Figure 1.50 shows how such a valve might be used to cause the piston
in a single-acting cylinder to move; the term single-acting is used when a
pressure signal is applied to only one side of the piston. When the switch
is closed and a current passes through the solenoid, the valve switches
position and pressure is applied to extend the piston in the cylinder.
Figure 1.51 shows how a double-solenoid activated valve can be used
to control a double-acting cylinder. Momentary closing switch S 1 causes
a current to flow through the solenoid at the left-hand end of the valve
and so result in the piston extending. On opening S 1 the valve remains
in this extended position until a signal is received by the closure of
switch $2 to activate the fight-hand solenoid and return the piston.