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Archimedes - now he was a pretty smart fella wasn't he? He was the one that pushed his wife into a full bath and, when he got his feet wet, realised that the volume of water that came out of the bath was the same as the volume of the wife that went in. By catching the water he could measure the volume of his wife. Very useful.
He is also remembered for his famous word "Eureka" which is of course the traditional cry made while pushing one's wife into a bathfull of water (or anywhere else for that matter).
Archimedes was also famous for inventing the Archimedes Screw which has, I assure you, nothing at all to do with wives but is in fact a clever device for lifting water. By modern standards the Archimedes screw is a rather inefficient way of lifting water but in its day it was revolutionary.
I recently had one of those Eureka moments I realised it was time to talk about swimming pools. A subject we have not covered before and let's face it for many people a swimming pool is an essential item when buying or selling a property in Bali.
So what type of pool? Infinity edge or skimmer box?
I was recently asked why it is that here in Bali swimming pools tend to have a balance tank while they don't in Australia. The answer is related to the type of pool you have. Let me explain.
In Bali most pools have an infinity edge of some sort. You know the type, you will have seen the photos of some glamorous looking model leaning on the edge of a sheet of water that appears to stop in space with sweeping views across a forested valley beyond. The look on the model's usually face suggests some orgasmic sensation resulting from being in an infinity edge pool, it isn't you know, the orgasm may well be the name of that cocktail she is sipping but is more likely to be the anticipation of getting your mug shot in some glossy magazine.
Anyway the point is that an infinity edge pool is full to the brim. To keep a swimming pool exactly full to the brim, rather like a full pint of best bitter, the volume of water in the pool must always be the same. However, the volume of water in a swimming pool varies, it is never constant. There is always some loss from evaporation, leakage or from the displacement of water by the entry of the mother in law or, in Nigel Mason's case, elephants who need a bath. Anyone who has a pool knows that there is a constant need to top it up.
To make sure the pool itself is always full to the brim we use a balancing tank. The balancing tank takes up the slack, so to speak, carrying a reserve of water so that, as the mother in law gets in the displaced water overflows into the balancing tank and, when she gets out, the pump quickly replaces her displaced water back to the pool from the balancing tank. The water level in the balancing tank goes up and down while the pool itself remains constant.
An infinity edge pool of course needs a trough under the infinity edge to collect the water that overflows and return it to the balancing tank. The pump also needs to run to keep the pool full and the water overflowing.
In Australia (and other countries I am sure) most pools are not infinity edge pools. These pools are not full to the brim. The water leaves the pool from what is known as a skimmer box, a small box built into the side of the pool with a drain in the bottom that goes straight into the filter and pump, no balancing tank. The water in the pool can fall as much as 4 inches and the skimmer box still works fine. As the water in the pool circulates the surface water is drawn to the skimmer box bringing any floating debris such as leaves with it. The skimmer box has a filter basket in the bottom where the leaves are caught and easily removed.
When the mother in law gets into the pool the water level rises, when she gets out is falls again. It has been carefully calculated that four inches is sufficient to allow for the rise in water level caused by an average mother in law.
So you are thinking of buying a house or taking possession of your newly completed pride and joy. The big question for any swimming pool is - does it leak? To check it you need to fill the pool and watch it over several days to see how much the water level drops. It will drop from evaporation but this shouldn't be much. It will become fairly obvious if it is leaking. If it leaks you have a problem that might not be easy to fix.
The most critical part of any swimming pool is the integrity of the shell of the pool. Usually made out of reinforced concrete (fibreglass is often used in Australia) the shell of the pool must be strong enough to withstand the stresses and strains of ground movement and, we mustn't forget, those inevitable earthquakes. We need to consider the ground the pool is to be built in, old rice field land is clay and needs particular care when designing a swimming pool. If the shell cracks there is little you can do, even if you could manage to repair it the likelihood is that it will crack again. The best thing in such a case is to cast a new shell inside the old one but this time - make it strong enough.
If you are having a pool built make sure you go to someone who knows what he or she is doing when they design it. The reinforcing steel must be large enough and the concrete must be thick enough to take the strain. Remember water is very heavy stuff (a metric tonne for every cubic metre) and the strain on a pool can be very high especially if the pool is large or in some spectacular position such as on a hillside.
