Copyright Goodheart-Willcox Co., Inc.
Chapter 6 Cylinders 141
of 19.25 is used. It was derived by dividing the quantity of a gallon (231 in3) by
12″ (foot), which equals 19.25. The same factor can be converted to solve for feet
per second by dividing the 19.25 by 60 seconds, equaling 0.3208.
The same cylinder can be computed in metric units of measurement. A
fl ow rate of 75.7 lpm and an area of 45.6 cm2 would equal a cylinder speed of
0.277 m/sec.
Cylinder Electronic Sensing
Electronically controlled machines use a variety of sensors to measure a
cylinder’s position and the load on a cylinder. Sensing the position and/or cyl-
inder load provides inputs for two types of systems: automatic implement con-
trols and automatic guidance systems. Some examples of automatic implement
controls are:
• Automatic header height on a combine.
• Load control for an agricultural tractor’s three-point hitch.
• Slope control on a motor grader.
• Grade control on an excavator.
• Grade control on a dozer.
Two common technologies used for sensing a cylinder’s position are poten-
tiometers and magnetostrictive transducers. A potentiometer is a three-wire
sensor that provides a variable resistance based on the location of the signal
wiper. See Figure  6-25. Potentiometers provide an indirect method of mea-
suring a cylinder’s position. The sensor is often located on the implement away
from the cylinder, as on a combine’s feeder for example. As the lift cylinders are
actuated, the feeder moves, causing the potentiometer to rotate. This provides
the ECM with an indirect input of the position of the feeder cylinders.
Figure 6-24. External clamps can be used as a cylinder depth stop.
Depth stops