Agilent Technologies 6890 Series Service Manual page 634

Valve bodies
Body parts are made from Nitronics 60 nickel steel. If required, the valve may
also be produced from Hastelloy C. External tubing (plumbing) is connected
to the valve body ports by ferrules and fittings provided with the instrument.
The left (CCW, counterclockwise) and right (CW, clockwise) stops on general
purpose valve bodies limit rotor rotation so the correct flow path results
when the index pin is close to or against either stop of the index lip.
Caution Intermediate positions of the rotor may result in an interrupted flow path
which could cause damage to the valve or other components in the
chromatograph.
Valve rotors
Rotor type can be identified by color:
• An off-white rotor is made of a PTFE composite and may be used from
room temperature to 200° C.
• A black rotor is made of polyimide and may be used from 100 to 350° C.
Caution The life of a valve is shortened if used outside its specified temperature range
Do not mix rotor types in the same system.
The rotor seats on a highly polished conical surface. When properly seated,
the polished surface prevents leakage around the rotor and between non-
selected ports. The finish precludes adsorption of most GC samples.
The rotor assembly is a one-piece part with an integral molded and machined
conical hub and the parts necessary for proper seating. The sample contacts
only the PTFE composite (low temperature) or polyimide (high temperature)
as well as the stainless steel of the valve.
Grooves in the rotor surface form the paths between specific ports. The index
pin prevents rotation beyond either stop of the index lip. 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.
Jun 2001
Valves
Agilent 6890 Gas Chromatograph Service Manual
Valves
Valco W-series minivalves
1110
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