11
Toggle Valves
Toggle valves are used to start and stop gas flow in and out of the unit (see Sections III and IV) and
to select the appropriate reference volume according to the size of sample cell being used (see
Section IV).
They are closed when their handles are parallel to the cabinet face and open when perpendicular to
the cabinet face. Closing the toggle valves can sometimes cause a slight pressure increase in the
sample cell which can be observed on the pressure display. To relieve this slight pressure, press the
toggle valve’s handle down against the cabinet. This will slightly open the valve seat and relieve the
pressure without building up new pressure when it is released.
Needle Valves
Needle valves are used to control the rate at which gas flows in and out of the unit.
The "GAS FLOW IN” RATE needle valve is used to control the flow rate into the MULTI-
PYCNOMETER. It determines both the rate at which pressure builds in the Reference volume
during a measurement (see Section IV) and – in combination with the VENT needle valve - the rate
at which the sample is purged of contaminants (see Section III). This valve should not be used to
stop flow. Flow of gas in to the unit is stopped using the "GAS FLOW IN" ON/OFF toggle valve.
The "VENT" needle valve controls the rate at which pressure is released when venting the sample
cell (and reference volume) or when vacuum is required to decontaminate the sample (see Section
III). To prevent elutriation of a powder sample as the pressure is released, open the Vent toggle
valve and needle valve carefully to release pressure slowly. This valve should not be used to stop
flow. Flow of gas out of the unit is stopped using the "VENT" OPEN/CLOSE toggle valve.
Selector Valve
This valve is used to expand gas from the reference volume, V
R
, into the sample cell holder, V
C
. It
rotates 90degrees between “2 o’clock” (right) and “10 o’clock” (left); when pointing to the right
only the reference volume (V
R
) is in the gas path and when pointing to the left the sample cell holder
is also included in the gas path (V
C
+ V
R
).
Pressure Display and Transducer
Pressures within V
R
and V
R
+ V
C
are displayed on the LCD in psig. (Note, since pycnometric
measurements use pressure ratios, the units are in fact unimportant for calculating volume and
density (but can be useful for setting the gas supply regulator and for troubleshooting). The
display is zeroed using the zero knob to the right of the display when V
R
is open to ambient (Gas
flow toggle valve is OFF and vent toggle valve and needle valve are open).
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