Copyright Goodheart-Willcox Co., Inc.
148 Hydraulic Systems for Mobile Equipment
Synchronizing Cylinders
Hydraulic circuits frequently require multiple cylinders to extend simul-
taneously to lift a single load. Depending on how the cylinders are plumbed,
they can rise at different rates, causing the implement to lift unevenly. If the
cylinders are plumbed in parallel, without any additional provision, the cyl-
inders will extend at different rates due to variations in load. See Figure 6-34.
Mobile machinery uses multiple methods for keeping cylinders synchro-
nized and for rephasing the cylinders back into synchronization. The most
common method of extending two cylinders simultaneously is to plumb the
cylinders in a master/slave series confi guration. See Figure 6-35.
The master and slave cylinders must have a specifi c area relationship. The
slave cylinder’s piston area must equal the difference of the master cylinder’s
area minus the rod’s area. See Figure 6-36. For example, a planter that uses a
3.25″ diameter master cylinder with a 1.25″ diameter rod, will require a slave
cylinder with a 3″ diameter piston.
Three common applications for series cylinder confi gurations are reel lift
on a combine header, reel fore and aft on a combine header, and lift cylinders
on agricultural implements such as planters.
Figure 6-33. When the speed of a cylinder is controlled by restricting the return side of an extending cylinder,
pressure intensification will occur.