# Advice wanted



## Brad Anbro

Hello all,

I am new to this forum and came here to hopefully receive some advice on an air compressor system that I would like to put together. I am a retired industrial electrician. I know quite a bit about electric motors and the electricity that runs them but have very little experience with the compressors themselves.

Many years ago, I obtained an old air compressor form this factory where I was working. It is a "Curtis" compressor that was manufactured by the Curtis Pneumatic Machinery Company in St. Louis. The compressor is on a heavy-duty base and it is a 2-cylinder model. I was told that it is a "high pressure" compressor.

The nameplate information on the compressor is as follows: 
88 59-5158 Q108
Minimum 300 RPM
etc.

It has a 3-sheave pulley / flywheel on it that is approximately 14" in diameter. The compressor is not frozen up; the pulley / flywheel turns freely. I have a code vessel that I would like to use this compressor with. The vessel is 15" diameter and 36" long. It is rated at 200 PSI, at a maximum temperature of 650° F.

I guess my main question is: what size of a motor do I need for the operation of this compressor? I believe that the compressor originally had a 3 HP, 3-phase, 230V / 460V motor. I am not sure what the horsepower of the motor was.
Of course, I do not have 3-phase power here at my house, so I would be using a single-phase motor and would be
operating it from a 240-volt AC power source.

Thanks for any help with this!


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## motormonkey

I found no information on the web about that model number, if that is what it is. A "high pressure," compressor is usually a two stage compressor. This is usually apparent if there is a considerable difference in the sizes of the two cylinders. The larger cylinder is a low pressure cylinder and the other smaller one is a high pressure cylinder. Two stage compressors can usually deliver around 200 psi, as opposed to standard compressors, which usually deliver about 150 psi. Without more specific information, the exact power requirements and the performance of that compressor would only be a wild guess. I'm guessing that the tank you are proposing to use would likely be inadequate in volume, and possibly in pressure, for that compressor.

Pictures would help. This site appears to possibly be a source for identifying it.


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## Brad Anbro

motormonkey said:


> I found no information on the web about that model number, if that is what it is. A "high pressure," compressor is usually a two stage compressor. This is usually apparent if there is a considerable difference in the sizes of the two cylinders. The larger cylinder is a low pressure cylinder and the other smaller one is a high pressure cylinder. Two stage compressors can usually deliver around 200 psi, as opposed to standard compressors, which usually deliver about 150 psi. Without more specific information, the exact power requirements and the performance of that compressor would only be a wild guess. I'm guessing that the tank you are proposing to use would likely be inadequate in volume, and possibly in pressure, for that compressor.
> 
> Pictures would help. This site appears to possibly be a source for identifying it.


The unit is in my basement. I will go down there and take a picture of it. I'm pretty sure that both
cylinders seem to be the same dimensions. But I will look more closely at that when I take the picture.


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## Brad Anbro

Brad Anbro said:


> The unit is in my basement. I will go down there and take a picture of it. I'm pretty sure that both
> cylinders seem to be the same dimensions. But I will look more closely at that when I take the picture.





motormonkey said:


> I found no information on the web about that model number, if that is what it is. A "high pressure," compressor is usually a two stage compressor. This is usually apparent if there is a considerable difference in the sizes of the two cylinders. The larger cylinder is a low pressure cylinder and the other smaller one is a high pressure cylinder. Two stage compressors can usually deliver around 200 psi, as opposed to standard compressors, which usually deliver about 150 psi. Without more specific information, the exact power requirements and the performance of that compressor would only be a wild guess. I'm guessing that the tank you are proposing to use would likely be inadequate in volume, and possibly in pressure, for that compressor.
> 
> Pictures would help. This site appears to possibly be a source for identifying it.


I went down in the basement and looked at it more closely. Apparently it is a "high pressure" compressor, because the two cylinders are of different sizes. I took a couple of pictures and will try to upload them to my message.

I looked in my McMaster-Carr catalog at code vessels and my tank is a 30-gallon size. I was thinking about using this tank, with a 175 PSI safety valve and a pressure switch that cuts out at 125 PSI. With the compressor being a "high pressure" unit, would it not just run until the 125 PSI cut-out point is reached?

Thanks.

Brad Anbro
Bluff City, Tennessee


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## motormonkey

Those pressure settings sound like they should work, (assuming that the compressor has no problems) although you still don't know what size motor you need to run it. A couple of horsepower would be a good guess, if you select the right size primary pulley. Is that the vessel in question that I see in the background? You say that that is a "code vessel." Regardless of what it was originally rated at, things like rust, cracks, and time can compromise it, and you need to be sure it will safely handle the pressure. How long since it was hydrostatically tested?


