Air Compressor; shop tools question

[txSteve]

Specifically I started trying to restore the brake calipers on the spider I just bought. But I was unable to remove the pistons based on any manual means. So I started contemplating an air compressor purchase. I have never owned an air compressor aside from the basic tire inflater style, so I had a few questions.

I have seen really good reviews of this Makita compressor, but it is rated 40PSI (3.8 CFM) and 90 PSI (3.3 CFM). As a compressor noob, I have no clue why the 2 different numbers. My concern is that when I look at air impact wrenches, for example, most seem to be listed at 4.2 CFM or higher. So am I correct in assuming that those will not work well together because the wrench wants more air flow than the compressor will delivery? Am I reading these numbers correctly?

There is also a little more powerful model from Makita that is rated 40PSI (4.8 CFM) and 90 PSI (4.2 CFM). But its also $100 more. So I guess another question is what type of tools y'all using air compressors find useful in working on your Fiats?

[vandor]

Steve,

Those numbers are really only relevant if you will use a tool continuously, like a nail or paint gun. It means that if the tool uses 3.8 CFM of air the air compressor will be only able to maintain 40 psi of pressure.
If you are going to use it mainly for an impact wrench then it does not matter, as it only operates for a few seconds and will not deplete the air in the tank.

As far as removing the caliper pistons, hook it up to the car's brake hose normally, let it hang down, then pump the pedal until the piston pops out. Be sure to put a pan under it to catch the mess.

[azruss]

no offense to you, maestro Csaba, but if you are trying to break something loose and need to ratta-tat a while with an impact wrench, you will significantly drop the air pressure and the wrench becomes useless.
The higher the pressure, the lower the volume. Most air tools do not run on 40 psi and require much greater volume that 4.8 cfm. wont get much sandblasting done at that volume either. You will find that even the larger of the 2 compressors will leave you short much of the time. With an air compressor, more is better.

[courtenay]

Great explanation, Csaba. So what kind of numbers would you look for if you were going to be using a paint gun or media blaster? What difference does the size of the compressor tank make? I have a small (2 gallon) Porter Cable compressor that came with a brad nail gun that works OK with my impact wrench - although if I try to take all 8 lug nuts off my truck tires at once I have to wait for the compressor to catch up. What difference would a compressor with, say, a 5 gallon tank make - if any?

[txSteve]

azruss, I do not doubt that more is better. As long as you qualify "better" here. Money has to be a consideration. And based on the fact that the price of these things seem to go up exponentially as power increases not sure I can justify some of the $3k+ ones I have seen as "better" for my home garage. Surely there has to be a balance in here somewhere, which is what I am trying to find.

[124JOE]

last summer i rebuilt my front calipers
my standard compresser poped out one piston
but the other didnt.so i did as casba said and hooked it up to the car and pumped
the pedal,yes it makes a mess.


a 40 psi unit is great for a spray gun or air brush
but not for wrenching
mine tops out around 110 psi
and only costed $100 at biglots when they had them
2 years and running strong
make sure you drain it after use so it dont rust the inside of the tank

[txSteve]

Joe, what I find confusing is the PSI numbers though. For example the 2 I listed have multiple numbers for PSI. Take the bigger one. It says:

The 5.2 gallon tank sustains an operating pressure of 140 PSI and delivers 40PSI (6.9 CFM) and 90 PSI (6.5 CFM)

So when you say yours is 110 psi, I am not sure what to compare that with. The 140 PSI number? The 40? The 90? All very confusing

[vandor]

no offense to you, maestro Csaba, but if you are trying to break something loose and need to ratta-tat a while with an impact wrench, you will significantly drop the air pressure and the wrench becomes useless.

True. Then you have to wait for the pressure to build up again. It really depends on how much one wants to spend, a larger compressor is easier to work with, but may not be worth it for someone that only uses it a few times a month.

[Kent124]

I've heard good things about GMC Syclone Compressors.

If you can get free air nearby a cheapo option is a portable air storage tank.

[vandor]

Great explanation, Csaba. So what kind of numbers would you look for if you were going to be using a paint gun or media blaster?

You'd have to look at the specs of those tools and that of the compressor to determine if it can keep up with the tools.

[seabeelt]

See this link: http://fiatspider.com/f08/viewtopic.php ... compressor.

Compressor size depends on what you want to use it foar and anticipate using it for. max pressure is relative, but operating pressure and at what cfm are the keys. Also depending on usage, duty cycle is important. 50% duty cycle means that a unit requires 50% down time between runs to cool off properly before the next time it should turn on or cycle for proper operation. cfm and at a certain psi is tool dependent. you need to look at the tool you want to use and see if you compressor (selection ) will properly power that particular tool, paint gun, blaster, what ever... This will help you determin the proper compressor for your application.
r/

[azruss]

when a compressor shows a maximum pressure of 140 psi, then that is where the pressure relief valve is set at. DO NOT use 140 psi pressure. air nozzle and air tools are built to run at 90 psi and can disintegrate to shrapnel under high pressure. you can graph pressure vs volume in a straight line and be close enough. if you really care, many compressor mfg website have pressure/volume graphs for their equipment. with that said. most air sanders, wrenches, die grinders, sand blasters work at 90 psi. 3/4" impacts work at 120 psi (designed for BIG lug nuts). I have an industrial grade 3hp, dual cylinder portable with a 30 gal tank. runs off 220v. 1ph. I spliced off my spa power. With a 3/8" impact, i have to let it build up pressure if im working on something really stuck. it barely adequate for sand blasting. can paint lphv all day long. wont run a DA sander. Will run a long board but will drop pressure to about 60 psi if run continuously. used to have a 5hp home model that kept overheating when i tried to paint with it.

[124JOE]

Joe, what I find confusing is the PSI numbers though. For example the 2 I listed have multiple numbers for PSI. Take the bigger one. It says:

The 5.2 gallon tank sustains an operating pressure of 140 PSI and delivers 40PSI (6.9 CFM) and 90 PSI (6.5 CFM)

So when you say yours is 110 psi, I am not sure what to compare that with. The 140 PSI number? The 40? The 90? All very confusing

i guess mine would be a 140 max
and deliver 40 constantly
a bigger unit would deliver 90 constantly
but i have mine to shut off at 110