Time For a New Air Compressor

[SDSeville]

Well, my old 3 gallon HF air compressor is finally dying after 12 years. I am looking for a replacement and may be using the new one to spray gel or paint in the future. What are the minimum specs I should be looking for?

Thanks for the help.

 

[Woodonglass]

I'd recommend a minimum 3-5hp 60-80 gallon 13 CFM @ 40 PSI and 11.5 CFM @ 90 PSI Get a good Dryer/Drain system on it with NO OILER and ALWAYS use filters on your guns. Wire it to run on 220v and you're good to go!!! I bought a Craftsman on Craigslist for $250 and it's been running great for me everyday for 3 years. .

 

[gm280]

As big as you can afford... The bigger the better to be able to spray things and use all the pneumatic tools that are available these days. If you are using 115vac then the max is around 4 to 5hp size on a 20 amp circuit. But if you have access to 220vac, that is a completely different story. So buy as big as your wallet will allow. I never heard of anybody ever saying they wished the had bought a smaller compressor ever... But that is just my opinion!

 

[rickryder]

Yup the bigger the better!

 

[SDSeville]

Thanks guys! I am going to have to go with 110. I am no electrician, but with a new pool and a master bedroom/bath addition, I think my fuse/electrical box is maxed out. So, I should just go with the biggest one that runs on 110?

WOG - you got a smoking deal on that Craftsman.

 

[Woodonglass]

You might wanna take a look at this Husky from HD. It runs on 110 volts.

http://www.homedepot.com/p/Husky-60-gal-Electric-Air-Compressor-VT6314/100083906

 

[ondarvr]

Pay no attention to advertised HP, it means nothing, the only thing that is important is CFM, the higher the number at 90 PSI the better. You can spray small amounts of gel coat with a 115 V unit, but you will need to stop and wait for the pressure to build back up on larger projects.

 

[bonz_d]

, the only thing that is important is CFM, the higher the number at 90 PSI the better. You can spray small amounts of gel coat with a 115 V unit, but you will need to stop and wait for the pressure to build back up on larger projects.

Exactly. This is the issue and questions I have in another topic. The compressor I've been using is an old Craftsman 1hp Paint Sprayer model which only has a 12gal tank. It works fairly well for what I'm doing which of course are smaller jobs. With the smaller tank I can spray a paint cup full of paint and it will cycle once but takes less than a minute to complete it's cycle. I haven't noticed any drop off of paint quality while it's cycling.

In my case I'm going to try and size the pump and tank so that I can spray a full cup w/o a cycle and so that while I'm refilling the cup it cycles. I guess you could look at this as a dedicated compressor for spraying paint. It by no means will have enough supply to run high consumption air tools.

 

[Woodonglass]

Pay no attention to advertised HP, it means nothing, the only thing that is important is CFM, the higher the number at 90 PSI the better. You can spray small amounts of gel coat with a 115 V unit, but you will need to stop and wait for the pressure to build back up on larger projects.

Well..hHoresepower and CFM are tied together somewhat in that it takes horsepower to drive the pump to create higher CFM and not overheat the unit. Using units with lower HP and smaller tanks will cause more cycling to obtain higher CFM & WILL cause overheating and Shorter life of the overall Compressor unit. Using a 220v unit has some effect on this as well but NOT as much as increased HP. The CFM rating IS the most important rating when it comes to painting and cycling of the unit.

This is a good read...

http://www.spraygunworld.com/Information2/CFM.htm

 

[alldodge]

Picked up my last compressor based on CFM at 90 PSI. At the time the best bang for the buck for what I was looking for was the Kobalt from Lowes w/60 gallon tank

 

[Woodonglass]

This might be worth a short drive... I bet $275 or $300 could buy it..

http://fresno.craigslist.org/tls/4792421023.html

 

[lckstckn2smknbrls]

I don't like the oil free compressors. I prefer ones with a separate motor and oil filled pump.

 

[ondarvr]

Well..hHoresepower and CFM are tied together somewhat in that it takes horsepower to drive the pump to create higher CFM and not overheat the unit. Using units with lower HP and smaller tanks will cause more cycling to obtain higher CFM & WILL cause overheating and Shorter life of the overall Compressor unit. Using a 220v unit has some effect on this as well but NOT as much as increased HP. The CFM rating IS the most important rating when it comes to painting and cycling of the unit.

This is a good read...

http://www.spraygunworld.com/Information2/CFM.htm

Yes HP is a major factor, the problem is the compressor manufactures don't exactly tell the truth when it comes to HP on compressor motors. AMPs and CFM are the key to actual performance, the Claimed HP is meaningless.

 

[bonz_d]

Well..hHoresepower and CFM are tied together somewhat in that it takes horsepower to drive the pump to create higher CFM and not overheat the unit. Using units with lower HP and smaller tanks will cause more cycling to obtain higher CFM & WILL cause overheating and Shorter life of the overall Compressor unit. Using a 220v unit has some effect on this as well but NOT as much as increased HP. The CFM rating IS the most important rating when it comes to painting and cycling of the unit.

This is a good read...

http://www.spraygunworld.com/Information2/CFM.htm

Not quite true and you can see that in the link you posted. Cycling of the pump is all dictated by the demand put on it. If you are putting more of a demand on the pump than it can keep up with then yes it will over heat the pump, the motor or both. That is part of the Duty Cycle. The size of the motor and the size of the tank have little to do with it as long as it is within it's Duty Cycle..