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## iowagold

3-sheave pulley ... hummmm
most of the time those are used on high hp setups like 25 hp and up...

they use a special bonded belt in some mission critical setups...

yea watch using old tanks...
they can rust on the inside ...
i like a 500 psi tank for a 250 psi shop setup...

that tank you wish to use looks to be low cfm tank...
if this is a larger setup I like the idea of 50 to 100 gallon tank....


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## stevon

Brad,

My guess this is a small two stage but I have no idea the model number or the exact condition of your pump. I would think a single phase 2HP motor would run this pump fine. The question is at what RPM? If you can figure the original motor rpm, HP and pulley size you can calculate the targeted pump rpm. I would get a two stage rated tank in any case (200 PSI working pressure). What is the use going to be for this project? tire inflator or production grinding?

RPM calculator:






Pulley Calculator. RPM, Belt Length, Speed, Animated Diagrams - Inch







www.blocklayer.com





Stephen




Brad Anbro said:


> Hello all,
> 
> I am new to this forum and came here to hopefully receive some advice on an air compressor system that I would like to put together. I am a retired industrial electrician. I know quite a bit about electric motors and the electricity that runs them but have very little experience with the compressors themselves.
> 
> Many years ago, I obtained an old air compressor form this factory where I was working. It is a "Curtis" compressor that was manufactured by the Curtis Pneumatic Machinery Company in St. Louis. The compressor is on a heavy-duty base and it is a 2-cylinder model. I was told that it is a "high pressure" compressor.
> 
> The nameplate information on the compressor is as follows:
> 88 59-5158 Q108
> Minimum 300 RPM
> etc.
> 
> It has a 3-sheave pulley / flywheel on it that is approximately 14" in diameter. The compressor is not frozen up; the pulley / flywheel turns freely. I have a code vessel that I would like to use this compressor with. The vessel is 15" diameter and 36" long. It is rated at 200 PSI, at a maximum temperature of 650° F.
> 
> I guess my main question is: what size of a motor do I need for the operation of this compressor? I believe that the compressor originally had a 3 HP, 3-phase, 230V / 460V motor. I am not sure what the horsepower of the motor was.
> Of course, I do not have 3-phase power here at my house, so I would be using a single-phase motor and would be
> operating it from a 240-volt AC power source.
> 
> Thanks for any help with this!


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## stevon

Brad,

A couple of measurements would help too. How tall are those cylinders? what is the flywheel diameter? it's hard to tell the scale of the pump from a picture with nothing next to it to show it's relative size

Stephen


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## Brad Anbro

Hello all, I am replying to everyone who responded to my questions. I got the compressor from this company that I had worked at. We used to take "unauthorized" breaks and would crawl through this opening into a shallow "sub-basement. While crawling through the hole, we would occasionally run the compressor, by pushing in a manual starter. If I remember right, the motor was not all that "big," but it was a 3-pase motor and size for size, as 3-phase motor packs much more HP than a single-phase motor does. I do not have 3-phase here at my house, so I would have to go with a single-phase motor (or use a rotary phase converter, which I am not going to do).

I obtained the tank from a guy that I used to work with at a different company. He had a part-time "salvage business" on the side, in addition to his full-time job. He got the tank for me from a place that he was salvaging. The tank has always been stored inside and as I mentioned before, the specs on the tank are 200 PSI @ 650° F. Yes, that is the tank in the picture. I only plan on having a system pressure of 125 PSI. with the appropriate safety valve installed. Other than being very dirty, I believe that the tank is in good condition. 

I would just like to end up with an air system, that I can run an air nozzle off of, inflating tires and also being able to use a die grinder once in a while.

Thanks to all...


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## iowagold

i make the tank at 27 gallons.
die grinder maybe 5 cfm and run a 3/8 air hose.


Brad Anbro said:


> Curtis Pneumatic Machinery Company in St. Louis


well they are still in biz
click here for the curtis web site
1905 Kienlen Ave, Saint Louis, MO 63133
(314) 383-1300
i would reach out to them on exact specs on the compressor.
you need to know the exact range of motor you need speed in rpm, hp, and the cfm.


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## stevon

Brad,

This would be a very guess based design but here goes:
searched for a similar compressor 3-5 HP









K28 2-Stage Compressor Pump with Flywheel PMP22K28CH from ROLAIR - Acme Tools


K28 2-Stage Compressor Pump with Flywheel - PMP22K28CH from ROLAIR




www.acmetools.com





14 inch large pulley on pump
6.5 inch small pulley on 3 HP motor @1725 rpm
20 inch centers (or whatever)
Pump RPM = 800


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## stevon

Brad,

An incredibly expensive 3 groove motor pulley will not be necessary, a double groove will do fine.

