Need pneumatic control expert advice.

northcreek2624 · Aug 1, 2005

Hi!I'm new to the world of pneumatics and could use some advice.
I'm using two way cylinders to articulate water spray heads.
I would like to eliminate the drift and have a more precise positioning.
I have added needle valves at both ends of the cylinder and by adjusting them I have improved the operation but,I'm still not happy.I have thought about regulating the pressure down from the present 90psi but,I don't want to for fear of losing operating force.
Is there something that I'm missing? Is there some sort of quick exhauster that I should install at the cylinders?
Any advise would sure help.....thanks,Mike.

ronjhall · Aug 1, 2005

Flow control valves are used to control pnuematic cylinders. They should have free flow in one direction and controlled flow in the other. For best control the exhausted air should be controlled. Full pressure should be on the inlet side. This will give you the best control of cylinder movement. This is opposite of a hydraulic system. They normally have their inlet flow controlled and the outlet is free flow.
Here is a flow control that should work. It's on EBay. Click Here

northcreek2624 · Aug 1, 2005

Thanks Ron,your advise has thawed my brain.I think I can accomplish the exhaust control at the directional control valve which uses a common exhaust port for both directions and I shouldn't have to buy anything extra.I'm wondering though if it still might drift due to the compressability of the air on the outlet(low press.)side??......thanks a bunch,Mike.

ronjhall · Aug 1, 2005

My statement assumes that your valve is always energized in one direction or the other. If it goes to a mid position and lets air out of both sides of cylinder. It will be very hard to control the speed. Another item that can make it hard to control speed, is cylinder bore size. If cylinder has too small of a bore it will be very hard to regulate speed. A bore that is too large will make for slow operation. But will be easier to control.
Putting flow control as close as possible to cylinder will minimize compression. Long airlines will allow for more compression.

northcreek2624 · Aug 1, 2005

Ron,I have fabricated the actuators using dimensions from these manufactured units.

web page

The cylinders are expected to stop in any position and hold by captive air.If I cannot get them to be more precise with these changes I may convert the system to low pressure fluid...thanks,Mike.

ronjhall · Aug 1, 2005

OK now I understand what you are doing. To get the system to work well with air you need a valve that keeps air on both sides of cylinder. Then put a regulator on the line that feeds air to the blind side of cylinder. Air needs to be reduced on that side of cylinder to allow for rod on other side of cylinder.

northcreek2624 · Aug 1, 2005

Thanks Ron,I'll try the first change on the exhaust,if that doesn't work I will do as you suggest....Mike.

northcreek2624 · Aug 4, 2005

Ron,Just wanted to follow up since you took the time to help me out.
When you said to control on the exhaust side for pneumatics you got me thinking.
I had been trying to adjust with needle valves at the cylinders with poor results.Then I remembered that my selector valve has an exhaust port that is common in both extend and retract modes,I moved my needle valve there and I now have the kind of control that I had been trying to achieve.Had all the parts,just had to relocate a few.....thanks-a-bunch,Mike.

erich · Aug 5, 2005

Man, sharing knowledge is what makes this site great!

Eric

Charolais · Aug 5, 2005

Sounds like you got the control you were looking for. But I'll throw in another way to do the same.

I had to make a positioning system for a sheet machine years ago. I used a 5 way closed center valve and piloted fittings on the cylinder. Been close to 20 years ago now but I think they were called and's and or's back then. I used 2 sets of reed switches for the positions I wanted the stroke to stop/hold. It worked real well. I could leave the machine in one or the other positions over night and it would hold a hanging load.

You're working in a fun world of positioning. Sounds like you did a good job there.