Flow Calculator

Generant's Flow Calculator is a useful tool for determining relief valve flow capacity. In order to protect against an overpressure condition, pressure relief valves must be sized as a function of discharge flow capacity. The valve's required discharge capacity must be determined through an analysis of the total system design. Generant's application engineers can assist in this process.

How to Use the Calculator:

The user inputs the valve orifice diameter, discharge coefficient (Kd), upstream and downstream pressures, flow temperature, and the working gas.

Generant's flow calculator utilizes the formulas and method described in European Standard EN ISO 4126-1.

Flow Calculator Explanation: Click here for a detailed explanation of our Flow Calculator.

Flow Calculator

Orifice Diameter (inches)
(0.01 - 1)
Orifice Diameter must be between 0.01 and 1
Orifice Discharge Coefficient (Kd)
(0.01 - 0.80)
Coefficient must be between 0.01 and 0.80
Upstream Pressure (psig)
(0.5 - 2640)
Pressure must be between 0.5 and 2640
Downstream Pressure (psig)
(0 - 2640)
Pressure must be between 0 and 2640
Upstream Temperature (°F)
(40 - 100)
Temperature must be between 40 and 100
Gas

Reference Tables

Copy and paste the appropriate values below into the calculator:

Set Pressure Range (PSIG) Discharge Coefficient (Kd*)
From To
10.017.00.62
17.129.00.62
29.145.00.53
45.160.00.53
60.190.00.61
90.1125.00.76
125.1190.00.76
190.1275.00.67
275.1400.00.61
400.1600.00.48
600.1750.00.4

Valve Orifice .250" (6.35mm) Diameter
(same for 1/4", 3/8" and 1/2" NPT)
*Discharge Coefficient (Kd) is stated at 110% accumulation with a 90% safety factor applied.

Copy and paste the appropriate values below into the calculator:

Set Pressure Range (PSIG) Discharge Coefficient, Kdr
(90% derated per ISO 4126-1)
From To .192" Orifice
(4.9mm)		 .281" Orifice
(7.1mm)		 .312" Orifice
(7.9mm)		 .400" Orifice
(10.2mm)
10.021.90.140.070.050.04
22.045.90.610.520.460.28
46.062.90.610.550.430.28
63.089.90.680.60.510.31
90.0140.90.660.620.510.31
141.0275.90.630.580.510.32
276.0400.90.630.60.520.32
401.0615.90.420.230.180.27
616.0750.00.330.120.150.11

Note: Derated Discharge Coefficient (Kdr) is stated at 110% accumulation or 0.1 bar, whichever is greater.

Copy and paste the appropriate values below into the calculator:

Set Pressure
Range		 HPRV HPRVA & HPRVM
10 - 1250 1251 - 2400 10 - 1250 1251 - 2400
Inlet (NPT) Orifice Kd Orifice Kd Orifice Kd Orifice Kd
1/8" 0.215 0.14 0.215 0.16 0.215 0.57 0.215 0.65
1/4" 0.275 0.27 0.215 0.16 0.275 0.65 0.215 0.65
3/8" 0.275 0.27 0.215 0.16 0.275 0.65 0.215 0.65
1/2" 0.515 0.2 0.275 0.27 0.515 0.35 0.275 0.65
3/4" Consult Factory

Kd is stated at 10% of Nominal Set Pressure. Orifice sizes are stated in inches.

Copy and paste the appropriate values below into the calculator:

Set Pressure Range (PSIG) Discharge Coefficient (Kd*)
From To
10.028.00.59
28.145.00.59
45.162.00.59
62.189.00.54
89.1130.00.42
130.1180.00.35
180.1275.00.25
275.1400.00.12
400.1615.00.18
615.1750.00.14

Valve Orifice .312" (7.92mm) Diameter
(same for 1/4", 3/8" and 1/2" NPT)
*Discharge Coefficient (Kd) is stated at 110% accumulation with a 90% safety factor applied.

Copy and paste the appropriate values below into the calculator:

Set Pressure Range Discharge Coefficient, Kdr
From To .180" Orifice
(4.57mm)		 .312" Orifice
(7.92mm)		 .400" Orifice
(10.16mm)
10.019.90.050.440.25
20.028.90.30.570.3
29.045.90.30.570.34
46.062.90.340.570.34
63.089.90.60.570.34
90.0130.90.60.570.34
131.0180.90.60.550.28
181.0275.90.570.550.28
276.0400.90.370.430.28
401.0615.90.370.280.25
616.0750.00.370.170.12

Discharge Coefficient (Kd) is stated at 110% accumulation with a 90% safety factor applied.

