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Compressor tank size vs cfm

1/4/17       
Kevin Member

I am upgrading my compressor and am looking at 10hp units. Almost all 10hp models use a 120 gallon tank, but I did find a couple of 10 horse 80 gallon units. With the cfm being the same, would the smaller tank be a problem? One man shop, main reason for the upgrade is running a DA. Only asking because the 80 gallon is a little cheaper and a little smaller footprint. Thanks

1/4/17       #2: Compressor tank size vs cfm ...
AZ Engineer Member

An 80 gallon tank is about 10.7 cubic feet and a 120 gallon tank is about 16 cubic feet. DAs take say 10 cfm so the tank size isn't super critical. The pump will cycle more often but with 3 phase that's not really an issue.

1/4/17       #3: Compressor tank size vs cfm ...
Matt Krig Member

An electric Mirka or Festool sander with vacuum may be an altogether less costly endeavor. If you are spraying or looking to grow add the compressor, otherwise, you'll have a great portable sander that's nearly dust free.
http://www.mirka.com/tools/Electric_Sanders/#/

1/5/17       #4: Compressor tank size vs cfm ...
Kevin Member

Thanks. I have had the ceros pretty much since it came out, and although its been a good sander, the 3/16 orbit never leaves the finish as good as I want. I also have the small festool and it is a little better finish sander. After using the 3/32 mirka air sander, the finish is pretty much flawless with 180. I see the comprssor as a good investment and will help keep up with spraying when I use hvlp guns.

1/5/17       #5: Compressor tank size vs cfm ...
Jim Clark

You won't have a problem either way with
a 10 HP compressor. I have only a 5HP
and it keeps up with my sanders just fine.
My HVLP's use much less than a sander
and that's what I use the compressor for
mainly, painting.
But I do like a bigger tank because I have
my compressor in my spray area and I
like to turn it off while spraying and back
on once the air has cleared. I can spray a
lot off just the tank air.

1/5/17       #6: Compressor tank size vs cfm ...
Kevin Member

10 hp might be overkill, I was originally going to buy a 7.5hp, but it seems the general consensus is to go as big as you can. Still considering the 7.5hp. Its good to hear what people are actually using.

1/5/17       #7: Compressor tank size vs cfm ...
chris

what about looking at a duplex unit, twin 5hp motors and compressors. One unit runs unless the demand gets higher then the second unit kicks in giving you approx. 32 CFM. If one unit goes down you still have air from the second unit

1/5/17       #8: Compressor tank size vs cfm ...
Kevin Jenness

For a one man shop 5 hp is plenty- typically above 15 cfm. What are you doing that needs more? A bigger tank will give you some margin before the compressor kicks in against the load, but if you are consistently using more than the output you need a bigger pump. I used to work in a shop with 5 bench hands using Dynabrade DA's (about 13 cfm intermittently) plus nailers, wide belt, etc. and we got by for quite a while with an Ingersoll Rand T30 with a 5 hp motor. We eventually put in another 7.5 hp T30 with the 5 hp backing it up, but it was a rare occasion when both ran together. Overcapacity is good if you can afford it and expect to use it in the future but may be a waste of resources.

1/5/17       #9: Compressor tank size vs cfm ...
Kevin Member

Thanks for all the feedback. I currently use a 5hp 60 gallon, and although it is plenty of air for most of my equipment, the 17cfm sander runs it pretty constantly (compressor is 15cfm). Most everything I read on this site said 5hp was not enough for even one sander. I don't want to spend more than I should, but don't want to spend good money a 7.5 when I should have gone with a 10. Its really helpful to hear from people that are running smaller compressors without issues.

1/6/17       #10: Compressor tank size vs cfm ...
Jim Clark

Just remember that you can't go by HP.
Go by CFM.
My 5HP makes more air than my friends
7.5HP. Manufactures really like to
exaggerate HP ratings. Check the motor
name plate and compare the amperage
draw-that's the real comparison.
My 5HP is larger and draws more amps
than my friends 7.5HP.
Sears sold me a 3HP years ago that ran
on 110 volt-that's impossible, a real 3hp
can't run on 110V- they lied.
Imports do it all the time so check the
motor name plate for amperage and
compare-it's directly proportionate with CFM. Compare CFM output-not HP.

