Air Compressors for Newbies- by Forrest Addy

One thing they do not tell you is that the CFM Rateing is at 60 degs at sea level go above 60 degs or as the elevation gets higher you have to derate the CFM Rateing. I found this out, A 185 cfm compresser I used for mining only put out 145 CFM AT 95 DEGS AND 4000 FEET.

This topic hits the head on the nail,and the ones that posted to it/right on!i owned IRON-MAN-AIR a compressor factory located in mich and fla for over 25 years.
it is amazing the little knowledge that people know.
they buy tank size and hp,in most cases
The tank makes no air and there 5 hp motor in industrial ratings is about 3/4 hp.
and that was in the 70s 80s and 90s
now its even worse,a direct drive oiless unit running 3500 rpm? nuts..
in our shop we tore down many and did much research in the field/ the units have a 500 hour design life,cast iron pumps at 800 rpm in good quality unit 20,000 hours plus. with a tune up on average every 3 to 5 years.
and the biggest joke,ever go to sears and see a 6.5 hp vacuum sweeper?
the trick was back in the 70s after the hp rating on the name plate put eiether sp or spl after it, now its a special call it a 10 if you want..

a-1 posts from all

scott

One thing that isn't addressed here and that is the condensed water issue.

No matter what compressor you get, eventually, you will have a problem with condensed water in the lines either rusting (internally) your air powered tools or ruining a spray painting job.

When you compress air, you get water vapor that condenses in the tank, air lines and tools and causes rust and failure.

I have 3 compressors in the shop. I have a large IMC 20 horsepower 30 cfm at 175psi with a 150 gallon horizontal receiver that's inter cooled and after cooled as well as 2 5 horse CH single stage horizontal units plumbed in tandem. All the compressors are feeding a single air system. The IMC is de-rated to 120psi as you never need anything greater. Even a 1" IR impact runs fine at 120 psi. it's all about CFM required. Just before the main inlet to the air system is an IR refrigerated air dryer rated at 30 cfm @ 175psi.

My shop is entirely plumbed in schedule 60 white plastic pipe utilizing 1" main runners and 3/4" drop lines terminating in ball valves with drip legs and Milton QD style female disconnects. I incorporated the drip legs just in the event that any condensed water finds it's way past the air dryer, which it does. Always better to be safe than sorry. Plastic pipe has many advantages over metal lines, most notably ease of installation. All you need is a good plastic tube cutter, plastic fittings, primer and solvent weld glue versus threading dies and a bunch of iron fittings not to mention the cost of iron pipe. Plastic piping isn't prone to internal rust either. Rust particles in the air stream can cause tool failure or stuck valves.

At the inlet end where the compressors feed the main 1" runner, I used 1 wire hydraulic hose with NPT ends to mate the compressors to the runner, eliminating any vibration to the hard piping.

At the exits I have a couple of FRL and FR sets to plug in as needed. Mist lubrication is essential to tool life. Without internal lubrication, the air motors will fail quickly and the filters pull out any water droplets from the air stream before it reaches the tool. I tend to use Marvel Air Tool oil in my lubricators but there are many other good brands on the market. Don't use regular motor oil. Motor oil will eventually gum up the air motor as it emulsifies with the incoming air stream.

Any tool that is either stationary or is hard to couple has an in line lubricator attached, like my Lincoln bulk greaser or my IR overhead air hoist. If I need air outside, I just attach an air hose to an outlet.

One thing to note here is that many shops, even home shops have plasma cutters and plasma cutters require VERY CLEAN MOISTURE FREE air. To that end, on the air inlet of my plasma I have a Motor Gard cartridge filter that removes all the moisture. Moisture will, in short order, foul your plasma gun tip.

Whichever compressor I am using, whether the IMC or the tandem CH's, I drain the receivers daily or when I'm done using them. I also crack the ball valve on the main run to drain it. When I'm not using the compressors for any length of time, I drain the receivers to ambient pressure. I also change the compressor oil yearly and clean the intake filters (Solberg) monthly. I use Mobil Rarus synthetic compressor oil, but again, there are many good brands out there. Just be sure to get the proper viscosity.

I have had all my compressors a number of years with no failures. A little preventative maintenance goes a long way. Compressors and air systems are probably one of the most overlooked and neglected tools in any shop, that is, until they fail at a crucial time.

What is the criteria for screw type compressors? Our shop has a 10 HP IR roary screw with a aftercooler and dryer. It runs about 3 minutes, idles about 8 minutes, then repeats. Is this an overkill? I thought they were supposed to run continually. Are they a lot more expensive than piston? Run more effeciently? Less maintainence?
RJT

One recomendation I'll make: Avoid the vertical twin cylinder types. The v-twin design is much better. They run cooler, and they don't jack-hammer the floor. Less vibration and noise, since the v design has inherent balance. Might last longer, because they run smoother.
My little 2hp on wheels just let the smoke out of the electric motor(Dayton), but I bought it used back in '82. No idea how old it actually is. I'll have to clean in off to find out what brand it is. Probably time for new rings, as it was starting to blow a bit of oil thru the line. Maybe time for a new tank, as the drain water has been rusty for years.
Hey, if it aint broke, don't fix it- well, guess it's time...

