How does temperature affect the air-flow screen?

The standard-air equation uses absolute temperature. Keep standard and actual volumetric-flow bases distinct and use the manufacturer's method for binding selection.

Pneumatic Valve Cv Calculator #

Calculate a screening flow coefficient (Cv) for compressed-air and turbulent-liquid service from flow, pressure and fluid inputs, with Kv conversion. The page does not infer nominal valve size or velocity; verify expansion/recovery factors, geometry, travel and operating limits in the exact manufacturer sizing data.

Quick Calculator: Valve Parameters

Fluid Type

Flow Rate (SCFM) SCFM for gas, GPM for liquid

Inlet Pressure (PSIG)

Allowable Pressure Drop (PSI) Enter the maximum pressure loss allowed by the system design and exact valve application.

Unit System

Advanced calculator

Gas temperature or liquid specific gravity refines the Cv/Kv arithmetic screen.

Fluid Temperature (°F) Gas only — affects density

Liquid Specific Gravity Used only for liquid mode; water reference = 1.0.

About This Calculator

This calculator provides an equation-based Cv/Kv screen for standard air flow or turbulent liquid flow. Gas mode uses inlet absolute pressure, absolute temperature and pressure ratio; liquid mode uses specific gravity. It deliberately does not infer nominal valve size, rated Cv, pressure-drop performance or velocity because those require the exact valve geometry, recovery/expansion factors, travel and manufacturer data. Browse the pneumatic calculator hub for related airflow and actuator tools.

Results

Required Cv

2.12 Cv

Kv (Metric)

1.83 Kv

Valve Selection

Use OEM Cv table

Minimum Rated Cv

≥ 2.12 Cv required

Pressure Drop

Entered limit

Velocity

Requires valve geometry

Flow Regime

Sub-critical

Continue Your Calculation

After valve Cv and size, size the pneumatic cylinder for your actuator or the compressor for total system demand.

Size cylinder →

Standard Valve Cv Reference Chart #

Illustrative historical ranges only; this table is not used by the calculator and must not be used for automatic size selection. Port size alone does not determine Cv. Replace every value with the exact coefficient from the candidate model's current manufacturer datasheet.

Nominal Size	Ball Valve (full port)	Solenoid Valve	Globe Valve	Butterfly Valve	Typical Application
1/8"	3	0.5-1.5	1-2	—	Small cylinders, pilot valves
1/4"	8	2-5	3-6	—	Cylinders up to 40mm bore
3/8"	14	5-10	8-12	—	Cylinders 50-63mm bore
1/2"	24	10-18	15-22	—	Cylinders 80-100mm, branch lines
3/4"	48	20-35	35-45	40-60	Cylinders 125-160mm, small mains
1"	78	40-60	55-75	70-100	Cylinders 200mm+, main headers
1-1/4"	120	—	100-120	120-160	Large plant mains
1-1/2"	170	—	140-170	180-240	Heavy industrial mains
2"	275	—	220-280	300-400	Very large facility mains

Boundary: these unspecific historical ranges are retained only as orientation and are not selection evidence. The production result intentionally supplies no nominal size; use the exact current OEM coefficient and sizing method.

Cv Formulas and Calculation Method #

Liquid Flow (Incompressible)

Cv = Q × sqrt(G / ΔP)

Where: Q = flow rate (GPM), G = specific gravity (water = 1.0), ΔP = pressure drop across valve (PSI). This formula applies to non-choked, turbulent liquid flow. For viscous fluids (kinematic viscosity > 20 cSt), apply a viscosity correction factor. For cavitating or flashing liquids, use the ISA-75.01 liquid sizing equation with F_L (liquid pressure recovery factor).

Gas Flow (Compressible) — Sub-Critical

Cv = Q / (1360 × P1 × sqrt((P1-P2) / (P1 × T)))

Where: Q = flow rate (SCFH), P1 = inlet absolute pressure (PSIA), P2 = outlet absolute pressure (PSIA), T = absolute temperature (°R = °F + 459.67). This formula applies when P2/P1 > 0.528 (sub-critical flow). The constant 1360 assumes air at standard conditions (14.7 PSIA, 60°F, SG=1.0). For other gases, multiply by sqrt(1/SG_gas).

