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Operation
2Operation
Round bottles are used for sample containers. Pressure from a spring tensioned operating rod, which is rotated by
hand to bear upon the base of the sample bottle, holds and seals the bottle against a rubber gasket within the casting.
The contact between the sample bottle and the gasket should be air tight and should be tested by blocking off the air
exhaust tube with a finger and blowing into the nozzle each time a bottle is fitted to the sampler. The operating rod
assembly can be removed from the recess provided at the rear of the support beam, and the pressure exerted by the
operating rod can be adjusted by increasing or decreasing the compression of the operating spring. The axis of the
sample container is inclined at an angle to the vertical which permits sampling to within 90 mm of the stream bed.
With the instrument oriented into the direction of flow (nozzle horizontal and pointed upstream) a continuous stream
filament is discharged into the sample bottle during the period of submergence. The air displaced by the sample is
ejected through the air escape passage projecting from the instrument alongside the head and oriented to discharge
downstream. A fixed static head differential between the intake and air exhaust, facilitates sampling in low stream
velocities and slack waters. Three nozzles, 1/8", 3/16" and 1/4" diameter are supplied with each sampler. One is chosen
for each sampling cross section according to the velocity and depth to be sampled.
A clean bottle should be used for each separate sediment sample. At least one suspended sediment sample is taken at
each stream vertical selected in the cross section. In a sampling operation, the intake nozzle is oriented upstream,
directly into the current, while the sediment sampler is lowered into the stream.
Submerged obstructions directly upstream or adjacent to the sampler should be avoided to preclude interference with
the stream filament approaching the intake nozzle. The sampler should be lowered at a uniform rate from the water
surface to the bottom of the stream, instantly reverse the direction of the transit, and raise the sampler again to the
water surface at a uniform but not necessarily an equal rate. Each filled sample bottle when removed from the
instrument should be capped immediately and appropriately marked.
The sampler continues to take its sample in flowing water throughout the time of submergence, even after the bottle is
completely filled.
If the bottle becomes entirely full, the sample may not be representative and it should be discarded. Although the
capacity of the sample container is about 470 ml, the tilt of the bottle is such that any sample containing more than
440 ml of a water sediment mixture may be in error. In order.to provide sufficient sample for a laboratory analysis,
the length of time the instrument remains submerged should be adequate to produce a sample volume greater than
375 ml but not to exceed 440 ml. It is generally preferable to save an initial sample smaller than 375 ml but larger
than 300 ml than to discard the sample on the spot and re-sample into the same bottle. Moreover if the initial sample
volume is considerably less than 300 ml, the stream vertical may be integrated a second time, or even a third time,
each being additive to the same sample bottle. A minimum sample of 350 ml is suggested.
Sample Size
The volume of sample collected throughout any stream vertical is dependent primarily upon the mean stream velocity
in the vertical, the size of the intake nozzle, and the time of submergence of the instrument. The operator must
regulate the size of the sample accumulated by establishing the appropriate time period over which the sample is to be
taken. Thus the volume of the sample may be increased or decreased by varying correspondingly the sampling time.
The attached graph shows the relation between stream velocity and filling time to produce samples 395 ml in volume
for three different nozzle sizes. The filling time in seconds represents the total time of submergence of the instrument
and includes the time involved in traversing the stream vertical in both the downward and upward direction.
2.1 Example
(Refer Diagram 1 )
Mean Velocity 1.2 metres/sec.
Nozzle 1/4"
Filling Time 10 seconds
If the sampler is lowered from the water surface to the stream bed at a uniform rate in 5 seconds, it should be raised at
a uniform rate so as to break the water surface at the expiration of the next 5 seconds. The time of traversing the
stream vertical need not be the same in both directions of travel. However, the rate at which the sampler moves
vertically must remain uniform in each direction of travel. Thus, in the above example, the stream vertical could have
been traversed at a uniform rate downward in 4 seconds and the sampler raised at uniform rate upward to clear the
water surface in 6 seconds, the total submergence period still being 10 seconds.
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