Compressor CFM and PSI recommendations

[26 Flatrod]

I need some recommendations on min CFM and pressure for my next compressor. I will be using it for automotive (impact wrench, ratchets, DA sanders, cutoff wheels etc) and I don’t want to run out of steam like I have in the past. My old one was 9 cfm at 100psi and max pressure of 125. I would have to wait quite a while for the compressor to keep up to the cutoff wheel, and I could always tighten lug nuts more manually after putting them on with the impact wrench. What is considered a min CFM and pressure to keep up to these tools. I am thinking I need 15 cfm min and 155psi, but is there any advantage to going higher? Can you actually use 175 psi on any air tools?

 

[Gearhead00]

I just went through this...initially I figured I'd need a two stage, but then I found a used single stage (140 psi) with 18 cfm @90 psi. I'd think you'd need a minimum of 15 CFM @ 90 psi to do what you're listing...I'm in the same situation.

 

[26 Flatrod]

I just went through this...initially I figured I'd need a two stage, but then I found a used single stage (140 psi) with 18 cfm @90 psi. I'd think you'd need a minimum of 15 CFM @ 90 psi to do what you're listing...I'm in the same situation.

I would agree. I am looking at a Castair single stage that puts out 18.3 at 100psi, but the max pressure is 125. I always assumed that CFM runs the grinders and cutoff wheels, but the pressure is what you need for impact wrenches. is the 125 limit too low for that? they have a 2 stage version that puts out 175 psi.

 

[Gearhead00]

I'm sure someone will correct me if I'm wrong, but nearly every 1/2" impact I've seen is rated at 90 psi. I'm sure when you get up into the 3/4" drive arena you probably need higher psi. I'd guess a lot of it would depend on how well designed the impact is and how efficiently it uses the air.

 

[TheEquineFencer]

From past personal experience, trying to inflate a 16 inch tire for a 1 ton truck is a bit slow with a 125 PSI compressor. By the time you get out to the end of the air line you'll probably be waiting for the unit to cycle a couple of time to inflate to 100 PSI. It's that "last little bit" that gets to be a pain. The last compressor we bought was a 17.4 CFM @100 PSI, max 175 psi, 80 gallon, I went from a Craftsman 6 hp, 33 gallon oil less type up to this. It was like going from a bracket class up to Top Fuel, a heck of a jump in performance.

 

[26 Flatrod]

I'm sure someone will correct me if I'm wrong, but nearly every 1/2" impact I've seen is rated at 90 psi. I'm sure when you get up into the 3/4" drive arena you probably need higher psi. I'd guess a lot of it would depend on how well designed the impact is and how efficiently it uses the air.

Thanks, I guess the tools could be the weak link, I don't have the most expensive impact wrench and it is pretty old now. Maybe all I have to do is replace those with some good ones and I would not have to pay more for higher pressures.

 

[26 Flatrod]

From past personal experience, trying to inflate a 16 inch tire for a 1 ton truck is a bit slow with a 125 PSI compressor. By the time you get out to the end of the air line you'll probably be waiting for the unit to cycle a couple of time to inflate to 100 PSI. It's that "last little bit" that gets to be a pain. The last compressor we bought was a 17.4 CFM at 175 psi, 80 gallon, I went from a Craftsman 6 hp, 33 gallon oil less type up to this. It was like going from a bracket class up to Top Fuel, a heck of a jump in performance.

Good point, I do not have any truck tires to fill, but I will keep that in mind. So if you are using the full 175 pressure, do you have any problems wrecking tools or snapping off bolts? Also what do you use for piping and hose, is it easy to find something that is rated for that pressure?

 

[theoldwizard1]

CFM is much more important tan PSI. I can't think of any automotive tool that would use more than 125 psi.

