PTO Air Compresser

[srjones]

You mentioned sand blasting. Your going to need a BIG compressor to do any real sand blasting. They require a rather high CFM.

Yes, that's one of my intended uses, but from what I've read, soda blasting on wood is typically done at 40psi and I think the compressor could probably keep up with it.

The heart of the system is the following Harbor Freight compressor.

- Harbor Freight Tools - Quality Tools at the Lowest Prices

I purchased it on sale about 3 years ago for $99 and used a 20% off coupon. For a long time thought about how to drive it (belts, pulleys, chains, etc) but finally concluded the direct drive approach would be the best (and simplest) The max RPM of this compressor is 1200 RPM and my smaller tractor has a 540/1000 pto speed option. Running at 540 it could still meet most of my needs. Also, this means that instead of a driven pulley, it would be a driving pulley meaning that I could run other belt driven things. My specific (future) plan is to mount a belt driven pressure pump so it could become a snow machine. ( SNOWatHOME ｻ Free Plans - How to make a cool science project and build a homemade snowmaker )

I welded a PTO adapter to a flat of steel about 4-5" around and drilled three oversized holes equally spaced around the center. Once I was sure I had it centered on the pulley, I marked, drilled and then tapped threads so I could bolt the pto adapter 'plate' directly to the flywheel. The oversized holes were done so I could 'fine tune' the centering of the plate.

For the frame, I used some scrap and new steel, and built it in such a way that the pto shafts would be pretty close to level for both of my tractors and it would easily work with a quick hitch.

Even though the frame was done (and painted) I was still trying to figure out what to do for a tank. The final product, admittedly, looks kinda goofy, but functions well. It's a horizontal tank mounted vertically to the back of the frame.

The unloader valve came from Grainger (about $50) and is supplied by 1/2" copper tubing. The coil fins came from Harbor Freight as a replacement for the tubing between the two pistons. It does a good job of smoothing out the bends and making it look pretty. And it cools it down too. Coming from the bottom of the tank (and fed by the unloader valve) is 1" galvanized pipe and a drain cock at the very bottom of the tank.

I've got the pictures and will be uploading tonight.

 

[Soundguy]

Could always run in the 1000 rpm setting and reduce throttle / rpm a bit since yor hp requirements will be low..

soundguy

 

[srjones]

And the pictures. Warning: professional welders, machinists and perfectionists should look away now.

 

[R W]

I was thinking of building one and wanted to know if anyone here has built one.

I have thought about it too, about as far as I progressed.
Have heard of a used car engine being converted to work as a compressor
and have seen two SV Ford V8s set up with one engine driving and one as a compressor.
What CFM do you require?

 

[Bedlam]

Looks good to me..Look forward to the results of the test run...

 

[Iplayfarmer]

It's funny this thread came up again when it did. We just had a refrigeration compressor go down at work. The motor is what went bad on it, but the compressor part is just fine. It's a solid unit, and it costs more to rebuilt the motor than it's worth. I keep picking my brain trying to come up with a way to convert this compressor to run off a PTO.

Great Job SRJones! What do you figure your pressure and CFM are going to be?

 

[Wis Bang]

We used to PTO mount small vee air compressors under road tractors to blow off loads of acid. Quincy was one brand.

They were complete w/ unloader/pressure relief valves and were designed to supply 40 PSIG at sufficient CFM to push sulfuric acid [14.6 LBS/gal] out of a trailer to the receiving tank without a holding tank. Emglo makes one too.

The rush of air when the tank goes MT clears the hoses out making a safe & clean unhook for the delivering driver. I'm sure used ones could be found...

 

[srjones]

.Look forward to the results of the test run...

I did quick test the night I took the pictures. No leaks, the pressure built up really quickly (up to about 100 psi). I stopped the test because I heard what sounded like 'piston slap'. However, I don't know if it was the sound of the 1 cylinder engine under load, or the PTO drive shaft loose or if it's just normal for a new compressor (I seem to recall a similar sound on other piston compressors, but I could be wrong)

A question for those who know. Are compressors supposed to be 'broken-in' ie. run without load for a period of time? I seem to recall reading that somewhere, but I can find it now.

