z axis balanced whit pneumatic cylinder

[eloid]

I sketched up what the ideal pneumatic assist might look like with a reservoir.

You'll want some controls in place to operate the system - ideally you would use a pressure sensor on the accumulator to determine a high location and shut down the compressor when it is reached and a low pressure state where you require more pressure and the compressor turns on. If you size your components right, then your duty cycles will be appropriate and you will increase your compressor life. If not, you could burn out your compressor faster.

You'll require a 3 way valve if you just need force during moves against gravity. It wouldn't be a bad idea to have another 2 way valve in front of the precision regulator just to not waste air. Precision regulators bleed air off if the pressure is too high to achieve the desired pressure.


It's going to be tougher to package, but if you can orient the air cylinder as shown in the diagram then you will get more bang for the buck. The rod of the cylinder takes up surface area on the piston, if you push with the same pressure on the opposite side of the rod, you get a greater force.

Has anyone build this type of constant balance pneumatic cylinder for there machine...

[Jim Dawson]

Has anyone build this type of constant balance pneumatic cylinder for there machine...

Yes I have.

The diagram above is not correct. The regulator needs to connect to the tank, and the tank needs to connect to the cylinder. It will not work with the regulator between the cylinder and the tank.

The tank needs to have at least 20x the volume of the cylinder, more is better. My cylinder is about 8 cu/in and the tank is about 1100 cu/in or about 135x the cylinder volume

[eloid]

Yes I have.

The diagram above is not correct. The regulator needs to connect to the tank, and the tank needs to connect to the cylinder. It will not work with the regulator between the cylinder and the tank.

The tank needs to have at least 20x the volume of the cylinder, more is better. My cylinder is about 8 cu/in and the tank is about 1100 cu/in or about 135x the cylinder volume

Jim like this see below drawing?

[Jim Dawson]

Yes, that would work OK. You would be better to have an accumulator between the regulator and the compressor, and connect the pressure sensor to that one rather than the cylinder accumulator. Run the compressor accumulator at a bit higher pressure than the cylinder accumulator.

My shop air is 145 PSI, but I run my counter balance cylinder at about 40 PSI. That much difference is not needed, but it is better to feed the regulator with at least 15% or so higher pressure than is required on the output.

[skrubol]

Really only need a clean/dry compressed air supply (so a normal compressor and a filter/dryer,) regulator, accumulator and a piston (connected in that order) for a general purpose pneumatic counterbalance. Just that will be more linear and accurate than a gas spring or coil spring. Most air regulators will bleed off if the pressure is more than a few psi above the set point, so if you don't have enough accumulator capacity, you will bleed air on long downward moves and consume air on long upward moves.