A Reasonable Alternative to Water Aspiration Francis M. Mulcahy and Andrea M. Robbins
University of Pittsburgh at Bradford. Bradford, PA 16701 Much of the simple equipment in a chemical laboratory is taken for granted until it ceases to function properly or becomes an environmental problem. One such piece of equipment is the water aspirator. Deposits in water pipes and new construction in the area of the laboratory can cause a decrease in water pressure available for use in water aspiration. Easily clogged drains or leaking sewage lines often cause laboratory flooding when water aspirators are used. Environmental factors, such as pollution of water by organic solvents, or water shortages, may also discourage the use of water aspirators. In laboratories where these problems and concerns are present, vacuum pumps are oRen used to replace water aspirators. Use of vacuum pumps to replace water aspirators in the laboratory can be an expensive andlor time-consuming process. Most college and high school laboratories have few vacuum pumps available for this purpose, leading to long lines of students waiting to filter precipitated products or carry out vacuum distillations. Also, a pump that is exposed repeatedly to atmospheric pressure will require more frequent oil changes. The pump probably will have a shorter lifetime as well. In our laboratory, we have designed a manifold system to obtain the greatest possible use from our few vacuum pumps. The equipment described below allows more than one student to use a vacuum pump and should lead to loneer oumD life since the svstem is always under at least partial vacuum. The system is easy
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Schematic of finished vacuum manifold; P-schedule 40 PVC pipe; E-end cap; V-valves inserted through rubber stoppers;T- 518-in. copper tubing.
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and inexpensive to build and does not require a great deal of space. The vacuum manifold was built using a 10-ft. section of 4-in. diameter schedule 40 W C pipe, with two endcaps, obtained from a local builder supply store. This size of pipe was chosen so as to provide a large "reserve" of vacuum. One of the end caps was pierced with a hole 1 112 in. in diameter. Then both endcaps were glued to the pipe using plastic cement. Additional plastic cement was spread over the joints betweenthe endcaps and the pipe to make agood seal. An 8-in. length of 518-in. 0.d. copper pipe was secured in the hole in the endcap using a one-hole no. 8 rubber stopper. A vacuum pump was then connected to the copper pipe, and the system was checked for major leaks. Leaks were sealed using plastic cement, although rubberized caulking would probably work as well. Vacuum inlets were attached to the PVC pipe by drilling l-in. holes every 12 in. along the length of the pipe. Valves attached to 3-in. lengths of 114-in. 0.d. steel tubing were secured in each hole using one-hole no. 6 rubber stoppers. Plastic cement was once again used to seal leaks. When installing the inlets, it is suggested that a round drill bit or hole saw (not a spade bit) be used to drill all holes. Also, it is best to complete one inlet at a time so that leaks in the system can be isolated more easily. Finally, aRer drilling each hole, the PVC shavings should be removed from the pipe by shaking and tapping them from the newly drilled holes. The system can be made more cheaply by using screw clamps as inlet valves and copper or plastic tubing in place of steel tubing. Variations in tubing size can also be made; however, for best pumping speed, it is suggested that the diameter of the tubing in the endcap be much larger than that used on the inlets. Also, in the interest of maintaining high pumping speed, the rubber tubing used to conned the manifold to the vacuum pump should be made as short as possible. The cost of such a system built from scratch would be in the range of $20&2000. In our case, where we used scrap tubing and valves and already possessed a donated vacuum pump, our total costs for the system were $30 (PVC pipe, endcaps, and cement). Yearly operating costs for the system are less than, but comparable to, the costs of operating a water aspiration system.
