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8
15. Turn the Nitrogen valve on.
16. Set the top and bottom regulators to the recommended back pressure for
your test.
This instrument is equipped with check valves between the regulators and
the pressure outlet to protect the regulators from backflow. If you increase
the regulator pressure and then decrease it, there may be extra pressure
remaining in the lines.
The upper and lower limits of the test pressure differential are determined
by the test temperature. As this temperature exceeds 212°F (100°C), the
back pressure must be increased in order to prevent vaporization of the
filtrate. The 500 PSI differential pressure must be maintained, so the top
pressure will have to be increased accordingly. The table below shows
the pressures recommended for various test temperatures.
17. Open the top valve stem by turning it one quarter turn. This will add
pressure to the test cell. Maintain this pressure until the sample
temperature stabilizes. The heating time of the sample should never
exceed one hour.
18.
When the fluid sample reaches the desired test temperature, increase the
pressure on the top pressure unit to 500 PSI (3,448 kPa)
more than
the
back pressure. Open the bottom valve stem to initiate filtration.
19.
Collect the filtrate for 30 minutes. If the back pressure rises above the
initial setting during the test, cautiously reduce the pressure by opening
the valve on the receiver and drawing off some of the filtrate into the
graduated cylinder.
Recommended Minimum Back Pressure
Test Temperature
Vapor Pressure
Minimum Back Pressure
°F
°C
psi
kPa
psi
kPa
200-299
95-149
12.1-67
84-462
100
700
300-374
150-189
67-184
462-1269
200
1400
375-399
190-199
184-247 1269-1704
275
1900
400-424
200-219
247-326 1704-2245
350
2500
425-450
220-230
326-422 2245-2912
450
3100