Will

On average a v-twin can run up to 30% cooler at the high pressure discharge temp.and if the mfg does a good balance job,not just adding a few flat washers crudely.much smoother as well

Scott

Everything you guys say is true, especially about newbies beware. I was/am a newbie and I've been caught.

I'll tell the story sometime.

Meantime can you answer me this: Should I empty all the air out of the compressor everytime I switch it off?

I was doing this to leave it safe, I've got two little kids. But a guy on the internet said you shouldn't do it. It will strain the compressor tank too much and it might fail.

But everyone seems to think it is a good idea to get the water out - the paperwork that came with the compressor says to drain it at every new use. But the drain is at the bottom of the tank - how can I drain it without letting all the air out?

regards,

ab

Fox max tank life it is best to drain your tank daily.Many dont,and if you have a small portable or a non asme tank,they are very thin.made as throw aways.none of the tanks are coated on the inside they are bare steel.besides eztending tank life,draining the tank of course helps keep moisture out of the air tools.The guy that gave you a tip from the internet is a bone head,if your tank was straining it would be with air in it and not empty,and if straining, time to cut a hole in it with a torch and pitch it in the dumpster so no one pulls it out to use it as you yourself are liable.at my compressor factory it was standard procedure.and to get textbook the hot compressed air cools in the tank,this air releases its moisture at dewpoint,you then drain the tank and re-seal it.In many cases the humidity will be higher outside the tank than in.

I have now a bell air compressor, 80 gallon 7.5 hp on the nameplate, had it for 3 yrs and it looks brand new still, at 175 psi i can run the crap out of the tools before it comes on.....Some say to adjust it down, but at 175 the tank is hold more cubic feet of air as well....Maybe it is good maybe it is not....Just my opinion, they are a bit spendy..But about half the cost if not a 3rd of a sailor beal machine....

It seems that most compressor mfg's don't put the condensate drains in convenient places especially on horizontal tank models of which I have 3. On my big IMC I have an automatic cyclic drain and my smaller 5 horse horizontal units which set under a bench, I attached elbows and extension drains in galvanized pipe with WOG valves that I can dump easily. My IR refrigerated dryer also has a cyclic drain like the IMC.

One thing I've never noticed is any thump or vibration associated with the vertical twin compressors. I have the IMC on anti-vibration machinery mounts but the 2 fives are setting on a concrete floor.

Eaton compressors were mentioned high up on this thread. Their compressors are good, for sure, but their website may be even better because it contains a detailed schooling on just about everything to do with compressors and in it they don't hold back about false or misleading claims and the ways that compresors are marketed. They tell us all about those sticker claims seen on the offerings at Home Depot, Sears, and most other sellers of home use machines. They'll also sell you what may well be the last compressor you'll ever have to buy.

http://www.eatoncompressor.com/page/page/504413.htm

ARD Farm

My shop is entirely plumbed in schedule 60 white plastic pipe utilizing 1" main runners and 3/4" drop lines terminating in ball valves with drip legs and Milton QD style female disconnects.

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I like the idea of running plastic lines for the rust reason except I worked in a shop that had them (300 psi rated) with 120 psi in the lines and the first time one of those lines exploded, that ended that thinking. It was like an M-80 going off in the shop and blew pieces of plastic shrapnel everywhere. Lucky no one was hurt. But the boss insisted on using it, and we had a second line blow, again off in a corner where no one was hurt. No way I'll ever run plastic airlines in my shop. I'm sure those plastic pipes are tested to 300psi, but did they consider the fatigue of day after day expansion and contraction of that plastic which can produce stress cracks at well below yield strength of the material after thousands of cycles?

Steve

Years ago the company I work for moved into a new building they had built(approx 15000 sq ft). The air was all plumbed in sch 60 pvc,1 1/2 trunk lines with smaller drops. No problems for about 6 weeks.................then the pipe bombs started going off. Failures were at connections as well as in long runs of pipe. These daggers of plastic stuck in cushions of chairs and dented rollaways,it was like a war zone. Had one blow above the jig grinder one afternoon. I was all zoned in on a half tenth bore and KABLAM!!!!!!!!!! I had to go home.

Using PVC for air is mad, the material suffers from brittle fracture and the cracks can propogate faster than the speed of sound in air meaning that an entire length of pipe can explode. In Australia we use 100 grade polyethylene which doesn't suffer from brittle fracture no need to wait 24 hours for the glue to dry either as it uses compression fittings. This material has been used in shops for over ten years and gives nice clean air I worked for a shop that tried pvc 25 years ago and the results were similar to what people here have experienced.

sch 40 black pipe it will outlive us.
they were playing with the plastic in plants in the 80"s when i had iron-man air of florida there.not cool,blow ups and plastic flying.
i would never experiment with it now.
Why? black pipe is cheap!

pepo

Had one blow above the jig grinder one afternoon. I was all zoned in on a half tenth bore and KABLAM!!!!!!!!!! I had to go home.