 

[Streetbu]

Air tools are designed to be run at 90psi. That being said MANY people run them at a higher psi for multiple reasons. No need to run a regulator inline being the first. Second, if you live in the rust belt you'll understand stuck/seized fasteners. Even with my good IR impact gun, there are many times bolts wont come at 90psi, but will @ 135psi. I would not however run the tools @ 180psi or more though like most 2 stage compressors run at. Sanders are known air hogs, you'll need at least 15cfm for the compressor and tool to work properly. I've used them on mine, you can do it, but you're placing a lot of extra wear and tear on the compressor.

 

[Rickss96]

And be sure your air hose is big enough. If you use 50 ft of 1/4" air hose you'll never get enough pressure and volume at the impact wrench or cutoff wheel. Recommend 1/2" and it will likely make your old impact wrench young again.

Search around on GJ for other discussions on what compressor to get. Here is a recent on the General Tool Discussion that you may be interested in:
http://garagejournal.com/forum/showthread.php?t=255928

 

[PanelDeland]

Tank size also makes a difference. Just getting a bigger tank wont help because you'll wear out the pump building pressure. Bigger hose should make a lot of difference.

 

[TheEquineFencer]

Tank size also makes a difference. Just getting a bigger tank wont help because you'll wear out the pump building pressure. Bigger hose should make a lot of difference.

Bingo, I run 1/2 inch out to where I'm tapping into it. When I worked at Ryder, we used 1/2 inch hose on the 1 inch air wrench. You couldn't hardly break nuts loose with a 3/8 air line.

 

[TheEquineFencer]

Good point, I do not have any truck tires to fill, but I will keep that in mind. So if you are using the full 175 pressure, do you have any problems wrecking tools or snapping off bolts? Also what do you use for piping and hose, is it easy to find something that is rated for that pressure?

200+ PSI rated hoses. I usually turn the pressure down for most use, but when I'm running high CFM, like a sandblaster, I run it up to 175 and use a regulator at the working end, that way I have the extra volume/pressure of the tank at the high CFM. The light bill is lower too. I've thought about having a small cheap compressor for normal things and not running the big one.

 

[TheEquineFencer]

FWIW, after the shop burned down, my G/F tried to pump up a flat lawnmower tire with a HF pancake compressor and couldn't understand to start with why it was taking so long. I told her' "that's the difference between a $39.95 compressor and a $2800 compressor."
My neighbor had the same problem with his new compressor, it gets to around 80-90 PSI and took forever to get the last 10 PSI. It's a 125 PSI compressor. It has to build the pressure in the tank and the tire to 100 PSI. If he let's it sit a couple of minutes, it cycles off, he adds air and it kicks back in a couple of times because of the volume needed in the bigger truck and horse trailer tires. With mine, I just pump it up in a minute or less. For most of what I used it for, it's was WAY too big, but when I needed it, it was nice. I guess it's like cruising around town in a Big Block powered car. I think I'm going back with a Quincy from Northern Tool, something like this http://www.northerntool.com/shop/tools/product_200350477_200350477
This would be another choice because of the lower amperage draw. http://www.northerntool.com/shop/tools/product_200350476_200350476

 

[Jvvmusme]

Buy the biggest compressor you can afford

 

[26 Flatrod]

Thanks for all the input, I have a few things to add, but I am running out of time tonight. I will check back tomorrow

 

[600SL]

10 CFM@90PSI should be good for just about anything except a Die Grinder running continuously and it will be totally useless for a sand or bead blaster. Pressure is not important for running the tools because generally it should be regulated down to about 90PSI anyway. But an 80 gallon tank with 175PSI is about 40% more air than an 80 gallon tank with at 125PSI. Essentially its like having a bigger tank.

If you want to run a sand blaster then a 2 stage 5HP 80 gallon 175 PSI, about 17 CFM at 175PSI unit is an absolute minimum. 7.5HP is a real nice solution.

Make sure its a real 5HP > 20 Amp @ 230V.

 

[f575gtc]

Do 2 Stage compressors always produce more CFM at 90PSI vs 175PSI?

