为了正确选择自动控制阀的通径，用户需要了解下列事项：
　　To properly size an automatic control valve you need to know the following:

• 最高和最低的进口压力
  Highest and Lowest inlet pressures
• 出口压力
  Outlet pressure
• 最大流量要求
  Maximum flow requirements
• 最小流量要求
  Minimum flow requirements

　　步骤1：利用高流量表，并且在横轴上找出符合用户最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.
　　步骤2：从这一点划垂线，延伸到与相应的最小压差的水平线相交。（此时，最小压差将是最低进口压力减去所需要的出口压力，这也就是所说的∆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.)
　　步骤3：从这一点向右移动直到第一个阀门的通径线。这就是在25英尺/秒间歇流量时应该采用的最小阀门通径。如果最大流量是连续的，那么不要超过最大连续流量表上所列的美制加仑/分钟（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.

　　步骤4：利用流量表，在竖轴上找到最大压差。（用户的最大压差将是最高进口压力减去所需要的出口压力，这也就是所说的∆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.)
　　步骤5：从这一点划水平线与步骤3选择的阀门通径相应的线相交。
　　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.
　　步骤6：从这一点划垂线向下与横轴相交。这就是以这些变量为基础的阀门的最小流量能力。
　　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) 如果通过步骤6得到的最小流量能力比用户实际的最小流量要求高，则用户应该考虑采用并联安装方式。采用这个最小流量能力，从步骤1开始选择用户需要的用于低流量旁路的通径。
　　　　　2) 采用空穴图表并且确定进口和出口压力的相交是否落在阴影区域内。如果是，用户应该考虑串联安装方式。两个阀门都应该按照上述步骤选择通径。
　　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.

压降指数 - 减压阀
PRESSURE DROP INDEX - PRESSURE REDUCING VALVES

　　通过从最大进口压力减去所需要的出口压力来计算压差。找出压差线上的数字，并且注意出口压力指数。这是不会落入空穴区的最低的出口压力设置。美国瓦茨自动控制阀的结构将可能导致空穴现象的阀门损坏潜在危险降低到最小程度。避免在空穴区域内持续运行。
　　Calculate the pressure difference by subtracting the desired outlet pressure from the maximum inlet pressure. Find the number on the pressure difference line and note 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.

空穴图表
CAVITATION CHART

　　阀门通径选择后，在这个图表中找出进口和出口压力。如果交点落在阴影区域，则可能产生空穴。应该避免在空穴区域内持续运行阀门。请咨询美国瓦茨ACV，了解其他解决方案。
　　After selecting valve size, locate inlet and outlet 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.