Stephen


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## Brad Anbro

stevon said:


> Brad,
> 
> This would be a very guess based design but here goes:
> searched for a similar compressor 3-5 HP
> 
> 
> 
> 
> 
> 
> 
> 
> 
> K28 2-Stage Compressor Pump with Flywheel PMP22K28CH from ROLAIR - Acme Tools
> 
> 
> K28 2-Stage Compressor Pump with Flywheel - PMP22K28CH from ROLAIR
> 
> 
> 
> 
> www.acmetools.com
> 
> 
> 
> 
> 
> 14 inch large pulley on pump
> 6.5 inch small pulley on 3 HP motor @1725 rpm
> 20 inch centers (or whatever)
> Pump RPM = 800
> 
> If I remember correctly, the 3-sheave pulley on the motor was about 2-1/2" diameter. I don't remember it being over 3" in diameter. That was over 27 years ago...


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## iowagold

stevon said:


> Brad,
> 
> An incredibly expensive 3 groove motor pulley will not be necessary, a double groove will do fine.
> 
> Stephen


that 3 groove has me questioning the hp required for the compressor..
most of the time they do not use them unless they need it...
it make have horrible run up power demand..
unless they did not have a good un loader on the system...

i wish the un loaders had a 2 second time delay on them to let the engine come up to speed before closing.


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## stevon

Iowagold,

The 3 pulley is way overkill for this application, you can drive 7.5 HP through a 6" diameter, single groove "B" pulley and it will transfer the power and not slip. With a 3 inch diameter single groove pulley you can drive up to 2 HP









Stephen



iowagold said:


> that 3 groove has me questioning the hp required for the compressor..
> most of the time they do not use them unless they need it...
> it make have horrible run up power demand..
> unless they did not have a good un loader on the system...
> 
> i wish the un loaders had a 2 second time delay on them to let the engine come up to speed before closing.


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## Brad Anbro

motormonkey said:


> Those pressure settings sound like they should work, (assuming that the compressor has no problems) although you still don't know what size motor you need to run it. A couple of horsepower would be a good guess, if you select the right size primary pulley. Is that the vessel in question that I see in the background? You say that that is a "code vessel." Regardless of what it was originally rated at, things like rust, cracks, and time can compromise it, and you need to be sure it will safely handle the pressure. How long since it was hydrostatically tested?


I just removed the 1/4" plug from the bottom of the tank. There was about a half & half mixture of oil and water in the bottom of the tank. I noticed that there was a pop-off valve installed on the tank. i removed it and cleaned it up, hoping to find some PSI info on it. The only marking I saw on it was "FIG 112" - whatever that means. Probably some number from the manufacturer of the valve, I am guessing.


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## stevon

Brad, 

I would test this tank if you have any doubts about it's origin and condition. the video shows you how to accomplish this yourself.






Stephen


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## stevon

Brad,

If it were me I would test the tank, then build this for 145 or 175 PSI operation. You can do this because you have a 2 stage pump. If you had a single stage pump I would only set it to 140 PSI max.

Stephen


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## Brad Anbro

Thank you for the very informative video, Stephen!


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## Brad Anbro

Brad Anbro said:


> I just removed the 1/4" plug from the bottom of the tank. There was about a half & half mixture of oil and water in the bottom of the tank. I noticed that there was a pop-off valve installed on the tank. i removed it and cleaned it up, hoping to find some PSI info on it. The only marking I saw on it was "FIG 112" - whatever that means. Probably some number from the manufacturer of the valve, I am guessing.


I have another question! After I get done hydrostatically testing the tank to 200 PSI, what is the best method for cleaning the inside of the tank, practically speaking? Since there was both water and oil in the bottom of the tank, I was thinking about putting in a gallon or so of water-soluble cleaner and then rinsing it out with plenty of clean water. Then I thought that I'd get some charcoal briquets burning and then setting the charcoal under the tank, to allow the remaining water to evaporate. Then I would pour in a half gallon of (petroleum-based) oil and then drain that out. The oil would serve as a means of coating the bottom of the tank against further rust.

Is that a workable idea, or is there some better way to go about the cleaning & future rust prevention? Thanks...


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## stevon

Brad,

I wouldn't bother myself, the hydro test and letting the water out will flush out the tank. I wouldn't use any soap or cleaners as oil in a steel tank is a good thing. The oil is a quasi barrier between the water generated during normal use and the steel in the tank, that's why tank has lasted this long! I'm sure this has all been considered in the original designs of the tank back in the 1800's. A steam pressure tank is a different animal and has other design parameters and regulations.

Stephen


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## stevon

Brad,

Some info on pressure vessels:









Pressure vessel - Wikipedia







en.wikipedia.org





Stephen


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## motormonkey

Here is another pretty good video on hydrostatic testing.


