One compressor.... Multiple pressure ranges.. or switches.

Been bugging me for years. The compressor in the shop would kick on, the pressure would come up through the range
really quickly, and then that last 10psi seemed to take forever to build... Up to 140psi or so... I was wondering
how much $$$ that was costing a month..

Had a little compressor problem lately and had to go to the backup, another one going to 140... Turned around and
bought a backup to the backup, this one cycles from about 80 to 110psi... My electric bill has dropped like a rock,
not a rock, but consistant $60 a month. $438 and $441 vs $501 and $496 the months prior to that.

I now know that I can get away with a much lower pressure, the machines are all happy, it doesn't cycle often, and its just
a little guy.. Problem being, sucks when using a grinder or attempting to use the sand blaster. The die grinder, even
at full pressure just doesn't have the *OOOMPH* that it does at a higher pressure.

I'm doing some re-configuring of the big compressor (new motor and plumbing) and I'm thinking 2 pressure switches. One for the normal
daily stuff, cycling 85 to 110 or so, and then a second pressure switch for 115 to 140 or so for when I got the air tools or
sand blaster going.

Should be easy enough to wire and plumb.. Does this sound like a good idea? Any suggestions on how to go about it?
Are there any new fancy gadgets that will do what I want without Mickey Mousing around with multiple pressure switches?

I'm just looking to see if my idea has any merit, and to see if anybody has any alternate ideas or opinions.

Hi Bob - what I have found is that volume is much more important that pressure to die grinders and sand blasters. The reason the die grinder and sand blaster worked better at the higher pressure is that they had more volume due to being compressed at higher pressure so that they run much longer at a time.

I would say a better solution is to increase volume as in plumbing the tank from the other units back into the current unit to increase your volume. At least that is what I would do. When I have to do any work that requires a significant expenditure of compressed air I fill up all the tanks I have and usually put a tank in the immediate area of the device I am using so that the air is available right now. Air tools seem to love it.

Many companies utilize air at pressures much greater than they need. Years ago the company I worked for sold a product to a large manufacturing company. That company used a lot of air at about 3 psi, which they throttled down from probably 140 psi. I proposed a staged blower to supply the 3 psi air at a great energy savings. I was surprised when they declined to make the investment in the new blower.

I strongly recommend that you set up a two stage pressure system. You could probably do it with electrical switching, or manual valveing to the two pressure switch systems. Compressing air generates a lot of heat, which is wasted energy when the pressures are higher than required. Your power costs vividly demonstrate the savings obtainable.

Jim

Well, you're out of my league if you're spending $500 a month on compressing air.

Could the valves on the big (HP) compressor need refurbing? At the pressures you are talking about, Boyle's law should be a pretty good approximation. That is, PV = nRT. The "n" is the number of moles of gas. Each cylinder full of air drawn in has about the same volume and intake pressure, and so each cycle should squeeze the same additional "n" into your tank. in an ideal world, the pressure should go up linearly with time and then kick off when the high pressure cuts off. There are certainly some non-ideal things that go and, and temperature changes and such, but If it takes ten minutes to get the big tank to 130, and another half hour to get to 140, I'd suspect a valve leak and back-flow in the compressor.

Not sure what the pressure drop is from your tank to your die-grinder. If you can get a pressure gauge on the thing, at the grinder, while you are using it, it may show you that with HP air not only do you start at the tank with higher pressure, but because the scfm flow is at HP, you get less drop. Maybe a better way to test is to close-couple your die grinder to the tank (for an experiment, not for production!). Eliminate as much plumbing as you can. Test the grinder to see how zippy it is. If this setup restores the die-grinder performance it may make sense to run larger lines and hoses (hosiery?) to allow you to run the grinder from a lower pressure source.

A bigger tank won't improve the initial performance, but as you know will lessen the rate of pressure loss with use.

The situation is interesting. I hope you find a way to continue to save that money.

bosleyjr said:

Well, you're out of my league if you're spending $500 a month on compressing air.

I'd suspect a valve leak and back-flow in the compressor.

The situation is interesting. I hope you find a way to continue to save that money.

Click to expand...

$500 a month, total electric bill, I'm guessing about 1/4 of that is for air.

The backflow valve, that was not in the best shape, and has been replaced.. Though I haven't had a chance
to test it out yet. I'm also wondering if the rings in the compressor are a bit shitty, and the reason
it takes so long to build pressure up in the higher ranges. Common compressor head, so I might just
give that a little R&R while I'm at it.

If you are using a coalescing filter the element will show the oil.

My compressor was originally setup for 175psi. I changed that to 150.

Have you thought about using a digital pressure switch? You can change the setting by the keypad.
I got a few of theseSMC pressure switches which I am planning to incorporate into my air system.
A transistor switch internal to the part would require that you use a external
relay to turn on/off the coil to you motor contactor. I'm not sure if I can get
by with just one, if not then I will use two. On the back there is a 1/4 NPT connection
and a three wire connector. The one in the pic is ISE30-T1-65-L.

rons said:

If you are using a coalescing filter the element will show the oil.

My compressor was originally setup for 175psi. I changed that to 150.

Have you thought about using a digital pressure switch? You can change the setting by the keypad.
I got a few of theseSMC pressure switches which I am planning to incorporate into my air system.
A transistor switch internal to the part would require that you use a external
relay to turn on/off the coil to you motor contactor. I'm not sure if I can get
by with just one, if not then I will use two. On the back there is a 1/4 NPT connection
and a three wire connector. The one in the pic is ISE30-T1-65-L.

Click to expand...

That's the kind of gadget I was hoping existed, and they are cheaper than a mechanical pressure switch..
Any chance they make one with an unloader valve in it, or can be wired to an unloader valve?
How big of a pain in the ass is it to change your cut in and cut out pressures on it?

