These Variables in the Net Torque Equation Are Defined in Your Document on Page 22 And

These variables in the Net Torque equation are defined in your document on page 22 and shown below. The API RP 11E standard equation for calculating Net Gearbox torque for Pumping Units is:

The Net Gear Box Torque, TN, as shown in the equation above is the difference between the Rod Torque and the Counterbalance Moment at any crank angle. CBE is the load W that would make the TN equal zero if the cranks are set to 90 degree crank angle. The load CBE is used to determine the moment of the rotary counterweights and cranks about the crankshaft center. The CBE load is often measured, but some manufacturers provide CBE tables, so that the Moment, M, can be calculated. M depends upon where the weights are placed on the cranks. CBE is usually calculated at 90 degrees of crank angle where the sine of the crank angle is equal to 1.

1st step is to rearrange the Net Torque equation using the following assumptions:

At 90 Degrees Crank Angle W is equal to the CBE load when TN=0.

Sine of 90 = 1

TN =0

W =CBE

Then, M = TF90*(CBE-B)

OR

CBE = M/TF90 + B

This equation is the same as shown on your page 44:

The counterbalance effect load from either a field test or calculation from a Pumping Unit catalog is used to calculate the net torque acting on the gearbox. Various procedures are available to perform the test, but in general the counterbalance effect load is determined by stopping the unit on the upstroke with the cranks level. The following equation is used to calculate the existing counterbalance moment from the measured counterbalance effect load:

Me = TF90 x (CBE -SU) / sin (Crank Angle + Phase Angle)

Once the Counter Balance Moment is determined and the Weight of the counter weights is known, then the net Gearbox Torque and the distance required to move the weights to balance the TN peaks can be determined.