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## stevon

This looks like a 40s to 50s Vintage Curtis model 80 that would require a 5 HP electric motor to drive it. the 3 pulleys are overkill but in the 40s that was the tendency to "over build stuff to make it last"






Vintage (probably 1929) Curtis Compressor Pum...


Vintage (probably 1929) Curtis Compressor Pump Size 2 5/8 x 2 5/8. Model 3069-6225. Patent 1869362, 1396391, 1708158 Stands approx. 19 inches high. Inspect for condition and detail...




www.k-bid.com













Vintage Curtis Air Compressor Pump Model 80 | eBay


It has a external centrifugal unloader (easy to bypass), 3 belt pulley, all cast iron. Sits on a cast riser (original) so pulley is clear of mounting plate. You will need 3-5 hp motor depending on its sheave- run it slow and it will outlast you and I.



www.ebay.com













Air compressor Curtis - $350 (Manteca)


For Sale: Curtis Air Compressor made by Curtis Mfg. Co. St. Louis, Mo. Curtis Mfg. is the top of the line high quality manufacturer for air compressors. This unit was made in 1947 and may be a little older, but is in excellent working condition, and...




stockton-ca.americanlisted.com












Stephen


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## Brad Anbro

stevon said:


> This looks like a 40s to 50s Vintage Curtis model 80 that would require a 5 HP electric motor to drive it. the 3 pulleys are overkill but in the 40s that was the tendency to "over build stuff to make it last"
> 
> 
> 
> 
> 
> 
> Vintage (probably 1929) Curtis Compressor Pum...
> 
> 
> Vintage (probably 1929) Curtis Compressor Pump Size 2 5/8 x 2 5/8. Model 3069-6225. Patent 1869362, 1396391, 1708158 Stands approx. 19 inches high. Inspect for condition and detail...
> 
> 
> 
> 
> www.k-bid.com
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Vintage Curtis Air Compressor Pump Model 80 | eBay
> 
> 
> It has a external centrifugal unloader (easy to bypass), 3 belt pulley, all cast iron. Sits on a cast riser (original) so pulley is clear of mounting plate. You will need 3-5 hp motor depending on its sheave- run it slow and it will outlast you and I.
> 
> 
> 
> www.ebay.com
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Air compressor Curtis - $350 (Manteca)
> 
> 
> For Sale: Curtis Air Compressor made by Curtis Mfg. Co. St. Louis, Mo. Curtis Mfg. is the top of the line high quality manufacturer for air compressors. This unit was made in 1947 and may be a little older, but is in excellent working condition, and...
> 
> 
> 
> 
> stockton-ca.americanlisted.com
> 
> 
> 
> 
> View attachment 8225
> 
> Stephen


Stephen,

What is that vertical "rod" in the above picture? Part of the unloader system? My Curtis has one of these too and it can be moved freely. It actuates something (?). Exactly what is the purpose of an unloader? To allow the motor to start the compressor with a reduced load?

I just finished wire-brushing all of the paint off of my yr 1957 code vessel, in preparation for painting it. There is a 1/4" NPT tapped hole on the bottom of the vessel, for draining the water out of the tank, I assume. The threads in this tapped hole do not seem to be very "deep" and I was wondering what would be the best kind of a thread sealant to use, when I get ready to install the new pipe fittings & valve?

Thanks...


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## Brad Anbro

Stephen,

I forgot to mention a couple of things. I just obtained an Allen-Bradley "size 1" contactor (motor starter) and the required thermal overloads for the compressor motor. The contactor is used, but it looks like brand-new! I was going to go with a Square D contactor but the ones for sale were very expensive and this Allen-Bradley is every bit as good. I will be using a Barksdale industrial-type pressure switch for energizing the contactor. The size 1 contactor is good for 30 amps and it will be just fine for my 5-horsepower, 20-amp motor that I will be using.

As a side note, I went back over to my neighbor's across the street and again looked at his 15 year-old, 80-gallon Porter Cable compressor. He bought it 15 years ago but it still looks like new. His compressor has a 6-horsepower motor and only uses ONE belt - probably a steel-reinforced belt. I am going to go with two belts on my compressor, just to be on the safe side...


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## iowagold

quote: The threads in this tapped hole do not seem to be very "deep" and I was wondering what would be the best kind of a thread sealant to use, when I get ready to install the new pipe fittings & valve? 

if you use tape the blue monster works well.
for liquid sealer use the white teflon sealer.
pm me and let me know if you need links


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## stevon

Brad,

I have never owned one of these type compressors so I don't know how this design works, maybe someone who has worked on these can chime in. An unloader is needed to start compressor with no "head" pressure in fill tube to the tank. As for the motor starter, they are rated for current at normal use and HP rated for LRA (locked rotor amps). The current rating is less important than the HP rating on the motor starter in this case. An electric motor load is 6 times or more at startup and motor starter has to be rated for that load. Also a "remote" type starter has to be used. A manual type starter is cheaper but useless in a compressor application.