1/9/17       #11: Compressor tank size vs cfm ...
Rich Kuban Member

Website: http://closetexperts.com

The tank size provides a buffer to lessen the start/stop cycles that affect power usage and wear. You can also improve the capacity by using larger pipe and creating a loop for the air distribution.

Two aspects of an air compressor to keep in mind when selecting. One, any reciprocating compressor should not run more than 50% of the time, you will shorten its life span. Second, do not enclose an air compressor without adequate air flow. The heat build up will also shorten its life span. I have seen a two year old machine that needed a new pump due to these two factors. On the other hand a bought a rebuilt 5 Hp that I sold 30 years later still running well. It ran about 25 - 30% of the time and fed a 3/4" loop in a 2300 sq ft shop. I did not use air sanders though.

1/9/17       #12: Compressor tank size vs cfm ...
Larry

Recip compressors should not be run continuously! They over heat, the oil gets charred and goes to hell, then the compressor wears rapidly. Like said HP ratings are usually a marketing ploy. CFM should be stated @ 90psi. If it doesn't say that, it likely is another marketing ploy. A good compressed air system is expensive to buy and run. Water in pneumatic tools leads to a shorter life. I'd go for the 10hp (about 17cfm) on a 120 gallon tank to reduce cycling. Go for 3 phase if you can. Motors last and use a little less $ of power.

1/9/17       #13: Compressor tank size vs cfm ...
Mark V.

So when Ingersoll-Rand, Quincy, etc. advertise “continuous duty” or “continuous duty pump” or “100% duty cycle rated”, what do they mean?

Lately I have heard a lot of people saying that you can’t continuously run a piston compressor and I’m not buying it, because I keep seeing manufacturers that say the opposite.

Mark

1/9/17       #14: Compressor tank size vs cfm ...
Larry

I suspect they mean "buy our compressor" and bet on few people ever running them at full load continuously. Compressing gas takes a lot of energy almost all of which is turned into heat. Recip compressors don't have a very good cooling system. The head and cylinder will get hot enough to burn the paint off. Those cast fins aren't much for cooling. If the oil gets hot enough it will char and stick the rings, end of game. Some top of the line compressors have oil pumps but most are just splash lubed. The ones with pumps usually have a spray that shoots against the bottom of the pistons to help cool them and an oil cooler with fine fins. Sort of like diesel engines.
Compare the cooling system on the recip to that of a similar sized screw. The screw will have both an oil radiator with fan and a air to air radiator section to help dissipate the heat. It will also have something similar to the piston pumps fan on pulley arrangement to blow air over the motor and compressor unit. The screw will have a lot more oil capacity also. Bottom line, the screw can run continuously and not degrade the lube (much.) Do they go to all that expense for a reason? If you won't run the recip very much at full load it will be fine. Voice of experience here. We smoked a 10hp recip by not buying more capacity when we should have.

1/10/17       #15: Compressor tank size vs cfm ...
Hen Bob Member

I 2nd Larry's opinion, when we got started we bought what we could to get running. 2 Ingersoll T-30s, they ran a lot. Our 1st upgrade was a 10hp rotary screw w/built in dryer, best money we have spent. Bought another 15hp rotary screw a year and a half ago, run one for a few weeks and then the other.

Yes it seems like overkill but when almost every tool in the shop requires clean dry air it becomes a quick reality that without air your shut down.

Look at a small rotary screw you wont regret it

1/10/17       #16: Compressor tank size vs cfm ...
Kevin Member

I was under the impression rotary screws need to be run pretty much continuously, and it was actually detrimental if they were say, run 30 mins, off an hour, run 30 mins. Is this accurate? I have come across smaller machines that weren't too expensive.

