Quote:
Originally Posted by ligerbots
Hey,
I was wondering if anybody knew of a relatively simple method of adjusting the speed or volume of air flow into the piston? Basically allowing the piston to shoot out real fast or to slowly shoot out.
Thanks for your help!
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This is quite easy to do.
1) Y-tie your exhaust ports together on your piston control valve and run it into the pressure input port (P) of a second valve (call it valve2).
2) On one output of valve2 (A or B), attach a flow control to meter the exhaust. Leave the other output port (B or A), and the exhaust ports open.
Now, when valve2 is set to the open position, the cylinder runs at full tilt (or at whatever rate the flow controls are set to on the cylinder itself, if included). When valve2 has the flow control switched in, your cylinder will "exhaust slowly", based on the flow control's setting.
Couple this with additional flow controls on either or both ends of the cylinder to adjust individual full speed 'default' flow rates in each direction (and considering the limited amount of total air we have anyway), and this should give you plenty of rate options. I've found it covers over 90% of typical FIRST multi-rate applications.
Note that many valves are "piloted", which means that they need a bit of air pressure on the input (P) port to accomplish switching so YMMV with them. IOW, depending on what valve you use for "exhaust plugging", if it is spring return or not, AND which way you default it, it may take a fraction of a second for the exhaust air to build up in front of it enough to switch the valve.
Therefore, with spring return valves I normally suggest the "unenergized" state to be the metered/restricted flow state, JUST to make sure it WILL build up enough air pressure to switch to the other state. Those valves will automatically return to the unenergized state (regardless of coil signal !) once the pressure drops enough. In this app, that is OK.
BTW, you COULD try to meter the source with a second valve, but if you try it and set the restricted flow rate too low, you will find under some pneumatics plumbing circumstances (and valve choices) the directional valve will fail to respond due to insufficient pilot pressure (or on spring return valves, it can go the WRONG WAY!). Switching a flow control in/out of the EXHAUST plumbing instead overcomes this problem.
Does this make sense?
- Keith