I have seen some 2 stage pumps show numbers like 16.5CFM @ 175PSI and 15.0CFM @ 90PSI. Is it possible that some pumps are less efficient at lower PSI and produce less CFM or will the CFM at 90PSI always be higher than at 175PSI?

 

[sublimate]

I don't think I've ever seen that.
That would be like a truck that accelerates faster hauling a heavy load than it does unloaded.

 

[tlmartin84]

Buy the biggest compressor you can afford

Best answer here. You use this item probably more than anything else, splurge.

My next one will be a minimum of 20cfm and 80 gallon.

My current is 15cfm 60 gallon and it runs continually painting and blasting.

 

[600SL]

I have a 13 CFM Lowes that I got on sale for $400. Its so Cheep I may just buy another and run 2 when I need more air.

 

[BFBOB]

Buy the biggest compressor you can afford

... and have room to store and enough power to run. That's the easy answer, but I'd guess matching the CFM and PSI of your biggest air hog would be a good starting point. My compressor is only about half the CFM of my windiest tool (straight line sander), but has an 80 gal. tank. That lets me work long enough at a time that I'd mostly be off doing something else during the pump-up time anyway.
Lots of good advice here - take it into consideration and draw your own conclusions.

One thing I've seen mentioned is using larger-than-necessary piping, say 1", to add storage capacity and cut losses to the point of use. My runs are pretty short, but I still went to 3/4" when 1/2" would have been adequate.

 

[26 Flatrod]

After reading all the input, I bought a Castair C518VC1 compressor, it is a 2 stage, has 18 cfm at 175psi with an 80 gallon tank. price is reasonable at $1475 and they deliver it free in the Mpls area. I think this is the best of all worlds, it has 2x the CFM I had before and the extra pressure if I need it. price is not crazy high either.

The one drawback is the motor and switching system. It has a 3450rpm motor with a smaller case and just a pressure switch. the next level up comes with a 1750 rpm motor in a larger case with a magnetic starter. This was $400 more for that compressor. Since I am not running a shop, I figured I would take my chances and save the money. I can always get a bigger motor if this one burns out.

 

[CompressorPros.com]

As a general rule, allow 4-5 CFM for your impacts...8-10 CFM if you go with a 3/4". Your sanders will use somewhere around 12-15 CFM. You want to oversize your compressor by 25% to keep the compressor working more than its recommended duty cycle.

 

[evintho]

After reading all the input, I bought a Castair C518VC1 compressor, it is a 2 stage, has 18 cfm at 175psi with an 80 gallon tank. price is reasonable at $1475 and they deliver it free in the Mpls area. I think this is the best of all worlds, it has 2x the CFM I had before and the extra pressure if I need it. price is not crazy high either.

Good choice! CFM is everything. I have an IR 80gal - 90psi - 18cfm. I'll never need another compressor! I've never had an issue breaking the most overly torqued or rusted nuts. I can run my 90gal pressure sandblaster all day long with the compressor hardly ever having to play catch-up. I use a 3/8" hose but 1/2" would probably be better. Your 2-stage with 175 psi and 18 cfm is all you'll ever need! Make sure you have a quality regulator and lots of water traps. The key is clean dry air.

 

[26 Flatrod]

One thing I've seen mentioned is using larger-than-necessary piping, say 1", to add storage capacity and cut losses to the point of use. My runs are pretty short, but I still went to 3/4" when 1/2" would have been adequate.

That is my next project, installing piping throughout the garage. I have used sweated copper in the dim dark past, but I am wonderring if there isn't a better choice these days, Friend of mine suggested schedule 80 gray CPVC piping. said it is rated for high pressure and you can just bond the joints. Any comments on this or any other tubing to use?

 

[26 Flatrod]

Good choice! CFM is everything. I have an IR 80gal - 90psi - 18cfm. I'll never need another compressor! I've never had an issue breaking the most overly torqued or rusted nuts. I can run my 90gal pressure sandblaster all day long with the compressor hardly ever having to play catch-up. I use a 3/8" hose but 1/2" would probably be better. Your 2-stage with 175 psi and 18 cfm is all you'll ever need! Make sure you have a quality regulator and lots of water traps. The key is clean dry air.