1/10/17       #17: Compressor tank size vs cfm ...
Mark V.

Kevin,

That was going to be my very next question. There seems to be a lot of ambiguous information out there when talking about compressors.

Mark

1/10/17       #18: Compressor tank size vs cfm ...
Hen Bob Member

They Do not need to run continuously at all, they run X amount of time after actually producing air for a cool down period. Its bad for the motor to constantly restart a few seconds after it turns off. The cool down period time is adjustable on ours. We have Atlas Copco's

Find a compressor dealer in your area, pick his or her brain. That should yield the most effective advice for your application

1/10/17       #19: Compressor tank size vs cfm ...
chris

Does anyone have experience with a rotary vane compressor? I've been watching this thread and started doing some research as I'm going to be upgrading as well and came across a handful of sites stating that a rotary vane is better than a rotary screw both in efficiency and longevity.

Didn't want to hijack the thread but might be useful discussion for anyone looking to upgrade

1/10/17       #20: Compressor tank size vs cfm ...
Larry

Chris, We had a Becker rotary vane vacuum pump on our first router. It was fine. Basically the same as the compressors in operation. The vanes wear but aren't horribly expensive to replace if you do it yourself. The first set will take you most of the day, faster next time.
Kevin, We have a Curtis 25hp screw compressor, certainly not a top of the line machine. Whether they run continuously or not depends on their controls. Ours has a timed system to shut the motor off if there isn't much demand during the unload period. They go into unload state when the tank is up to pressure. When air is used the unloading valve restarts the compressor end. The motor continues to run during the unload stage. After no demand for the set time the motor shuts off. When air is drawn down the motor restarts in the unloaded state runs for a short time and the unloader operates, starting the compressive cycle. This system prevents too frequent of motor on & off. There are more advanced control systems available but they all provide for limiting the frequency of motor starts. Some have variable frequency drives that slow the motor to produce just the air that is needed. The claim is less power used. Those are expensive controls and subject to occasional failure, expensive. Our 25hp unit sometimes isn't quite enough but most of the time too much. I've decided when we need to replace it I'll put in two 15hp screws with alternator control. I'm thinking that most of the time only one unit will run, when needed the 2nd will start, when demand slacks the first one will go off line. Simple control and reasonably economical to run. Screws are not cheap to maintain. Every 4-6000 hours they need an oil, filter & separator change. If you run synthetic the 6000 hour schedule applies to the one we have. We have a Quincy 40HP (16,515 hours on it)screw vacuum pump that is a higher quality unit than the Curtis (21,313 hours on it.) I think Quincy is now owned by Atlas Copco. The Quincy had a motor failure but other than that just routine maintenance. The Curtis has had leaks, control failures, drive belt failures, cracked mountings due to vibrations... and has a sloppy design that makes working on it a pain. It was quite a bit cheaper than a new Quincy or Atlas but you get what you pay for.

1/10/17       #21: Compressor tank size vs cfm ...
Kevin Jenness

The original question was in regard to a one man shop. I have learned considerable from the discussion, but I still think a low rpm well made 5 hp unit (IR, Quincy, etc.) well maintained will do the necessary for a long time in this situation.

1/11/17       #22: Compressor tank size vs cfm ...
Rich Kuban Member

I pretty much concur with Kevin Jenness' recommendation for a low rotation speed pump reciprocating air compressor for the OP at this time.. Get a 7.5 hp if you want some extra capacity. I agree with the Quincy, although I would rate a Gardner Denver over an Ingersoll Rand industrial compressor. With proper care, it will last for years. I would stay away from home center machines. You will pay more but will have a quieter machine that will withstand a wider range of temperature, and require less attention. This type of compressor could be purchased used due to their long term durability.

