pneumatics for featherweight

[Liftoff]

Chris, what I would do is to drill some holes at the top end cap, say six 6mm holes - that will eliminate back pressure when you fire the ram ( the air on the top side of the piston is creating a restriction as its being forced out of the top port)
QEV on the exhaust is not such an issue as long as you have strong enough bungees to retract the ram. Have a look at the ram on my build, it has two ports at the bottom, one connected to the QEV/buffer (inlet) and a small one as exhaust.

[Liftoff]

Something like this, top end drilled (1st photo)
Bottem end two ports (2nd photo)
Mine is a custom ram, but you can modify yours in similar way.

20141005_112224.jpg20141005_112443.jpg

[Max]

I'm surprised that circlip can take the forces exerted on it- I would have expected it to pop out

[Liftoff]

Nah it won't....as long as its not operated at fp! Those are the same circlips from the original manufacturer ram. It's not the circlip which could fail but the ram itself if there's not enough recess for the clip to rest on....

parker-p1q-cylinder-cut-off-2012(1).jpg

[Eventorizon]

Chris, what I would do is to drill some holes at the top end cap, say six 6mm holes - that will eliminate back pressure when you fire the ram ( the air on the top side of the piston is creating a restriction as its being forced out of the top port)

I had a chat about back pressure at the champs. It seems it is actually better to leave it as is. The air in that side of the cylinder will easily compress and will also prevent the piston slamming into the end of the ram, improving reliability. The actual improvement in terms of force and speed is negligible. Got no data to back this up but I agree with the reliability option and think that is better than a minute increase in speed as you have more than enough power anyway.

[Liftoff]

You got a point there, to counter this some rams incorporate cushions in the endcap...on mine I placed a rubber disc on the piston so the impact will be dampened

http://m.machinedesign.com/pneumatic...atic-cylinders

[ChrisKazoo]

I have drilled 4mm holes in the top of the ram since I made that video. Where can I get my hands on these rubber cushions Chris?

[Liftoff]

I doubt you'll find any off the shelf for your ram, there are kits you can buy, but only for branded parts eg festo, parker, smc etc. On mine I used a piece of rubber, punched it into a disk and glued it to the piston. You could do the same, take the circlip off and remove the top cap, put a piece of rubber say 5mm thick and you're good to go.

[Rahulvyas]

Is my 8mm pipe fine? Or do I need bigger?
I bought a 50mmx50mm stroke and bore cylinder which didnt have smooth action. Can it be fixed?
When I supply co2 into it, the piston doesnt have a sudden action like all the videos I have watched of you guys.

Also, where do I connect the QEV in double acting cylinder? Will that help me in anyway?

[Liftoff]

Rahu your 8mm pipe should be ok
What's the port size of the cylinder you bought, and at what pressure are you operating?

[Rahulvyas]

I am operating at about 100-110psi
I am not using buffer tank.
Port size I am not sure, its about 6mm I guess

[Liftoff]

Then you got your answer... not using a buffer means you're relying on the regulator for flow, the regulator orifice is very small and flow is low, you got yourself a lifter not a flipper.
You need a buffer tank to achieve anything close to what you see on videos you've seen.
A better idea would be to enlarge the port orifice on the cylinder and install a QEV on the inlet...all this has been discussed at length on various threads...and I believe on this thread as well...on the first pages there's a schematic

[Rahulvyas]

Okay I will see that Thanks,
The schematic was for single acting, so I was a bit confused with the connection of QEV

[leorcc]

Your issue is indeed flow. You need enough of a reserve of pressurized gas to be able to get the ram filled quickly. The best way to achieve this is with a buffertank between the regulator and the valve. Rule of thumb, the volume of the buffertank should be at least 3 times the volume of the ram. But even if it is smaller, it all helps.

[Rahulvyas]

I am planning to use a co2 catridge 30g-50g ( quite small) , should do the work as we are not storing 50 bar pressure into it directly, its just a small co2 collector, right?