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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:
- 高和低的進口壓力
Highest and Lowest inlet pressures
- 出口壓力
Outlet pressure
- 大流量要求
Maximum flow requirements
- 小流量要求
Minimum flow requirements
步驟1：利用高流量表，并且在橫軸上找出符合用戶大流量要求的流量值。
Step 1: Utilize the high flow chart and select the flow as found on the horizontal axis which corresponds with your maximum flow requirements.
步驟2：從這一點劃垂線，延伸到與相應的小壓差的水平線相交。（此時，小壓差將是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小閥門通徑。如果大流量是連續的，那么不要超過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.
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步驟4：利用流量表，在豎軸上找到大壓差。（用戶的大壓差將是高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 chart and select the 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得到的小流量能力比用戶實際的小流量要求高，則用戶應該考慮采用并聯安裝方式。采用這個小流量能力，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**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 select the size you will need for this low-flow by-pass.
2) Use the cavitation chart and determine if the intersection of the inlet and outlet 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.
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