To maximize your compressor, I recommend
1: Locate in well ventilated area where heat generated by compressor is easily dissipated.
2: A larger tank to add more capacity buffer and reduce cycling.
3: Horizontal tank instead of vertical, to lower the center of gravity and lessens the impact of inherent vibration
4: Place on vibration pads to minimize vibration effects
5: Plumb inlet air from outside if in cooler weather zone and no shop air conditioning. This will cut down noise around the compressor.
6: Create ¾” loop to connect all usage to minimize pressure drop and add storage buffer and reduce cycling
7: Pressure regulator at output to avoid pressure swing effect at usage points.
8: Accessible tank drain to remove water daily

If your usage demand grows and develops a constant usage over time, you could move to a rotary screw that is sized for constant demand, and use this compressor as a back up and auxiliary supply for higher peak demand. You could plumb it in series to add buffer storage and automatic supplemental capacity.

By the way, I sold industrial air compressors for 3 years before entering the woodworking industry.

Regarding the rotary vane configuration, it would be less critical in tolerance compared to a rotary screw. I agree, you will have to replace the vanes, as the design requires centrifugal force to thrust the vane edges against the compression chamber, resulting in vane edge wear. It will be more forgiving in terms of contaminants in the air.

Rotary screws require bearings to maintain precise relative position of the screw lobes. Thus the stringent oil change requirements. Inlet air contaminants could cause lobe damage in extreme cases.

1/11/17       #23: Compressor tank size vs cfm ...
Kevin Member

Thanks for all the great feedback. Although my current compressor(5hp quincy) will technically run the da, it runs almost continuously and gets very hot. I would rather upgrade now and sell the quincy before it self destructs. I was leaning towards a 10 hp, 34 cfm unit (champion centurion series) mainly because it wasn't all that much more than the 7.5 hp 25cfm unit. I think 25 cfm would be ample, but didn't want to get the 7.5 only to need another upgrade in a year. Guess it boils down to what I want to shell out right now. Rich, thanks for all info, very helpful.

1/11/17       #24: Compressor tank size vs cfm ...
Rich Kuban Member

You are welcome Kevin. In the meantime, you can place a fan to blow over the pump during heavy use to help dissipate the heat generated.

Please be aware the Champion you are considering will not be as durable as the Quincy you have now. Also, the reason there is little difference in cost is because the only change is the motor and rotation speed. On that model the same pump is used from 7.5 - 15 hp. The difference is a 21% rotating speed increase from 7.5 hp to 10hp, and from 10 hp to 15 hp. I guess you can look at it that you could convert it to 15 hp in the future if needed.

1/11/17       #25: Compressor tank size vs cfm ...
Kevin Member

Thanks. Sorry to hear you aren't a fan of the champion units. I was under the impression they were a quality unit like quincy, curtis or saylor beall.

1/16/17       #26: Compressor tank size vs cfm ...
Gary

I've had a 10hp 120 gallon Champion for about 8 years and run the hell out of it in a 6 man shop without missing a beat. I should get a bigger one. I disagree with the quality thing.

1/27/17       #27: Compressor tank size vs cfm ...
Adam West  Member

Website: http://www.surfprepsanding.com

Our Surge electric sanders with the "on-board" power supply weighs close to the same as a aluminum body DA, but it only draws 120 watts and feels like it as just as much power as an air driven random orbital sander. Part of the reason is the outer runner 24V DC motor that puts out lots of torque for very low amps. 5 hp is around 3700 watts of energy.

5/1/18       #29: Compressor tank size vs cfm ...
Mr Waker Member

Tank size is one of the main and first factor before choosing an air compressor for any purposes. Personally, I have the California Air Tools 5510SE ultra quiet 5.5 gallon air compressor. Its motor produces 120 psi max of pressure and delever 3.10 CFM at 40 psi & 2.20 CFM at 90 psi of compressed air.

Best quiet air compressor

5/1/18       #30: Compressor tank size vs cfm ...
Mr Waker Member

Tank size is one of the main and first factor before choosing an air compressor for any purposes. Personally, I have the California Air Tools 5510SE ultra quiet 5.5 gallon air compressor. Its motor produces 120 psi max of pressure and delever 3.10 CFM at 40 psi & 2.20 CFM at 90 psi of compressed air.

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