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> Pneumatic Components

In Depth

Valve Sizing

Valves are typically sized based on how much air they can move. The flow coefficient or 'C_v of the valve' is critical to determining if a cylinder or other actuator can move with sufficient speed for the application. A valve with a higher C_v can move more air. To account for various losses in all pneumatic systems, remember to oversize by at least 25%. Here is an interactive timing chart showing actual C_v values for Nitra^® valves and bore sizes for Nitra^® cylinders.

How to Calculate C_v

The formula below can be used to calculate the MINIMUM C_v or 'coefficient of velocity' required for operating a particular size air cylinder in a specific time period. There are many other factors that affect cylinder speed, such as tubing size and length; fitting size and shape (ninety-degree bends are especially disruptive to air flow), etc. This formula should be used as a guideline ONLY to determine a MINIMUM C_v for a given system.

Interactive C_V Calculator:

Select
Bore
Size:

b

Enter
Stroke
Distance(in)

s

Enter
Time(sec)

t

Select Inlet
Pressure

P_i

Select % Expected
Pressure Drop
Across Valve:
2% ΔP
5% ΔP
10% ΔP

Select Air
Temperature (F°):

T

Select Atmospheric Pressure (PSI):

P_a

C_V =			= C_v
	b² s (P_i + P_a)	T + 460

	824.33 t P_a	ΔP(P_i - ΔP + P_a)

Notes:

There are many formulas for determining C_v. Many are simplified, they may ignore ambient air pressure and/or temp, and may use lookup tables for various values. We are providing a somewhat complex, yet accurate formula here - and offering to solve it for you, enjoy!
The pressure drop in this eqauation is the DROP ACROSS THE VALVE ONLY. In practice, you can not choose ΔP (pressure drop) - the pressure drop of a given system is dependent on many things. This calculator offers you the ability to see what the effect of various pressure drops might be for a hypothetical system.
NOTE: This calculator does not take into account tubing diameter or length, number or size of fittings and orifices, size or weight of the load, etc. You may need to factor in these (and other) values to determine cylinder speed. There are also practical limits to how fast a cylinder can physically operate.

Here is an interactive timing chart showing actual C_V values for Nitra^® valves and bore sizes for Nitra^® cylinders.