VICI Selectors (multiposition) Standard electric - Manual (Page 15)


. Shock from heavy or continuous use
Occasionally, when valves are used in applications requiring a high-duty
cycle, wear or shock can cause the screw and clamp ring to loosen. Instru-
ment vibration may have the same effect. This allows the standoff to move,
causing inaccurate rotor rotation. The most obvious symptom is observable
movement of the standoff, valve, or actuator, which normally do not move
when the valve is actuated.
Chromatographic Symptoms of Misalignment
. Loss of flow or blocked flow
When the valve body, rotor, and actuator are not in proper alignment, the
ports do not completely intersect the flow passages on the rotor. In the
worst case there is no flow in any position, but slight misalignment may
eliminate flow from ports on one side of the valve only. With a rotometer or
a line placed into liquid, gas flow may be observed between positions as
the actuator cycles the valve. In liquid applications, blocked flow may cause
pump shutdown or failure of other components due to pressure buildup.
. Mixing of samples
In some configurations with large ports and their corresponding large flow
passages which are very close together, poor alignment can cause mixing
of samples even when a flow restriction has not been observed. This may
be manifested as “ghost” peaks or poor reproducibility.
Alignment Procedure
NOTE: The alignment procedures for air actuated and electrically actuated
valves are not the same. For an air actuated valve, see Technical Note 707,
Operation Notes and Alignment Instructions, Air Actuated Multiposition
Valves.
Description
The valve will have either one (SD and SC types) or two (SF and ST types)
rows of ports evenly spaced around the circumference of the body. See
Figure 10. In addition there will be one (SD and SF types) or two (SC and
ST types) “common” ports offset to either side of these rows. By convention,
Position 1 falls counterclockwise from these common port(s) when the valve
is viewed from the end away from the actuator. The rotor will have either
one or two flow passages appearing as engraved rings around the seal,
which intersect the common port(s). Flow passages perpendicular to the
ring(s) connect the ring(s) to the selected port(s).
STUW
The only configuration which does not fall within this description is
the STUW. Unlike the standard ST, these have one row of ports
around the circumference, with two common ports offset in the
same direction. The common ports are 180° apart, so only one
shows in
Figure 10. Special instructions and descriptions regarding
STUW’s will be highlighted in this manner at several points in the
procedures which follow.
Valve Alignment