Pneumatic cylinder valve CV sizing

[MGZmechanical]

Hi, I'm dimensioning some pneumatic actuators and I have a doubt choosing the valves. I think the correct option is number 1 in the file attached. The I saw the reccomendations from Parker
Link

Which one is correct? the difference in Kv (and money) can be quite big.

regards,

 

[gerhardl]

Hi,

I read from your notes your cylinder to have 160mm diameter and be 100mm long, with about 17L volume??? This is a fairly 'normal' size to operate for a 'normal' pneumatic solenoid valve. Anyway the logic is the same, disregarding size of sylinder:

1. Mounting of series or limited (batch- some few) cylinders?
2. Flange available for solenoid mounting on sylinder? Rack mounting/single mounting?
3. With answers from 1 and 2 check commercial available types for your solution based on available current types and control solutions.
4. One solenoid or two solenoids for the 5/2 valves (see you have drawn 2)
5. If 17L volume nominal size would normally be 1/8" inch bore, or 1/4" inch bore, check commercial available types/brands.

Answer to your question:

6. The nominal bore of a solenoid valve (say 1/8") is not directly related to inner boring/restrictions and capacity, and can vary vastly from type to type, and brand to brand. All available commercial solutions will likely have a capacity far above both calculations. The most common trap of dimensioning operting valves for cylinders is to select valves with too low capacity. Necessary loosening force for thr cylinder can vary over time with wear, impurities or longer stops. Air silencers on return ports will also in some degree give resistance. In addition valves with larger openings is less given to give problems with impurities.

Advice:

7. Select oversized valves, regulate and calibrate speed by throtteling valves. Note: best on air return ports. Warning: some valves can 'stall' (stop in mid movement) if there is not sufficient pressure difference between in port and opposite side of cylinder. Alternative: throttling of inline.

 

[MGZmechanical]

Hi, the cylinder is to operate a valve. One solenoid or two depending on clients spec. I know in this particular case the required flow is not big but I'm trying to define a way to standarize the sizing of the pneumatic valve. Iin this case they wanted 5 s but sometimes they want 1 s or bigger actuators with huge volume. In this cases choose a pneumatic valve of 3/4" or 1" can be a lot of money. That's why I don't know if I must use the differential pressure between the inlet pressure and the cylinder pressure OR a constant differential of 0,7 bar (much bigger valve).

Regards,

 

[gerhardl]

OK. All noted above is still valid, but: for valve operation the valve releasing torque can vary in range 1:5, or even more, depending on field conditions and fluid. This again gives that you can need a 'boost' (large opening giving fast pressure increase inside cylinder) to move the cylinder/valve at all.

The only sure way to calibrate timing for cylinder and valve together is to start 'large enough' and throttle down mounted togeter and control/recalibrate under practical operating conditions.

Simplest way is to use valves where the internal smallest bore/throughlet in the valve is about the same size as the inlet boring of the cylinder.

Use available advice from solenoid valve producers based on cylinder size.