Siemens Maxum II PD PA AP Service Manual page 83

Figure 4-25
The two actuating pistons are spring loaded in a manner that assures that all six passages are
momentarily closed during the switching operation (both energized and de-energized). This
feature prevents unwanted mixing of gases during the switching cycle. The plungers and disc
move only a few thousandths of an inch to permit flow through the passages.
For external loop sample valve applications, ports 2 and 5 are connected externally by means
of tubing. The standard sample volume is 170 microliters. For internal loop sample valve
applications, ports 2 and 5 are connected internally by means of a machined passage in the
valve cap. The standard sample volumes are: 2, 5 and 10 microliters.
The Model 11 valve must be protected against dirt, filings, column packing material, or anything
else that might affect the Teflon-to-metal seal. Filter elements should be 5 micrometer or finer.
Purging below the seal disc area may be necessary in a trap valve, when permeation through
the seal disc causes air peaks or in a sample valve, when corrosive gases attack the seal disc
cushion and/or other valve parts. (In the latter case the expected mean time between failure
can be increased significantly.)
Purging is normally accomplished with the carrier gas. 1/16 tube fittings are provided as inlet
and outlet connections for the purge gas. Typically a tee can be placed in the carrier inlet line
and a needle valve can be used to regulate the flow at 5 cc/min.
Maxum II Valves and Oven Components
Service Manual, 10/2018, A5E42019844001
Model 11 Valve, LDV Version Exploded View
Valves
4.6 Model 11 Valve
83