為了正確選擇自動控制閥的通徑，用戶需要了解下列事項：
　　To properly size an automatic control valve you need to know the following:

• Z和Z低的進口壓力
  HighestLowest inlet pressures
• 出口壓力
  Outlet pressure
• Z大流量要求
  Maximum flow requirements
• Z小流量要求
  Minimum flow requirements

　　步驟1：利用流量表，并且在橫軸上找出符合用戶Z大流量要求的流量值。
　　Step 1: Utilize the high flow chartthe flow as found on the horizontal axis which corresponds with your maximum flow requirements.
　　步驟2：從這一點劃垂線，延伸到與相應的Z小壓差的水平線相交。（此時，Z小壓差將是Z低進口壓力減去所需要的出口壓力，這也就是所說的∆P。）
　　Step 2: From this point draw a vertical line until you intersect with the horizontal line corresponding with the minimum differential pressure. Your minimum differential pressure will be the lowest inlet pressure minus the desired outlet pressure, this is also known as the delta P.
　　步驟3：從這一點向右移動直到*個閥門的通徑線。這就是在25英尺/秒間歇流量時應該采用的Z小閥門通徑。如果Z大流量是連續的，那么不要超過Z大連續流量表上所列的美制加侖/分鐘（20英尺/秒）。
　　Step 3: From this point move right to the first valve size line. This will be the minimum valve size which should be used on intermittent flow of 25 ft./sec. If maximum flow is continuous, then do not exceed the GPM 20 FT./sec. listed on the maximum continuous flow table.

　　步驟4：利用流量表，在豎軸上找到Z大壓差。（用戶的Z大壓差將是Z進口壓力減去所需要的出口壓力，這也就是所說的∆P。）
　　Step 4: Utilize the flow chartthe maximum differential pressure as found on the vertical axis. Your maximum differential pressure will be the highest inlet pressure minus the desired outlet pressure, this is also known as the delta P.
　　步驟5：從這一點劃水平線與步驟3選擇的閥門通徑相應的線相交。
　　Step 5: From this point draw a horizontal line until you intersect with the line corresponding to the valve size as selected in step 3.
　　步驟6：從這一點劃垂線向下與橫軸相交。這就是以這些變量為基礎的閥門的Z小流量能力。
　　Step 6: From this point draw a vertical line down to the horizontal axis. This will be the minimum flow capabilities of the valve based on these variables.
　　注意：1 如果通過步驟6得到的Z小流量能力比用戶實際的Z小流量要求，則用戶應該考慮采用并聯安裝方式。采用這個Z小流量能力，從步驟1開始選擇用戶需要的用于低流量旁路的通徑。
　　　　　2 采用空穴圖表并且確定進口和出口壓力的相交是否落在陰影區域內。如果是，用戶應該考慮串聯安裝方式。兩個閥門都應該按照上述步驟選擇通徑。
　　Notes: 1 If the minimum flow capability obtained from step 6 is above your actual minimum flow requirements, you should consider a parallel installation. Using the minimum flow capability, begin at step 1 to the size you will need for this low-flow by-pass.
　　　　　2 Use the cavitation chartdetermine if the intersection of the inletoutlet pressures falls in the shaded area. If so, you should consider a series installation. Both valves should be sized in accordance with the above steps.

壓降指數 - 減壓閥
PRESSURE DROP INDEX - PRESSURE REDUCING VALVES

　　通過從Z大進口壓力減去所需要的出口壓力來計算壓差。找出壓差線上的數字，并且注意出口壓力指數。這是不會落入空穴區的Z低的出口壓力設置。美瓦茨自動控制閥的結構將可能導致空穴現象的閥門損壞潛在危險降低到Z小程度。避免在空穴區域內持續運行。
　　Calculate the pressure difference by subtracting the desired outlet pressure from the maximum inlet pressure. Find the number on the pressure difference linenote the outlet pressure index number. This is the lowest outlet pressure setting allowed without failing into the cavitation zone. Design of the WATTS Automatic Control Valve minimizes potential valve damage that can be caused by cavitation. Avoid continued operation within the cavitation zone.

空穴圖表
CAVITATION CHART

　　閥門通徑選擇后，在這個圖表中找出進口和出口壓力。如果交點落在陰影區域，則可能產生空穴。應該避免在空穴區域內持續運行閥門。請咨詢美瓦茨ACV，了解其他解決方案。
　　After selecting valve size, locate inletoutlet pressures on this chart. If the intersection point falls in the shaded area, cavitation can occur. Operation of valves continually in the cavitation zone should be avoided. Consult Watts ACV for alternatives.