Solenoid control

[StanleySmith]

hey guys, I'm new in the field and I'm running into this basic problem that's giving a headache.
I got a pneumatic slide that's supposed to go up and down. It's controlled by a double sol, 2 position (I'm pretty sure that's the type of valve on the machine now). The valve power is tied to a safety relay's output. For safety issue, when the gate's opened, the output of the relay drop and so is power to the valve. This does not stop the slide from moving instantaneously; but the slide stops when it's either fully up or down. I think the problem's it's a 2 position valve. Am I on right??? I think I should use a double, 3 position.

Thanks,
Stan

 

[ScottyUK]

How far away from the solenoid valve is the actuator? Is there enough stored energy in the line beyond the valve to account for the continued motion? The valve can only control air flow through it - it can't affect what has already gone through.

Are you switching inlet or exhaust air?

Have you leak-tested the valve at working pressure?


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Sometimes I only open my mouth to swap feet...

 

[fangas]

3-position, spring return to center, closed center valve. It will stop your cylinder about as fast as anything, allowing for residual air pressure in the system.

Ed

 

[controlsdude]

Sounds like a double detented valve and when you have it in estop the mechanism should not move. I believe that the way it is now is correct for safety. Since the valve is stuck (by the mechanism of the detented) under estop this is ok for safety reasons.

The only issue I would look at, is air still charging the pneumatics to keep it in position? Or is the cylinders still charged by the air that is trapped by the detented position of the valve?

I know some facilities want you to also lock out air when entering a gated area. If you do this will the slide stay in position?

I guess you have to ask this question. Under estop, the equipment should not move. But entering an area to recover a problem, do you want these cylinders charged with air? I would think you would not want these cylinders still charging with air when you enter the area. Is there a locking mechanism to keep the slide in place when air is not present?

 

[pooslinger]

Check the integrety of the seals on the slide. If there is a leak, even a tiny one, the mechinism will wander. In theroy if there is equal pressure on each side of the neumatic device, there is no movement possible. If there is a leak in one seal, it will allow air to pass thru on way and not the other. Try to explain that to a mechanic. It sounds weird but it is what I have experenced alot.

 

[HEC]

If it is for a safety gate, use a pneumatic cylinder with a brake on the cylinder rod. This is the only reliable method of locking the cylinder at mid stroke.

Mark Hutton