Unknown Air Pump

While helping a friend we came across this small air pump and can't quite figure out what it was used for.  The base is about 12 inches wide.  The cylinders are about 5 inches tall with the diameters being about 2 and four inches respectively.  The framework and handle pieces are cast iron and the pump cylinders are brass.  The check valves are oriented as if it is a vacuum pump (but could originally have been the other way) and possibly mounted on a vertical surface.  I have seen similar pumps in old catalogs but they have equal size cylinders.  If you have any idea what the actual original purpose was please let me know at :

March, 2017  --  Since the original posting 11 years ago I have come across these two items from a 1906 and a 1911 Cycle and Automobile Trade Journal which define it as a two stage air pump capable of 150 psi most often used as a tire pump.  Look at the bottom two of the thumbnails to read them.

Click on the thumbnails for a larger view

Measures about 15 inches tall with no handle.  Note the check valves at bottom.
The base is about 12 inches across and the cylinders are brass.  The push rods seem to be steel and the base and rocker are cast iron.
Reads "ESCO No. 99" and was made by S & Company of New York, New York.
Some of the bits and pieces.  No internal connection between cylinders.
Plunger from small cylinder.  Leather cup oriented to work on "up" stroke making it a vacuum or suction pump.  I feel that it has been converted from a pressure pump.
External check valve also oriented for suction stroke but of course could be reversed.  Size of plumbing leads me to believe it is for air and not liquid.
This is scanned from an old catalog that shows a similar pump but with equal size cylinders.
This is scanned from a 1906 Cycle and Automobile Trade Journal.
This is scanned from a 1911 Cycle and Automobile Trade Journal.

Updated 03/06/2017

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