Specifications

Model 50 Valve
This section provides maintenance instructions for the Model 50 Valve.
The Model 50 is a pneumatically operated diaphragm valve specifically
designed for process gas chromatography. It uses pressure-on-
diaphragm activation with no other moving parts. The valve can inject
vapor samples and switches columns simultaneously. It is capable of
switching gasses up to 75 psig (515 kPa).
Description
The Model 50 valve is equipped as part of the Analytical Module that
installs in a Modular Oven. Depending on configuration, multiple Model
50 valves may be equipped on a Module. This section describes the
Model 50 valve and its detailed maintenance instructions. For
information regarding the overall Analytical Module, refer to the section
relating to the Analytical Module later in this chapter.
Figure 4-4: Model 50 Valve
The following equipment is required to repair the Model 50 Valve:
Repair Kits & Fixtures
• Model 50 Repair Kit: Siemens PN 2020164-001 (includes 10
diaphragms, 10 screws with washers, and 12 Valco fittings).
• Valve Assembly Fixture: Siemens PN 2020281-001
• Torque screwdriver with Allen head bit: Siemens PN
1631005-003
Particulates introduced to the valve either from the sample or from the
columns can prevent the diaphragms from sealing against the center
plate of the valve. Also, to insure proper sealing of the diaphragms, the
actuation pressure should be 25 psig higher than the carrier gas or
sample gas pressure.
Preventing Port to
Port Leaks
To help prevent leaks always turn the Sample and Carrier Gas off before
the Actuation Gas is turned off. Without Actuation Gas the Model 50
Valve is in an undefined state and the flow path of the carrier or sample
cannot be controlled. Leaks in the Actuation Gas lines could result in a
lower Actuation Gas pressure which could result in port to port leaks.
The symptoms can include small peaks, repeatability problems,
contaminated columns and noise on the detector.
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