Sampling 



Pumping System and Apparatus . The sampling was done by pumping (or 

 sucking) the sediment-laden water through an intake nozzle into a collect- 

 ing and settling tank (Figure 5). The pumping was accomplished by a 

 vacuum pump (Figure 6) driven by a 1/4 horsepower motor capable of 

 maintaining a vacuum inside the collecting tank equivalent to 26.5 inches 

 of mercury. The collecting tank (Figure 5) was a 2-i gallon pyrex bottle 

 equipped with a two-hole rubber stopper, which permitted air-tight entry 

 of two pipes. The two pipes entering the collecting tank were made of 

 copper tubing; one served to connect the vacuum pump to the collecting 

 tank; the other served as an intake line for the sediment-laden water. 

 The connecting pipes for the entire pumping system were made from copper 

 tubing with sections of rubber tubing inserted where necessary to obtain 

 flexibility. The pump, piping, valves, and collecting tank comprised a 

 closed system necessitating the use of air-tight valves and connections 

 throughout. 



It was desired to keep the intake nozzle and that portion of the 

 tubing inserted in the water as small as possible to minimize effects 

 on the flow regime, but yet it had to be large enough to permit easy 

 flow of the fluid- sediment mixture through the line without clogging. 

 Quarter-inch copper tubing was finally selected as the best compromise 

 between these two requirements and was used in all tests. 



Filtration Devices and Methods. Several mechanisms were tested to 

 extract the sediment from the fluid-sediment mixture. The first, and 

 most obvious, was simply to use the two-gallon pyrex bottle as a settling 

 container with subsequent decantation of the excess water. The remaining 

 water was then boiled from the wet sediment mixture leaving only the 

 dry sample. This method was cumbersome and time consuming and was 

 therefore discarded; yet it served a useful purpose in that it gave a 

 rough estimate of the range of sediment concentrations to be expected 

 in the sampling tests. 



A second device for extracting the sediment from the fluid-sediment 

 mixture consisted of a clamping mechanism housing a filter and equipped 

 to fit water tight over the mouth of the pyrex collecting tank (Figure 7a). 

 It was of plywood construction and required that the collecting tank 

 be inverted to allow the water to drain through filter paper and thus 

 separate the sediment from the water. A pressure equalizing tube 

 (Figure 7b) was necessary to maintain atmospheric pressure above the 

 water surface inside the inverted bottle thus aiding the effective force 

 on the filter and therefore the filtering rate. This method of sediment 

 separation was accurate and worked fairly well but lacked the flexibility of 

 the method which follows. 



The third system of sediment separation employed the use of filters 

 throughout the collection and separation process. The fluid- sediment 



47 



