Air compressor pressure

[Marc Nicoloudis]

Good Day Everyone!


Was hoping for some advice regarding my air compressor.


I am working on a cnc router that requires roughly 100psi to operate a pnuematic valve that opens and closes a chuck. All is well holding the 100 psi for the first operation, however when it goes to perform the next operation, the pressure has dropped to 50 psi, and does not have time to recover fast enough to perform the second operation, which happens roughly 2 seconds later.


Can anyone pont me in the right direction as to how to achieve a more linear psi range during tool changes?


Would plumbing in a large aux tank help out or is this strictly a HP issue? THanks,
Marc

[Mike Heidrick]

Describe your compressor for us. Tank size, cfm, type of pump, etc.

Also are you only doing two cylcles?

Adding larger tank will only give you more air before the compressor starts and then it will take longer to compress more air to the regulated pressure.

[Rich Engelhardt]

The pneumatic valve (or the CNC router it's attached to if it's a whole unit) should have specific air requirements as far a how much air is required (listed in SCFM or CFM).

And +1 to what Mike posted.

[daryl moses]

Sounds like you need a larger compressor and tank...........

[Al Launier]

What are the specifics of your compressor and have you checked for leaks in the compressor?

[Anthony Whitesell]

Where are you measuring the air pressure? At the tool or at the tank? Definitely need details on the compressor and on the plumbing from the tank to the machine.

What is the time between these two operations?

Depending on the responses, one solution may be a small tank near the CNC machine, or a large 1 to 1 1/2" diameter supply pipe between the source and load, and possibly increasing the on/off settings of the compressor to recharge sooner. Send us some info and we can help some more.

[Jerome Stanek]

You could put a reserve storage tank just before the CNC that would hold enough air to allow your compressor to catch up

[Marc Nicoloudis]

6.3 gal tank at 40psi rated at 3.80cfm, at 90pst rated at 2.35 cfm

[Marc Nicoloudis]

The pneumatic actuator(Tool CHanger) is calling for 80-100 psi.
I had originally purchased this small compressor because it was going to be dedicated to the machine, and ran super quiet. It operates the tool changer fine the first time, but I did not anticipate the second cycle.

[Marc Nicoloudis]

Pressure is being monitored about 1 foot away from the tool, about as close as it can be, and I can watch it build and hold to 110, then it drops off the tool, and the pressure drops to 50, taking about 3-4 seconds to rise back up to 110. In the meantime, the router is programmed to almost immediately go pick up another tool, but the compressor does not have quite enough time in between.

Just 2 cycles, as the compressor has plenty of time to catch up while the router is cutting, before needing to pick up a different tool.

A sure fire way to fix this problem is with a nice($$) screw compressor, but was hoping this could be achieved another way, seeing as how it needs the boost of pressure for such a small amount of time. If an aux tank were an option, how could I calculate the volume of air needed to withstand a 60 psi drop like that?

Also, just for the heck of it, I hooked it up to my 6hp 30 gallon compressor, and it did the same thing.

[Marc Nicoloudis]

Thank you for all of the replies, much appreciated!

[Anthony Whitesell]

Where is the pressure gauge you are reading?

At what pressure does the compressor turn off at? At what pressure does it turn on?

I assume that since you mentioned "dedicated to the machine". The compressor is right under the table so the hose is short. Is that correct?

Is there a rating for the air consumption on the tool changer (SCFM)?

[Garth Almgren]

Is there a way for you to add more delay into the CNC programming between the tool changes? Just have the program pause for the 3-4 seconds it takes to recover the air pressure?

[Sean Tracey]

30 gallons is quite a bit. The cnc manual should tell you air requirements in flow rate, pressure and volume. If the valve you refer to is actually a pneumatic cylinder, you might be able to find the air volume required per cycle.

Also, you describe a valve that operates a chuck. I have seen cnc tool changers and there is a tool holder that contains the tool with a knob on top of it that a pneumatically operated draw bar grabs. The old tool holder is taken to a dock and released by operating the pneumatic cylinder that pulls or pushes on the draw bar depending on whether the tool is being ejected or picked up and grabbed. I wonder if this is what you are talking about or something else.

It may be that the hose or tubing you are using to connect from the compressor to the CNC and the fittings are restricting the air flow to the tool changer. In other words, the air can't get from the tank to the cnc fast enough because the flow is choked. Your description seems to indicate this as a posibility. Most portable compressors would be set up with 1/4" quick disconnects for hand tools like nailers, so you would probably have them on both ends of the hose which is very restrictive.

It would help if you determined how long it takes the compressor to recover. If it recovers quickly, then it may mean little air was used, but the restriction made the pressure drop since the rate the air is used was rapid.

A sufficiently large hose and piping to the machine is required and quick disconnects can reduce flow by a large amount. Just eliminating the quick disconnects if they are installed may do the trick. Also, hose length can really kill air flow.

Also, the regulators on portable compressors are usually really small, really cheap regulators. The regulator on the compressor may be too small to allow sufficient flow rate to the cnc. So you would need a system with a sufficiently sized regulator.

