How to Use Pressure Differential Sequencing
FLUID POWER - Design Data Sheet 15
Sequencing circuits are those that automatically program two or
more cylinders on a machine to cause them to extend and retract in
a pre-determined sequential order on every cycle.
While sequencing may be accomplished in several ways, the
problem to be discussed in this sheet is the successful use of
meter-out (instead of meter-in) speed control with
pressure-activated devices such as sequence valves and pressure
Meter-out speed control is generally conceded to be more
accurate and stable for most applications than meter-in control,
but when combined in the same circuit with pressure activated
devices, premature sequencing may occur because the high back
pressure on the rod end of a cylinder caused by meter-out control
may deceive the sequence valve into believing that full load has
been reached. While there is some small rise in pressure when the
cylinder reaches full load condition, adjustment of the setting on
the pressure-activated device may be very critical. Special
circuitry, as shown on this sheet can give improved results.
A limit switch actuated by extension of Cylinder 1 could be used
to start Cylinder 2 provided the sequencing is to occur when
Cylinder 1 reaches a certain point in its stroke. But, if
sequencing is to take place when full load has built up on Cylinder
1, or when it bottoms out, pressure activated devices are usually
preferred over limit switches.
In choosing a pressure activated device, sequence valves are
preferred over pressure switches because they require fewer and
less expensive components, and do not have to be wired into the
For sequencing of hydraulic cylinders, the circuit of Figure 1
will permit the use of meter-out speed control while also giving
reliable action from the sequence valve.
Differential pressure across Cylinder No. 1 is used as the
Figure 1. The operator energizes Solenoid A to
start Cylinder 1 forward. The sequence valve remains closed, and
all oil goes into Cylinder 1. When this cylinder bottoms out, or
when load resistance against its piston reaches a pre-set maximum,
the sequence valve opens, allowing oil to flow into Cylinder 2.
A separate meter-out speed control valve is installed for each
cylinder to regulate its extension speed.
This circuit is shown in simplified form. Refinements such as
speed control valves for retraction, programmed retraction with
another sequence valve, strainers and filters, can be added as
desired or needed.
The sequence valve shown in Figure 1 is a standard hydraulic
model with internal pilot, external drain connections, and is sized
to handle the pump volume. The novel feature of this circuit is
that the external drain port is connected to the rod end port of
the cylinder instead of back to tank in the usual manner. This
makes the sequence valve sensitive to the difference in pressure on
opposite sides of the piston. Pressure drop across the speed
control valve while the cylinder is moving in an unloaded condition
does not give a false indication to the sequence valve-and cause it
to open prematurely. In other words, the sequence valve when
connected in this manner is actually measuring the amount of load
In choosing a sequence valve for this circuit, be sure to select
one that will handle pressure in the drain line; some valves may be
capable of only limited pressure in this line without damage to the
If pressure switches are preferred over sequence valves, the
circuits of Figures 2 and 3 may be adapted for hydraulic use.
Compressed Air Circuits
The circuit of Figure l is not suitable for compressed air
because, to our knowledge, air sequence valves are not available
with threaded exhaust port. The spring pocket is vented to
atmosphere through a plain vent hole and it is not possible to make
a connection to it.
For compressed air, differential type pressure switches are
available and may be used instead of a sequence valve. They have
two pressure inlets, and the switch contacts respond to the
difference in pressure between the two. Thus, they are able to
measure the actual air pressure exerted against the load without
being influenced by pressure drop generated across a meter-out
speed control valve.
The circuits on this page are only two of the many ways
differential-sequencing circuits can be set up:
Sequencing on the Forward Strokes Only.
Figure 2. Both cylinders are controlled through
one 4-way directional valve, but since only one cylinder at a time
is moving, the valve is sized as if for 1-cylinder operation.
When the 4-way valve is shifted, air flows to Cylinder l to
start its advance. When it bottoms out, or when load resistance
builds up to the pressure switch setting, the pressure switch
contacts close, and energizes the 2-way valve. This directs air
into Cylinder 2. This gives the same priority action as does a
sequence valve - if pressure is lost on Cylinder 1, then Cylinder 2
will also stop.
Sequencing is shown only on the extension strokes of the
cylinders. If required on the return strokes, an additional
pressure switch and 2-way valve can be added.
Figure 3. One
Method of Sequencing in Both Directions.
Figure 3. If the cylinders are to be sequenced
in both directions of travel, or if both will be in motion at the
same time for part of the cycle, separate 4-way valves should be
used to prevent unwanted interaction.
Solenoid A is momentarily energized to start Cylinder 1. Its cam
passes the limit switch without actuating it. When pressure
difference across the piston reaches pressure switch setting,
Solenoid C is energized. This starts Cylinder 2 forward.
To retract the cylinders, the operator momentarily energizes
Solenoid B to start Cylinder l back. Its cam actuates the limit
switch on the way back to energize Solenoid D, causing Cylinder 2
to retract also.
The 1-way roller type limit switch-may be mounted at any point
on the return path of the cam. Or, an impulse type limit switch
could be used instead, mounted at home position.
Variations of Figure 3 are possible. Retraction could be made
automatic by mounting a standard limit switch at the forward end of
Cylinder 2 stroke, and wiring it to Solenoid B. Sequencing on the
return strokes could be done with another differential pressure
switch, although a means should be provided in the electrical
circuit to remove current from all solenoids when both cylinders
are at rest.
If differential pressure switches for high-pressure operation
are available, the above circuits could be adapted for hydraulic
Download a PDF of Fluid
Power Design Data Sheet 15 - How To Use Pressure Differential
© 1988 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