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Oh, can I relate to that. When running an O.D. grinder and trying to touch the wheel off, if somebody dropped something in the shop, I'd jump to the ceiling. Some people though it was funny and would purposely drop a plate behind a guy when he was "zoning in" on a dimension on the O.D. grinder. I never found it funny. Couldn't imagine having an airline blow next to your machine when trying to hit your final dimension, especially if the part has a lot of time in it.

Steve

I just talked to somone this morning that had a sch 40 line blow,he said he had used it for 6 years,when it blew,it sunk some plastic into a plywood covered wall as well as blowing rusty water all over.black pipe sch 40 is the way to go at 140 psi

I've got a question about the V-twin vs. twinned vertical cylinder design issue noted above. The point was to always get a V twin and avoid the vertical side-by-side types. I'm pretty sure that's not always true. Here's a comparison, both true 5 hp, single phase, 2 stage, cast iron pump, 80 gal. tank compressors costing around $1500 new. Both have reed valves. Both compressors look well made to me, and have a repuation for lasting many thousands of hours.

So, it's an apples to apples comparison, with the only main differences being that the CH has the supposedly superior V twin and also has a squirrel cage blower to cool the cylinders, while the Quincy is a simpler and "inferior" vertical design.

#1 Is a Campbell Hausfeld "Extreme Duty" true 5 hp compressor with specs that claim about 13 cfm at 100 psi and 12.5 at 175 psi. It has the V-twin configuration and a coil of intercoolor tube between the stages. There's also that squirrel cage blower cooling off both cylinders and the intercooler tube.

#2 is a Quincy QT-5 compressor, whose 5 hp motor pulls an amp more at 220 volts. This is an entry level compressor for Quincy. It claims around 17.2 cfm at 100 psi and 15 to 16 as I recall at 175 psi. The two stages share a single vertical casting, with a finned intercooler tube snaking from one to the other. The pulley for the pump has vaned spokes and probably contributes a little to cooling.

As far as I can tell the "wrong" design uses about 5% more power (21 amps for CH, 22 amps for Quincy) and puts out about 25% more air. It also runs quieter, based on personal comparison.

Is Quincy puffing up its specs or is CH too conservative? Did CH somehow manage to botch a superior pump design in what, at the time, was its premium commercial duty compressor.

My own guess is that the twin versus vertical cylinder layout doesn't matter much, and that Quincy probably benefits from a heavier cast iron pump, an ample intercooler tube, and possibly a slightly better reed valve design? The CH may lose a little power to the blower, but might also have slighly drier air (though it looks like the Quincy has a longer and beefier intercoolor tube that gets reasonably cooling from the pulley/impeller.

Air compressors are rated bore x stroke x rpm = displ c.f.m. then the eff comes in.
a 5 h.p. compressor is 20 c.f.m.
a 3 h.p. is 12 c.f.m.
Quincys model 325 compressor pump is top shelf.oil pump,oversized pistons,rings,undersized bearings availible.
what you are comparing is a 4 h.p. and a 3 hp.
and both have a bad reputation if used hard.QT-5 And C/H
reed valves are junk,and used on throw away pumps.
Disc and spring valves,quincy,saylor-beal,champion,Kellog-american and others is the proven design.
the v-twins run cooler but put out no more air than a side by side.A real 5 h.p. single phase motor draws 25 amps..2.8 amps per h.p. if 230 volt 3-phase.You just cant get any more air with less amps.
If you are in the market for a compressor,give me a call anytime.I have had them apart and know them inside and out.27 years wrenching on them.even ingersoll= rand is a joke nowdays.What they sell as there 5 h.p. 2 stage is there 3 h.p. cranking it fast.Air compressor motors should be 1750 r.p.m. and pump speed no more than around 800 r.p.m. if you want them to hold together.if i can help in anyway give me a call.

Best Regards

Scott

Thanks for the info, Scott.

I'm still a bit confused by the Quincy and CH specs -- given that Quincy claims 25% more air (17.2 cfm vs. 13 cfm at 100 psi) with just 5% more amps (22 vs. 21 amps, both at 230 volts single phase).

Not sure about the efficiency of the US motors on either unit, but I'd think either one might squeek into the true 5 hp range (e.g. 230 volts x 21 amps x an optimistic 80% motor efficiency / 746 watts = about 5.18 hp for the CH. I'd guess the CH motor probably is not more than 70 - 75% efficient, while the motor on the Quincy draws an amp more and looks a bit better built). It does seem, to me, to be reasonable to call them both 5 hp based on the manufacturer specs, rather than 3 and 4, especially if premium motors are used. Certainly, nothing like the Sears-type specs based on peak locked rotor amps.

Anyhow, thanks for the info -- if you can shed light on the accuracy of the cfm and power draw claims, I'd appreciate it. I do agree that reed valves aren't a plus for either one, but then these aren't $2000 compressors either.