Metrohm 774 Oven Sample Processor - Manual (Page 20)

2 Installation
774 Oven Sample Processor, Instructions for use 14
2.4.5 Installation of the tubing system and the drying flask
A stream of gas with a constant flow rate is required to transfer the moisture
which is released when the sample is heated to a measuring vessel. You
can either use the built-in pump to supply air or use an inert gas such as ni-
trogen for this purpose.
Inert gas connection
Connect the inert gas to the 'Air/N
2
in' connection on the left-hand side of
the instrument. Make sure that the pressure in the supply line is less than 1
bar. The inert gas should be dried by passing it through the drying flask.
The flow rate is measured and monitored by the 774 Oven Sample Proces-
sor. A solenoid valve is used to switch the gas flow on and off.
Air supply from the built-in pump
A stream of air can be used for the determination of chemically and ther-
mally stable samples. The pump built into the tower of the 774 Oven Sam-
ple Processor provides a sufficiently large and stable flow rate.
Gas flow
Air/N 2 in
Drying flask
from to
It is essential that the flow of gas is dried and filtered. If the pump is used
the air is drawn in through the right-hand side of the instrument. A dust filter
(6.2724.010) should be mounted on the 'Inlet filter' connection. The gas is
dried by mounting a drying flask on the left-hand side of the instrument, as
shown in the drawing alongside.
The drying flask is filled with molecular sieve and the outlet tube
(6.1821.050) with its filter is fitted to the drying flask insert (6.1602.140).
Screw the completely assembled insert onto the drying flask and attach the
two tubing connections (6.1805.520, 7 cm long) to the drying flask cap.
Place the flask in the drying flask holder and then attach the free ends of
the tubing connections to the corresponding connections on the tower of
the 774 Oven Sample Processor. The tubing connected to the inlet tube in
the drying flask is connected to the left-hand connection marked 'from
Drying flask'. The carrier gas will stream into the head space of the flask
and penetrate the molecular sieve. Then it can stream up inside the outlet
tube and enter the tower's gas tubings via the 'from Drying flask' connec-
tor'.
The filling of the drying flask must be replaced from time to time. The interval
may vary depending on the length of use, moisture content of the gas and
atmospheric humidity. Read the information given on the label of the mo-
lecular sieve container for more details.