Pneumatic power unit, updated design

[Evan]

I have added to the design of my power unit I plan to build to operate my slotter/hobber.

http://vts.bc.ca/pics/ppu1.gif

It now includes a complete air cycle shuttle valve system. This allows the unit to operate either in full automatic stroke mode or in a single cycle mode. If the stroke length is set for full stroke the unit runs continuously in and out at a rate controlled by the upper needle valve.

If the stroke length is reduced to 1 1/2" or less (full stroke is 1 3/4") then the unit runs in a single cycle mode doing one out and back stroke and stopping. The green start plunger initiates each stroke cycle. Pressing the reset plunger immediately sets the unit to return stroke mode at any point in the cycle and pressing the air cuttoff and the reset together stops the action.

This drawing is partly a schematic as the actual orientation of the parts need not be as shown. The speed control needle valve would be placed to the front instead of as shown but that doesn't change the design. The entire shuttle valve assembly and air inlet would be rotated 90 degrees to place the air inlet to the rear and allow for mounting.

Although the design may appear complex it only has two main moving parts during operation, the ram and the shuttle valve (check valves excepted). The black dots represent O-ring seals for the ports. I may simplify the design a bit more by machining the entire cylinder assembly from solid.

[Rustybolt]

Evan. This is not meant as a criticism,but that looks exactly like a Schrader-Bellows unit. The only thing it's missing is the solinoids. My late father and I designed one much like yours in the late 70s only using alum. extrusions wherever possible.
you might want to use U cup seals on the piston, just a suggestion.

[Evan]

I'm sure there isn't much new in the field of pneumatic/hydraulic design when it comes to purely mechanical systems. Although I did not refer to any other design I would be suprised if it didn't resemble something that already exists. I have worked on quite a few pneumatic systems as many of the machines I used to work on had air actuation systems in the large units.

As for air leakage, that really isn't a concern. All of the areas where leakage may occur, including the shuttle valve, are designed so leakage doesn't really matter in small amounts. A little blowby on the piston will simply be exhausted as the exhaust port will be open on the other side. The same applies for any oil leakage past the piston on the damper as it only needs to be a close fit, no seal should be required.