Late 40's Curtis compressor re and re

[DannyD]

Picked up this guy locally the other day. Not sure why I went with such an old machine but something just drew me in. Sounded awesome while running. I spoke to Curtis and they told me it was made between 1945 and 1950.

Built pressure quick and seemed to flowed alot of air. The Curtis rep told me with a 5hp it should be able to put 16cfm. Not sure where he got that number from or if it is correct at all. Owner says it will build 200psi.

Going to be cleaning it up with out a full disassembly. Any tips on cleaning/prepping the pump in its current state? It has been resprayed before and is flaking.

Came with what I think its a air dryer, pressure regulator and 50' of hose

Love the cast feet and the concave/convex tank. Damn is it heavy

 

[Outlawmws]

Picked up this guy locally the other day. Not sure why I went with such an old machine but something just drew me in. Sounded awesome while running. I spoke to Curtis and they told me it was made between 1945 and 1950.

Built pressure quick and seemed to flowed alot of air. The Curtis rep told me with a 5hp it should be able to put 16cfm. Not sure where he got that number from or if it is correct at all. Owner says it will build 200psi.

Going to be cleaning it up with out a full disassembly. Any tips on cleaning/prepping the pump in its current state? It has been resprayed before and is flaking.

Came with what I think its a air dryer, pressure regulator and 50' of hose

Love the cast feet and the concave/convex tank. Damn is it heavy

Nice find!

Please look for the information plate on the tank, it should be there somewhere, or possibly stamped directly into the tank itself. that should give you test pressures, and you should stay well below it's tested rating... 200 PSI would scare me for most air compressors...


Your motor is 2 HP so not sure why the 5HP CFM comment/figure is relevant, However since the bore and stroke (presumably in that order) is on the case, it can be calculated. The basic equation (without factoring any volumetric efficiency losses from porting, pipes, and valves, or back pressure losses)

[RPM X CID (cubic inch displacement)] / 1728 = CFM


Assuming your numbers are Bore X Stroke,

((3.375/2) X (3.375/2)) X 3.1415 = 14.5 inches square for the bore.

X 3.3 = 50.76 CI per stroke

400 RPM X 50.76 = 20,305 CI (Cubic inches)
20,305/1728 (A cubic ft) = 11.75 CFM

Now that 400 RPM was pulled from the Min Compressor speed, and I'm guessing it's higher. Your Motor is 1740 RPM, what are the pulley diameters?

Whatever these figures come to, a reasonable VE (volumetric efficiency) would be .7 so take 70% of whatever the piston is pumping as a ball park figure, although pressure will also affect CFM capacity significantly. (The higher the pressure, the lower the CFM delivered)

 

[DannyD]

Thanks for the calculation.

I could not find the badge on the tank. Wondering if it was knocked off or removed during its life. The machine currently is at a buddys shop so the weekend will be the next time I am at it.

I will measure the pulleys. The gentleman from Curtis was just assuming its output I think. I told him I had a 2hp after and he suggested a lower cfm.

 

[stratman977]

Theres a good chance that tank was not designed to the ASME boiler and pressure vessel code. The first year for the ASME code was 1914 but im not totally sure when small tanks like this were required to be built to the pressure vessel code. The name plate is a requirement of ASME so if it wasn't designed to ASME it may not have had one.

 

[Lookin4'67Galaxieconv]

That's a sweet looking compressor!

 

[oilslick]

cool

 

[DannyD]

Pump pulley is 14" and the motor is 6". I assumed 1/2" for the belt and used 13" and 5" and figure the pump is spinning at around 670rpm. Gives me a cfm of 19.7 assuming 100%. Given this beasts age I am happy with its output at 60%. Painting is the largest draw it will see from me. Rarely use impacts and rachets, but that might change now.

No stamp on the tank. I searched it good today. There is one on ebay right now with the same tank. No pictures of a tag on that one either.

http://www.ebay.com/itm/Antique-Cur..._Automotive_Tools&hash=item58926b38e3&vxp=mtr

 

[Outlawmws]

Looks like you got it down!

I took a look at the Eprey listing and the pressure switch on that one stops pumping at 150 PSI, which is a far more realistic number IMO..

You might Email the seller and ask about a tank tag.

 

[DannyD]

So I pulled the pump and motor off the tank. And cleaned it up. Found a date stamped into the tank, 20-8-41. There were a few other numbers stamped into it aswell. I will get the picture up later today.

Not sure if I should clean it and spray it assembled or take apart and spray it up nice. It runs well as is, and I am assuming I figure I will have to make my own gaskets to put it back together. No biggy though.

The output line from the pump spirls around the pumps pulley shaft. I think it should be redone. Is there a specific length these should be? Just trying to understand why the PO did it so oddly like this.

 

[Outlawmws]

That line is run that way to help cool the air coming out of the pump, and that is a good thing.

I'd recommend you pull the inspection plate on the tank, and do as good a visual on the interior of the tank as possible.

EDIT: I should have looked closer (thought one pump pic was a tank pic..) does it have an inspection plug? (something large enough to look inside.)

 

[71flh]

"[RPM X CID (cubic inch displacement)] / 1728 = CFM"

Interesting. What does 1728 represent, or what is the equation w/o the magic number?

Also, where does pressure enter the discussion, since CFM is always in relation to pressure as mentioned above.

Sort of like answering how fast a car goes and the answer being 100 miles, not 100MPH...

Just curious.

BTW, Great looking vintage compressor! I'd paint it in pieces.
I'd guess the CFM guestimates are a bit generous based on my trolling of compressor posts.

 

[Outlawmws]

"[RPM X CID (cubic inch displacement)] / 1728 = CFM"

Interesting. What does 1728 represent, or what is the equation w/o the magic number?

Also, where does pressure enter the discussion, since CFM is always in relation to pressure as mentioned above.

Sort of like answering how fast a car goes and the answer being 100 miles, not 100MPH...

Just curious.

BTW, Great looking vintage compressor! I'd paint it in pieces.
I'd guess the CFM guestimates are a bit generous based on my trolling of compressor posts.

The calculation is based on pumping air only no back pressure. this is why the parasitics of flow (think porting an intake and head...) and back pressure have to be considered.

the 1728 is a cubic foot, the calc is for CID (and is based on the calculation for determining CFM for a 2 stroke motor, which is a variation of the calc for a 4 stroke motor)

Since the base calc is RPM (Revs per Minute) you have to convert it to CFM (1728)

 

[hickmlg09]

Nice

 

[71flh]

Interesting...

Ok, so 12*12*12=1728"=the volume of a foot in inches. Duh. I should have figured that out on my own.

Heh, with 65% or so motor efficiency, 14.5PSI atmospheric, and x PSI (variable) in the tank fighting this becomes interesting...

Still, you didn't deal with the question of CFM@xPSI, and you're discussing CFM input to the tank. That makes me wonder what CFM ratings mean; input, output or what?

What's of interest is CFM@xPSI out, or so I would guess since air toys are seemingly rated at CFM@xPSI in.



hickmlg09: You're pretty cute!

 

[DannyD]

First we have the tank date stamp and some other numbers.

Wire brushed, steel wooled, degreased pump.

Another number on the rear of the pump. I cant fully make out the number

 

[Outlawmws]

I get 2 B, which is probably a casting number.