Applications for Cam-Actuated Valves
FLUID POWER - Design Data Sheet 44
A cam valve (or more properly, a cam-actuated valve) is a
directional control valve, and is available for both air and
hydraulic operation. For air service, 2-way, 3-way, and 4-way cam
valves in sizes up to 1-inch are available. For hydraulics, most
cam valves are 2-way, either normally open (N.O.) or normally
closed (N.C.), but are not generally available larger than 1/4 or
3/8-inch size. However, as shown in these circuits, they can be
used to pilot larger valves.
For applications like those described here, in which the action
takes place at an exact position of the cylinder piston rod, a cam
valve may be used in preference to a limit switch because, being
mechanically actuated, it is more reliable and will repeat every
cycle to a greater accuracy. Also, it is not dependent on the
presence of an electrical power supply.
Figure 1. Small Cylinder. The cam valve is
located near the end of the cylinder stroke to reduce the speed of
travel before impact of the piston against the cylinder end
During the forward stroke a free-flow path is provided through the
cam valve for oil leaving the cylinder, and travel speed is a
maximum. When the cam valve is actuated, the discharge oil is
forced to go through the variable restrictor (needle valve) and
speed is reduced.
Deceleration at end of cylinder stroke -
low-flow circuits and small cylinders.
A check valve allows free flow of oil into the cylinder on its
return stroke. To add deceleration at the end of the return stroke,
a second cam valve and needle valve can be added. Point x indicates
the location for installing a flow control valve for setting the
maximum speed throughout the stroke up to the deceleration
Figure 2. Large Cylinder. Where oil flow is too
great for a 1/4 or 3/8˝ cam valve, a small cam valve can control a
pilot-operated check valve. Pilot pressure source is the 4-way
valve inlet. During the forward stroke, pilot pressure holds the
check valve open. But when the cam valve is actuated, pilot
pressure is blocked. The check valve closes, forcing discharge oil
to pass through the flow control valve.
Deceleration circuit for high
flow circuits using large cylinders.
Figure 3. This circuit can be used on machine
tools to reduce speed as the tool approaches cutting position, then
to restore full speed at the end of the cut. The length of the cam
determines the distance through which the cylinder will remain in
slow feed. Several cams may be used where several cuts are to be
made with "rapid traverse" between them.
Figure 3. Skip
Cam to Reduced Pressure
Figure 4. One or more cams may be placed where
they will actuate the cam valve at pre-determined points in the
cylinder stroke where system pressure is to be reduced.
Highest pressure must be set on the pump relief valve. The vent
relief valve, 1/4" in size, is set to a lower pressure. The cam
valve, when actuated, connects the vent port of the pump relief
valve to the vent relief valve which reduces the setting of the
pump relief to the value set on the vent relief.
Actuation of the cam
valve reduces system pressure.
Two circuits are shown in which a cam valve is used to unload the
oil supply as the cylinder piston reaches home position. The
advantage of these methods over a tandem center 4-way valve for
unloading is the resultant simplicity of the electrical control
circuit, with one or more holding relays and complicated wiring
eliminated. A simple pushbutton or toggle switch will control the
solenoid 4-way valve.
Figure 5. Low-Flow Circuits. If the cam valve
is rated to pass the full oil flow this circuit may be used. When
the cam valve is actuated at home position, the oil unloads through
the cam valve, through the 4-way valve to tank. When the solenoid
valve is energized to start a forward stroke, the unloading passage
through the 4way valve becomes blocked, and the cylinder starts
forward under full pressure.
Figure 5. Pump
oil unloads directly through the cam valve.
Figure 6. High-Flow Circuits. If the oil flow
is too high to be handled directly through the cam valve, the cam
valve may be used as a venting device for the main system relief
valve which must be a pilot-operated type relief valve. The full
pump flow can unload through the vented relief valve when the
cylinder has retracted to home position and has actuated the cam
When the solenoid valve is shifted to extend the cylinder, the
vent line becomes blocked, causing high pressure to build up behind
the piston. The check valve prevents high pressure oil from back
flowing into and saturating the pilot section of the relief,
causing improper action of the valve.
Figure 6. Cam
valve vents pump relief for oil unloading.
Figure 7. The slave cylinder automatically
responds to certain stroke positions of the master cylinder. For
example, with the master cylinder extended, the cam valve is
unactuated. Pilot flow to the 4-way valve is being vented off to
tank without building up pressure. When the cam valve is actuated
by the retracting master cylinder, the pilot vent becomes blocked.
Pilot pressure builds up on the 4-way valve, causing it to shift
and to extend the slave cylinder.
During the forward stroke of the master cylinder, when the cam
valve is allowed to return to its normal position, pilot pressure
on the 4-way valve is lost and it returns to its normal position,
retracting the slave cylinder.
The orifice should be as small as practical to minimize oil
bleed-off to tank when the cam valve is unactuated.
The hydraulic circuit for operation of the master cylinder is
not shown in the diagram.
Master/slave cylinder system.
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Design Data Sheet 44 - Applications for Cam-Actuated
© 1990 by Womack Machine Supply Co. This
company assumes no liability for errors in data nor in safe and/or
satisfactory operation of equipment designed from this