User manual HONEYWELL ZF DATASHEET

[. . . ] 18 Pressure switches Mechanical pressure switches Mechanical pressure switches Te c h n i c a l f e a t u r e s / Advantages Diecast aluminium housing IP 54 or IP 65 version also available Wall mounting or directly on the pressure line Switching element (microswitch) Lead sealable setpoint adjustment Setting spindle locking element Terminal connection or plug connection to DIN 43 650 Form A Stainless steel sensor housing Stainless steel bellows with internal stop Pressure connection G 1/2" external G 1/4" internal Centring pin 26 Pressure switches Mechanical pressure switches Pressure switches General description Operating mode The pressure occurring 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). [. . . ] 1 is a cross-sectional diagram of a pressure sensor which fulfils the "special construction" requirements. The measuring chamber is bordered by the housing (1), base (2) and measuring bellows (3). All parts are made of stainless steel and are welded together without filler metals. When the pressure rises the measuring bellows (3) moves upwards, supported by the back pressure spring (5). The setpoint spring installed in the switching device acts as a counterforce. A transfer bolt (6) which transfers the pressure-dependent movements of the measuring bellows (3) to the switching device located above is placed on the inside of the base. A plastic diaphragm (7), which is not in contact with the medium and in normal operation follows the movements of the measuring bellows but itself has no influence on the position of the bellows, is clamped in the upper part of the transfer bolt. On breakage of the measuring bellows (3), the medium can escape into the interior of the bellows. The medium pressure is now on the underside of the diaphragm (PL). An additional force is generated because of the far larger effective area of the diaphragm compared with the bellows, and this pushes the transfer bolt (6) upwards. This results in cut-off to the safe side. The cut-off condition thus achieved is normally interlocked electrically or mechanically, so that the system also remains cut off when the pressure drops again. The plastic diaphragm (7) is not a pressure-bearing part; it has no function in normal operation and is effective only if a leakage occurs to the measuring bellows. Safety diaphragms of the described design are permissible up to 32 bar. This should be sufficient for most applications. b) Pressure sensors with certification of 2 million operating cycles (DWR series) In this design it is assumed that the pressure sensors which have withstood dynamic loading of 2 million operating cycles during component testing can be considered as reliable elements. They do not have an additional safety device in the sensor. Although the units are produced and tested with very great care, maximum pressure limiters without additional safety device can lead to dangerous conditions if errors which cannot be detected in the tests occur due to secondary effects. These may be caused by hole corrosion due to deposited metal particles on the (usually very thin-walled) bellows of the pressure sensor, material defects in the pressure bellows or a broken weld seam. Despite careful production and testing, a residual risk remains in the case of maximum pressure monitoring. It is ultimately up to the user and operator of the systems themselves to decide on the degree of safety to which pressure vessels should be monitored. Pressure sensors without safety diaphragm are self monitoring when used in minimum pressure monitoring applications. Self-monitoring maximum pressure limiter with safety diaphragm DWAM. . . , DWAMV. . . , SDBAM. . . Pressure limiter without safetydiaphragm (not self-monitoring for maximum pressure) DWR. . . 46 Pressure switches Pressure switches "of special construction" Safety analysis for maximum pressure monitoring Observing the direction of action The preceding description and safety considerations relate to the monitoring of maximum pressure. [. . . ] They are TÜV-tested for steam and hot water, but thanks to the self-monitoring sensor can also be recommended for other, particularly safety-critical applications (e. g. Sensors of the DWR series are self-monitoring when used in minimum pressure monitoring applications. Equipment of a boiler with pressure monitor and pressure limiter Pressure monitor for burner control: DWAM. . . (without adjustable switching differential) or (better, because switching differential adjustable) DWAMV. . . or DWR. . . ­205 (with internal interlock, unlocking button on the pressurelimiter) or DWAM. . . [. . . ]