Pneumatic Circuit Doubt: Understanding Force and Pressure in Pneumatic Systems

[ukesh]

Hello,
I"m designing an pneumatic circuit. I have an doubt regarding the force exerted by the actuator. The maximum pressure which I will be using is 8 bar (approximately 116 PSI). The compressed air will be stored an air tank. The tank will be connected to the regulator, then the valve and then finally the actuator (pneumatic cylinder, single acing,spring return). The circuit is an open loop system. Initially the pressure inside the cylinder will be at 8bar. when the valve is opened, the air from the tank flows through the circuit and actuates the cylinder. when the valve is closed the air inside the cylinder comes out as exhaust. Here comes my doubt, since some amount of air is released from the tank for one actuation (stroke), will pressure inside the cylinder reduce for the next actuation? If the pressure reduces, automatically the force provided by the cylinder reduces. Correct me if I'm wrong?

 

[FredGarvin]

The job of the regulator is to maintain a constant pressure downstream (assuming it is not a back pressure regulator). The only time you should see a reduction in pressure is if the mass of air in the tank and the system is inadequate to produce that required pressure.

If your tank is sized properly or your compressed air source that charges the tank is timed properly to maintain the pressure in the tank, you should have no issues.

 

[ukesh]

If your tank is sized properly or your compressed air source that charges the tank is timed properly to maintain the pressure in the tank, you should have no issues.

What do u mean by sizing of the tank? And should the compressor, which charges the tank, be continuously running?

The only time you should see a reduction in pressure is if the mass of air in the tank and the system is inadequate to produce that required pressure.

So, if the tank is fully charged and actuation is made once, Since this is an open loop system, the mass of air inside the cylinder reduces rite?

 

[FredGarvin]

What do u mean by sizing of the tank? And should the compressor, which charges the tank, be continuously running?

I mean that if you are running off of a compressed air tank (which you said you were doing) the tank needs to store an amount of air that can accommodate the size/volume of your system based on the flowrates and pressures you hope to operate at.

So, if the tank is fully charged and actuation is made once, Since this is an open loop system, the mass of air inside the cylinder reduces rite?

Yes. You will need to replace that mass of air required by your system for that one actuation. Your tank size will dictate how many cycles you can get before the amount in the tank is insufficient to maintain the system pressure.

 

[ukesh]

Sir, I'm new to designing pneumatic circuits. Can you tell me how to calculate the number of cycles? And during the cycle, will the force exerted by the piston be same, I mean constant?

 

[nucleus]

It is hard to design a pneumatic system “site unseen.” Either you need to employ someone fanilar with designing pneumatic systems (recommended), or get into the books and spend time familarizing yourself with a pneumatic systems.

The first book covers the basics with some design information. The second book listed (free) covers more design starting page 410, chapter 10. The third site under pneumatics gives the basics.

As for running full time – no it should start and stop no more than 20 times an hour. http://www.parker.com/training/descript.asp?GroupID=1&SectionID=1&ProductID=22
http://www.scribd.com/doc/10512227/Fluid-Power-Circuits-and-Controls-Fundamentals-and-Applications
http://www.hydraulicspneumatics.com/200/FPE/IndexPage.aspx