Online Leader In Above Ground Pools
|
|
HOW IT WORKS | |
Pool Basics
Swimming pools come in all shapes and sizes, but nearly all of them, from your pool in your own backyard
to the pool at the local YMCA to the wave pools ath the water parkl, work in the same basic manner.
They use both filtration and chemical treatment to continually clean a large amount of water.
A typical swimming pool needs seven major components:
- A water basin (the pool)
- A pump (usually driven by an electric motor)
- A filter
- A chemical feeder
- Drains
- Returns
- Plumbing connecting all of these elements
The basic idea is to take water from the pool, pump it through the filtering and chemical
treatment systems and then back into the pool again. By means of filtration and chemical treatment
this cycle keeps the water in the pool relatively free of dirt and bacteria. Some pools also include heaters
in the mix, in order to keep the water at a certain temperature.
Types of Pools
There are several different types of pools. The main difference in these types is how the pool is constructed.
The basic operation of each type is the same. Each type of pool has its own advantages and disadvantages.
Above-ground pools are the cheapest construction option, as well as the easiest to build.
Most above-ground pools are made from prefabricated kits, which the average home-owner can put together
(though most people go with professional installers). First, the installers clear the area in which the pool
is to be installed, leveling off the ground to form a flat building surface. Then they assemble a perimeter, a track
which supports the outer wall. Next, they spread sand in the pool area and rough in the plumbing. Finally,
they secure the vinyl liner (either over the pool walls or in a track), fill the pool with water, smooth the
liner and fasten it into place. As soon as they hook up the pump and filtering system, the pool is ready to be
used. The main disadvantage of this sort of pool is that it's less durable than other designs, and generally
less attractive.
Fiberglass pools are made from fiberglass-reinforced plastic, which has been molded into a
basin shape. To install the pool, the installation crew digs an appropriately sized hole, rough in the necessary
plumbing, adds some sand filler and lowers the preformed pool structure into the hole. Then they level the
pool, hook up all the plumbing and backfill in the area around the pool.
Vinyl-lined in-ground pools are a lot like above-ground pools, structurally, but they look more
like conventional in-ground designs. The construction crew digs a hole and assembles a metal or composite
frame wall around the pool's perimeter. As in an above-ground pool, the crew lays a concrete/sand based mixture
along the bottom of the pool and secures the vinyl lining to the wall.
Gunite pools are the most popular design in much of the United States. To build one of these
pools, the installation crew digs a hole, puts the plumbing in place and assembles a framework grid with 3/8-inch
steel reinforcing rods (rebar). The rebar rods are secured together with wire. When the grid is in place, the crew
sprays a heavy coating of gunite around the frame (constructed with rebar). The sprayer unit combines dry gunite
mix with water just before spraying -- this produces the wet concrete material. The crew trowels the gunite smooth
and lets it sit for a week or so before applying a smooth finish to the rough surface. The most popular finish is called
plaster, but a lot of people finish their pools with special concrete paint. Gunite pools can also have tile, exposed
aggregate or even fiberglass finishes. Gunite pools are durable, and they can be built in any shape or size.
Poured-concrete pools are similar to gunite pools, but they're a lot harder to build. Instead of
spraying concrete material around a rebar framework, concrete is actually poured into forms.
With the rise of gunite methods, poured-concrete pool construction has mostly fallen by the wayside.
All of the aforementioned pools use the same basic principles to keep the water clean. Lets look at the components used
in this process.
The Drains
We've already seen that the water in a swimming pool needs to circulate through a filtering system, to remove
dirt and debris. During normal operation, water flows to the filtering system through main drain(s) at the bottom
of the pool and one or more skimmer drains around the top of the pool.
The main drains are usually located on the lowest point in the pool, so the entire pool surface slants toward them.
Most of the dirt and debris that sinks exits the pool through these drains.
The skimmers draw water the same way as the main drains, but they suck only from the very top of the pool
Debris that floats -- leaves, suntan oil, hair -- leaves the pool through these drains. The picture below shows
a common system.
