Copyright Goodheart-Willcox Co., Inc.
Chapter 6 Cylinders 151
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Figure 6-38. Some planters use rephasing relief valves when the cylinders are connected in parallel. When one
cylinder reaches the end of travel, the operator can continue to hold the DCV control valve in the raise position,
and the remaining oil will be routed to the other cylinder that is continuing to extend.
Cylinder Safety
Technicians are frequently tasked with repairing a hydraulic cylinder. It
is common for the cylinder’s piston or gland to be seized, making it diffi cult
to remove, even after the snap ring has been removed and the gland has been
unthreaded. Do not attempt to use compressed air or heat the cylinder’s barrel
with a torch.
A September 2001 Hydraulics and Pneumatics Journal article by Rory
McClaren recommends placing the hydraulic cylinder with the rod down-
ward inside a bucket. See Figure 6-39. A vise might be needed to hold the cyl-
inder in place. At the opposite end, fi ll the cylinder with hydraulic oil. With
the cylinder’s snap ring removed, use a hydraulic hand pump to slowly push
the piston rod and gland assembly out of the barrel. Observe the pressure
gauge while applying pressure with the hand pump. If the pressure exceeds
the cylinder’s specifi cation, the cylinder must be scrapped. The bucket is used
to catch the oil when the rod is freed from the cylinder. Use only a hand
pump; do not use a running hydraulic system.