Air Valve Sizing

Valve Sizing With Cv = 1 Table

This method can be used if the required air flow is known or has been calculated with the formulas as shown below:

Valve Sizing

Air Flow Q (SCFM) for Cv = 1

Example 2: Find Cv if air flow Q (SCFM) is given.

Valve Sizing

low through valve from Table 28 for Cv = 1:30 SCFM

Cv = Air Flow Q (SCFM)
        Air Flow at Cv = 1 (SCFM)

Cv = 60 SCFM
30         = 2.0

A valve with a Cv of minimum 2 should be selected.
Example 3: Find Cv if air flow Q (SCFM) to atmosphere is given.
Primary Pressure P1 = 90 PSIG
Air Flow to atmosphere Q = 100 SCFM

Flow to atmosphere through valve from Table 28 for Cv = 1:51 SCFM
Cv = Air Flow to atmosphere Q (SCFM)
Air Flow to Atmosphere at Cv = 1 (SCFM)

Cv = 100
51

Flow given is equivalent to valve with Cv = 2. This conversion is often necessary to size a valve properly, since some manufacturers do not show the standard Cv to allow a comparison.

Inlet  Valve Sizing  Air Flow Q
Pressure(SCFM) ToSCFM) To
(PSIG)2 PSID5 PSID10 PSID15 PSID20 PSIDAtmosphere
106.712
207.911.916.9
30913.818.221.8
409.915.420.623.826.6
5010.816.922.826.729.231.5
6011.618.224.829.232.336.4
7012.319.526.731.635.141.2
801320.728.433.837.746.1
9013.721.83035.840.251
10014.422.931.637.842.555.9
1101523.933.139.644.760.7
12015.624.934.541.446.865.6
13016.125.835.843.148.870.5
14016.726.737.144.750.775.3
15017.227.638.446.352.580.2
16017.728.439.647.854.385.1
17018.229.340.849.35690
18018.730.14250.757.794.8
19019.230.943.152.159.499.7
20019.631.644.253.460.9104.6
21020.132.445.254.862.5109.4
22020.533.146.356.164114.3
2302133.847.357.365.5119.2
24021.434.548.358.666.9124
25021.835.249.359.868.3128.9

Example 1: 

Find an air flow Q(SCFM) if Cv is known.
Cv = 1.8

Air Valve Sizing

Flow through valve from Table 28 for Cv = 1:21.8 SCFM
Q = Cv of valve x air flow at Cv = 1 (SCFM)
Q = 1.8 x 21.8 = 39.2 SCFM<

Example 4:

Find Cv if cylinder size and stroke speed is known, using formulas 1 and 3.
Primary Pressure = 90 PSIG
Pressure Drop across valve = 5 PSID
Cylinder Size 4″ Diam. x 10″ Stroke
Time to complete stroke 2 sec.