Air Cylinder Force?

When the associated solenoid energises, there is a time delay before the supply pressure appears at the cylinder. The delay is related to the restrictions in the pipe through which the air is expected to travel as well as the volume of the cylinder. All one is doing with a speed reducer is restricting the air flow further than might be otherwise possible without the reducer.

Force = pressure x area of piston (neglecting any losses through seals, etc.).

The area is fixed, so the force on the extension rod and the pressure in the cylinder at any moment are inter-related. So the answer is, no, the force on the rod cannot be greater than the force that the cylinder can supply given its area and the pressure of the air.

Don't forget that if you're using the rod side of the cylinder to fill with air, the effective area of the piston is reduced by the area the rod takes up on the piston.

As the rod is at ambient pressure and the rest of the piston only is being pressurized (or is that pressurised?).

John.

Quite.

The speed reducer which I use with a double-acting cylinder operates by restricting the exhaust flow from the cylinder so that full pressure is maintained. Also, while it is true that the cylinder has a known volume, the volume behind the piston is variable during extension of the rod, while the pressure is constant.

Volume is irrelevant. Maximum force is pressure-differential x bore* of cylinder. You can degrade this, but not improve it.

*bore is the same as cross-sectional area

The force cannot be more than Force = pressure x area of piston, even if you control with metering out control instead of speed reducer.

The force on the 'rod' is zero until something tries to stop it, and when it does, the force on the rod equals the difference in (absolute) air pressure acting on each side of the piston.

It would never be greater, but can be less depending on how much you restrict the flow. Also, depending on your air consumption, I've found when designing production systems that use air cylinders, to first determine the force required, then to use cylinders capable of providing the required force at around 60psi. This way it gives you adjustment ability. Once you get into the 80psi area, you need to worry about sufficient volume provided. I've had associates make crimping stations for high volume production lines & when all lines were running, the stations would create poor crimps. They did it to save money on the cost of the cylinders, instead the company spent alot more on upgrading the air compression system along with alot of scrap.

No force of the cylinder would be the same. But in a working system it may be less do to loss of momentum of the attached parts. As in a punch press

I am not sure if this is what "ozzb" was referring to, but in a fast moving mechanism, there is impact force to be considered. This is not the constant force which can be developed in a static equilibrium, and which has been described by many others already. Constant force exerted by an air cylinder is equal to the differential pressure between inlet and outlet multiplied by the net area this pressure is acting on, which would be the inside area of the cylinder (∏ x ¼ ID² ) minus the cross-sectional area of the rod.

The impact force is difficult to calculate, but relatively easy to measure with maximum reading force gauge. It is dependent on the mass of the mechanism which is moving and the speed it is moving at when it makes contact, if the cylinder does not "bottom out" or reach its end of stroke first. Then the question is how long (milliseconds) this force acts, because that determines the energy imparted. Either maximum force or total energy may have an effect on what the cylinder does, in addition to the constant force it is capable of generating.

Your speed control will affect the impact force (and therefore impact energy transfer), since it slows down the extension speed. It will also lower the constant (or static) force, since the restriction reduces the pressure differential.

I'm the author of the original question. Will all who have answered and those who might answer, please read the additional information I posted in #5. Thank you, Max

I did read your #5 before posting.

"The speed reducer which I use with a double-acting cylinder operates by restricting the exhaust flow from the cylinder so that full pressure is maintained."

If you restrict exhaust flow, only, you will maintain full INLET pressure. However, you have now created a back-pressure, that will REDUCE the net differential pressure, therefore reducing the constant force which the cylinder is able to exert.

"Also, while it is true that the cylinder has a known volume, the volume behind the piston is variable during extension of the rod, while the pressure is constant."

The volume of the cylinder matters not when it comes to the force the cylinder can exert:

F (e.g, in pounds) = P (e.g., PSI or Pounds / in.²) x A (net of the cylinder face minus piston rod, in in.²)

You see, your units cancel and you are left with Pounds. Try that with Volume! Volume, V (in.³) = A x S (stroke, in inches)

Since you have restricted your flow rate (CFM, or cubic feet per minute), if you measure it and convert CFM to CIS (cubic inches per second) you can calculate average speed, in in./second, IPS:

IPS = Flow rate (in.³/sec.) / A (in.²)

Now if you know the actual stroke (not the free cylinder stroke, although it could be the same) by measuring the extension of the cylinder rod at BOTH beginning and end positions, you can calculate the time the cylinder acts (but not the time of impact, which is nearly instantaneous unless your cylinder/mechanism includes a shock absorber!), t = S / IPS.

I am not sure what you want to do with this information, but there it is! The key here is speed. If you slow the speed by restricting the outlet flow, you will certainly reduce the impact force (or shock) whether that is desirable or not. It is usually desirable to reduce wear and tear on you mechanism and cylinder, but may NOT be desirable if you are trying to achieve a large momentary impact force.