Camozzi Pneumatics Manual

Figure 35

Solenoid valvewith electric command and pneumatic return

The end cap to the right, commonly called “pneumatic end cap”, has a threaded port to which an external pilot

can be connected. The two control pistons have the same diameter. The repositioning of the spool takes place only

in the presence of external pneumatic piloting. When removing the electrical signal from the solenoid, the valve

position does not change, it does so only in the presence of an external pilot. In this condition it is called aBistable

with electric commandwith external pneumatic repositioning.

In the situationwhere the external pneumatic command is always present thoughwith reduced pressure, the valve

would beMonostablewith electric commandwith pneumatic repositioning spring.

Fig. 35

Solenoid valves with external servo pilot

As shown in indirect command valves this is a solenoid valve, which provides control to the pilot (signal) by

opening or closing a passage of compressed air.

The pneumatic supply to the solenoid is the same as that supplied to themain solenoid valve and is obtained via

an internal channel to the valve. Depending on the type of solenoid valve the minimum pressure required for

piloting control is approx. 2 bar. In situationswhere a low pressure or vacuum is used, it is necessary to supply the

solenoid valvewith a different pilot pressure. In this situation, the solenoid valves that have a separate connection

for the power supply are used and are defined as

with external servo pilot

There are no particular differences between the two types.

Figure 36

Solenoid valvewith dual electric command and external servo pilot

The central body is that of a normal valve where the channeling of the servo-pilot is absent or intercepted. Each

end of the body is closed by an end cover which has the function of a pilot valve. The air supply of themain valve

is independent from that of the pilot valve, the output of air drives their respective pilot pistons. The solenoid on the

right is energized; the outgoing pilot airmoves the pilot piston, whichmoves the spool to the left. In this phase, the

solenoid valve on the left should not be energized. When removing the electrical signal to the solenoid, the valve

holds the position. This solenoid valve is calledBistablewith external servo pilot.

Fig. 36

Figure 37

Solenoid valvewith electric command, mechanical spring return and external servo pilot

In this case, the solenoid on the right has been replaced by a mechanical spring. The solenoid on the left is

energized, the outgoing airmoves the pilot piston,whichmoves the spool to the right, the return spring compresses.

When releasing the electrical signal to the solenoid, the solenoid valve returns to its rest position due to the effect

of the spring. When the solenoid is not energized, the solenoid valve assumes the position defined by the spring.

This solenoid valve is calledMonostablewithmechanical spring return and external servo pilot.

108

CAMOZZI

VALVES