[Tom Deutsch]

Sounds like that machine take a BIG gulp of air for each "hit." I'm no pneumismatist (ha ha) but my first suspicion would be air volume delivery. Make sure you have, what, at least a 3/4 inch diameter opening from the tank, through the regulator/filters, through the hose and all fittings (no choke points). Just a stab.

[Anthony Whitesell]

If the compressor only builds the tank pressure to 110psig, I would (a) increase the turn off pressure of the compressor (perhaps 130-150 psig) and then add a (big) regulator at the machine.

A 60 psig drop in 4 seconds is huge consumption. Tanks are not sized based on psig drop, but air volume supply. A 60 psig drop in 4 seconds is about 25 standard gallons of air or 6 gallons per second. That is really a huge demand. It could be the regulator is undersized and restricting the air flow.

My air compressor has two gauges. One displaying the tank pressure, the other displaying the line pressure. What is your gauge displaying? If it is displaying the line pressure, then the regulator is too small. Which also explains why the recovery is so quick. If it displays the tank pressure, then adding a 30g tank would result in dropping from 110 to 97 psig under the same circumstances (25 standard gallon draw in 4 seconds).

[Art Mann]

A 6.3 gallon tank is tiny. You probably need a 30 or at least 20 gallon reserve tank based on your description of what is happening. I see you have 2 options. You can buy a compressor that is adequate for your needs. If the tool changes are not frequent, you can probably get by with your current compressor and a big auxiliary reserve tank that has the necessary reserve capacity. Your little compressor will run a long time to replenish that big tank, but it won't have to do that very often.

[Steve Peterson]

Pressure is being monitored about 1 foot away from the tool, about as close as it can be, and I can watch it build and hold to 110, then it drops off the tool, and the pressure drops to 50, taking about 3-4 seconds to rise back up to 110. In the meantime, the router is programmed to almost immediately go pick up another tool, but the compressor does not have quite enough time in between.

Just 2 cycles, as the compressor has plenty of time to catch up while the router is cutting, before needing to pick up a different tool.

A sure fire way to fix this problem is with a nice($$) screw compressor, but was hoping this could be achieved another way, seeing as how it needs the boost of pressure for such a small amount of time. If an aux tank were an option, how could I calculate the volume of air needed to withstand a 60 psi drop like that?

Also, just for the heck of it, I hooked it up to my 6hp 30 gallon compressor, and it did the same thing.

This sounds like an air delivery and/or storage issue. No compressor would ever be able to build up from 50psi to 110psi in 2 seconds. One solution would be to mount an auxiliary air tank right next to the equipment. It needs to be sized so that the tank has enough capacity to do the first cycle and still have enough pressure for the second cycle 2 seconds later. You may need large tubing between the tank and the equipment. Small tubing between the tank and compressor should be fine.

I recently replaced my 30 year old Craftsman noise generator pretending to be a compressor. The new one is a California Air Tools. It is much smaller and whisper quiet. My 11 year old daughter suggested using the tank from the old one as an auxiliary storage tank. This would give me a 30 gallon tank with built in wheels. The primary purpose would be to wheel it out to the cars when I am too lazy to unroll the hose.

Steve

[Mike Schuch]

It sounds like you need a 2 stage compressor made to operate at 175psi. This should give you the reserve you need to operate at a constant 100psi without dipping below 100psi. Ex. when your chuck closes your reserve tank might drop from 175psi down to 125psi (How big is this chuck anyway? What is the volume of the cylinders of the chuck?) then your compressor will kick in and start pumping back up to 175psi. Your supply will never dip below 100psi.

[Marc Nicoloudis]

Wow, thanks guys, lots to think about.

Compressor is right next to machine, with a short line. I would say the hoses on the machine are at least 3/8, but the lines going from compressor to the machine are only 1/4.

Garth, yes am checking into slowing the tool change down, as this is an option.

Sean, Yes this is exactly the type of set up the machine has. Draw bar releases the tool, pressure drops to 60, compressor kicks on but the machine is already ready for more air to pick up the next tool. Draw bar doesnt open up all the way, essentially crashing the Z of the machine causing a fault code. The compressor cycles for about 15 seconds, but by then it's too late.

Because the cycle time to recover after the first tool change is quick, this leads me closer to the idea that maybe the lines/regulator(1/4) going from the compressor to the machine are inadequate, while the lines from the side of the machine to the tool head are stock, and surely up to par. Maybe the restriction in volume is being choked by the smaller lines. I do know that while this machine was under power at my last shop with a huge compressor, this was never an issue.

Steve,
yes, the one currently powering it (or not powering it) is a CA air tools model. Love them, but might not be up to the job no matter how big the lines are. I guess at this point I can try bigger lines, unless of course the compressor fittings will not allow this.

Mike,
Maybe 2 stage is the way to go as well, I am going to research them a bit now

Thank You guys!!

