The figure shows an oil field pump mechanism. The head of the rocker arm is

shaped such that the lower end of a flexible cable attached to it will always be

directly over the well head regardless of the position of the rocker arm 4. The

pump rod, which connects to the pump in the well casing, is connected to the

lower end of the cable. The force in the pump rod on the up stroke is 2,970 lb

and the force on the down stroke is 2,300 lb. Link 2 weighs 598.3 lb and has a

mass moment of inertia of 11.8 lb-in-sec2 (blob-in2); both include the

counterweight. Its CG is on the link centerline, 13.2 in. from O2. Link 3 weighs

108 lb and its CG is on the link centerline, 40 in. from A. It has a mass moment of

inertia of 150 lb-in-sec2 (blob-in2). Link 4 weighs 2,706 lb and has a mass

moment of inertia of 10,700 lb-in-sec2 (blob-in2); both include the counterweight.

Its CG is on the link centerline where shown. The crank turns at a constant speed

of 4 rpm CCW. At the instant shown in the figure, the crank angle is at 45° with

respect to the global coordinate system. Find and plot all pin forces and the

torque needed to drive the crank for one revolution of the crank.

head end

P

76 cable

47.5-

pump rod

well head

51.26 156.6%

OT

14.03⁰

47.5-

14

36.9°

B

3

02

CG4

counter-

weight

002

counterweight

80

B-CG4 = 32.00

P-CG4 = 124.44

04-CG4 = 79.22

12 X