pneumatics for featherweight

[Eventorizon]

It's this one from eBay, 50mm bore 45 mm stroke. Modified like Chris suggests by drilling port holes bigger and had to drill and tap an exhaust port at the bottom to vent it after it's fired.
http://m.ebay.co.uk/itm?itemId=190837115480

Why not use a QEV? (Quick Exhaust Valve)

[ChrisKazoo]

Why not use a QEV? (Quick Exhaust Valve)

I have a QEV on the inlet and have pondered whether having a QEV on the exhaust would be worthwhile but I would still have to drill and tap a port for it as it's a double acting ram so normally would be vented by putting gas in the top port and exhausting through the bottom port back through the solenoid valve. Without a new port drilled the ram fires and then the gas has nowhere to go to vent.

[Rahulvyas]

is QEV necessary? I am using mine without it, no trouble till now

[Revsmin]

Not necessary no, but very helpful to increase the flowrate and thus the power

[Rahulvyas]

okay thanks

[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.