Copyright Goodheart-Willcox Co., Inc.
Chapter 6 Cylinders 147
Figure 6-32. The needle valve is being used to control the speed of the cylinder. The cylinder has an overrunning
load, which will cause cavitation in the cylinder.
Metering-In and Metering-Out Overrunning Loads
Manufacturers choose different methods for controlling the speed of
hydraulic cylinders. Metering-in and metering-out are two methods used for
controlling cylinder speeds. If a cylinder is actuating an overrunning load,
then both metering-in and metering-out will cause problems.
A metering-in circuit will restrict the oil fl owing into a cylinder. If the
cylinder has an overrunning load, the weight of the cylinder can cause the
rod to extend faster than the pump can supply oil, resulting in cavitation. See
Figure  6-32. Make-up valves and counterbalance valves provide solutions
to resolve this problem. Those valves will be explained in Chapter 7 and
Chapter 8.
If the needle valve was placed in the other working line of the cylinder
to limit the cylinder’s return oil, the cylinder’s speed would be controlled in
a metering-out fashion. See Figure 6-33. When a restriction is placed in the
return line of an extending double-acting cylinder, the cap side of the cylinder
will cause pressure on the rod side to intensify. The pressure can intensify
enough to damage components. As mentioned, Chapter 7 will explain coun-
terbalance valves, which are used to resolve this problem.