Plugged Valve
If the valve is plugged, plungers are pressed upward by air pressure or spring action and will
not release to their open position when sample pressure drops.
Ruptured Diaphragm
Escaping air from valve vent hole indicates a ruptured diaphragm (4), which must be replaced.
Check for liquid substances escaping from the vent hole.
Slow Erratic Piston Switching
Improper lubrication and/or contamination of O-rings will increase friction on valve-actuating
piston. This causes valve switching to be erratic, slow or inoperative.
This condition requires disassembly of the entire valve (maxi-maintenance). It is recommended
that the valve be returned to Siemens for service.
4.4.1.3 Model 20 Valve Cap Maintenance Procedure
If customer maintenance personnel are not technically trained to repair the Model 20 valve on
site, it is recommended that the valve be returned to Siemens for service, repair, or direct
replacement.
Within the following procedures, the numbers in parenthesis are callouts. They denote parts
referenced in the lists contained in the figure in section 6.5.2; refer back to the figure for
locations.
Valve Cap Disassembly, Cleaning, and Reassembly
1. Loosen the three Allen screws (16), holding the plunger valve body (13) to the valve cylinder
base (14). The screws should be loosened to the point that most of the spring pressure is
relieved (approximately 1/8 inch or 3.2 mm).
DO NOT remove these three screws.
2. To remove valve cap (1), remove the three Allen screws (3) and six Belleville washers (2)
holding the valve cap (1) to the valve plunger body (13).
3. Remove the valve cap (1) from the plunger valve body (17).
NOTICE
Do not place polished valve cap (1) against any abrasive surface. Place it on an
uncontaminated lint free cloth.
Valves
4.4 Model 20 Valve
Maxum II Valves and Oven Components
Service Manual, 10/2018, A5E42019844001 57
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