Gas Flow — Choked (Critical)

Cv = Q / (816 × P1 / sqrt(T))

When P2/P1 ≤ 0.528, flow becomes choked (sonic at the valve vena contracta) and depends only on inlet pressure, not pressure drop. This is common in high-pressure pneumatic systems with large pressure drops. The calculator automatically detects the flow regime and applies the correct formula.

Cv to Kv Conversion

Kv = 0.865 × Cv   |   Cv = 1.156 × Kv

Kv (metric flow coefficient) = flow in m³/h of water at 5-30°C with 1 bar pressure drop. Cv (US) = flow in GPM of water at 60°F with 1 PSI drop. The conversion factor 0.865 derives from unit conversions: 1 GPM = 0.227 m³/h, 1 PSI = 0.0689 bar, sqrt(0.0689) = 0.2625, 0.227/0.2625 = 0.865.

Assumptions and Limitations

This calculator provides an equation-level screen for standard air or turbulent liquid. It does not model valve-specific expansion factor, pressure recovery, piping geometry, travel, noise, cavitation, flashing, viscosity correction or real-gas behavior. Treat the result as a minimum coefficient input to the exact manufacturer's sizing method, not a valve selection.

Valve Type Comparison for Pneumatic Systems #

Factor	Ball Valve	Solenoid Valve	Globe Valve	Butterfly Valve
Cv per size	Highest (full port)	Low (limited orifice)	Medium	High (large sizes)
Actuation	Manual / pneumatic / electric	Electric (solenoid coil)	Pneumatic / electric actuator	Pneumatic / electric / manual
Flow control	On/off only (poor throttling)	On/off (2-way, 3-way, 5-way)	Excellent throttling	Good for large sizes
Response time	Slow (actuator)	Fast (5-50ms)	Medium (0.5-5s)	Medium
Typical use	Shutoff, isolation	Cylinder direction, automation	Pressure/flow control	Large duct/mains isolation
Cost	Low-Medium	Low (small sizes)	High	Medium (large sizes)

Frequently Asked Questions #

What is valve Cv and how is it calculated?

Cv (flow coefficient) is a measure of a valve's flow capacity. One Cv allows 1 gallon per minute of water at 60°F with 1 PSI pressure drop. For liquids, this screening calculator uses Cv = Q × sqrt(G / ΔP), where Q is flow in gpm, G is specific gravity and ΔP is pressure drop in PSI. For gases, it applies separate sub-critical and choked-flow screening equations using absolute inlet pressure, standard flow, gas specific gravity and absolute temperature. Use the resulting Cv or Kv as a minimum screen, then verify the exact valve with the manufacturer's published sizing data.

What is the difference between Cv and Kv?

Cv (US) and Kv (metric) both measure valve flow capacity but use different units. Cv = flow in gpm of water at 60°F with 1 PSI drop. Kv = flow in m³/h of water at 5-30°C with 1 bar drop. Conversion: Kv = 0.865 × Cv, or Cv = 1.156 × Kv. European valve manufacturers typically specify Kv, while US manufacturers specify Cv.

How do I choose the right valve size for pneumatic cylinders?

Start with standard-air demand and a documented pressure-loss limit, calculate the Cv screen, then use the exact candidate valve's published coefficient, response, porting and operating envelope. Cylinder bore or nominal port size alone cannot select the valve.

What pressure drop should I use for valve sizing?

There is no universal percentage for all valve functions. Use the pressure-loss budget required by the actuator/process at design flow and verify it with the exact valve sizing method and downstream minimum-pressure requirement.

How does temperature affect gas valve Cv sizing?

Gas density decreases with temperature, requiring a larger Cv for the same mass flow. The gas Cv formula includes absolute temperature (°R = °F + 459.67). At higher temperatures, the same volumetric flow represents less mass, so if your requirement is mass flow (scfm), Cv must increase. If your requirement is actual volumetric flow (acfm), temperature is already accounted for. Always specify whether flow is in scfm (standard) or acfm (actual) when sizing valves.