Air Compressor Recommendations?

[Iplayfarmer]

You can hook up two compressors together, no problem, just tee them both into a common line. When you're using a low-demand item, you could actually only turn one compressor on, if it keeps up with the volume needed...then for higher demands, turn the other one on. (No need to close valves, just flip the electrical switch on or of for the second compressor)

Many factories will do exactly this, they will have several compressors teed into their plant's air supply header.

Worst case, if the air pressure leaks out through the non-working compressor, you simply put a check valve in the line at that compressor. A check valve allows air to freely flow in one direction, but completely blocks the air in the other direction of flow--so it will let air exit the compressor, but not flow back into it.

We are actually getting a second compressor at work and we are planning on setting them up in a loop so that pressure and flow are equal throughout the plant. I thought about doing that at home, but I don't have anything hard plumbed.

I'll just have to get the new compressor and the old compressor and see what is going to work best. I do know at least one of them is going to be easily removable via quick connects so that it's portable.

 

[VA_Joe]

Several years ago - I bought a oil-free compressor at Sears just for the 60 gallon tank (to hook up to my existing 5HP, 15 gallon oil lube unit that had good CFM output but no storage). It was a return that I got for about half the price of a new unit (and far cheaper than buying an ASME rated tank at Grainger).

As it turns out - there was nothing wrong with the compressor - just that the original purchasers were unhappy with the slow fill rate (the compressor was marked "defective - does not come up to pressure"). If you look around - you will likely see other returned oil-free compressors out there for the same reason. It is the cheapest way I know of to increase storage.

Joe

 

[Iplayfarmer]

Yeehaw!!

I just got my new Eaton Compressor!

At first I was a little dissapointed. As near as I can tell, it is the exact same compressor unit as my cheapy Homier Tools compressor. All of the rest of it, however, seems to be at least a step up. The tubing from the compressor to the tank has fins on it to dissipate the heat. The oil reservoir has a threaded plug rather than just an O-ring friction cap. The drain plug seems to be a lot better, the compressor came with quick connects already on it, and the quick connects are the push lock style. The guages and regulator seem to be pretty good too. It seems well thought out.

I added the oil and plugged it in. This unit is QUIET! I was really surprised. My wife and I were able to have a conversation about "make sure you don't lose track of the other projects you have unfinished and just play with the new compressor" right next to it while it was pressuring up. It seemed to come up to pressure pretty quickly. I didn't time it or anything to compare to what I had already, but it seemed faster.

All in all I'm pleased so far. I got my money's worth. The next few weeks will tell whether I got a bargain or not.

 

[svcguy]

Just a thought for the build it yourself discussion page. Attached are a couple of pictures of my unit, built from components commonly available. The compressor head was purchased on sale for $299, the 5hp commercial motor was the same. The electrical (heater start and switch) portion was purchased new off Ebay for $40 and the pressure hose (stainless weave over silicone hose) was $70. The tank is a propane tank from a large truck. I picked it up at a local auto wrecker for nothing. (They cannot be reused as fuel tanks unless tested, a costly proposition. The guys thought it would make a great tank and just gave it to me). Total cost was $750 dollars including the belts and pulley. The unit produces 18 cfm @ 175 psi. Because of a number of issues (the used propane tank and an off shore two stage compressor head), I set mine to cut in at 125 psi and out at 150 psi. I use it for everything, but built it mainly for sandblasting, which uses a LOT of air. I can blast none stop @ 90 psi without drawing the tank below 125 psi. This compressor runs really well and is extremely quiet. The reason it is so quiet is simple, the compressor head is mounted on a steel frame and not on the tank. A tank simply acts as an amplifier for the head, kind of like a drum. While this is running, you can easily have a conversation standing directly in front of the bench. I am going to have a plywood cover for the front which will make it even nicer.

 

[Iplayfarmer]

I cut the fittings off the refrigeration tank with my sawzall leaving about a 3 inch stub on each one. You'd be surprised how hard it is to find someone who can tap female threads in a pipe. Everyone can put the male threads on, but no one seems to have the tap for the female pipe threads.

