22

Mechanical pressure switches

General description

Operating mode

The pressure prevailing in the sensor housing (

1) acts on the measuring bellows (2). Changes in

pressure lead to movements of the measuring bellows (

2) which are transmitted via a thrust pin

(

4) to the connecting bridge (5). The connecting bridge is frictionlessly mounted on hardened points

(

6). When the pressure rises the connecting bridge (5) moves upwards and operates the microswitch

(

7). A counter-force is provided by the spring (8), whose pre-tension can be modified by the adjusting

screw (

9) (switching point adjustment). Turning the setting spindle (9) moves the running nut (10) and

modifies the pre-tension of the spring (

8). The screw (11) is used to calibrate the microswitch in the

factory. The counter pressure spring (

12) ensures stable switching behaviour, even at low setting values.

Pressure sensors

Apart from a few exceptions in the low-pressure range, all pressure sensors have measuring bellows,

some made of copper alloy, but the majority of high-quality stainless steel. Measured on the basis of

permitted values, the measuring bellows are exposed to a minimal load and perform only a small lifting

movement. This results in a long service life with little switching point drift and high operating reliability.

Furthermore, the stroke of the bellows is limited by an internal stop so that the forces resulting from

the overpressure cannot be transmitted to the switching device. The parts of the sensor in contact with

the medium are welded together without filler metals. The sensors contain no seals. Copper bellows,

which are used only for low pressure ranges, are soldered to the sensor housing. The sensor housing

and all parts of the sensor in contact with the medium can also be made entirely from stainless steel

1.4571 (DNS series). Precise material data can be found in the individual data sheets.

Pressure connection

The pressure connection on all pressure switches is executed in accordance with DIN 16288 (pressure

gauge connection G 1/2A). If desired, the connection can also be made with a G 1/4 internal thread in

accordance with ISO 228 Part 1.

Maximum screw-in depth on the G 1/4 internal thread = 9 mm.

Centring pin

In the case of connection to the G 1/2 external thread with seal in the thread (i.e. without the usual

stationary seal on the pressure gauge connection), the accompanying centring pin is not needed.

Differential pressure switches have 2 pressure connections (max. and min.), each of which are to be

connected to a G 1/4 internal thread.

1 = Pressure connection

2 = Measuring bellows

3 = Sensor housing

4 = Thrust pin

5 = Connecting bridge

6 = Pivot points

7 = Microswitch or other

switching elements

8 = Setting spring

9 = Setting spindle (switching

point adjustment)

10 = Running nut (switching point

indicator)

11 = Microswitch calibration

screw (factory calibration)

12 = Counter pressure spring