What do you figure your pressure and CFM are going to be?

I wish I had a good way to figure that out. The specs say at 1050 RPM it will deliver 15.1 CFM @40psi, 13.5 CFM @90psi and 12.3 CFM @ 115 psi. At 1000 RPM, it should be pretty close. At 540 RPM, all bets are off. If I were to guess, I'd probably be wrong. (half? less than half? more than half?)

Is there such a thing as a pneumatic CFM meter? I'd be really curious as to how to figure that out.

-srj

 

[DieselPower]

Yes there are air CFM meters/gauges. I have a couple I have taken off of utility company service trucks over the years. They have nice hydraulic driven 4 cylinder air compressors on them and really nice CFM flow gauges. They look just like the CFM gauge you would see on a mig welder only a lot bigger. I'll have to dig one out and take a picture of it.

 

[Soundguy]

looks good to me!

soundguy

 

[Brad_Blazer]

Nice work. I like the protective frame. It should lend itself nicely to adding some simple guarding.

I have one of those HF compressors in my home shop running off a 3hp motor at reduced RPM. It's been in service at least a couple of years now and it works great. Within reasonable limits the output should be proportional to RPM. Strangely, those floating ball flow meters are called rotameters.

Rotameters, Basic Flowmeter Principles

Is there a check valve built into the unloader? That could be a source of noise as the pressure gets higher. I started out with a plain swing check on mine and it was noisy above 100psi.

 

[srjones]

Nice work. I like the protective frame. It should lend itself nicely to adding some simple guarding.

I have one of those HF compressors in my home shop running off a 3hp motor at reduced RPM. It's been in service at least a couple of years now and it works great. Within reasonable limits the output should be proportional to RPM. Strangely, those floating ball flow meters are called rotameters.

Rotameters, Basic Flowmeter Principles

Is there a check valve built into the unloader? That could be a source of noise as the pressure gets higher. I started out with a plain swing check on mine and it was noisy above 100psi.

Thanks Brad. That's good reminder on the safety aspect. If I can't find/borrow a rotameter, I've found a simple method to calculate CFM by using a stopwatch and looking at the pressure gauge. Since the tank is of a known volume, CFM can be calculated as volume over time.

Here's a good write-up on the subject. Evaluating True Horsepower and CFM Ratings of Air Compressors

The unloader has a built-in check valve and I'll pay closer to it on the next run. That makes a lot of sense and I'm hoping that's it.

 

[srjones]

looks good to me!

soundguy

The more I look at it, the better it's starting to look to me!

 

[srjones]

The unloader has a built-in check valve and I'll pay closer to it on the next run. That makes a lot of sense and I'm hoping that's it.

Update 6/3/09.

It's not the unloader making the noise. My next suspect is the PTO telescoping shaft. When I took it off, I noticed there was play in the shaft, and the 'clanking' noise was similar (but much softer).

It needs to be greased, so I'll do that and see if it make a difference.

Any other suggestions out there for ways to eliminate PTO shaft noise? Would a few strategically placed hammer dents tighten it up a bit?

BTW, the PTO shaft is a Eurocardan so it's got that unique shape.

 

[Soundguy]

any ujoint play?

soundguy

 

[srjones]

any ujoint play?

soundguy

I checked that, and it seemed pretty tight. But they'll get a good shot of grease tonight to be sure.

 

[have_blue]

I checked that, and it seemed pretty tight. But they'll get a good shot of grease tonight to be sure.

How straight of a shot is the drive shaft? If it's on an angle greater than ~15 Deg, it may be noisy and inefficient.

 

[DieselPower]

How straight of a shot is the drive shaft? If it's on an angle greater than ~15 Deg, it may be noisy and inefficient.

They also don't like being run at 0 Deg either. They need to have a slight drive line angle or the needle bearings within the U-Joint caps will not spin. This leads to premature U-Joint failure due to flat spots on the needle bearings.