5 HP Single 1 Phase Magnetic Starter Motor Control 220-240 Volt 22-34 Amps | eBay


Find many great new & used options and get the best deals for 5 HP Single 1 Phase Magnetic Starter Motor Control 220-240 Volt 22-34 Amps at the best online prices at eBay! Free shipping for many products!



www.ebay.com





Stephen



Brad Anbro said:


> Stephen,
> 
> What is that vertical "rod" in the above picture? Part of the unloader system? My Curtis has one of these too and it can be moved freely. It actuates something (?). Exactly what is the purpose of an unloader? To allow the motor to start the compressor with a reduced load?
> 
> I just finished wire-brushing all of the paint off of my yr 1957 code vessel, in preparation for painting it. There is a 1/4" NPT tapped hole on the bottom of the vessel, for draining the water out of the tank, I assume. The threads in this tapped hole do not seem to be very "deep" and I was wondering what would be the best kind of a thread sealant to use, when I get ready to install the new pipe fittings & valve?
> 
> Thanks...


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## stevon

Brad,

I think size 1 motor starter is too small, size 2 or bigger would be my 5 HP single phase choice according to this chart:



https://my15.digitalexperience.ibm.com/9044a799-c194-4640-9cdc-9b5096daacf4/US/Datasheets/99999999999991137106-Datasheet-13697879.pdf



Stephen


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## Brad Anbro

stevon said:


> Brad,
> 
> I think size 1 motor starter is too small, size 2 or bigger would be my 5 HP single phase choice according to this chart:
> 
> 
> 
> https://my15.digitalexperience.ibm.com/9044a799-c194-4640-9cdc-9b5096daacf4/US/Datasheets/99999999999991137106-Datasheet-13697879.pdf
> 
> 
> 
> Stephen


According to the Allen Bradley spec sheet on their contactors, the 709 BOD is good for 7-1/2 HP max, with a 27-amp continuous current rating (at 230 volts, single phase). You had me wondering for a minute!

https://literature.rockwellautomation.com/idc/groups/literature/documents/td/500-td014_-en-p.pdf

Brad


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## Brad Anbro

Brad Anbro said:


> According to the Allen Bradley spec sheet on their contactors, the 709 BOD is good for 7-1/2 HP max, with a 27-amp continuous current rating (at 230 volts, single phase). You had me wondering for a minute!
> 
> https://literature.rockwellautomation.com/idc/groups/literature/documents/td/500-td014_-en-p.pdf
> 
> Brad


I forgot to mention - the motor I'm planning on acquiring is rated at 20.4 full-load amps and I doubt very much if the compressor will work the motor hard enough to achieve 20.4 amps of current draw.

Brad


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## stevon

Brad,

looks like you got it figured out correctly! my bad

Stephen


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## Brad Anbro

Stephen, or any one else (!), I need some help. I would like to remove the flywheel / pulley assembly from my Curtis compressor, so that I can thoroughly clean the compressor. But I do not know how to go about doing that. I see that there is a square-headed set screw that goes to the key on the shaft. But there is also an additional mechanism on the shaft, with a rod going up to actuate some type of device. is this the unloader mechanism?

My Curtis compressor has the numbers: 88 (space) 59-5158

Thanks for any assistance!

Brad


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## Brad Anbro

Hello again all,

I just went out in the garage and tried turning the flywheel / pulley by hand. It turns free enough but when I try to turn it either way, it will turn for around 300 - 310 degrees and seems to hit some kind of a "fixed stop" that will not let it turn any further. I know that this compressor worked just fine, when it was given to me 27 years ago. Thanks for any help!


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## stevon

Brad,

Looks like the head or the side cover will have to come off to take a look. Start with taking off the side side cover then try to see what the issue is. If the resistance or a bad part/defect is not found then the head will have to come off to look further. If the problem can't be seen, then a disassembly would be your next step. Without a manual and a source of replacement parts, it may be a lost cause if you can't rig or machine/weld parts. You will need a manual, contact Curtis and see if they can help. Have you rebuilt engines in the past?









