Week 8 (In Lab) - Pump Modifications

In lab this week, Michelle and Le worked on modifying the pump, while Davina and Parm worked on further documentation of the project's progress, including updating the pages on this blog. The latter two also began to create the final presentation for the project.

Previously, the pump had exhibited unwanted behavior in that it continued to siphon water through the tubing while turned off. The team had conjectured that this was because stopping up one outlet and solely using the other had created a vacuum inside the pump: this meant that air pressure was sufficient to push the water through the whole pump apparatus. To remedy this, Michelle and Le tried several solutions:

1. Insert tubing system into the previously stopped-up outlet, and keep a small tube in the other outlet for aeration purposes.
• The tube was too smooth for hot glue to adhere correctly, so it had to be connected with electrical tape instead. This was an extremely weak and unstable connection.
• This solution was unsuccessful. Water was forced through both outlets rather than just through the one intended.
2. Put a cap on the water container to seal it off from the air, reducing air pressure on the water around the pump.
• This was Parm's and Davina's idea, but a cap for the container was hard to come by - they were only able to find a large piece of cardboard in the lab.
• This seemed like it wouldn't work, since several holes would have to be cut into the cardboard for the tubing and power cord, and this would let in the air anyway.
3. Use the original design, except make sure the ends of the tubes remain above the level of the pump.
• This was the simplest solution and the one that ended up working. It turned out that the problem was more related to gravity than to the presence of a vacuum. A diagram of the problem and solution can be seen in Figure 1. 

Figure 1. Diagram showing how position of tubing affects movement of water when pump is off.