Oil in Water | Part III | |
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4.1.5 Sample Delivery System
The sample delivery system should be designed to operate at the full capacity of the interconnecting pipe. Ideally, both the sample and bypass valves should be adjusted to maximum so that the only impedance to sample flow is the length and diameter of the delivery pipe. Such a delivery system will virtually eliminate problems associated with oil and debris collecting in the sample line. Air ingestion will also be reduced to a minimum, as will analysis lag time.
TET/AI recommends that the sample line be constructed of 1/2” sched- ule 80 PVC pipe capable of pressure to 150 psig maximum. Unless abso- lutely necessary, do not install any valves or restrictions in the line other than those required to bypass the customer installed external sample pump. All control over sample flow should be performed at the system inlet and the pump if provided be allowed to operate at full efficiency against only the resistance of the line.
A pump is required only if there is insufficient pressure to lift the sample to the top of the system equipment panel. Do not complicate the delivery system by adding a pump unless it is absolutely necessary. A low pressure system will be prone to sample line depositing, but this can be alleviated by scheduled flushing with the high pressure utility water.
If a pump is required, TET/AI recommends a total submersion centrifu- gal type. Sub- merging the pump in the sample water automatically elimi- nates the most common problem - priming the pump. Also, the sample should be drawn from a point where there is a minimum of turbulence; in this way, air or turbid suspended solids will not be ingested along with the water.
The intake side of the system should be equipped with a coarse screen filter. However, do not filter the water downstream from the sample point, or use a fine filter anywhere in the sampling system. High filtration will prevent a representative analysis of the undissolved oil in the sample water.
The inlet of the pump should be placed at a depth where the best representative concentration of oil can be obtained. Positioning will vary with the application; however, as a general rule, to avoid skimming, the inlet should be about 2 feet beneath the surface of the sample water.
4.1.6Safe Vent (Drainage)
Teledyne Analytical Instruments | Part III: |