The Drain System
In the system described here, the weir, the door at the inlet passageway, swings in and out to let a
very small volume of water in at a time. To catch debris effectively, the goal is to skim just the surface level.
The water flows through the strainer basket, which catches any larger debris, such as bugs, twigs, and leaves.
The water is pumped through the filtering system and back out to returns, inlet valves around the side of the pool.
This system involves a lot of suction, but if the pool is built and operated correctly, there is virtually no risk of
suction holding somebody against one of the drains. The only way the plumbing system could apply this sort of
suction is if there were only one open drain. In a safe pool, there are always multiple main drains as well as
several skimmer drains, so if somebody or something blocks one drain, the pumping system will pull water
from one of the other drains. This eliminates the suction on the blocked drain.
The Pump
The heart of the pool system is the water pump. In a typical pump system, an electric motor spins an impeller inside
the pump housing. The impeller drives the water from the various drains through the filter and back out to the pool via
the water inlets.
Pipes from the main drain, skimmer and vacuum ports lead to the pumping system.
Just before it flows into the pump, the water passes through a strainer basket that catches leaves and other
large debris that might clog up the pump.
The Filter
Most pools today utilize either a sand filter or a cartridge filter. Sand filters consist of a large tank containing a bed
of sand.
Sand filter
During filtering operation, dirty water from the pool comes in through the filter's inlet pipe, which leads to the water
distribution head inside the tank. While gravity pulls the water down through the sand, the tiny sand particles catch
any dirt and debris. At the bottom of the tank, the filtered water flows through the pick-up unit and out the outlet pipe.
Over time, the collected dirt and debris in the sand slows down the water flow. Pressure gauges at the filter inlet
and outlet give the pool owner an idea of the blockage level inside. If gauges show much greater pressure on
the inlet pipe than the outlet pipe, the owner knows there's a lot of collected debris in the sand. This means it's
time to backwash the filter. To backwash, the owner adjusts a valve to redirect the water flow. He
or she closes the return pipe leading to the pool and opens the drainage pipe, which lead to the sewer system. He
or she adjusts a valve at the filter to connect the pipe from the pump to the outlet pipe and connect the drainage
pipe to the inlet pipe. With this arrangement, water from the pump pushes up through the sand, dislodging the
dirt and debris. At the top of the filter tank, the dirty water flows out through the inlet pipe and into the sewer.
To redirect the water flow for backwash, the owner adjusts a valve.
In place of a sand filter, some pool systems use a diatomaceous earth filter or a cartridge filter. In a
diatomaceous earth filter, water from the pool passes through filter grids coated with diatomaceous
earth, a fine powder made from the chemically inert, fossilized remains of sea organisms called diatoms.
In a cartridge filter, dirty water passes through a filter made out of polyester cloth or corrugated paper.
Instead of backwashing, you simply remove the filter and hose it off. After a few years (or as many as
eight years), it's time to discard the old filter and put in a new one.
In most regions, the law dictates that all the water in the pool (or more accurately, the equivalent volume)
must pass through the filter in a certain amount of time -- typically between 30 minutes and six hours. For
the apartment-complex pool pictured above, that means pumping 167,000 gallons (630,000 liters) of water
through the filtering system every six hours!
The pump and filter system is also connected to a well or municipal water line so fresh water can be added to the pool. This is necessary to replace water lost to evaporation, backwashing and "splash-out" (water that splashes on the deck or is carried out on people's bodies and swim suits). When it's pretty hot out and there's heavy swimmer activity, this 167,000-gallon pool could lose 300 gallons (1,100 liters) or more in one day.
Pool Chemistry: Disinfecting
A pool's filter system does the heavy lifting in keeping the water clean, but it takes chemistry to do the
fine-tuning. It's important to carefully manipulate the chemical balance in pools for several reasons:
- Dangerous pathogens, such as bacteria, thrive in water. A pool filled with untreated water would be a perfect place for disease-carrying microorganisms to move from one person to another.
- Water with the wrong chemical balance can damage the various parts of the pool.
- Improperly balanced water can irritate the skin and eyes.
- Improperly balanced water can get very cloudy.