Support - FS-Curtis


Resources Download help resources such as product brochures, white papers and case studies for additional support and information. Read More Warranty Registration FS-Curtis offers industry leading Extended Warranty Programs! Simply maintain the compressor per the maintenance schedule and use...




us.fscurtis.com





Stephen


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## stevon

Brad,

These guys might be able to help:






C96/D96-Inventory - Air-Flo, Inc







www.airfloinc.com





Stephen











stevon said:


> Brad,
> 
> Looks like the head or the side cover will have to come off to take a look. Start with taking off the side side cover then try to see what the issue is. If the resistance or a bad part/defect is not found then the head will have to come off to look further. If the problem can't be seen, then a disassembly would be your next step. Without a manual and a source of replacement parts, it may be a lost cause if you can't rig or machine/weld parts. You will need a manual, contact Curtis and see if they can help. Have you rebuilt engines in the past?
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Support - FS-Curtis
> 
> 
> Resources Download help resources such as product brochures, white papers and case studies for additional support and information. Read More Warranty Registration FS-Curtis offers industry leading Extended Warranty Programs! Simply maintain the compressor per the maintenance schedule and use...
> 
> 
> 
> 
> us.fscurtis.com
> 
> 
> 
> 
> 
> Stephen


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## Brad Anbro

Thanks for the reply, Stephen. I am at a loss as to what might be wrong with the compressor. I can turn the flywheel / pulley assembly about 320 degrees in either direction until it encounters some kind of a "fixed stop." When I reach this point, I can hear a "clunk" that tells me that it cannot be moved further. The flywheel / pulley assembly seems to turn very freely until this point is reached.

Before I was given this compressor 17 years ago, we used to operate it briefly, just for something to do. It was not in use and was just sitting there. It always ran just fine. I have stored the compressor inside ever since I got it.

That drawing just above this message - it looks exactly like my compressor. Where did you obtain the drawing? I called Curtis and am waiting for them to return my phone call. I am really hoping to be able to use this compressor to make a working air compressor system and already have the code vessel (ASME-certified tank) cleaned up and ready for a good coat of paint.

Thanks for all your help!

Brad


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## stevon

Brad,

If the compressor sat for years there could be rust in the bores and piston rings would hit that and stop further movement, this is just speculation on my part. But without access to the cylinder bores there would be no way to confirm, or deal with that. I have some machining and engine building skills from years ago, without some previous mechanical skills it may be tough to fix this. You could try adding some penetrating oil into the bore to free up the cylinders if that is the problem. Of course there is no guarantee that the compressor will work efficiently with damaged bores. As long as parts are available I would rebuild it but that's just me. The efficient and direct way to quickly remedy the situation is to buy another pump. It just depends what your needs and desires are

Stephen



Brad Anbro said:


> Thanks for the reply, Stephen. I am at a loss as to what might be wrong with the compressor. I can turn the flywheel / pulley assembly about 320 degrees in either direction until it encounters some kind of a "fixed stop." When I reach this point, I can hear a "clunk" that tells me that it cannot be moved further. The flywheel / pulley assembly seems to turn very freely until this point is reached.
> 
> Before I was given this compressor 17 years ago, we used to operate it briefly, just for something to do. It was not in use and was just sitting there. It always ran just fine. I have stored the compressor inside ever since I got it.
> 
> That drawing just above this message - it looks exactly like my compressor. Where did you obtain the drawing? I called Curtis and am waiting for them to return my phone call. I am really hoping to be able to use this compressor to make a working air compressor system and already have the code vessel (ASME-certified tank) cleaned up and ready for a good coat of paint.
> 
> Thanks for all your help!
> 
> Brad


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## Brad Anbro

Stephen,

I can turn the flywheel / pulley assembly very freely. As I said before, I can move it about 330 - 340 degrees in one direction and then it hits some kind of a "fixed stop." Then I can rotate it back the other way and again after 330 - 340 degrees, it will hit that "fixed stop."

That tells me that the pistons, connecting rods and crankshaft move very freely. There is something that is physically not allowing for the continuous movement of the flywheel / pulley assembly. Also, as I mentioned before, even though the compressor was not "in service," we used to run it all the time (for just a short period).

Brad


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## Brad Anbro

Brad Anbro said:


> Stephen,
> 
> I can turn the flywheel / pulley assembly very freely. As I said before, I can move it about 330 - 340 degrees in one direction and then it hits some kind of a "fixed stop." Then I can rotate it back the other way and again after 330 - 340 degrees, it will hit that "fixed stop."
> 
> That tells me that the pistons, connecting rods and crankshaft move very freely. There is something that is physically not allowing for the continuous movement of the flywheel / pulley assembly. Also, as I mentioned before, even though the compressor was not "in service," we used to run it all the time (for just a short period).
> 
> Brad


Stephen,

I just took off the side plate on the air inlet / discharge side. The crankshaft and connecting rods move freely. I rotated the flywheel / pulley assembly and noticed that when the large piston neared the top dead center point, that was when I heard the "clunk" and could then not rotate the flywheel / pulley assembly any more. I really hate the thought of removing the cylinder assembly, since I don't have any new gaskets and according to the guy I talked with at Curtis, none are available.