That model might have a bit more than an orgasm as the pool collapses and she is washed by ten gazillion gallons of water into that beautiful forested valley below.
Imagine the difference between a pool being full of water and it being empty and you start to realise the stresses involved. With so much weight putting a large swimming pool in say a 20th floor penthouse is an engineering challenge that affects the design of the whole building.
Incidentally pools are not meant to be left empty. Talk to any experienced swimming pool man and they will tell you of the time they had a pool empty and they went away for a widdle and returned only to find the pool had "popped out" and was left floating in a hole full of water, I kid you not.
When building swimming pools the cost of concrete and particularly reinforcing steel is such that the PAG (that devious little poverty avoidance gene) can all too easily kick in during the construction phase and that wonderful builder may leave you with a swimming pool that is not strong enough.
If you are building a pool get the design double checked by someone who has civil engineering qualifications (not a master builder) and have the construction carefully monitored to make sure the steel is as specified and the concrete is correctly mixed and placed. The steel bar must be measured and compared to the design drawings, do not simply believe the word of the builder. Beware, it is standard practice (but of course incorrect) here to install one size less than the drawing specifies.
The shell should also be cast as a single piece so during construction the builder should have enough concrete mixers and enough men to put all the concrete in place at one go (usually within one day). This way the shell is cast and cures as a single piece.
If the pool shell is strong enough just about anything else with a swimming pool can be repaired although special care is needed to make sure the circulation pipework is properly installed and the joints are sound before the concrete is poured (can you imagine trying to repair a leaking joint in that plastic drain under the bottom of your pool? it is about as easy as training a rhinoceros to fetch a stick). Any penetrations through the wall of the pool shell for circulation pipes or electrical lighting cables need to be very carefully installed in fact it is far better if there are no such penetrations. Lighting cables can be brought up inside the pool.
Talking of lighting note that all swimming pools require 12 volt electrical lighting ever since some poor chap cooked himself while swimming in a pool with an electrical fault.
A while ago I went to see a row of four half completed villas. They were at an early stage of construction and as we entered we had to walk very carefully along the side of the 3 metre deep hole in the ground and ……..
Just a minute. 3 metre deep hole in the ground? That is some septic tank, perchance the owners are expecting regular visitations of liquid bowel syndrome.
It couldn't be, this hole was huge fully 6 metres wide and 10 metres long and set only a couple of metres from the living room entrance doorway. Perhaps it's a bear pit I thought.
"It's the swimming pool" they said. Sure enough an inspection of the bottom with a handy pair of binoculars revealed telltale signs of swimming pool plumbing.
"Why so deep?" I queried "are you going to hold aquatic conventions for Sumo wrestlers or perhaps you have a pet sperm whale?"
"I don't know", came the reply "the architect designed it that way."
So this leads me to the next of my architectural "blind spots" or perhaps in this case not quite so blind as one might think. All over this island people are building villas with swimming pools so deep you could float the Queen Mary.
I'm sure Nigel Mason will need a deep swimming pool but unless you want to give your elephants a bath I have to ask what do you want a deep swimming pool for?
Oh alright let's look at the Pros and Cons of having a deep swimming pool:
Pros
• You will be able to bathe your elephants.
• Your architect will be able to afford a new car
• Your builder will eat well next year
• The cement factories in Java will be able to pay their staff this week.
• The steel reinforcement manufacturers will survive the financial crisis.
• The tile manufacturers will send you a bottle of whisky at christmas time.
• The water tanker drivers will say hello to you in the street.
• The chlorine salesman will meet his sales quota every month.
• PLN will be able to sell you lots and lots of elecrons.
• You will be able to rent it out to the Dive operator next door to train his students.
• Nice and quiet, more than a metre is too deep for the kids to play in.
• The mother in law will not be able to get out.
• You will be able to sleep soundly at night safe in the knowledge that you are doing your best for the local economy.
Cons - not many really other than you will have to pay for it all.
Ok, ok, yes a deep pool is a good idea and of course would be very useful if you wish to measure the volume of a hippopotamus.
Phil Wilson
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