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.