old compressor that slows down 2hp

[joe121]

Hi, I bought an old cast iron small single stage 2cyl compressor at estate sale for $50. I mainly bought it for the 3hp dayton compressor motor that was on it that looked way to big for this little pump.I put a 2hp comp.motor that came from a working larger comp. on it. the problem is it starts to slow down this motor with only 30psi in the tank. It did the same thing to a 1.5hp motor at 20psi. I don't understand how this little pump can do this. It was supossed to work before they disconnected it. From looking at it i would say its only about 4-5cfms. If i disconnect it from tank it seems to pump with no problem. No name on pump except these numbers- 3314-k, s-501 and ab117 on flywheel. Can this little pump really need a 3hp motor? Thanks joe

 

[jkuro]

If it worked with the 3hp, put it back on.

 

[larry_g]

Have you confirmed the pressure gauge is correct?
Are the 'new' motors the same speed as the old one? 1750 vs 3400,
Are the drive pulleys the same size?
Have you confirmed the 3hp motor runs the pump and makes pressure to 125 psi?
How big is the tank?
If single phase is the start cap dropping out?
If it runs without the tank connection are you disconnecting before or after the check valve?

LOts of possibilities here that need to be checked and known before moving on...

lg
no neat sig line

 

[joe121]

Have you confirmed the pressure gauge is correct?
Are the 'new' motors the same speed as the old one? 1750 vs 3400,
Are the drive pulleys the same size?
Have you confirmed the 3hp motor runs the pump and makes pressure to 125 psi?
How big is the tank?
If single phase is the start cap dropping out?
If it runs without the tank connection are you disconnecting before or after the check valve?

LOts of possibilities here that need to be checked and known before moving on...

lg
no neat sig line

2 gauges, compressor motors(1750) i put a 4in pulley,had a 5in
tank is about 20gal.
new cap
i did not try the 3hp,it really looks goofy big on this thing,
I will try running with gauge out to check the check valve somewhat. If you look at the pic's you will see how small this thing is, at least compared to my 1959 kellog with a 3hp

 

[James-W]

If the electric motor slows down, you have a problem. If it slows down it will overheat and eventually burn out. Apparently that particular pump requires a 3HP motor (or larger) to run it.

 

[joe121]

If the electric motor slows down, you have a problem. If it slows down it will overheat and eventually burn out. Apparently that particular pump requires a 3HP motor (or larger) to run it.

You might be right, i am just really surprised because of the size compared to other pumps i have rebuilt that are much bigger with 3hp motors. The only difference is this is the first single stage pump i have experianced. I think these pistons are about 2.5 to 2.75in wide compared to my kellogg with a 4.75in first stage piston. But i still find it hard to believe it struggles at 30psi. thanks

 

[FredWanaker]

the Devilbiss made compressors I have both sport much larger pulleys on the compressor and 5hp motors (which are probably 2.5 or so in real life). You may need a larger pulley on the compressor or a smaller pulley on the motor. Also make sure you haven't wired the motor incorrectly to run on 240 but are using 120 etc.,.

 

[Ike Carlson]

A 2hp motor should run 10cfm to 140 psi. Something is wrong there. Is the compressor full of new oil?

I am guessing there is a restriction somewhere on the exit side of the compressor, and that includes the line and check valve going to the tank. Check the valves, passages, line, and check valve. Air requires a pressure differential to cross a restriction and if that differential is close to the max of the motor hp, it will quickly overload it as pressure builds. I made a thread about porting my air compressor because of small passages increasing the pressure differential, which increases heat and hp.

A 2hp motor should easily run that compressor up to 100 psi. Take the valves out and take some pictures. There may be a piece of filter material, bug nest, or a rag stuck in there. Don't assume it is clean and ok.

 

[nadogail]

Changing the compressor pulley to s smaller size may have been an error. The compressor pulley should be made larger or the motor pulley made smaller.
The gearing of bicycles explains this.

 

[joe121]

A 2hp motor should run 10cfm to 140 psi. Something is wrong there. Is the compressor full of new oil?

I am guessing there is a restriction somewhere on the exit side of the compressor, and that includes the line and check valve going to the tank. Check the valves, passages, line, and check valve. Air requires a pressure differential to cross a restriction and if that differential is close to the max of the motor hp, it will quickly overload it as pressure builds. I made a thread about porting my air compressor because of small passages increasing the pressure differential, which increases heat and hp.

A 2hp motor should easily run that compressor up to 100 psi. Take the valves out and take some pictures. There may be a piece of filter material, bug nest, or a rag stuck in there. Don't assume it is clean and ok.

I agree with your comments, i will check the air path to the tank and will let you know. thanks,joe

 

[redmondjp]

A defective or missing check valve will also cause this behavior as the pressure rises. So check (erg) that as well!

 

[kwb]

I can see that compressor using a 3hp 3600rpm motor. Could it be that the 3hp that was on there was a 1800rpm motor? That would us a pulley 2x the size of a 3600rpm motor.

 

[joe121]

I am embarrassed to say what the problem was. Since i was testing these motors on this unit i had a sort of makeshift motor mount cause i was trying different motors, i did not have the belt tight enough so the motor pulley start to slip **** the punp start slowing down making it sound like it was the motor also. the 1 1/2hp works just fine.I will save the 3hp for a backup. sorry and thanks for the help, joe

 

[Ike Carlson]

Sometimes it's the simple things....

 

[nadogail]

The simple stupid stuff has tripped me up many times