Pneumatic problem
Pneumatic problem
(OP)
Hi,
I have a problem with one of my project:
I'm building a movable cover for my machine, see image below.
I want to move this with a pnematic cylinder. The cover is normally opened and the cylinder need to push it colsed.
The problem is that when I give pressure, the cover close way too fast, I think almost 1 m/s. The cover is 60 Kg so this is very dangerous.
I have tried a flow limiting valve on the upper chamber but I don't have any improvement (the air in this chamber get compressed without any difference in the speed of the cylinder).
I have no experience using pneumatic system so any halp is greatly appreciated.
Thank you

I have a problem with one of my project:
I'm building a movable cover for my machine, see image below.
I want to move this with a pnematic cylinder. The cover is normally opened and the cylinder need to push it colsed.
The problem is that when I give pressure, the cover close way too fast, I think almost 1 m/s. The cover is 60 Kg so this is very dangerous.
I have tried a flow limiting valve on the upper chamber but I don't have any improvement (the air in this chamber get compressed without any difference in the speed of the cylinder).
I have no experience using pneumatic system so any halp is greatly appreciated.
Thank you






RE: Pneumatic problem
RE: Pneumatic problem
The leverage from the cover acting on the cylinder will drag the cylinder out. Even if you add some flow controls to the cylinder, I think that the mass of the door combined with how close the cylinder is to the fulcrum, the door will drag the cylinder out.
Move the cylinder or use a hydraulic system...
Have you done the equations to calculate the forces in this system?
RE: Pneumatic problem
With the weight on the rear the center of mass works agaist the cylinder (see image below), the lid is normally open.
No, I had this cylinder in stock so I only made sure its force was enough to lift the cover (Ø50 bore).
My problem isn't the cylinder pushing force, but its speed.
I thought about that(...we produce hydraulic cylinders) but my boss want to use air of the centralized line.
Yes, they are good
Maybe I need to add some more wheigt on the rear
RE: Pneumatic problem
RE: Pneumatic problem
Hydraulic fluid is much less compressible than air so position control is far more "rigid". 100 psig air is much more "rigid" than 0 psig air.
RE: Pneumatic problem
RE: Pneumatic problem
If you close the flow control on the rod end of the cylinder and pull the cover down, how far does the cover move before the pressure in the rod end is high enough to hold the cover?
My bet is that the cover will go all the way down.
RE: Pneumatic problem
I know this is not a very precise way but I have use it once and worked for me.
Best regards
RE: Pneumatic problem
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Pneumatic problem
I tried adding some pressure on the rod side and applying the flow regulation valve on the inlet. Now I have a good speed for 2/3 of the stroke but it greatly reduces at the end (when the air in the rod side is compressed).
I now have to figure a way to reduce the lenght of this reduction in speed.
RE: Pneumatic problem
Ted
RE: Pneumatic problem
RE: Pneumatic problem
Parker have a unit called a hydro-check. Web search hydro check for more...
RE: Pneumatic problem
To start there should be full 100 psi air in the rod end and no air pressure on the other. When you switch the valve to close your gate, full unrestricted flow of air enters the bottom of the cylinder and comes to equilibrium with the air pressure on the rod end. The piston should only move after air is exhausted slowly from the rod end through the speed control valve. The air pressure in the rod end will stay at about 100 psi until the piston meets a mechanical stop, at which point the pressure in the rod end will drop to zero. The pressure in the bottom of the cylinder will stay at 100 psi as long as the gate is closed.
When you switch to open the gate, the rod end will quickly pressurize with an unrestricted flow of 100 psi air, but the piston will not move until air is slowly exhausted through the flow control valve on the bottom of the cylinder. The air pressure on both sides of the cylinder will stay essentially the same and constant on both sides of the piston until it hits a mechanical stop, at which time the air pressure on the bottom of the cylinder will drop to zero and the air pressure on the rod end will stay at 100 psi as long as the gate is open.
Now in reality there will be differences in pressure across the piston due to the load on the piston rod but this will be small if the load is not near the capacity of the cylinder. Your gate has counter-balance weights to keep this load small, so you should have no problem with this.
RE: Pneumatic problem
You may benefit from a pressure regulator on the supply air to the bottom of the cylinder to lower the supply pressure. You have a relative large rod diameter compared to piston diameter so the piston areas are different. This causes a pressure amplification effect where putting 100 psi of pressure below the piston will compress the rod end air to a greater pressure, say 120 psi. This will cause an initial jump in the piston position when the valve switches to "close the gate" (due to the rod end pressure jumping from 100 psi to 120 psi, even though your supply pressure is only 100 psi).
If you have long runs of tubing the flow resistance will cause problems, which a "quick exhaust valve" will address.
Consider what happens when you first apply air pressure to your machine. You do not want anything moving and creating a safety hazard. With no air pressure the machine should be in a fail-safe position. Accomplishing this could be the most complicated part of designing the controls.
RE: Pneumatic problem