Routine Maintenance: General
Maintaining a sampling valve (rotary type)
Released: March 2004 6850 Series II GC User Information page 110 of 256
Maintaining a sampling valve (rotary type)
The rotary sampling valve (gas or liquid) is actuated by a pneumatic solenoid
controlled by the GC. The left (counterclockwise, CCW) and right (clockwise,
CW) stops on general purpose valve bodies limit rotor rotation. The correct
flow path results when the index pin is close to or against either stop of the
index ring. See Figure 16. Grooves in the rotor surface form the paths between
specific ports. The index pin prevents rotation beyond either stop of the index
ring. Valve ports are connected by the grooves only when the index pin is close
to or against either stop. Intermediate positions result in flow shutoff through
the valve and possible damage if left in this position.
Figure 16. A typical 6-port rotary valve
Aligning the rotor
Typically, the rotor index pin stops near, but does not contact, the CW and
CCW stops. Occasionally, however, it may strike one of these stops when
engaging or disengaging. Over time, the stop will wear down. This typically
causes misalignment of the rotor with the valve ports, which causes flow
problems such as low sample amounts, carryover, or restricted carrier gas
flow. To correct this problem, realign the valve rotor.
ON (CW) stop
OFF (CCW) stop
Rotor index pin
Preload assembly
Body
Rotor
Valve body
Index ring
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