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25P英國斯派莎克導閥型蒸汽減壓閥它是指用在蒸汽系統管道中，通過調節，將蒸汽管道的進口壓力減至某一需要的出口壓力，并依靠蒸汽介質本身的能量，使出口壓力自動保持穩定的閥門，主閥出口壓力不因進口壓力變化而改變，并不因主閥出口流量的變化而改變其出口壓力。適用于工業給水、消防供水及生活用水管網系統。

25P英國斯派莎克導閥型蒸汽減壓閥通過對同一主閥、不同型號異閥的多元化組合，可有效的控制蒸汽溫度和/或壓力。斯派莎克25系列調節閥的設計制造完全依據使用者的需求，其多元化的組合在工業界沒有任何其他的調節閥可與之媲美。為了實現多目標控制設備的獨立性和經濟性，可在同一個主閥上組合多種控制，無論是溫度控制、壓力調節還是二者在一起，都能做到反應迅速、控制精確、安全可靠。

同時，25系列調節閥的所有零件均能夠分解檢查或保養，而無需移動管路中的主閥體。正確的選型和安裝保養，更能保證其長期無故障的工作。

25P英國斯派莎克導閥型蒸汽減壓閥工作原理：

啟動前導閥彈簧處于自由狀態時，主閥和導閥處于關閉狀態。導閥有彈簧力作用打開，蒸汽經由導閥進入主隔膜室，一部分蒸汽則經由控制孔流出，當導閥流入的蒸汽大于由控制孔流出的蒸汽，主隔膜閥中的控制壓力增大，打開主閥。隨著蒸汽流過主閥，下游壓力的增量經由感應管反饋，作用在導閥隔膜下，平衡隔膜上部的彈簧壓力，使導閥組建關閉節流，維持主隔膜中的壓力，控制主閥開度輸送適量的蒸汽。調節導閥隔膜上的彈簧即可改變下游壓力。

25P英國斯派莎克導閥型蒸汽減壓閥主要特征：

導閥彈簧：三種顏色的彈簧，可提供從0.2-14bar g范圍內不同壓力的準確控制。

溫度調節刻度盤：快速準確的設定所需溫度。

溫度感應器：在溫控元件中有無需補償的液體，感應瞬時溫度的變化，提供準確的控制。

百分之百的測試：每一個25P系列的減壓閥在出廠前都經蒸汽測試，以確保無故障的操作。

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 connections, 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 options, such as on-off operation, dual pressure control, pressure and temperature control, pressure reducing and surplussing control, and remote manual adjustment. Three of these variations 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.