Walthers Cornerstone
Cornerstone Series(R) Built-ups

Operating Oil Pump 2-3/4 x 1 x 1-13/16" 6.8 x 2.5 x 4.5cm
Walthers Part # 933-2614, p. 190 Walthers 2012 N&Z Scale Reference
N scale, $98.98, currently in stock at Walthers
This product is on-sale today for $68.98

 
Designed from the ground up to be a working model, this weathered and fully assembled pump has a hidden drive (mounted under the layout surface for extra realism) with a slow speed motor and gearbox that simulate the steady motion of the real thing. The design is typical of those in use since the 1920s. It features a detailed stationary diesel power plant, walking beam, rear crank and counterweight along with the horsehead front counterweight. For added realism, there's a chain link fence with a positionable gate. This operating model makes a great addition to any oil industry scene.