Brad


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## Brad Anbro

Stephen,

This coming Monday I'm going to the local (tool) rental agency and rent a puller and also a 7/8" "line wrench" (also called a flare nut wrench). I want to remove the flywheel / pulley from the shaft of the compressor and I also want to remove the aftercooler line, so that I can better get at the compressor for cleaning.

I am no mechanic but in my opinion, my problem can only be one of two things. Either the flywheel / pulley is hitting some obstruction, which I cannot see it hitting anything. Or, the head of the 1st stage piston (the larger piston) is coming in contact with something when it approaches top dead center.

If I have to remove the head, I will need to obtain some suitable gasket material and make my own. I doubt very much that Curtis has new gaskets for that old compressor.

Brad


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## stevon

Brad,

I believe there are aftermarket gasket sets available if you figured out the pump model number/matched them up or you could make your own gaskets in the worst case. Judging by your description my guess is that something is in the top of the bore impeding piston travel. removing the head may be your only option. To remove the flywheel you will need a pretty large puller and a press may be needed to reinstall it. Good luck with your reconditioning project.

Stephen


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## stevon

Brad 

The 7.5 HP rating is for a 3 phase motor and only a 2 HP on single phase. Do you have 3 phase power? If so you are a lucky dog as 3 phase power is cheaper to run.

Stephen 



Brad Anbro said:


> According to the Allen Bradley spec sheet on their contactors, the 709 BOD is good for 7-1/2 HP max, with a 27-amp continuous current rating (at 230 volts, single phase). You had me wondering for a minute!
> 
> https://literature.rockwellautomation.com/idc/groups/literature/documents/td/500-td014_-en-p.pdf
> 
> Brad


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## iowagold

Brad Anbro said:


> Stephen,
> 
> This coming Monday I'm going to the local (tool) rental agency and rent a puller and also a 7/8" "line wrench" (also called a flare nut wrench). I want to remove the flywheel / pulley from the shaft of the compressor and I also want to remove the aftercooler line, so that I can better get at the compressor for cleaning.
> 
> I am no mechanic but in my opinion, my problem can only be one of two things. Either the flywheel / pulley is hitting some obstruction, which I cannot see it hitting anything. Or, the head of the 1st stage piston (the larger piston) is coming in contact with something when it approaches top dead center.
> 
> If I have to remove the head, I will need to obtain some suitable gasket material and make my own. I doubt very much that Curtis has new gaskets for that old compressor.
> 
> Brad


keep in touch!
it could have trash in the bore.
or even a mouse? or bugs?


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## Brad Anbro

iowagold said:


> keep in touch!
> it could have trash in the bore.
> or even a mouse? or bugs?


Stephen & all,

I was able to disconnect the two ends of the intercooler line from the cylinder head. I was not able to borrow a 7/8" line wrench (also known as a flare-nut wrench), so I used a pair of Vise-Grip pliers to loosen the two fittings. To my surprise, they were not that hard to break loose. I had soaked them for a couple of days with Kroil penetrating oil. I was very afraid to use a 7/8" open-end wrench, for fear of rounding the corners on the fittings. I probably didn't need to have the Vise Grips on the fittings so tightly; when removing the fitting from the 1st stage cylinder, the fitting made some very shallow "threads" in the copper tubing. Other than that, removing the intercooler fittings went fine.

I next unhooked the mechanical unloader linkage and removed the bolts holding the cylinder head from the main body. I found that the very top area of the 1st stage cylinder and piston head were caked with rust. Apparently, all of those years of the compressor sitting around and not being operated and keeping the water from the humid air evaporated was what caused the rust. I took some WD-40 and used it as a solvent to remove all of the rust.

The cylinder head areas above the two bores also have some rust on them, as well as the valve openings. The head gasket pretty much remained intact and I think that if I use a high quality, high-temperature gasket sealer, it will be OK. I was very relieved that nothing had dropped down from the valves and the only thing keeping the flywheel / pulley assembly from rotating a full 360 degrees was the build-up of rust.

It appears that the valves & unloader mechanism are an integral part of the cylinder head. Apart from removing all of the rust from the underside of the cylinder head, is there anything that I need to do with it? A I mentioned before, I am not a mechanic; I am a retired industrial electrician. So I am basically "flying by the seat of my pants."

I also wanted to remove the flywheel / pulley assembly but have not been able to do that yet. I removed the setscrew and soaked the shaft with penetrating oil but by hitting the sides of the assembly, it has not wanted to move. I imagine that I will need to get a good puller to accomplish this. I wanted to remove the flywheel / pulley assembly, so that I could thoroughly clean the compressor.

The cylinder bores appear to be in very good shape, other than being "sticky" from the coating of old oil on the cylinder walls. When I get the compressor put back together, I plan on using 10 weight oil to flush all of the old oil
from the compressor. Then I will drain that and use some good compressor oil. My plan is to use a 1/2 HP, 1725
rpm motor to spin the compressor slowly, to get the old oil flushed out. I will not have the compressor piped to any tank, so the compressor will be basically running "unloaded." Does this sound like a good plan of attack?