Copy and paste the appropriate values below into the calculator:

Valve Size Orifice (in) Nominal Spring / Set Pressure Range (PSIG)
1
0.5–2.5		 5
2.6–7.5		 10
7.6–15		 20
16–35		 50
36–75		 100
76–125		 150
126–150
FlowKd FlowKd FlowKd FlowKd FlowKd FlowKd FlowKd
1/8" NPT (VRV-125) 0.187 7.70.03 340.06 550.07 900.08 2600.12 5000.13 6100.11
1/4" NPT (VRV-250) 0.275 80.01 370.03 690.04 1230.05 5150.11 20110.24 22900.19
3/8" NPT (VRV-375) 0.345 120.01 580.03 1080.04 1500.04 5500.07 13000.1 11400.06
1/2" NPT (VRV-500) 0.410 500.04 1100.04 1500.04 2200.04 14580.14 37250.2 40000.15
3/4" NPT (VRV-750) 0.570 740.03 820.01 950.01 2250.02 10500.05 20800.06 34500.07
1" NPT (VRV-1000) 0.785 Consult Factory 1750.02 1140.01 3100.02 13600.04 46000.07 55000.06

Flow and Kd (discharge coefficient) are stated at 110% accumulation above set point with Nitrogen and zero downstream pressure.
Interpolate charts for set pressures between points given.
Restrictions in the inlet or outlet piping may reduce flow.
Exceeding 115% accumulation may result in valve failure.
Generant offers complete design assistance. Consult factory for correct relief valve sizing.
Individual flow curves available on request.
Orifice sizes are stated in inches.

Copy and paste the appropriate values below into the calculator:

Valve SizeOrifice (in)Nominal Spring / Set Pressure Range (PSIG)
1
0.5–2.5		5
2.6–7.5		10
7.6–15		20
16–35		50
36–75		100
76–125		150
126–150
FlowKdFlowKdFlowKdFlowKdFlowKdFlowKdFlowKd
1/8" NPT (VRVD-125)0.18710.30.04390.07950.121000.092800.135800.157800.14
1/4" NPT (VRVD-250)0.275110.02400.031000.051720.0723400.542720.566500.55
3/8" NPT (VRVD-375)0.345130.01770.041300.051950.057380.143530.3362750.33
1/2" NPT (VRVD-500)0.410600.052460.094200.116580.1226050.2568000.3776000.29
3/4" NPT (VRVD-750)0.570500.02760.011160.0225000.2360000.3110000.320000+0.34
1" NPT (VRVD-1000)0.785Consult Factory5600.065000.046000.03100000.27120000.1820000+0.2

Flow and Kd (discharge coefficient) are stated at 110% accumulation above set point with Nitrogen and zero downstream pressure.
Interpolate charts for set pressures between points given.
Restrictions in the inlet or outlet piping may reduce flow.
Exceeding 115% accumulation may result in valve failure.
Generant offers complete design assistance. Consult factory for correct relief valve sizing.
Individual flow curves available on request.
Orifice sizes are stated in inches.

Copy and paste the appropriate values below into the calculator:

Valve SizeOrifice (in)Nominal Spring / Set Pressure Range (PSIG)
1
0.5–2.5		5
2.6–7.5		10
7.6–15		20
16–35		50
36–75		100
76–125		150
126–150
FlowKdFlowKdFlowKdFlowKdFlowKdFlowKdFlowKd
1/4" NPT (VRVI-250)0.1877.70.03340.06550.07900.082600.125000.136100.11
3/8" NPT (VRVI-375)0.27580.01370.03690.041230.055150.1120110.2422900.19
1/2" NPT (VRVI-500)0.345120.01580.031080.041500.045500.0713000.111400.06
3/4" NPT (VRVI-750)0.410500.041100.041500.042200.0414580.1437250.240000.15

Flow and Kd (discharge coefficient) are stated at 110% accumulation above set point with Nitrogen and zero downstream pressure.
Interpolate charts for set pressures between points given.
Restrictions in the inlet or outlet piping may reduce flow.
Exceeding 115% accumulation may result in valve failure.
Generant offers complete design assistance. Consult factory for correct relief valve sizing.
Individual flow curves available on request.
Orifice sizes are stated in inches.

Copy and paste the appropriate values below into the calculator:

Valve SizeOrifice (in)Nominal Spring / Set Pressure Range (PSIG)
150
125–175		250
175–350		500
350–600
Flow (SCFM)KdFlow (SCFM)KdFlow (SCFM)Kd
1/8" NPT (VRVH-125)0.1567.50.1212.50.12330.16
1/4" NPT (VRVH-250)0.293500.22900.241500.2

Flow and Kd (discharge coefficient) are stated at 110% accumulation above set point with Nitrogen and zero downstream pressure.
Interpolate charts for set pressures between points given.
Restrictions in the inlet or outlet piping may reduce flow.
Exceeding 115% accumulation may result in valve failure.
Generant offers complete design assistance. Consult factory for correct relief valve sizing.
Individual flow curves available on request.
Orifice sizes are stated in inches.

Copy and paste the appropriate values below into the calculator:

Valve SizeOrifice (in)Nominal Spring / Set Pressure Range (PSIG)
150
125–175		250
175–350		500
350–600
Flow (SCFM)KdFlow (SCFM)KdFlow (SCFM)Kd
1/8" NPT (VRVHI-125)0.156120.1813.50.13350.17
1/4" NPT (VRVHI-250)0.250450.27800.31750.33

Flow and Kd (discharge coefficient) are stated at 110% accumulation above set point with Nitrogen and zero downstream pressure.
Interpolate charts for set pressures between points given.
Restrictions in the inlet or outlet piping may reduce flow.
Exceeding 115% accumulation may result in valve failure.
Generant offers complete design assistance. Consult factory for correct relief valve sizing.
Individual flow curves available on request.
Orifice sizes are stated in inches.