7.5hp compressor build, am I trying to do too much?

[metalmagpie]

We all use compressed air. So do I. I've wanted to upgrade my compressor for awhile. I found a donor compressor which was someone else's uncompleted project and bought it. It's got a Champion R30A air pump (4 piston, disc valves, splash lubricated), 7.5hp motor, Square D pressure switch, and a 120 gallon horizontal tank.

I am in the midst of going through the air pump. I straightened the ribs on the intercooler tubes, bought new air filters, cleaned and relapped the valves, and removed the tubing between the pump and the tank to rethink it and refurbish it. I also tested the motor and am in the process of hydrotesting the cylinder.

My game plan has multiple possible pathways. If the tank tests good I'm going to just build it into a compressor. If it doesn't, I plan to remove the air pump and 5hp single phase motor from my existing vertical compressor (80 gallon vertical tank) and install the bigger air pump and motor up there. That would probably involve extending the top plate.

Along the way, I plan to pipe in a heavy duty oil cooler between the pump and tank, with a filter between the cooler and tank to trap water.

The rest is just details. But I have a lot of little problems to solve. For example, Champion compressors have a check valve where the air enters the tank, as is common among many compressors. This guy just screwed pipe into the tank to a vertical T. An overload valve is on the top part of the T. Going sideways from the T is a freestanding check valve of the type I never would have guessed would hold air. Then on up to the air pump. Have you ever seen a freestanding aftermarket check valve on an air compressor before? That bit of plumbing was rusty and looked pretty bad but after I took everything apart and wire brushed it and put it back together it doesn't look half bad. I took apart the check valve and extracted the disk. I lapped the disk and cleaned its seat, but it sure doesn't look like new. I can't really imagine it wouldn't leak.

More later.

metalmagpie

 

[dkmc]

Please write an essay here, detailing the exact reasons why you didn't buy a Quincy QR series machine.

 

[PackardV8]

Anyone can throw money at a project. It takes a real Practical Machinist to build his own and add several degrees of complexity to settled science.

jack vines

 

[metalmagpie]

While I have not yet succeeded in obtaining my goal of a lot more compressed air, I have learned a lot of useful lessons. I learned how to hydro test a 120 gallon tank safely by myself. I used my $15 yard sale electric pressure washer to pressurize a tank full of water. The goal was to apply 150% of the max working pressure to the tank for 20 minutes. The fact that my tank didn't get there before pinhole leaks revealed themselves in no way invalidates the procedure. I am happy to have avoided future problems, and a guy will be by this morning to pick up the tank to make it into a meat smoker. Win-win.

I learned that it's entirely possible that an old air tank may not be suitable for reuse, and how expensive ASME tanks are. I learned how simple it is to clean and re-lap disc valves in an air pump. I learned that new I-R compressors may not be worth rebuilding, but units from Quincy, Champion, Saylor Beall or Jenny may be.

I learned that running a 3 phase compressor on power from a RPC is probably not suitable for full-time operation. So unless I come across an affordable single phase 7.5 hp motor, the compressor I'd planned is going to be relegated to occasional use when I need more air than my 5 hp can supply.

I learned that it can be a lot cheaper to not pump air all the way up to 175 psi. Dollars per cfm are less at lower max pressures.

I learned that it's easy to buy parts for industrial grade air pumps, but that there are sharks in the water so you have to be careful who you deal with.

And I started on the road to learning about HVLP painting.

Like I said, lots of lessons.

metalmagpie

 

[steve45]

I've got a 175 PSI compressor and run it at a lower pressure. Much quieter and less wear on everything.

 

[stephen thomas]

While I have not yet succeeded in obtaining my goal of a lot more compressed air,

Perhaps you don't have the room -
An easy means is simply plumb a couple (or more) compressors and tanks together.
When my wife was still doing a lot of sandblasting, i plumbed in a 7.5 Kellogg-American along with the legacy 5HP IR T30, both single phase.
Set the cut on pressures staggered so the bigger compressor only comes on line when needed. Or turn it off with a disconnect until needed. More air storage with multiple tanks, lower energy costs including lower start costs most of the time. Installed back-up air source when one of the components dies.

smt

 

[TaperPin]

Have you ever seen a freestanding aftermarket check valve on an air compressor before?

Those are commonly available parts and work well. The air doesn’t know if it’s a check valve built in to a pump or on the tank side.

Ive become a big fan of having multiple pumps/motors on the same tank. For small stuff only one relatively quiet pump runs, if it’s going to take more air flow than one pump can handle the second kicks in about 5 psi lower than he first, and if it’s a really heavy air demand the third kicks in when pressure is about 10 psi lower than the number one pump. No way would I ever prefer all three to run at the same time for small stuff. My three pumps are all the same, but I think a 15 amp 120v motor/pump would be a great compliment to a bigger 5hp or 7hp 220v setup.

 

[TaperPin]

And I started on the road to learning about HVLP painting.

I’ve known a lot of guys who use large 125gal or even 250gal propane tanks for air - not for OSHA inspected businesses, but for home use.

I’ve always made due with an undersized compressor for my hvlp painting, but decided to keep adding 15 amp 120v pumps to my 20 gal tank until there was enough air volume to keep up with my main sprayer - an .011mm Iwata, and three is the magic number. I can run that gun wide open for as long as need be.

If you don’t have one, a viscosity cup can help determine how much thinner is required to reach the viscosity your gun sprays well with.

Just remember, the psi rating a hvlp gun has is the maximum pressure for it meet hvlp standards, not necessarily the best overall atomization - more pressure will give better atomization.

 

[jccaclimber]

^^IIRC Kustomizer did something like that, but he also set it up so that his control would cycle through the compressors rather than have one take all the wear.