I looked up an old friend of the family who has a plumbing shop and he helped me get the accessory tank fittings threaded. I bought the necessary pipe fittings from him and he didn't charge me a dime to tap the threads. I also bought a ball valve to replace the drain valve on the opposite side of the tank from the other fittings. See the first picture. The total bill came to $17 and change. That gives me a 10+ gallon air tank good to 400 PSI for under $25.

The fittings and hoses I needed to get the two compressors and the tank plumbed together were not so cheap. I could have bought everything I needed from Harbor Freight for about $20, but because of my impatience I went to the local hardware store and bought the quick connects and had them make me the short hoses. Total bill for these was almost $60. I got three female I/U type quick connects, four male, a five foot hose, and a ten foot hose. See the second picture. The last picture is a close up of the connections.

The two hoses have a male QC on both ends to allow me to go from the QC on either compressor to the Tee'd inlet on the tank. I already had the little regulator that is on the outlet.

The guy at the plumbing shop warned me that there was still some oil left in the tank. I dumped as much as I could out of the drain valve opening before I plumbed the valve in. Flash forward to when I am filling the tank for the first time. I plugged in the first compressor and started it up. Things were moving along nicely, so I went to plug in the second compressor. As luck would have it I left the QC that is straight up to connect to while the tank was under pressure. I pushed the hose connector into the tank connector and before I could get everything hooked up properly, I got a face full of oil out of the tank.

Boring is not something I complain about in my life.

 

[Blk88GT]

I just went through this 2 weeks ago. I ended up with the 60 gallon twin cylinder Husky for $599. It's great for what I need. I have no complaints at all.

 

[svcguy]

Just thought I would address an item that came up with this thread that could be a problem building your own compressor. Air storage, the size of your receiver or tank can be a double edged sword. Receiver size should be calculated and sized to compressor capacity and need. That is, there is an optimal size tank for a given output, neither too small or too big. If your compressor head is rated 9 cfm, you should size the tank accordingly to what you plan to use it for. Trying to run a bigger receiver may not work in your favor. While there are some complicated formulas out there, there are simple calculations too.

A common simplified formula is:

V= (Q *Pa)/ (Pi+Pa)
where: V= receiver size (ft3)
Q=compressor output (cfm)
Pa= standard atmospheric pressure (psi)
Pi= Compressed pressure (psi)

Pa is roughly 15 psi at sea level.

So for example, a 17 cfm compressor head would result in a calculation result of 7.968 ft3. A cubic foot of air = 7.48 gallons, so a roughly calculated tank size for 17 cfm would be about a 60 gallon tank.

This formula is an over simplification of a problem, as it doesn't take into account what PSI you are compressing to, what PSI you are drawing or a calculated volume need. This is not to say that more capacity won't work for you or that it won't be to your advantage, but based on a number of different factors, this is just a simple recommendation. Otherwise, you may end up with excessive cycling with smaller tanks or excessive run times with larger. There are other considerations for sure, but for simple calculations, this one is commonly used.

My 18 cfm compressor is matched up with a 65 gallon tank and it works quite well. Running @ 150 psi allows me to sandblast steady. The compressor can keep up nicely without excessive cycling, but when not sandblasting, it's a decent size for the air tools. If I was sandblasting continually, day in and out, I would add additional storage.

While realizing this isn't perfect, thought I would offer it as a suggestion.

 

[Dan69GTX]

That is a good point to bring up. I didn't mention the pros/cons when I said about adding air storage. Excessive cycling will shorten motor life while excessive run times could damage the compressor if it's not rated for that and/or if there is inadequate cooling.

For reference purposes for those who read my previous post.
I do a fair amount of sand and bead blasting. My compressor is rated at 24+ CFM at 175PSI. I have forced air cooling for the compressor and I have a fan cooled air-air heat exchanger after the compressor tank before my extra tanks. The air goes into the extra tanks and out a different port to help cool the air as much as possible. Drains in the line are also installed where needed. This gives me nice cool and dry air. About the only way to get drier air would be with a refrigerated dryer.

Thanks again for bringing up that point.

