Air Consumption Calculation for ON/OFF Valves

Air Consumption Calculation for ON/OFF Valves

Generally we specify air consumption in SCFM ( standard cubic feet per minute) for on/off valve as an intermediate (Non-continuous) service.

Air Consumption calculation for ON/OFF valves are given in liters by many European actuator vendors and Process Engineer demands consumption in SCFM. (I faced this in one project here)

Now let us learn how we can calculate the consumption in SCFM from Liters .

Actuator Manufactures select actuator based on Valve details and Torque Valves and selected actuator Displacement volume is in Liters (capacity)

1) ESDV -100 with 18″ full bore 900 RTJ size , Selected actuator is having 160.15 Liter (Displacement volume)

2) Convert the actuator displacement volume, Liter in SCF (standard cubic feet)

1L = 0.035315ft³

160.15 Liter – 5.65 ft³

3) Now ESDV is fail close valve and air consumption is more during opening of the valve ( actuator volume gets filled) and valve closing time for ESDV-100 is say 54 Sec (3 Sec per inch)

Actuator volume 5.65 cubic feet has to be filled in 54 sec (Air consumption)

Per second air consumption is 5.65 / 54 = 0.1046 Cubic Feet per second

Now convert this in Minutes

0.1046 CFS = 6.276 Cubic Feet Minute.

It shall be noted that air consumption always depends on air supply pressure and need to be specified as SCFM @ air supply pressure.

Credits : VINAYAK DUMBRE

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9 thoughts on “Air Consumption Calculation for ON/OFF Valves”

1. The last sentence need to be checked for accuracy. SCFM references volume at standard conditions of temperature and atmospheric pressure so ‘SCFM @ air supply pressure’ is contradictory.

2. was gonna write this and then I saw your comment

3. What is normal pnematic On/off valve sizes say100 nb,150nb,200nb

4. Anyone please suggest how to calculate compressor capacity for pneumatic valves.

5. This is incorrect calculation. The air will be consumed during the opening process, not closing which is venting to ATM. Also the volume is not converted into standard condition.

6. This is not correct. If the air consumption is sized like this for every valve in the plant, you will need a giant air compressor. The calculation for air consumption would be:

Actuator Vol / cycle x no of expected cycles per hr or day
In this case the valve needs 5.65 ft3 say at 80 psig (convert this into std conditions) = 33 SCF and the valve opens once per hr this valve consumes require 33 SCF/hr on average. For peak Conditions add a factor to size the total consumption. Ensure the accessories can handle the peak flow (6.276 SCFM) for the max specified Pressure Drop.

7. This calculation in incorrect. Because we cant consider displacement volume , we have to understand that compressed air can be stored more or less within that displacement volume as per air pressure. Lets consider an example. If you have 1 bottle having 1 L volume then @ 4bar this bottle can store say 3L air but @ 5bar same bottle can store about 4L air. So, to calculate air consumption you must consider an Air pressure. Please find attached calculation for more understanding.

air consumption for one cycle in L/stroke = volume of actuator for open stroke in L x (( air pressure in bar +atmospheric air pressure in bar )/atmospheric air pressure in bar)

Kindly note that in single acting actuator, closing or backward motion needs no air supply this stroke is achieved by spring force Hence for spring return actuator, no need to consider closing stroke air consumption. For double acting actuator you must have to consider.

To convert this in to Litres per hour you must know operating time of actuator. Assume that opening time is 5 sec & closing time is also 5 sec then total operating time for spring return/single acting actuator will be 10 sec for 1 complete cycle.

for Double acting actuator,
total air consumption for one cycle = air consumption for opening stroke + air consumption for closing stroke

air consumption in LPH=(air consumption for one cycle/total operating time)x3600
air consumption in LPM=(air consumption for one cycle/total operating time)x60

Now you can convert it to any unit easily through any calculator on google.

8. Dear Pruthviraj,

But finally not conclude air compressor sizing selection or consumption calculation in statement.

• Dear Arun,

for double acting actuator,
air consumption for opening stroke= volume of actuator for open stroke in L x (( air pressure in bar +atmospheric air pressure in bar )/atmospheric air pressure in bar)

air consumption for closing stroke= volume of actuator for close stroke in L x (( air pressure in bar +atmospheric air pressure in bar )/atmospheric air pressure in bar)

Air consumption for one cycle in L/stroke =air consumption for opening stroke + air consumption for opening stroke

air consumption in LPH=(air consumption for one cycle/total operating time)x3600
air consumption in LPM=(air consumption for one cycle/total operating time)x60

for higher than 55CFM or 76410 LPH
Screw type Compressor sizing= summation of all actuator & pneu. eqp. air consumption x factor of safety 1.4

for less than 55CFM or 76410 LPH
for piston type Compressor sizing= summation of all actuator & pneu. eqp. air consumption x factor of safety 1.6

You may not found exact required compressor in market hence consider higher available compressor model.