream side. This valve should be set at, or below, the maximum allowable working pressure of the equipment, but with a sufficient margin above its normal operating pressure. It must be capable of handling the full volume of steam that could pass through the fully open reducing valve, at the maximum possible upstream pressure.
Pilot operation also allows the reducing valve to be relatively compact compared to other valves of similar capacity and accuracy, and allows a variety of control opti***, such as on-off operation, dual pressure control, pressure and temperature control, pressure reducing and surplussing control, and remote manual adjustment. Three of these variati*** can be seen in Figure 7.3.6.
Direct acting and pilot-operated control valves can be used to control either upstream or downstream pressures. Pressure maintaining valves (and surplussing valves) sense upstream pressure, while pressure reducing valves sense downstream pressure.
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