[Art Mann]

You need to monitor the pressure at the compressor. If it drops to 60 psi there then a bigger hose will do absolutely nothing for you.

[Anthony Whitesell]

You need to monitor the pressure at the compressor. If it drops to 60 psi there then a bigger hose will do absolutely nothing for you.

That is key. Which air pressure is dropping to 60psi? The tank or the regulator outlet? With that information, we/I can provide some more options.

[Marc Nicoloudis]

Pressure is being monitored at the machine head. Will check pressure at the compressor next.

[Anthony Whitesell]

Pressure is being monitored at the machine head. Will check pressure at the compressor next.

Yes please.

If you have enough pressure (or can build more) in the tank and the pressure at the machine is dropping, it may be showing us the regulator is too small. (the 1/4" hose isn't going to help either).

[Peter Quinn]

We had this problem when the CNC was new at work, much bigger compressor but machine was almost picking up then dropping heads at the tool change, turns out it was in routines where the swap was quick, like head one for head 2. Its a 10 head tool change so if it had to travel further it didn't do it. Solution was simply to increase the lag between tool changes a few seconds, problem solved at the programming end. Certainly no harm in upgrading your air system to high flow components, make sure you have a good air dryer in line and that its a high flow device as well as the regulator, those should all have the specs listed if they are decent quality. You can power it with a 30CFM screw jack bit if the regulator it passes through is only capable of allowing 8cfm...you will get 8cfm. Kind of like getting a 4000CFM dust collector to pull a 4" hose.....

[Kelly Craig]

Go with the in-line reserve tank others suggested. All you need is a hose and one, two or three after market tanks connected by hoses and you've upped the capacity of your compressor. One nice thing about this approach is, they can be secured out of the way without complication.

If you go this route, buy quality hose and not the Freight garbage, which cracks and splits just sitting around. Coming to work and finding and air leak is disheartening, at the least.

[Lee Schierer]

You probably need an accumulator (storage tank) near the machine for extra volume in your system. If your compressor capacity is low or your runs are long sometimes there aren't enough scfm available for a task. The lowest cost way to solve most issues of this type are to install an accumulator right next tot he machine with enough capacity to handle the needed volume and allow the compressor to build back up to the shut off pressure at a slower rate.

[Marc Nicoloudis]

Think I have it almost figured out. Pressure at the compressor did not fall, leading me to believe that the problem was farther down the line. In the interim, I lessened the blow off time, used to clear any debris before it grabs the tool holder. Also did as Peter said, adjusting the tools, so that there was more lag time in between tool changes.

Finally removed the dessicant filter, and one of the 4 regulators(:confused:), and that did the trick. Pressure now drops about 15psi for less than 1/2 a second, and is right back up there. Glad to keep my super quiet dedicated compressor. Will plumb in another dessicant line with larger fittings, hoping to not restrict flow too much. Thank you everyone as would not have come to this conclusion in such a hurry. Best,
Marc

[John K Jordan]

Marc,

Hey, it is interesting to read about this. If you decide to see if you would benefit from an auxiliary tank you might test it first with perhaps an unusual method. If you have it, try connecting a very long air hose.

When using two pneumatic framing nailers at once to build a horse shed out in the field where there was no power, I ran a couple of hundred feet of air line from a pancake compressor so I could minimize the electrical run to the site. An unexpected benefit was the extra line increased the storage capacity significantly and let us drive more nails before it cycled. The compressor did take longer to cycle, but since we weren't nailing all the time (did have to cut and fit) there was usually plenty of time to build the pressure back.

If you can make it fit some day, you might be really happy with a larger compressor. I put a 60 gal 2-stage compressor with a 5hp motor in my new shop and plumbed air lines to outlets all over, to every room and outside. I can't believe how useful this is! It pumps to about 175 but I regulate to 150. I have yet to run out of air during use, impact drivers on farm vehicles, airing up tractor tires, framing nailer, blowing leaves from the gutters, plasma cutter, etc. It is noisy so I put it in a sound insulated closet along with the cyclone dust collector and ran the dryers/regulator/valves outside the closet to the main shop.

JKJ

[Anthony Whitesell]

The problem is not the compressor nor the storage capacity. It is a delivery limit of the regulator(s) combined with the diameter of the hose used. Why 4 regulators? I can see two; one at the compressor and one at the tool. If you economize on the regulators, you may be able to reinstall the dessicant filter.

How high is the compressor charging the tank pressure?

[james mc guire]

Fine you A say 60 gal.compressor tank, just the tank (CL),or a 100 lb+ purged propane tank,call a dealer they cost just above scrap and are safe for compressed air after a purge.Then put that as your in-line reservoir air.once both tanks are full the reserve and the compressor,you shouldn't have any problem.

[Anthony Whitesell]

A 1,000,000 gallon tank won't do any good if the regulator is undersized. Which appears to be the case, or there are too many regulators and too small diameter hose which is causing the pressure drop. This is indicated by the quick recovery time by the pressure on the regulator gauge.