What external clues can I look for when trying to differentiate 8-1/2"-120 CC air compressor versus 8-1/2"-150 CC? I know that there are significant differences in diameter of low- and high-pressure air cylinder bores between the two types, and lesser differences in diameter of low-pressure steam cylinder bore. For the task at hand, it would not be practical to remove a head and measure a cylinder bore.

I have not been able to come up with a list of Westinghouse or NYAB casting pattern numbers which relate to the CFM rating or cylinder bore diameter.

Might it be so simple as checking the amount of space between the low- and high-pressure air cylinder outside diameters? I believe I've seen one compressor with a significantly larger amount of space there, and so I suspect that it is 8-1/2"-120.

Thanks in advance!

Regards,
Bob Milhaupt
IRM Steam Shop Volunteer

Bob -

You have found the best way to tell the difference. Both sizes use the same bottom head so the bolt patterns are the same. This requires the bottom flange for both sizes to have to same outside diameters. Since the cylinder diameters are smaller for the 120 cfm compressor, there is more "free space" between the bolts and cylinder wall on the 120 cfm compressor.

I have a complete parts (drawing) list for one of the WABCO 8+1/2 x 150 versions. If you are interested I can work on getting it posted as soon as I can get it into Excel.

If you are interested, I have a want add that I need posted;

WANTED: Someone that enjoys entering lines and lines of old steam locomotive appliance data into Excel.

You can easily place your hand between the air cylinders of the 120 pump. Not so with the 150. After a few such examinations; you will be able to discern the difference by sight.