Thanks in advance for the helpful comments & suggestions.

Brad


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## iowagold

use synthetic compressor oil.
most places have that now.
it lasts longer.
diesel fuel works good for a solvent to clean the out side as well as the inside.
cheap by the gallon too! grin.

for the baked on junk easy off oven cleaner works.
we use that on gear boxes in industrial LARGE stuff...
I think the diesel works the best for me.

and gasoline is a good dry solvent for the oil diesel.
or green can brake cleaner.
nice for a perfect clean.


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## Brad Anbro

Thanks, Paul. I was just going to use the 10 weight oil as a flushing agent, to get all of the rust, etc. out of the compressor. Then I was going to drain it and then refill it with a good quality compressor oil.

I fashioned a kind of a "stand" to allow the cylinder head to rest in an upside-down and level position, so I could remove the visible rust from it. Do I need to squirt either WD-40 or Kroil penetrating oil into the valve openings? I imagine that there is probably some rust in there, too.

As far as a cleaning agent is concerned, I have discovered some solvent that works just as well as the Stoddard solvent that I used to use in gas stations & garages when I was a kid. The stuff is called "PSC1000" and I have been using it lately. It seems to work just as well as Stoddard solvent and leaves no oily residue. It is flammable but much less flammable than gasoline.

Brad


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## iowagold

just watch some solvents as there might be plastic or teflon seals for some brands of compressors
after the piston area.
like further down towards the tank and regulator area.
and tank pop off valve... and electrical shut off switches.

not familiar with that solvent... check the msds sheet for a break down on what is in it.
and watch for cancer stuff. 

both the wd, and the kroll is good stuff.
there is a few others that work well too.
i will try to find them.


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## Brad Anbro

iowagold said:


> keep in touch!
> it could have trash in the bore.
> or even a mouse? or bugs?


Hello Stephen & all,

I found out why I could not rotate the flywheel on my old Curtis compressor a full revolution. I removed the cylinder head and found an accumulation of rust at the top of the large piston. I removed all of the rust and cleaned the heads of both pistons, so that they look like new. I built a kind of a "stand" for the cylinder head, so that I could have it placed upside down and level on my bench. I then used WD-40 and filled in the cavities of the cylinder head, in an attempt to dissolve any rust in the valves / unloader mechanism.

I bought a brake cylinder hone and honed the cylinder walls of both cylinders. They cleaned up just fine. I had borrowed a 7-ton puller and used it to remove the 14" flywheel / pulley assembly, because I wanted it out of the way so that I could do a good job of cleaning the outside of the compressor. When it came time to put the flywheel / pulley assembly back on, I first used some fine-grit emery cloth and polished the shaft of the compressor, as well as the bore of the flywheel / pulley assembly. I then coated the polished areas with 10-weight oil. I used a hydraulic floor jack to raise the assembly to the proper height for installing it on the compressor shaft. I used the jack, because the assembly weighs almost 40 pounds and I did not want to try to hold the assembly in place, while aligning the bore with the compressor shaft. The assembly went on just fine, although I had to use a block of wood and a hammer to "help it along."

I had used WD-40 to flush the ball bearing assemblies and also the connecting rod bearings. After doing this, I soaked up all of the liquid in the compressor and after installing the two covers, I filled up the compressor with 10-weight motor oil. I figured that I would use this oil to flush out any remaining dirt in the compressor and then drain it and install a good grade of compressor oil.

The nameplate on the compressor says to run the compressor at a minimum of 300 RPM and I am going to use the motor from my drill press to temporarily run the compressor. I have a Browning variable-pitch pulley that I am going to install on the motor and from my calculations, that should give me a compressor rotating speed of about 381 RPM. I will not have the outlet of the compressor plumbed up to a tank, so it will be basically running without any actual load.

So that is where I am at with my Curtis air compressor project. I was able to purchase a 5-HP Ingersoll Rand air compressor with an 80-gallon tank from a local individual. The I-R compressor has about 50 hours of use and it looks like brand new. I will have the old Curtis compressor and the 30-gallon tank on which it is mounted as a "museum piece."

Brad Anbro


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## stevon

Brad,

Long road but at least you have a fun hobby! You can tell less mechanically inclined folks it's an old steam engine! Modern Manufacturing doesn't make machines or anything this well any more! Design something to last 100 years? An Engineer would be shot by the company President if he tried to do that today! lol

Stephen


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## Brad Anbro

Stephen, you have that right! The flywheel / pulley assembly for this compressor weighs just less than 40 pounds. Take care...


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