Proportional Valve; Automatic Purge Control Unit - Siemens Maxum II Manual

Safety Systems - Purging
2.3 Electronics Purging System (with Automatic Purge Unit)
2.3.3

Proportional Valve

This valve provides proportional control of the input air flow. This means that air flow is
dependent on the pressure difference between the air inside the electronics enclosure and the
ambient outside air (lower pressure difference results in greater flow). Operation of the
proportional valve is controlled by the Automatic Purge Unit (APU) which is described below.
In the Modular Oven model, the proportional valve is located inside the electronics enclosure
on the lower left wall toward the rear. In the Airless/Airbath Oven model,the proportional valve
is located in the right, rear, lower section of the electronics enclosure. In this location, it is not
visible through the door of the electronics enclosure. It is only accessible via a screw-on access
panel.
Maxum Modular Oven Proportional Valve
mounted on the inside of the electronics
enclosure left wall, lower rear.
Figure 2-13 Proportional Valve
2.3.4

Automatic Purge Control Unit

This component is designed to control the purge system of the Maxum II analyzer. The APU
monitors the internal and external pressures and sets flow accordingly via the proportional
valve. It will also detect when purge pressure is lost and, using the disconnector unit, disable
power to the analyzer in the event that proper purging is not present.
The APU also controls the process by which power can be reconnected to the analyzer. If
power has been turned off on the analyzer, purge pressure must be restored to the electronics
zone, and it must be flushed out with fresh instrument air for about 8 minutes before power is
connected to remove potentially hazardous levels of flammable gases and vapors from the
analyzer before power up.
The APU is mounted inside the electronics enclosure of the Maxum II as shown in the following
figure.
28
MMO
Pro Pro Pro Pro Pro Proportional
Valve Valve
Air Input to
Electronics cs cs
Enclosure ure
Control Wiring Con ng
for Proportional for
Val Valve (to APU)
MAA
Proportional nal nal
Valve
to
Maxum Airless/Airbath Proportional Valve
mounted on the outside of the electronics
enclosure right wall, lower front.
Explosion Protection Safety Standards
Manual, August 2017, A5E02220442001 Rev 8