To take care of pathogens in the water, you have to introduce a disinfecting agent that will get rid of them.
The most popular pool disinfectant is the element chlorine, in the form of a chemical compound such as
calcium hypochlorite (a solid) or sodium hypochlorite (a liquid). When the compound is added to the water,
the chlorine reacts with the water to form various chemicals, most notably hypochlorous acid. Hypochlorous
acid kills bacteria and other pathogens by attacking the lipids in the cell walls and destroying the enzymes
and structures inside the cell through an oxidation reaction. Alternative sanitizers, such as bromide, do
basically the same thing with slightly different results.
An automated chlorine feeder hooked into the pump and filter system
Chlorine is typically prepared in liquid, powder or tablet form (though some professionals use gaseous chlorine),
and it can be added to the water anywhere in the cycle. Pool experts generally recommend adding it just after
the filtering process, using a chemical feeder. If it's added directly into the pool, using tablets in the skimmer
boxes, for example, the chlorine tends to be too concentrated in those areas.
One problem with hypochlorous acid is that it's not particularly stable. It can degrade when exposed to
ultraviolet light from the sun, and it may combine with other chemicals to form new compounds. Pool
chlorinators often include a stabilizing agent, such as cyanuric acid, that reacts with the chlorine to
form a more stable compound that does not degrade as easily when exposed to ultraviolet light.
Even with a stabilizing agent, hypochlorous acid may combine with other chemicals, forming compounds
that are not very effective sanitizers. For example, hypochlorous acid may combine with ammonia,
found in urine, among other things, to produce various chloramines. Not only are chloramines poor
sanitizers, but they can actually irritate the skin and eyes and have an unpleasant odor. The distinctive
smell and eye irritation associated with swimming pools are actually due to chloramines, not ordinary
hypochlorous acid -- a strong smell usually means there is too little free chlorine (hypochlorous acid),
rather than too much. To get rid of chloramines, pool owner have to shock treat the pool -- add
an unusually strong dose of chemicals to clear out organic matter and unhelpful chemical compounds.
Chloramine formation is related to the second major element in pool chemistry, maintaining the
right pH in the pool. In the next section, we'll discuss pH maintenance.
Pool Chemistry: pH Level
The water's pH is a measure of its total acid-alkalinity balance -- the relative proportion of acids and
alkalis in the water (check out Chem4Kids: Acids & Bases for a description of acids and alkalis). Simply
put, water that is either too acidic or too alkaline will cause undesirable chemical reactions. If the
water is too acidic, it will corrode metal equipment, cause etching on the surface materials and cause
skin irritation. If the water is too alkaline, it can cause scaling on the pool surface and plumbing equipment
and can cloud the water. Additionally, both high acidity and high alkalinity alters the effectiveness of the
chlorine. The chlorine won't destroy pathogens as well if the water is too alkaline, and it will dissipate much
more quickly if the water is too acidic.
On the pH scale, zero indicates extreme acidity, 14 indicates extreme alkalinity and 7 indicates a neutral
state. Most pool experts recommend a pool pH between 7.2 and 7.8. To raise or lower pH, a pool owner
simply adds acids or alkalis into the water. For example, adding sodium carbonate (soda ash) or sodium
bicarbonate (baking soda) will generally raise the pH, and adding muriatic acid or sodium bisulfate will lower the pH.
Maintaining the proper balance of chemicals in the pool is a continual process, because any new element -- oils
from a swimmer's body, a shot of chlorine, stuff that falls in the water -- shifts the water's total chemical
makeup. In addition to pH, pool owners also monitor total alkalinity, calcium hardness and total dissolved
solids.
When you consider all the chemistry and machinery involved in swimming pools, it's clear that they really
are remarkable pieces of technology. It takes a surprising amount of work and ingenuity to build and maintain
these summertime staples.
| |
|
Copyright © 2008 Swimming Pool World
Swimming Pool World sells Above Ground Pools, Aboveground swimming pools, pool supplies, automatic cleaners, and swimming pool covers at unbeatable prices.
Sitemap | Partners
Leaders in Above Ground Pools
|
