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Mechanical pressure switches

S2 type series

S2 type series

Examples of use for two-stage pressure switches

Pressure monitoring and controlling can be greatly simplified by using pressure monitors with two

built-in microswitches which can be made to operate one after the other under rising or falling

pressure. For example, minimum and maximum pressure monitoring can be achieved with only

one pressure switch, doing away with the need for a second pressure switch (including the cost of

installation). Step switching, e.g. pressure-dependent control of a two-stage pump, is of course also

possible using this special series.

Example 1:

Requirement

Pressure holding devices and automatic expansion valves usually have a gas cushion whose pressure

must be kept constant within a certain range. If the pressure is too low, a compressor is switched on.

If the pressure is too high, a solenoid valve must be opened to vent the gas. Between these two

levels is a neutral zone, in which the compressor and the solenoid valve are at rest.

Solution

All pressure switches of types DCM, DNS, each with additional function ZF217 and switching scheme

A 2, are suitable. All pressure ranges listed in the technical documents are possible. Example for

ordering: see page 24

Switching function / connection scheme

Switch I:

With falling pressure, contact 1–2 closes (compressor on)

With rising pressure, contact 1–2 opens (compressor off)

Switch II:

With rising pressure, contact 2–3 closes (valve open)

With falling pressure, contact 2–3 opens (valve closed).

In between there is a neutral zone in which the compressor is not switched on

and the solenoid coil is not energized (off position).

Example 2:

Requirement

In a process engineering system, the pressure in a nitrogen line has to be monitored. A green signal

lamp indicates that the pressure in the line is between 2.2 and 2.6 bar. If the pressure goes below 2.2

bar or above 2.6 bar, the indicator lamp goes out and the system shuts down.

Solution

The first contact of a DCM3–307 pressure switch with 2 microswitches opens under falling pressure

at 2.2 bar; the second microswitch opens under rising pressure at 2.6 bar. If the pressure is >2.2 bar

or <2.6 bar, the circuit is closed via both microswitches and the signal lamp is lit.

Minimum and maximum pressu-

re monitoring in a nitrogen line

For pressure-dependent control

of automatic expansion valves

and pressure holding devices