The problem you likely need to overcome is flow limits. It is impossible for me to say where that happens in your system, but, at the simplest level, figure out how many liters per second you need to pump/control/pass in order to get the linear speed you want. Then look to see if your components are sized properly. Remember to consider all the Reynolds numbers, constrictions, weird Bernoulli effects, choked flow, and so on.

In other words, hire a pneumatics guy for a couple of hours consulting.

Your stroke time is going to be limited by the acceleration that the force can give to your mass.

Force = force ( pressure * area ) in the cap end minus the force ( induced back pressure * area ) in the rod end.

If you have enough force then you need ..as indicated by the previous poster ...sufficient flow.


Here's a link to a basic Excel flow calculator.
http://www.controlandpower.com/catalog/Software/RossSizingValvesCylinders.zip


Regards Woody

Ultimately the speed of a pneumatic cylinder is set by how fast the exhausting end air can get out.

Check this side of the circuit first for limiting of flow as TVP & Woody suggest.

If you are cutting, this is most likely a exhaust volume feed control circuit.

Reducing the supply pressure, may give higher speed.

Seems counter intuitive, but feed rate is set by exhaust volume, and the feed force by inflow (push side) pressure. So the higher the inflow pressure, the higher the pressure in the exhaust side, so there is more volume to vent per mm piston movement.

If you go too low in supply pressure the cylinder becomes elastic, or spongy, or springy. This is not good in a saw feed, so don't make huge adjustments. Say if you want 20% faster, try dropping the system pressure 10%.

You are certainly right that this is counter-intuitive! Less pressure provides faster feed???

Less back pressure, yes. Less supply pressure, I don't think so!

There is probably some form of flow restrictor, either on the supply or on the exhaust, or conceivably both. If that (or those) is (are) fully open, then he needs higher supply pressure, larger tubing, and/or higher-flow valves.

Hi DK,

To make a pneumatic cylinder behave 'rigidly' (for such as a feed situation), you pressurise both sides, and control the flow leaving the feed direction side.

This is usually the rod side.

Push is therefore regulated below supply to allow for rod area and retract force/speed/ pressure req. "push" therefore is a fixed power available and below system power.

'Feed rate' therefore is how fast that 'push side pressure' can exhaust the 'system pressure charge' from the rod side, via plumbing and flow controls.

So;

Fill the rod side to bursting and it's more mass flow to dump = longer.

Fill it 'just enough' and less mass flow to dump = quicker.

In principal

The higher the opposing pressures – the higher the mechanical rigidity

The higher the opposing pressures – the higher the mass flow out/unit of feed

So I'm saying to him "Shortest cycle is at the lowest system pressure it will reliably retract at. This = lowest PV charge to dump = fastest feed."

But you are right to the extent that upping the push side 'aught to give more speed'. It should, except it also scales up the reset energy input by the rod to piston multiplier, so increases mass flow to dump faster than rise in push power.

And I guess I should add; "how do you make it faster?" 99% of the time is because someone tried the 'intuitive' method.

It's easy to tell; there is a big delay between trigger and feed starting (as system charge excess vents down to less than piston null balance), then it feeds "slower' (due to the charge air density change ( P/T), then it resets at the speed of light.

Does that answer?

But to tell him how to alter the makers preset maximum feed – when he is probably just misadjusted, is unwise without a lot more information about what he's got and what is the actual goal/situation.

For instance the same circuit can operate a cylinder at 4 ft /sec rate or 1 foot per hour rate. To want one and get the other is either a head scratcher or quite a dangerous surprise.

Thanks - Good explanation! Much clearer than your original.

I've only controlled the exhaust rate, never pressurized the exhaust side other tha by decreasing its volume. But then I do small stuff - the largest cylinder I've used was around 20mm ID.

Dick

But no vote

It works on small stuff best if you add an accumulator to the other end. firstly as the bore to stroke in the little guys tends to be a higher ratio (compression/expansion) and the porting microscopic in terms of direct regulator driven following. Try it, you may like it.

Mostly though it suits 2" up to around 6". I've done 8" and 12" but really you're better off going air over oil unless it's super fast. ie 2 ft/second in a 4" hydraulic cylinder needs a reporting and hose exercise, a 12" pneumatic 'may' be easier.

To accelerate the saw speed , just add a vacuum tank next to the compressed air tank. Connect the vacuum tank to the exhaust of the pneumatic cilinder and also to the intake of the compressor (removing first the air filter).A closed loop between compressor and the tool ,via two buffers ,one high and other low pressured will be done. Further, you can heat the pressured tank and keep kool the vacuumed one and you have a thermodynamic cycle with higher efficiency and of course higher speed and higher power too.See THP Engine from nemes-invent.

Just remember- increased speed also means increased force on the cylinder. Check up whether the shaft or the supports will be in position to take it.

Eif it can take it, it may be much easier to put a single stage gear mechanism at its output and step up the speed. If the drive is by pulley/ chain it is much simpler to change speed.

The cushining effects at the end of stroke can not be compromised, which may take place if you try to overspeed it, along with the other aspect- the velocity of the air at the nozzles and pipes, which may exceed the designed/ safe limits and you may land up in many problems, starting with cavitation.

I propose mechanical speeding up.

Depending on your cylinder and how it is made, there are a couple mechanicial changes that also can help this.

We have in the past added a second set of ports to the cylinder, we also added a second valve of the same type to this circuit.

When we replaced the cylinder after several years of operation we had the cylinder suppy co add the second set of ports.

A cylinder stroke can easily (and inexpensively) be be made to react faster by using an quick bleed (also called quick exhaust). This is installed at the valve port. The exhausted air is therefore dumped at the cylinder rather than from the control valving. Install a restriction muffler on the exhaust port of the quick bleed to add an element of control to the exhausting. For best control, do this at both ports (if it is double acting). If it is spring return, put this setup on the energized port at the cylinder and a variable restriction check valve on the coltrol side of the port to enable contol of the energize and the de-energize.

As stated by "guest (comment #5) you wiull also need to consider how smooth your machine reacts to the quickeer response of the cylinder.

Have you considered that perhaps you don't realy want to speed this up? There may be a valid reason why this movement is what it is. You may plunge the saw into the workpiece and have worse problems than you had. You didn't specify the material you are cutting, but saws that engage the work piece too fast can result in broken shafts, dulled teeth, poor cuts or worse yet, personal injury.