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How are swimming pools built and worked?
Conceptually speaking, a swimming pool is very simple. It is a large pool of water. However, in the hot summer, swimming pool seems to be the greatest invention known to mankind. In fact, ordinary pools use a lot of advanced technology, and the number may be far more than you think.
Basic knowledge of swimming pool
Swimming pools vary in shape and size, but almost every pool works the same way, from a backyard private pool to a water park surf pool. Swimming pools are integrated with filtration and chemical treatments to keep water clean.
A swimming pool of apartment buildings under construction: it looks like a big hole in the ground, but in fact it is much more complicated.
Swimming pools generally include seven important parts:
:: Electric pumps
:: Water filters
:: Drainage pipes
:: Backflow tube
PVC plastic pipes connecting all these elements
The basic principle of the swimming pool is to continuously recycle the water: from the swimming pool to the filtration and chemical treatment system, and then send it back to the swimming pool. In this way, the suction system can make the water in the pool cleaner, basically free of sludge, garbage and bacteria. Some pools also have heaters that keep the water temperature constant.
Swimming pool type
The main difference between different types of swimming pools is the construction method. Here are several different types of swimming pools. Each type has its own advantages and disadvantages.
· The above-ground pool is the pool with the lowest cost and the lowest construction difficulty. Most ground pools are made of prefabricated devices. Even laymen can combine these devices. Of course, most people still ask professional installers to build such pools. Firstly, the installer levels the ground to form a flat building surface. Then they assemble the surrounding tracks to support the outer wall. The outer wall is made of metal, plastic or wood. Then they laid sand and pipes in the pool area. Finally, they installed vinyl pads on the wall of the pool, injected water into the pool, trimmed the pads and fixed them in place. After they connect the pump and the filter system, the swimming pool is installed and ready for use. Compared with other types of swimming pools, the main disadvantage of such pools is that they are not durable and usually have an unattractive appearance. Such pools are also less durable, which can be seen as an advantage, even when they are disassembled and transferred.
· The fiberglass pool is made of fiberglass plastic shaped into a swimming pool. When installing the swimming pool, the construction team first digs a pit of the appropriate size, lays the necessary pipes, fills the sand, and then puts the pre-formed swimming pool structure into the pit. Then they levelled the pool, connected all the pipes, and backfilled the area around the pool. Usually, the pool is reinforced with concrete slabs.
· Vinyl-lined underground pools are very similar in structure to underground pools, but they are more like traditional underground pool design. The team first dug a pit and then assembled metal, plastic or wooden frame walls around the pit. As with the construction of ground pools, the team will lay sand along the bottom of the pit and install vinyl pads on the structural walls. These pools are much cheaper than other underground pools, but not durable enough. Generally speaking, it is necessary to replace the liner every 10 years or so.
· Jet pool is the most common design in most parts of the United States. In building these pools, the team dug a pit, laid pipes, and then assembled the frame with 1 cm of steel bars. The spacing of reinforcing bars is about 25 centimeters, fixed together by metal wires. After installing the frame, the team sprayed a thick layer of cement mortar (a mixture of cement and sand) around the reinforcing bar. Before shotcreting, the ejector will mix the dry cement mortar into the water to make wet concrete material. The construction team will flatten the cement mortar, dry it for about a week, and then apply a smooth coating on the rough surface. Mud (actually a mixture of cement and marble sand) is the most commonly used outer coating, but many people use special concrete paint to paint swimming pools. The smooth surface of the grouting tank can be tile, exposed aggregate or even glass fiber. Shotcrete pools (and similar shotcrete pools) are very durable and can be constructed in any shape or size.
· The pouring concrete pool is similar to the grouting pool, but it is much more difficult to construct. In building these pools, concrete is not sprayed around the reinforced frame, but poured into the traditional wooden frame. With the increasing popularity of grouting methods, poured concrete pools have almost withdrawn from the mainstream swimming pools. In stone pools, the walls of the pools are made of concrete blocks.
The floating pool underground swimming pool may look like a solid fixed structure, but it is actually more like a boat, which can float in the surrounding underground water. When there is no water in the pool, the groundwater pressure can actually lift the pool out of the ground. This is one of the reasons why underground pools need to store water all year round. That is to say, the pressure on both sides of the pool must be roughly equal.
In most modern underground pools, special hydrostatic pressure valves are installed near the main drainage pipes to avoid damage to the pool by groundwater pressure. Simply put, if the groundwater pressure is large enough, it will push up small floating blocks, thus opening the pressure valve. When the pressure valve opens, groundwater pours in to keep the pressure balanced.
Drainage systems, pumps and filters
We already know that the water in the swimming pool needs to flow through the filtration system to remove sludge and garbage. During normal operation, water flows into the filtration system through two or more main drains at the bottom of the swimming pool and several skimmed drains around the top of the swimming pool.
The main drain pipe is usually located at the lowest point of the pool, that is, the whole pool plane tilts to the main drain pipe. Most sediment sludge and garbage are discharged from the pool through these drains. To prevent people's hair or limbs from getting stuck in pipes, these drains are almost always covered with grilles or whirlpool caps (caps that divert water flow to prevent dangerous whirlpools).