The pump head dictates everything. Which is what I'm learning from doing research on this subject. The motor is just a means to drive the pump and yes from what I am finding the same pump head can be supplied with many different sized motors which also results in different specs. Some of these same motors can be wired for high or low voltage. For instance a 2 hp motor wired low voltage may draw 15 amps yet when wired for high voltage will only draw 8 amps. Still the same hp, same RPM, Same heat generated. Advantage being that High voltage lower amps can be safely run on a smaller sized wire.

Also as I've learned the same pump head can be used with a higher hp motor which in turn can run at a higher RPM which will increase the CFM output yet not increase the operating temp again as long as it does not exceed the Duty Cycle of the pump head. Then tank size starts to play into the Duty Cycle. A smaller tank will not increase duty cycle unless you are demanding more supply than the pump and tank can supply. You can out demand a small compressor by just blowing up a tire or a large compressor by trying to use multiple high demand air tools.

I know it's all so confusing!

 

[SDSeville]

This might be worth a short drive... I bet $275 or $300 could buy it..

http://fresno.craigslist.org/tls/4792421023.html

Thanks WOG. That is exactly what I am looking for and it's a great deal, but a little too far from Oceanside in my vehicle. I would eat up all the savings in my 12 mpg truck.

 

[gm280]

Folks be very careful with Horse Power ratings on so many electrical tools these days, especially on Air Compressors! If you seriously understand HP which is: A Unit of power, equal to 746 watts (joules per second) or 550.22 foot-pounds per second (fps), slightly higher than mechanical horsepower (745.7 joules per second or 550 foot-pounds per second) you will see how it gets used incorrectly! But the manufacturers play around with their HP claims and therefore make it look like theirs is better then the exact same everything from another vendor so often. So basically forget about HP ratings, they seriously are meaningless with compressors. If fact some places even state equivalent HP trying to skate on their claims. Sear is notorious for that!

And another item to be questioned too is amps! If one vendor says their motor uses 10 amps and another states their uses 12 amp, it honestly doesn't mean anything. And the reason why is, any poorly designed motor (and there are tons of them available) will read and use higher number of amps without seriously outputting any difference in their capability. So amps is another misnomer that the manufactures are using to promote their products knowing the general public always thinks more is better...not so! Better quality copper motor windings with quality materials, bearings and their actual designs will always use less current then some haphazardly assembled junk. Everything requires more current if it isn't of quality construction...even things as simple as bearings and alloyed metal windings to save a penny! Even a finely turned and balanced armature can work better will less amps!

Now if you really want to do side by side comparison, use the CFMs at 90psi and hope their numbers are truthful. A compressor that can deliver X number of CFMs continuously at a set pressure is the only real spec you can compare. Everything else is pure horse dodo. So for a better compressor, check out two items, the ability to supply a certain CFM at 90 psi AND the life expediency of the actual air pump. Both are listed for every air compression I've ever seen. That IS just my knowledge of this issue after reading too much about compressors over the years... JMHO!

 

[ondarvr]

The only reason amps become relevant is because when they claim it's 5 HP and runs on 115 V at 10 amps you at least know it's closer to 1 HP. A 2 amp difference between an efficient motor and a less so one isn't as important.

It's unfortunate that the exaggerated claims are still allowed on these products.

About 30 years ago I did a great deal of work involving water filtration, I worked on electric motors and replaced them frequently. I also had several small compressors and noticed in the service factor spot on the ID plate the compressors frequently said SPL, meaning special, not the typical 1.15 (or some number) in the box.

I was talking with a rep from Franklin Electric (they make motors) and asked him about why it said SPL, he didn't really want to say it was a lie when they claimed 3HP on 115V motor, but said this was how they got around giving an accurate rating. And that no, these motors did not put out more power than an identical one from them with the same amp rating.

 

[SDSeville]

Thanks for all the help everyone! I am keeping an eye on CL and will check back in when I find something.

 

[bonz_d]

SD, I do hope you are now a little more enlightened on this subject, keep reading and researching. There are a number of very informative websites on compressors that cover wide ranges of compressors and issues with them.

I am more confident in looking for an old belt driven compressor than the newer direct drive models. Especially if you can find one with a cast iron pump and not an aluminum one.

gm's suggestion of comparing by the 90# psi rule is about the safest way to judge what you're looking at. Though as I have found out a pump can have different out-put specs depending on the hp of the motor and at what RPM is it turning. Such in the case of the pump I have. They sold this exact pump with 3 different electric motors on it. 2 were hp motors of which one has a 2 pole motor and the other a 4 pole motor. Both have the same out-put specs.The 4 pole draws more amps than the 2 pole motor does. The other model has a 2 pole 2 hp motor. It has a slightly higher out-put, a higher cut in and higher cut out psi and also operates at a slightly higher RPM which as I've been told is how they get the out put increase. So in essence what they did was that a pump capable of running at 2hp with higher RPM and throttled it down with a smaller motor so more people could plug it in to their 115v service and run it.. Good marketing and wise manufacturing if you ask me.

 

[SDSeville]

SD, I do hope you are now a little more enlightened on this subject, keep reading and researching. There are a number of very informative websites on compressors that cover wide ranges of compressors and issues with them.

Yes. I can't believe how much I did not know that I did not know about compressors. Lot's of great information.