Air cylinder help

[BSchend]

I guess my last question would be what cylinder bore size should I get for the stops? I'm guessing I only need a 1.5" or 2" stroke, but don't want to get too small a bore (or waste money buying too big a size either).

Thanks again for all the feedback.

 

[kicknargel]

If you know how much force you need to exert (in the parking brake case, slightly less than the weight of the unit) you multiply the area of the cylinder bore in inches by the psi of the air pressure. For an example with easy math: a 2" bore has an area of (pi x r-squared) 3.14". At 100 psi, 314 lbs. (For a retracting cylinder you have to subtract the area of the piston, but that doesn't come into effect here.)

If the piston is driving a lever mechanism, you'll need to add a multiplier of the length of piston throw verses brake throw.

 

[beachbum]

I built about 30 of the pvc pipe/diaphram units 16 years ago and they have been in fairly constant use ever since with minimal maintenance. We generally use portable air carry tanks--about 5 gallon--from the auto parts store or Grainger filled to 120psi with a secondary regulator set for the load--rarely over 40 psi. This usually gets us through a full performance, although on a heavy movement show we have refilled at intermission. If you have the time to build them they are well worth it, as they can lift really heavy units. We have occasionally replaced the caster with a wood block with a rubber pad to make effective brakes/locks on rolling units.