5 Maintenance & Troubleshooting | Model 356WA |
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flowmeter column or humidifier column.
5.9 Leak Detection
The most frequent cause of trouble in trace measurement is leakage. Tiny leaks which may be unnoticeable can cause serious errors in trace measurements. One of the principal problems is that air can diffuse into a gas line through a small leak, even though the gas pressure in the line may greatly exceed atmospheric pressure.
When a leak occurs in a system where the mass flow velocity is less than the molecular velocity, gas molecules move in both directions through the leak. The net flow of a particular gas, e.g. oxygen, will depend on the relative partial pressure of that gas on each side of the leak. In a sample having only a few
5.9.1 Leak Detection Procedure
The procedure outlined here is based on the premise that the leak rate is independent of sample flow rate.
a)Stop the sample flow to permit oxygen to accumulate at the point of the leak.
b)After approximately one minute, restart the sample flow. It is advisable to practice establishing the flow rate to 150 cc/min., the reference flow indication on the flowmeter, with one quick turn of the throttle valve.
c)Simultaneous to restarting the flow, start a stopwatch to measure the time required for the recorder/meter to respond to the accumulated oxygen.
d)The following are approximate times for the accumulated oxygen to reach the cell from various points in the sample path through the analyzer at 150 cc/min.
1.5 to 2 seconds | Calibrator |
3.5 to 3.75 seconds | Base of humidifier column* |
5.5 seconds | Flowmeter |
6.5 seconds | Metering valve |
7.5 seconds | Gas connection at rear of analyzer |
> than 7.5 seconds | Sample connection lines leading to |
| analyzer |
*A leak at this location may indicate a leak in the column or in the reservoir system.
5.9.2Cell Leak
Teledyne Analytical Instruments |