Dan

 

[gizmo]

It looks like I'm a bit late as you have already made your purchase. I was in the market for a larger compressor and had a number of interesting finds on Craig's List. I finally picked up the unit shown for $300 which included an industrial regulator, drier, 50ft of hose and a handful of QD fittings. I spent another $100 on a rebuild kit for the compressor. It is a two-stage compressor with a true 5HP motor that delivers 21CFM at 90psi. This big hunk of American thumping iron is one of the better purchases I have made. And it is much quieter than the oiled, fake 5HP I had previously.

 

[LetsRoll]

This link ~ SCFM - the definition ~ will help you understand scfm which is the real number you need to pay attention too when purchasing a air compressor.

For me, I purchased a air compressor from my local NAPA autoparts store. Cause I knew it would need parts in the furture, so I decided to purchase locally. I mainly use my compressor for sandblasting. Which we all know uses a ton of air. Sandblasting is the hardest job for a air compressor. I paid a little over $1600 dollars for my air compressor. Which is high, but my air compressor has paid for itself over several times. But, I had to purchased a blast cabinet also. I use the blast cabinet and air compressor to clean parts that I then paint and put on eBay. The blast cabinet cost me a little over $1000. All of the parts that I have cleaned and painted and sold on eBay, I have $O dollars now in my compressor and blast cabinet. Auto restoration is big on eBay, so if you guys want a big compressor, you can take my route and in the end, you'll have a free air compressor.

 

[LetsRoll]

My compressor is rated at 24+ CFM at 175PSI.

Dan...that is your pump displacement cfm. What is your scfm? Also, cfm is not calculated at 175 psi, its calculated @90 psi. Most manufactors know most users wont use 175 psi, so its calculated @90 psi. Just some food for thought.

 

[Dan69GTX]

Dan...that is your pump displacement cfm. What is your scfm? Also, cfm is not calculated at 175 psi, its calculated @90 psi. Most manufactors know most users wont use 175 psi, so its calculated @90 psi. Just some food for thought.

You are right - sort of. I used the wrong acronym. And you are right - most manufactures use 90 PSI instead of 175 PSI because the specs look better.

My compressor is a Champion Centurion II Model VRV7F-8 (7.5 HP baldor motor with the RV-15A pump). According to their web site
http://www.gardnerdenverproducts.co...iprocating/Brochures/C1-1-7-220 _5th_1-06.pdf
the specs for my compressor is...compressor rpm 990, 125PSI CFM displacement is 28.7, CFM delivery 23.9, 175 PSI is CFM displacement is 28.7, and CFM delivery is 23.1. My manual shows what I posted but the RPM is greater - just over 1000. However I'm sure specs have changed in the past 5 years.

Just for kicks I looked up Saylor-Beall compressors and they also rate the compressor at 175. Vertical Tank Mounted Air Compressors

It's tricks like that which make comparing compressors difficult. And its the different acronyms that keep people really confused if they don't pay close attention.

 

[VA_Joe]

Dan...that is your pump displacement cfm. What is your scfm? Also, cfm is not calculated at 175 psi, its calculated @90 psi. Most manufactors know most users wont use 175 psi, so its calculated @90 psi. Just some food for thought.

That's correct. Because most tools use either 40 or 90 psi there is really no use for a 125 or 175 cfm spec (doesn't provide much useful info for comparison). All that 175 psi really gets you is more storage in a given volume.

BTW - it is no longer a certainty (as it once pretty much was) that the 175 psi compressor will provide greater CFM output over the 125 psi compressor. The max psi of the single stage compressors are creeping upward without any increase in cfm output (it's the new selling point now that the manufacturers got caught with the horsepower scam).

If someone really needs the capacity and continuous CFM output of a 175 psi compressor - and few do - I strongly suggest spending a little more and getting a quality two stage, oil compressor with either a 60 or 80 gallon tank (I would go 80 - not much bigger sizewise).

Joe

 

[LetsRoll]

My compressor is a Champion Centurion II Model VRV7F-8 (7.5 HP baldor motor with the RV-15A pump).

