| September/October 1964

Red River Thresher

A 30-60 Hart-Parr and a 32-52 Red River Thresher was taken at Kelso, Saskatchewan, Canada in 1928.

1961 West-Side Drive, Rochester 1, New York


Dear Editor:

It has occurred to me that some of the readers of your fine magazine might be interested in an introductory discussion of the ordinary flyball governor as used on the steam engine and in the terminology of control instrument engineering. To accentuate the control instrument point of view, I have capitalized terminology common to the process control field.

For the same governor setting, it is well known that within the limits of engine operation with the governor valve being neither fully opened nor practically closed, the heavier the load, the slower the speed. Speed is the CONTROLLED VARIABLE in this PROCESS. When a LOAD CHANGE occurs, say the load is increased, the speed falls because the governor must open the steam valve wider to permit the passage of more steam to handle the extra load; and the steam valve will be opened wider by the governor only as the speed is reduced.

Conversely, a reduction in load will cause the speed to be increased to a higher value. With the system IN BALANCE so the speed is again steady, the deviation of the new value is known as OFFSET. Should the exact same speed be required with the different loading, the operator would have to 'touch-up' the governor setting. The control instrument trade would call the means of 'touching up' the setting MANUAL RESET.