Bob,

Is your compressor a 2 stage? If not you are likely pushing it to the max and that is why it runs so much near the end of it's cycle. I'd turn the pressure switch down to 125 or so and try that.

Its a 2 stage. Kellog American 331, nothing big or fancy...

I just looked, rebuild kit, $90, not too bad.

rons, I am currious what the maximum pressure differential is on that pressure switch. Most mechanical ones don't go past 40 psi.

Bobw, how are your head gaskets? I had one go bad on the low pressure side but the compressor still worked fine. I didn't find out about it until I started running my Kitamura and all of a sudden the compressor would run continuously, instead of 70% of the time. The gasket failed between the intake and exhaust sides inside the head so there were no external indicators.

DavidScott said:

rons, I am currious what the maximum pressure differential is on that pressure switch. Most mechanical ones don't go past 40 psi.

Bobw, how are your head gaskets? I had one go bad on the low pressure side but the compressor still worked fine. I didn't find out about it until I started running my Kitamura and all of a sudden the compressor would run continuously, instead of 70% of the time. The gasket failed between the intake and exhaust sides inside the head so there were no external indicators.

Click to expand...

I'm sure its torched.. My guess is that the compressor has been hanging on the wall for almost 40 years, with little to no maintenance. By hanging,
I mean its on a shelf about 9 feet off the shop floor, not knowing the history, means it was here when I got here. It leaks like a sieve too, so its
definitely getting a little rebuild/overhaul when I take it down...

Also being up on the wall, and being a metal building, it shakes the hell out of this place. Most of the noise it creates is from the building,
not the compressor.. So I'm going to pull the head and the motor off and put them on the floor WELL ISOLATED under a bench and put the tank back
up on the shelf. Should quite it down a lot, and make it easier to maintain/work on if/when it needs it.

Can't you put it outside?????

Drain your tank to atmospheric. Tell us what size it is. Turn on the compressor and time how long it takes to hit 140 psi. Figure out what rpm your compressor is running. Post these 3 numbers and we can tell you if something is seriously out of whack or not...

DavidScott said:

Can't you put it outside?????

Click to expand...

I thought about that, but I now have people living literally right outside the back door. I was here first making noise, but
I try to not be an asshole, so for my sake and theirs I'd like to keep it quite, inside and out.

Jim,
Would you mind if I had your message below carved into a stone tablet?
I'd then like to take said tablet and hit some folks I know over the head
with it....(including a few dozen morons over on the Garage Journal board that think you "can't ever have ENOUGH pressure with compressed air"!
They'd run 500 PSI if they could.

It's OK, I'm calming back down now.....

Jim Williams said:

Many companies utilize air at pressures much greater than they need. Years ago the company I worked for sold a product to a large manufacturing company. That company used a lot of air at about 3 psi, which they throttled down from probably 140 psi. I proposed a staged blower to supply the 3 psi air at a great energy savings. I was surprised when they declined to make the investment in the new blower.

I strongly recommend that you set up a two stage pressure system. You could probably do it with electrical switching, or manual valveing to the two pressure switch systems. Compressing air generates a lot of heat, which is wasted energy when the pressures are higher than required. Your power costs vividly demonstrate the savings obtainable.

Jim

Click to expand...

Jim McIntyre said:

Drain your tank to atmospheric. Tell us what size it is. Turn on the compressor and time how long it takes to hit 140 psi. Figure out what rpm your compressor is running. Post these 3 numbers and we can tell you if something is seriously out of whack or not...

Click to expand...

120 gallon tank, plumbed down stream to a 20 gallon, plus all the lines.

17.2cfm @175psi. is what the specs say... It was somewhere around 9 minutes to get to 140psi...

The motor is torched, it shorted, for some reason there was shoddy electrical work up there, and electrical tape
does fall off, especially when its not actually wrapped... So I can't do any experiments yet... I need to get that
thing down off the wall, and I need the fork lift to do that.

But there was another issue there. It wasn't all put
together, and here is what the recently freshened motor looked like when I busted it apart. I figured I'd pull the head
since all that came out of the crank case was water, and dirt, and tin foil. Cracking open the old motor to take a look,
the one that has been out in the yard for 2 years, with no tarp or carb, and its looking a lot less rusty and dirty. You can see the
compressor up on the side, top of the ladder.

The motor was given a "fluffy fluffy" and half assed put back in, but never finished. It ran on the stand a few years ago.


I'm not quite sure how that happens when there is a carb and an air cleaner on it. And I'm in the F'n desert!!!

Turned out the oil filter was just attached randomly, wasn't actually plumbed into the oiling system.

Compressor, top left. (Edit right, NOT left, I still get those confused sometimes)

Bob......I think you just speed shifted between "compressor" and "forklift" a few times here?

Looks like you still have dew and condensation out there....

dkmc said:

Bob......I think you just speed shifted between "compressor" and "forklift" a few times here?

Looks like you still have dew and condensation out there....

Click to expand...

Its all related.. What came first, the chicken or the egg?
Need the compressor to use the sand blaster efficiently to clean the rust off the fork lift motor.. Need the fork lift
motor running to fix the compressor, but I need the compressor running to fix the fork lift motor... on and on and on......

Shazam!

................................

Bobw said:

120 gallon tank, plumbed down stream to a 20 gallon, plus all the lines.

17.2cfm @175psi. is what the specs say... It was somewhere around 9 minutes to get to 140psi...

Click to expand...

Kinda need the RPMs, and bore/stroke. Couldn't find your 331 in a Google search. But based on a swag, with 150 gallons of storage going from 0 to 150psi in 9 minutes, there's nothing seriously out of whack.