Thanks, it was delivered a couple weeks ago, and looks great. the pump is huge compared to the motor, and is really geared down so it only runs at 900RPM or so. I can't wait to get it hooked up and running. Gotta wait for power to be run to the garage.

 

[MoonRise]

That is my next project, installing piping throughout the garage. I have used sweated copper in the dim dark past, but I am wonderring if there isn't a better choice these days, Friend of mine suggested schedule 80 gray CPVC piping. said it is rated for high pressure and you can just bond the joints. Any comments on this or any other tubing to use?

Comment?

Your 'friend' is an idiot.

There is NO commonly available plastic 'pipe' that is rated for use with compressed air or gases.

http://www.usplastic.com/catalog/item.aspx?itemid=23484 and read the part that says

Not recommended for use with compressed air or gases

From Charlottle Pipe

http://www.charlottepipe.com/Documents/PL_Tech_Man/Charlotte_Plastics_Tech_Manual.pdf

To reduce the risk of death or serious injury from an explosion,
collapse or projectile hazard and to reduce the risk of
property damage from a system failure:
• Always follow the warnings and procedures provided in
this manual.
• Only use PVC/ABS/CPVC pipe and fitting for the
conveyance of fluids as defined within the applicable
ASTM standards.
• Never use PVC/ABS/CPVC pipe and fittings for the
conveyance of gasses.
• Never use PVC/ABS/CPVC pipe or fittings in structural
application or in any load-bearing applications.
• Never strike the pipe or fittings or drive them into the
ground or into any other hard substance.

Testing with or use of compressed air or gas in PVC / ABS
/ CPVC pipe or fittings can result in explosive failures and
cause severe injury or death.
• NEVER test with or transport/store
compressed air or gas in PVC / ABS / CPVC
pipe or fittings.
• NEVER test PVC / ABS / CPVC pipe or
fittings with compressed air or gas, or air
over water boosters.
• ONLY use PVC / ABS / CPVC pipe or
fittings for water or approved chemicals.
• Refer to warnings in PPFA User Bulletin
4-80 and ASTM D 1785.

Copper pipe or 'iron' pipe (black iron pipe, which is actually steel nowadays) or the aluminum RapidAir or other brand aluminum air piping stuff. Or other metal pressure-rated tube/pipe rated for use with compressed gases.

Flat-out NO to the use of 'plastic' piping for use with compressed air (or other gases).

 

[C96]

The pump looks to be a cloned Saylor-Beall 705 which is absolute bullet proof if it were genuine S-B. Don’t know how well the knock-offs hold up, but then your Castair was about half the price of a genuine Saylor-Beall. Many companies have chosen to build their compressors around the imitation Chinese S-B pumps. Eaton and Sanborn are also building compressors using them today.

The one drawback is the motor and switching system.

I’m sure your Castair will serve you well, but just as you stated above, I also believe the weak link here is going to be the lack of the larger frame 1750 rpm motor and no mag starter.

Friend of mine suggested schedule 80 gray CPVC piping. said it is rated for high pressure and you can just bond the joints.

Your 'friend' is an idiot.

As far as your airline plumbing goes, if exposed, stick with copper, or black-iron pipe. No place for plastic anything in a shop environment (just my opinion). This goes for the electrical as well if exposed; use EMT, rigid steel pipe, armored cable, metal flex, etc. You get the idea, a shop can be a place where the plumbing and electrical can be easily damaged if exposed and not protected properly using the correct products.

Have fun with your project!

 

[26 Flatrod]

Comment?

Your 'friend' is an idiot.

Flat-out NO to the use of 'plastic' piping for use with compressed air (or other gases).

Thanks for the heads up. Just because he's a friend and they did this in his shop doesn't mean its safe. I would have looked this up before using it, but this jkust saves me the time.

Thanks again