As found, appears to be in working order, steam engine pump
⅜" Diameter Bore, ¾" Stroke A small hand-operated, piston-type hydraulic pump used to replenish boiler water while boiler is in use and under pressure. Also used to hydrostatically test your boiler and other hydraulic applications. These pumps have been known to produce up to 400 psi.Constructed of a cast bronze body, brass end cap and packing nut, with stainless steel piston and valves.Overall dimensions are 3¾" length, 4" height, 1¾" width, threaded 5/16-27 (1/16 NPT)