Air over oil pneumatics works !

As those of you who follow this group will have read, I have been
struggling to engineer a smooth control system raising and lowering my
tilting induction furnace body - the two 3" cylinders happily slapping
it up and (destructively) down with little control.
John suggested air over oil, to avoid the conpressability of the air
on the down stoke and this is the method I've adopted which is highly
satisfactory - thanks John. I have formed an oil reservoir (slice cut
from CO2 cyclinder) with the 'up' air entering at the top, forcing oil
out of the bottom, this goes to a 'tee' with two one way valves
pointing in opposite directions. Each has a flow control valve in
series and the flows rejoin at another 'Tee' and go to the bottom half
of the two paired double acting cyclinders. This way I can control
both the raise and lower flows and hence speed of furnace movement.
During this exercise I've started using Loctite 542 hydraulic thread
sealant and I must say I am very impressed. The new 'plumbing' has 32
threaded joints each needing rotational alignment and not a single
leak (tested at 150 psi with soap solution before putting to use).
Next thing I need to tackle is a quick disconnect system for the
furnace water coolant / power hoses so I can swap between the two
furnace bodies easily. These carry water /
antifreeze at 45 psi / 25
litres minute and drive power at peaks of 300 amps /
1000v at 3Khz
when at resonance. The hoses terminate in 3/4" BSP so I'm thinking of
using brass 'snap-tite' 72 hydraulic couplers with a welding 'dinse'
cable connector across them to carry the current - any comments?????
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Reply to
Andrew Mawson
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Oh yea of little faith
. -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:-
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Reply to
John Stevenson
WRT to quick disconnect fittings
Don't know if this is relevent or not, but don't expect these to operate without either some very minor fluid leakage, or, I guess, some air ingress. My little experience of these is on hydraulic systems on diggers and it's not possible to disconnect them completely 'dry'. Presumably power is off when you're doing this. IIRC , you also wrote about the need to get all the air out of the system: these may allow a small amount in. Finally, they are not easy to connect or disconnect if there is pressure in the system.
Reply to
John Montrose
Thanks for that input - very useful. Yes the power will be off and they will only be changed over once in a blue moon, but if just using an unscrewing connector, a total drain down would occur ! The pressure is very low in hydraulic terms (only 45 psi) so hopefully the weeping will be proportionally less. I have a pair of them on the hydraulic power pack for my EDM machine but only in the very small size (1/4" I think) and so far they have been quite well behaved !
Reply to
Andrew Mawson
Andrew, I am picking this one up a bit late, but did you try exhaust flow control on the cylinders before going to the hydraulic arrangement?
Reply to
Charles Lamont
Yes that was my first approach, but the volume of air in the lower half of the double acting cylinders just got squashed to even higher pressure as the furnace body descended with a crash !
Reply to
Andrew Mawson

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