Slag skimmers pump water in the same way as main drains, but they only pump water from the top of the pool (usually 3 mm at the top). All floating garbage (such as leaves, sunscreen, hair) is discharged from these drains into the swimming pool. The following schematic diagram shows a universal pool drainage system.
In the system described here, the floating weir (the gate at the intake channel) can swing back and forth, allowing only a very small amount of water to enter at a time. In order to ensure the efficiency of garbage interception, the floating weir only clears the surface water. When water flows through the filter basket, it intercepts all the larger trash, such as branches and leaves. In addition to the main intake pipe, the skimmer also has a secondary equalization pipe connected to the drainage pipe below the water surface. If the water level is below the level of the main intake pipe, the secondary equalization pipe can prevent the skimmer from pumping air into the pump system.
Water is first pumped into the filtration system and then flowed back to the backflow pipe (the inlet valve on the wall of the swimming pool). This system uses a lot of suction methods. However, as long as the construction and operation of the swimming pool are correct, there is almost no risk of people being sucked and pasted into the drainage pipe. Only when there is only one drain pipe left in the swimming pool can such suction occur in the pipeline system. In a safe swimming pool, there are always several main drains and several skimming drains. Therefore, if a drain pipe is blocked by someone or object, the suction system can also pump water from other drains. This eliminates the suction effect on the blocked drain pipe.
Most swimming pools have a pair of vacuum vents. Vacuum vents are only used for swimming pool cleaning. These vacuum openings are connected to the vacuum cleaner in the swimming pool, which acts like a common vacuum cleaner, except that it sucks water instead of air. Vacuum openings can be self-contained suction pumps, but in most swimming pools are driven by the main pump.
Swimming pool vacuum cleaner
When water flows through various drains, it reaches the stage of filtration.
Nowadays, most swimming pools are equipped with underwater lighting, partly for the sake of beauty, but mainly for the convenience of swimmers to see their movements at night. In one of the most common underwater lighting designs, incandescent bulbs are encapsulated in waterproof lamps embedded in grooves in the wall of the swimming pool. Insulated wires are connected to lamps through special sealing, so that water can not touch conductive components. Wires are connected back to the room (or where the power supply is) through long pipes. Most of the long tube is full of water. There are enough wires left in the pipe. When you want to change the bulb, you can pull the whole lamp out of the groove and out of the water.
Some people use optical fibers to illuminate swimming pools rather than embedded incandescent lamps. In this system, the actual light source does not need to be located underwater. Therefore, you will not encounter the replacement of light bulbs, waterproof electrical components and other issues.
In most people's eyes, the swimming pool is more or less like digging a big hole in the ground. We can't see most of the expensive equipment in the pool system because they are usually hidden in a nearby pump room. But it is these devices that keep the pool working properly.
The pump is the heart of the pool system. In ordinary pump system, the motor drives the impeller in the pump box to rotate. The impeller drives the flow of water in various drains through the filter and then back to the intake pipe.
The main drain pipe, the slag skimmer and the water pipe of the vacuum outlet are all connected to the suction system.
Water will flow through the metal filter basket before entering the pump. Filter baskets intercept leaves and other large garbage that may clog pumps. Then water flows into the filter (or, in this set of configurations, into one of the two filters).
The filter in this system is a high-speed sand filter. Sand filter is a large water tank made of glass fibre, concrete or metal. It has a thick sand bed with a slightly square super-fine sand.
Special filter sand
During the filtration operation, dirty water from the swimming pool passes through the intake pipe of the filter, which is connected to the water supply head in the tank. Under the action of gravity, water passes down through the sand, and fine sand grains intercept all the dust and garbage in the house. At the bottom of the tank, the filtered water flows through the catchment device and then out of the outlet pipe.
After a period of time, dust and garbage deposited in the sand will slow down the flow of water. The swimming pool administrator can check the pressure gauges at the inlet and outlet of the filter to determine the degree of blockage in the tank. If the pressure gauge shows that the pressure in the inlet pipe is much higher than that in the outlet pipe, the administrator will know that there is a lot of garbage in the sand. That is to say, the filter should be backwashed. To backwash the filter, the administrator can adjust several valves to change the direction of the flow. The administrator can close the backflow pipe connected to the swimming pool and open the sewage pipe connected to the sewage system. The administrator adjusts a valve in the filter, connects the pipe from the pump to the outlet pipe, and connects the sewage pipe to the inlet pipe. After these adjustments, water from the pump flows through the sand from bottom to top, taking away dust and garbage. At the top of the filter tank, dirty water flows out of the intake pipe and into the sewer.
The administrator rotates the big handle to adjust the pipe valve, which can change the direction of water flow and backwash.
