Week 4 – Pumps!

Preface

We started off this weeks’ lesson on pumps by listening to a lecture conducted by Mr Tune on how pumps work. He covered very interesting things like the types of pumps and impellers that are available. The objective of the lesson was for us to experiment with a pump and let us get a feel of what to expect before fabricating our robot.

Before the lesson, we were tasked with completing as much as we could of an assignment on pumps – to find out more about the different pump types and analyse various pump performance curves. By doing this work before class, we as a group had a much clearer picture of what was going to be covered during the lesson.

The experiment we had to conduct seemed very simple. At the core of it, all we had to do was hold a tube up to different heights and measure the flow rate of the water exiting the pump.

staticHead

We had to measure something called static head. Now, this term is not very direct in portraying what it actually is quantifying. Static head, as can be seen in the diagram above, is merely a height difference, and is measured in length. As such, its units would be metres in the metric system or feet in the imperial system.

Now, why does this matter to us?

This is important information when choosing a pump as we must be aware of its characteristics. What is the maximum height the pump can pump water up? After all, the pump is working against gravity to pump water upwards. Furthermore, we can also find out the flow rate of water at the outlet of the tube. If the manufacturer does not provide this information, it is up to us to obtain the pump characteristic graph.

Experiment

Items needed

  • Pump
  • Two buckets (Bigger bucket is Bucket A, smaller bucket is Bucket B)
  • Tube of length 1 metre
  • Measuring Tape
  • Stopwatch
  • Weighing Scale

Before the experiment

Weigh the empty buckets and record down their mass. This is needed when calculating the flow rate of the water.

To find the maximum static head

  1. Fill Bucket A up with water until it is about 3/4 full
  2. Attach the tube to the pump
  3. Place the pump in Bucket A
  4. Hold the tube vertically up, ensuring it is as straight as possible
  5. Turn on the pump
  6. Measure the height of the water level in the tube, taking reference from the water level in Bucket A

To find various data points for the pump

  1. Fill the Bucket A up with water until it is about 3/4 full
  2. Attach the tube, at least of length 1 metre, to the pump
  3. Place the pump in Bucket A
  4. Hold the tube up and ensure that the distance from the tube outlet to the water level in Bucket A is at least x cm (less than the maximum static head)
  5. Hold the smaller bucket, Bucket B, below the outlet of the tube
  6. Turn on the pump
  7. As soon as water starts flowing out from the outlet of the tube, start the timer
  8. Once 30 seconds have elapsed, turn off the pump and swiftly measure the weight of Bucket B
  9. Repeat steps 4-8 for various values of x

All data was recorded in a Microsoft Excel spreadsheet.

Carrying out the experiment

Before carrying out the experiment, we sat around and discussed the procedure to follow so that we could complete the experiment efficiently. We delegated the work accordingly and prepared all the necessary items.

IMG-20151111-WA0022

The very first thing we did was measure the maximum static head. However, we encountered a problem where the value was very low (~35cm) and we asked Mr Tune what the problem could be, as we were supposed to expect it to be larger than that. He pointed out that the pump had a sort of slider mechanism which acted as a filter to allow more or less water into the pump. We found that we had accidentally left the slider in the closed state and hence had to slide it back into the open state. This allowed us to obtain a more accurate reading of 47cm.

We then proceeded to obtain the data for different static heads at intervals of 5cm, ensuring that we carried out the experiment accurately.

IMG-20151111-WA0021IMG-20151111-WA0025IMG-20151111-WA0023

We recorded down the data and could observe the graph taking shape on the spot. Upon obtaining a sufficient number of data points, we showed our result to Mr Tune. He pointed out to us that some of our readings seemed slightly off and hence we repeated the experiment to obtain more reliable values for the data points he pointed out.

Another thing we realized while conducting the experiment was that initially, we started the timer as soon as the pump was turned on. However, Hwee Peng pointed out that the timer should be started only when the water exited the outlet of the tube. Due to this oversight, we had to repeat the experiment for some data points, but thankfully we realized this early on in the experiment and not towards the end.

Data Analysis

1The table above shows all the data we obtained. We found that the maximum static head for the pump was 47cm. What this means is that the pump is only capable of pumping water up to a height of 47cm. We also found that the maximum flow rate of the pump was 40.3 cm3/s. In other words, if we require a flow rate of greater than 40.3 cm3/s, this pump would not be suitable.

These are just simple numbers, but how do we interpret this data? We generated a scatter plot based on this data and subsequently generated a polynomial trend line given the various data points.

2

And so we have the performance curve of the pump!

Reflection

We as a group learnt a lot from this experiment. We learnt that while proper planning is very necessary before conducting experiments, there are some very minor mistakes we might make during the experiment that we might not foresee. Hence, it is necessary to maintain a vigilant eye and spot any errors that may occur during the experiment.

It is also extremely beneficial to have multiple minds thinking about a problem. By having different perspectives and views, one person may see flaws the rest of the people in the group do not see immediately.

Everybody was very willing to help out one another and take on any duty. We efficiently distributed the work and through working together well as a team, we were able to complete the experiment very well and in good time, leaving us with some extra time during the lesson to discuss about our robot.

I am very grateful for being in a group where everybody is eager to help out one another and is always focused on the task at hand, and also for always being able to see the fun in any activity we do! 😀

Ajay Pillay

 

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