Another Air Compressor question

[ms fowler]

My original post for information on my recently acquired Tecumseh 3 cylinder air compressor from ( assumed) 1958 produced no information. I guess it is a rare to you all as it is to me.

Let me try another tact.
Can anyone give some reasoning as to how fast I should run this compressor? To repeat some data--it is a 3 cylinder, apparently single stage, with a displacement of 75 cubic inches. The flywheel is 16 inches in diameter.

3 inch stoke

How fast do other compressors of this approx size run?

 

[scw1991]

I'm having trouble following you. My post to your thread a few days ago produced no information? Seriously...I appreciate the compliment! I've copied and pasted it below. What kind of research did you do on the Atlas and Puma Compressors?


While it's nice acquiring manuals, parts lists, etc. I'd be hesitant on ripping into the compressor itself. I'd assume parts due to vintage are long obsolete and once head gaskets and o-rings get torn up, now they must be custom made.

A few months back I helped a friend get an old Kellogg 5HP 2-Stage compressor from the early 60's up and running. All we did was drain the oil and replenish with new synthetic compressor oil. Sometimes the best approach is "if it ain't broke, don't fix it".

http://www.garagejournal.com/forum/s...d.php?t=113115

With respect to what RPM to run the compressor at, it's really dependent upon how long you want the compressor to last or what CFM you want it to produce (to a certain degree of course). Most will concur the slower the compressor RPM, the longer it will last. Most reciprocating compressors spin anywhere from 700 RPM up to 1500 RPM (from what I have seen). For instance, my IR 2475N5 compressor spins at 1000 RPM and puts out 16.8 cfm. That same compressor IR2475N7.5 coupled to a 7.5HP motor spins at 1450 RPM and puts out 24 cfm.

Now the million dollar question, how fast to spin the compressor and what size motor to use. The simple route would be to do some research on other current manufacturers products. There are still 3-stg single stage compressor suppliers out there. Atlas and Puma are a few I found with a quick web search. You'd have to find a comparable compressor that has equivalent bore/stroke and find out at what RPM the compressor spins and what HP rating/RPM the motor is. Once that is established, you can work backwards to calculate motor pulley size based on diameter of flywheel on your compressor.

Per engineeringtoolbox.com (http://www.engineeringtoolbox.com/ai...pes-d_441.html) 1HP ~ 4 cfm @ 100 psi.

I calculate volume of each cylinder bore to be 0.01435 ft3 based off of 3.25" bore x 3.00" stroke. Multiply by 3 cylinders and you have 0.04305 ft3 total volume. If I'm doing my math correct and assuming pump spins at 700 RPM/2 x 0.04305 ft3 = 15.067 CFM. I divided pump RPM by 2 since pump cylinder only compresses air every other revolution of the crankshaft.

I'm sure the mechanical engineers will hop on here and provide a more realistic equation to calculate this.

Steve

 

[nehog]

... I divided pump RPM by 2 since pump cylinder only compresses air every other revolution of the crankshaft.
...

Odd, all the single stage compressors I know of compress once per revolution, much like a two stroke engine. Is this compressor different, and how is it done?

 

[kams1973]

Post a picture of the compressor.

 

[scw1991]

nehog,

Yes, you are correct. My mistake as it compressor does act like a two-stroke engine. What threw me for a loop was the CFM output as it seemed too high at 30 cfm assuming 700 RPM speed. but it does seem feasible.

 

[ms fowler]

IF I did this right, there should be 4 pictures attached

 

[ms fowler]

Hmmmm I see no attachments.

 

[ms fowler]

One more attempt.

I went to "manage attachments", and uploaded 4 files of small size.


Is there an icon that shows the files have been attached?

 

[ietech]

One more attempt.

I went to "manage attachments", and uploaded 4 files of small size.


Is there an icon that shows the files have been attached?

Sorry I wish I could help but that is why I don't post too much. It's too time consuming to try to post pics. The same is true for me on GG and Tool Talk.

I just pretty much stay in the back ground and post only if I have something to offer or am interested in something someone has posted. I gave up on the pic thin a long time ago even tho there are some I would like to show.

On edit: I think there is an alternative -- you can use photobucket or tiny pics for you picture storage then just post a link in your posts.

 

[metalmagpie]

About 800 rpm should work fine. Is Tecumseh still in business? Call 'em up.

metalmagpie

 

[Outlawmws]

One more attempt.

I went to "manage attachments", and uploaded 4 files of small size.


Is there an icon that shows the files have been attached?

 

[ms fowler]

Outlawmws,

I did steps 1-3 OK.. Never saw the #4.
I'll give it another shot.

Thanks

 

[nehog]

Outlawmws,

I did steps 1-3 OK.. Never saw the #4.
I'll give it another shot.

Thanks

The images may have been the wrong type, or too large. Not sure if the software gives a significant message. But you will see #4 if things worked OK. Also to avoid publishing messages that are not meaningful (keeping the clutter down!) you can use the 'preview' option, which should display the message, images and have it look exactly as it would when posted. (That's what I do, then I can catch formatting errors, and the like too...)

 

[ms fowler]

Lets try again,

"Current Attachments" Yeah!!

4 pics showing overall size and details of cylinder and head. Interesting valve design in head. I hope to get into the head and valves later today.

 

[ms fowler]

More information.

I pulled the valve plate off the head, and was stumped--It looked like both sets of valves emptied into the same space. Of course they really didn't. The valve plate is about 1 1/4 inches thick and had a cast void that surrounds the valve holes on the perimeter of each cylinder. Pistons are about 5 inches long!!! with 3 rings each. Rings on all pistons look good, only the ones on the piston closest to the flywheel are stuck.
Con Rod bearings are unmarked, look very good.

What is a safe way to free up stuck rings w/o danger of damaging them?

 

[ms fowler]

I think I have found the fault.
The valves ( #1 on the sketch) on the bottom of the head have a cupped area. You can see the cupped area in the last picture. The size varies from about 1/4 to almost 1/2 of the way around. The valve and valve support (?)--numbers 2 and 3 on the sketch seem fine.
Is it possible to repair the cupped valves? How would one go about doing that? Heat, or no heat?
Are replacements available? does anyone recognize them and maybe offer a source?
How would I go about making replacements--or does anyone here offer that service?

The area labeled " open passage" on the sketch connects the recessed rings to the wedge-shaped areas on the bottom surface of the head that you can see in the picture.

 

[ms fowler]

One more thing--thinking thru some air compressor formulas...

The volume of this pump is about 4X that of my current compressor. The current compressor almost supplies enough air, so double that amount would be good. So if I run this one at half the rpm, I should be good. I read somewhere that 1HP can supply about 4CFM at 100 psi, so my 5HP ( yes 5-- my mistake) should be able to supply about 20 CFM. Current compressor turns at about 950 RPM and delivers about 10CFM at 100 PSI.

Does this line of thinking seem about right?

 

[nehog]

One thing to consider, is that some compressors have a minimum speed as well as a maximum speed (something I didn't know about until recently.) Has to do with the 'slinging' of oil for lubrication, if run too slow they don't properly lubricate the cylinders.

 

[ms fowler]

One thing to consider, is that some compressors have a minimum speed as well as a maximum speed (something I didn't know about until recently.) Has to do with the 'slinging' of oil for lubrication, if run too slow they don't properly lubricate the cylinders.

I hadn't though of that. I can't find any information on Tecumseh air compressors ( lots on A/C compressors). I am still thinking of running the large compressor at 400-600 rpm. My feeling is that such speed is sufficient to throw enough oil where it needs to be.