Ingersoll 242 compressor question

[Doug424]

I just bought an Ingersoll 242 compressor with a 3HP 3 phase motor, I don't know any history on the unit, but I get the feeling the 3 phase motor might be bad as the wires were cut off at the motor and motor starter was removed. I have a single phase motor to put on it, but want to be sure the motor pulley is the correct size, as the one on it seems kind of big for being 3HP. I can't seem to find any specs on the 242 as far as pump RPM with a 3HP motor. Does anyone know where I can find those specs for a 242?

 

[bob15]

The max speed for the 242 pump is 850 rpm.

So use this calculator: https://www.blocklayer.com/pulley-belteng.aspx and work backwards to get the proper pulley size with the proper motor rpm.

 

[Doug424]

Using max RPM doesn't really work as this compressor is rated for both 3HP and 5HP motors. And the RPM is different depending the max pressure you want to end up with. It's hard to believe I can't find any specs on line for this very common compressor model. I think somewhere in my piles of literature I had a catalog on I-R compressors but yet to find it.

 

[stonesfan68]

Contact your local IR distributor and have them send you the engineering data pages for the 242 compressor. The information is readily available from them.

 

[TonyJ]

242’s were made for several years. I have a 242 D3 from 1953 according to the IR tech that I spoke too. He also informed me that mine has a max RPM of 1000. The 242 In my year came as a 242 D3 and also they had a 242 D5. They told me that the difference between them that also confused the tech was that the D3 was rated to go as high as 230psi and the D5 was only rated to go to 175psi. What made it so strange was the D3 stood for 3 HP and the D5 stood for 5HP. So make life easier for yourself and just call them and have them look yours up so you know what your working with and so you won’t exceed the limits of the actual pump that you have


Tony

 

[bob15]

Look on this site: http://www.airtekltd.com/type30.htm

If you notice on the link, it lists a max rpm for the compressor. I would have to say that it is pretty close real considering the rpm for the 253 listed is about the same as what IR told me several years ago when I was replacing the 3 phase motor with a single phase and needed to order a new pulley. IR gave me a min/max for the 253 compressor and I already knew the pump flywheel size and the motor rpm.

 

[bob15]

Not sure why you think max pressure and motor hp are connected. Max pressure is set via the max pressure cut-off switch, not by motor output.

https://www.garagejournal.com/forum/showthread.php?t=254184

 

[TRWham]

Not sure why you think max pressure and motor hp are connected...

They are connected. At a given speed (and drive ratio), more motor horsepower is required to generate the torque at the crankshaft to push the piston up against the discharge pressure as pressure increases. It's just the reverse of how higher mean effective pressure generates more horsepower in a reciprocating engine.

 

[bob15]

They are connected. At a given speed (and drive ratio), more motor horsepower is required to generate the torque at the crankshaft to push the piston up against the discharge pressure as pressure increases. It's just the reverse of how higher mean effective pressure generates more horsepower in a reciprocating engine.

My point is, you can have the same max pressure (say 175 psi) with either a 3 or 5 hp motor. The motor HP will not dictate the max/cut-off pressure.

 

[TRWham]

My point is, you can have the same max pressure (say 175 psi) with either a 3 or 5 hp motor. The motor HP will not dictate the max/cut-off pressure.

That's true, but you give up flow to reach that higher pressure because the drive ratio you need to achieve the required torque will slow the compressor.

 

[Doug424]

It's very simple to look at max pressure vs pump RPM. Many of the old compressor catalogs would have a chart showing RPM for different max pressure settings. It makes a big difference if you have a 3HP motor driving a compressor set at 100 PSI vs 175. You would see how the RPM is reduced as the max pressure increases. Saying a compressor has a max RPM is meaningless unless you could consider the pressure. Pressure is load on the motor, more load calls for reduced RPM

 

[sweetk30]

i setup a I.R. 234 pump that was running on the 1.5hp spec size to the bigger size offered and she has been just fine with no problems .

i used the same calculator linked in above to figure out my pulley size to motor rpm i used .

 

[Doug424]

That calculator is fine, but if you don't know the correct RPM the pump should run at for a given HP and pressure it's useless.

 

[bob15]

That calculator is fine, but if you don't know the correct RPM the pump should run at for a given HP and pressure it's useless.

Have you looked at either link I posted? It lists pump rpm.

OR

Do like I did when I bought my 253, contact IR. They will give you an rpm range to shoot for.

 

[Doug424]

Yes, I looked at the links, one is a calculator. I really don't need as I can do the math. The other is a picture of a knock off I-R compressor that shows a max RPM. Max RPM at what pressure or HP it does not give. Unless you have the pump speed at, for example 175 PSI with a 3HP motor is what I'm looking for. You can't use a max speed, as that would be assuming a 5 HP motor. Thanks for your responses, but not what I need.

 

[bob15]

Did you contact IR?