Jan 17

I recently read in the January 2012 edition of the Engineers Australia magazine a letter which contained the sentence “Scientific truth is not obtained democratically”.

I believe that this statement is a grave misrepresentation of the way science is conducted and the way scientific hypothesis become scientific laws.

Science, like engineering, is carried out by people and as such is intrinsically bound within a social and cultural context. Indeed, even the matters that attract research attention and funding are determined by those factors, just as the engineering projects that get built are.

My issue is not with the primacy of scientific facts; but a collection of facts is not science in the same way that a collection of dates is not history. Those facts must be combined into hypothesis that explain them and ideally suggest new emergent facts to look for.

The facts of the physical science that engineers are most familiar with are demonstrable in repeatable experiments; the facts of sciences such as geology, climatology, cosmology, sociology, anthropology and economics are not so amenable.

The current paradigm in any field of science is determined by the consensus of the scientists working in that field and is inherently democratic. This is not to say that it is unscientific; consensus has been built from a large body of evidence and it would require an equally large body of new and different evidence to change.

General relativity did not replace Newtonian mechanics overnight. There were 50 years of experimental anomalies before the failures in Newtonian physics allowed general relativity to emerge and a further 30 years before it was democratically accepted.


[Published in Engineers Australia February 2012]

Jan 20

A toilet cisternYou use them every day, several times a day in all probability, yet how often do you stop to consider how they work or, more significantly, why they are there?

The photo to the left shows a typical toilet cistern installed (not by us!) in a client's premises. This is a relatively new cistern installed in a very old building; if you look closely you can see the holes in the wall where the older and larger cistern was secured.

From a user's perspective the operation is straightforward; press the button, the toilet flushes and in a little while you can do it again. But ... what is actually going on inside? To find out, let's lift the lid ... literally!

The photo to the right shows the inside of the cistern. We'll go through it one part at a time:

  1. The cistern itself is simply a reservoir to hold the water.
  2. In the centre is the flushing control consisting of two large buttons (white & blue) that activate a half or full flush respectively. They work by lifting the plunger and releasing the water into the flush pipe. Note that the overflow also drops down the flush pipe on newer cisterns (older styles dump it on the floor).
  3. To the right is the filling controls which is a simple float switch that opens when the water drops and closes when the cistern fills up again. The white plug on the left hand side allows the filling controls to be moved over to suit the water pipe.

The components used in a cistern are simple and pretty robust. The most common problem that occurs is the cistern running continuously; this is usually the result of a perished seal in the flushing control but can sometimes be from a maladjusted filling valve that does not cut off before reaching the overflow level.

So that is the how, now to the why. Why do we use cisterns at all?

Myth buster: It isn't to get water pressure. The pressure in a normal water service is typically 5m (50kPa) or more, what you get from a cistern is the height of the flush pipe; about 0.2m (2kPa), so the water pressure in the pipe will easily flush the toilet. So why?

The purpose of a cistern is to provide a physical air break between the water supply, which is usually what we drink, and the sewer, which contains stuff we'd rather not drink. In actual fact a cistern provides 2 air breaks, the break between the pan and the cistern, and the break between the cistern overflow and the filling valve. It is the first one that matters and it is possible and permitted to flush urinals directly from the water main using a device that creates the air break and a solenoid valve and eliminate the cistern entirely.

Now you know!

Dec 21

Last Sunday night I went with my family to the Bon Jovi concert at the Sydney Football Stadium. Despite the rain it was an awesome experiance but that is not the point of this post.

While I was there I observed an all too common problem: walls and walls of empty urinal trough in the gents while the ladies were queued out the door and down the vomitoriumW (I can't pass up a chance to use this word). More...

Nov 03

How much money should you spend on maintenance?

Like any other investment, and maintenance is an investment, you should keep spending on maintenance whenever the returns exceed the costs. Or, when operating with limited resources, as we always are, whenever the returns on this investment are better than the returns on the next best investment. More...

May 19

As I write, the American President is castigating an oil company over the massive oil leak in the Gulf of Mexico. This is what politicians do because they and the people they represent refuse to accept that life in general and engineering in particular is inherently risky. This appears to be a relatively new social phenomenon. More...

Jan 29

Snowy Mountains Scheme

Recently I had the opportunity to make a presentation to Year 11 Engineering Science students at my son's school. In preparing this I grappled with the concept of where engineeringW fits in the scope of human knowledge. Despite being an engineer for almost 20 years this was something that I had not really thought about.

At university it is easy to come to the conclusion that Engineering is a scienceW - you are bombarded with physics, mathematics, chemistry and don't get much (read any) exposure to, for example, music, literature and drama. However, this is a mistake - Engineers are not Scientists. More...