Page 75 - Instrumentation and Measurement

Figure 5.13 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 pass through the solenoid, the valve switches position and
pressure is applied to extend the piston in the cylinder.

FIGURE 5.13 Control of a single-acting cylinder: (A) before solenoid activated and (B) when
solenoid activated.
Figure 5.14 shows how a double-solenoid activated valve can be used to control a double-acting
cylinder. Momentary closing switch S1 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 S1, the valve remains in this
extended position until a signal is received by the closure of switch S2 to activate the right-hand
solenoid and return the piston.

FIGURE 5.14 Control of a double-acting cylinder.
As an illustration of valves that are available, Continental Hydraulics include in their range VSNG
valves from which firstly the basic valve format is selected from: Single operator 2 position spring
offset, double operator 3 position spring centre, single operator 2 position spring centred and single
operator 2 position 3-way spring operated. A single operator valve is one like the ones in Figure 5.13
which can only have an operator input at one position, double operator has operator inputs possible
at both ends, as in Figure 5.14. The next selection is for the spool to be used, i.e. the ports and the
connections, as in Figure 5.10.

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