Some pool systems use diatomite filters or core filters instead of sand filters. In diatomite filters, the water in the swimming pool flows through the screen covered with diatomite. Diatomite is a fine powder made from fossils of marine organisms called diatoms. Its chemical properties are inactive. In a filter element, dirty water flows through a filter made of polyester cloth or corrugated paper. You don't need to backwash, just move through the filter and pull out the hose. After a few years (or at most eight years), you should discard old filters and replace them with new ones.
Most U.S. laws require that all water in a swimming pool (or, more accurately, an equivalent amount of water) must flow through the filter within a certain period of time, usually between 30 minutes and six hours. For the apartment pool shown above, this means pumping 630,000 litres of water through the filtration system every six hours!
Pumps and filtration systems are also connected to wells or municipal water pipes, so fresh water can be injected into the pool. This is essential for replenishing the water lost by evaporation, backwashing and "splashing" (splashing onto the platform or body and swimming suit). When the weather is hot and swimmers are active, 630,000 litres of swimming pool can lose 1.1,000 litres or more of water a day.
Chemistry of swimming pool
The filter system of the swimming pool plays an important role in keeping the water clean, but you must also rely on chemical fine-tuning of the water quality. It is important to carefully handle the chemical balance of swimming pools for the following reasons:
· Harmful pathogens (such as bacteria) can grow in water. If the water in the pool is untreated, microorganisms carrying pathogens can easily spread from person to person.
· If the pool is chemically unbalanced, it may damage various parts of the pool.
· Chemically unbalanced water can irritate people's skin and eyes.
· Chemically unbalanced water becomes turbid.
In order to treat pathogens in water, disinfectants must be put in to eliminate the pathogens. The most common pool disinfectants are compounds containing chlorine elements, such as calcium hypochlorite (solid) or sodium hypochlorite (liquid). When chlorinated compounds are put into water, chlorine reacts with water to form various chemicals, the most important of which is hypochlorite. Hypochlorite attacks lipids in cell walls and destroys enzymes and structures in cells by oxidative reactions, killing bacteria and other pathogens. Bromide and other substitutes for disinfectants have the same effect, but the germicidal efficacy is slightly different.
Automatic chlorine feeder connected to pump and filter system
Usually you can use liquid, powder or sheet chlorine (and some professionals use gaseous chlorine) and put it into water at any point. Swimming pool experts generally recommend that chlorine be put into the chemical feeder immediately after filtration. If chlorine is thrown directly into the swimming pool (e.g. in the skimmer), the chlorine concentration in these areas may be too high.
One big problem with hypochlorite is that it is not particularly stable. Hypochlorite degrades when exposed to ultraviolet radiation from the sun. In addition, hypochlorite may combine with other chemicals to form new compounds. Pool Chlorinators usually contain stabilizers (such as cyanuric acid). The stabilizer reacts with chlorine to form more stable compounds. The new compound is not easily degradable when exposed to ultraviolet light.
Hypochlorite may bind to other chemicals even when stabilizers are put in, and the compounds formed cannot disinfect and sterilize efficiently. For example, hypochlorite may combine with chemicals such as ammonia in urine to produce various chloramines. Not only is chloramines ineffective in disinfection and sterilization, but they actually irritate the skin and eyes and emit unpleasant odors. Special odors and eye allergies in swimming pools are actually caused by chloramine, not by ordinary hypochlorite. Strong odors usually indicate that free chlorine (hypochlorite) is too little, not too much. To remove chloramines, pool administrators must shock the pool by putting in doses exceeding conventional chemicals to remove organic substances and useless compounds.
The formation of chloramines is related to the second major problem in pool chemistry, that is, to maintain the proper pH value of the pool. In the next section, we will discuss how to maintain the pH level.
The pH of water is a measure of its overall acid-base balance, i.e. the ratio of acid to base in water (see Chem4Kids: acid and base for instructions on acid and base). In short, excessive acidity or alkalinity of water can lead to adverse chemical reactions. If the water is too acidic, it will corrode metal equipment, corrode surface materials and cause skin allergies. If the alkalinity of water is too high, it may lead to oxide skin on the surface of swimming pool and pipeline equipment, and may make the water turbid. In addition, excessive acidity and alkalinity will reduce the efficiency of chlorine. If the alkalinity of water is too high, chlorine can not kill pathogens well; if the acidity of water is too high, chlorine will escape much faster.
On the pH scale, zero is strong acid, 14 is strong base, and 7 is neutral. Most pool experts recommend that the pH of the pool be between 7.2 and 7.8. To increase or decrease the pH, the pool administrator only needs to put acid or alkali into the water. For example, adding sodium carbonate (soda ash) or sodium bicarbonate (baking soda) usually increases pH; adding hydrochloric acid or sodium bisulfate can reduce pH.
Any new element (grease, chlorination, falling objects on the swimmer) changes the total chemical composition of the water body, so maintaining the proper chemical balance in the pool is a continuous process. In addition to pH, pool administrators also monitor total alkalinity, calcium hardness and total solubility.
The fact that swimming pools use so much chemical knowledge and equipment is obviously a remarkable technological achievement. The construction and maintenance of these summer facilities also require amazing workload and flexibility.
Correct equipment selection can ensure baby swimming fun.