Wooow...7.5 hp motor. Wonder what that bad boy spike up to when it kicks on? My compressor has a 5 horse motor and I have a 60amp double pole breaker in the box (30amps per leg=60amps total). I know when my compressor is running, the meter at the house is flying. I'd hate to see what the meter is reading if my compressor is running and it had a 7.5 motor on it.

BTW...if you dont mind me asking. What made you purchase a compressor with a 7.5 horse motor on it? 5 horse motor seems like enough for home hobby use.

 

[LetsRoll]

Since I knew I was going be doing a ton of sandblasting, I wanted a two stage and a 80 gal tank. Two stage is the only way to go if you need a ton of air like in sandblasting. When I use a impact or a paint gun, I have to turn the pressure way done. When I use a paint gun, the pressure has to be way done (35-40~ primer or paint). If I blast cast iron or steel that is real rusty, I use 100 lbs. I use about 70-80 lbs for my impacts. I've never used anything above 100 lbs.

 

[Dan69GTX]

Wooow...7.5 hp motor. Wonder what that bad boy spike up to when it kicks on? ........
BTW...if you dont mind me asking. What made you purchase a compressor with a 7.5 horse motor on it? 5 horse motor seems like enough for home hobby use.

The 7.5 motor uses 32 amp run (per leg)..Here are some specs on it:
Full Load Torque 22.5 LB-FT
Break Down Torque 52 LB-FT 231 % of F.L. Torque
Locked-Roter Torque 53 LB-FT
Starting Current (Amps) 184.0

I purchased the 7.5 HP because I don't have 3-phase at the house and it's the largest I could find to run on single phase current. I have a "serious" hobby and do all sorts of restorations, fixing, creating, etc. I knew I wanted it to run my bead blast cabinet, pressure sand blaster, etc. I considered a screw compressor, but most of those only do 125 PSI and I wanted the 175 PSI for operating my tire changing equipment. With 125 there were several times I couldn't easily dismount a tire that was on a rim for a long time. With my sand blaster the unit has a tough time recovering. - which is another reason for the 300+ gal air storage. The guy I bought the compressor from was trying to talk me into the 5hp version. Boy I'm glad I stuck to my guns and got the 7.5. I did a bunch of research and calculations and knew I needed over 20CFM for my max use.

Depending on my media I run 60-100 psi in the blast cabinet. I run 120-125 in the pressure blaster. I use line pressure for the tire equipment and I regulate the air line drops to 100. My spray gun is a Sata NR95 HVLP gun so it requires about 50 psi at the gun (which produces 10 psi cap pressure) it uses 13CFM. I also use my air compressor to feed a full face respirator for painting. (yes it runs through special filters to remove contaminates) So that is another 3-4 CFM for it.

So, yes, I'm very pleased with my compressor.

 

[Iplayfarmer]

I have a "serious" hobby and do all sorts of restorations, fixing, creating, etc.

Yep. That's a serious hobby to warrant that kind of compressor.

 

[The Fred]

Revamping this old thread,

I need a think out of the box idea for an outdoors sandblasting air compressor, my IR 7.5 is NOT big enough.

I want at least 75 CFM @100 psi. and not electric. I have tank space so that's not an issue. I had a VW air compressor but wasn't happy with it the darn thing was VERY loud.

Can you help? Ideas? How about a converted engine? How about something big that would run off a 540 RPM PTO?

I know I know I know I think too much.

Hmmmmm, too much time on my hands, Fred

 

[Scrambler82]

I used the IR 7.5hp, 27 CFM rated, compressor, a nice unit, noisey but more than kept up with my two sand blast cabinets and a lot of power tool work. Sold it when I just moved to SoCal.

You must plan on some heavy duty sand blasting wanting a 75 cfm rated compressor.
My neighbor used a commercial duty wheeled unit, made for major street work, we do a lot of larger pieces with it.
Maybe you can find a used unit for sale from a construction company, that would cover just about any of your needs.

What are going to do,with this BIG compressor ?

 

[buickanddeere]

A cast iron two stage about twice as large as what you think is required.