What is a pool pump?
A pool pump is a circulating pump designed to filter, turn over, clean and sanitise the water in a swimming pool. It is generally always an electric motor powered pump and except in commercial applications, a pool pump is powered by a small single phase motor. A pool pump is designed to handle certain things fairly specially.
The most critical thing that it is designed to handle is the water quality. Pool water is generally fairly neutral in pH but is generally high in dissolved salt (about 5g/L) and hardness (about 150ppm) and when you add the residual chlorine in the water can be very corrosive, cause large amounts of scale to build up and high wear and tear to components. In addition, pool water can have sand, leaves, lint and other rubbish in it that a pump needs to be able to handle.
Parts of a pool pump:
- Housing and pump parts are all plastic. Yes plastic is cheap and can get a bit brittle when exposed to acid too much but it doesn’t corrode like cast iron or stainless steel. It is also cheap to replace the parts that wear out.
- The mechanical seal. On cheaper pumps the seal seat is ceramic with a graphite rotating face. As there is a lot of salts in the water, when the pump is stopped crystals build up on this seal surface and the graphite is scored and wears prematurely. In better quality pool pumps, the seal materials are silicon carbide. That is both the rotor and stator faces are constructed of this very hard material that resists wear from salt crystals and gives you a greater service life.
- Motor. There are a couple of common types of motors on pool pumps.
- Close coupled. Where there is no significant space between the pump and motor.
- Open coupled. Where there is a space for leaking water to escape.
- Fully sealed. This is where instead of being air cooled by a fan, the pump is water cooled by passing some of the pressurised water from the pump over a sealed motor casing. Water can still drain from a leaking seal.
- Lead basket and pump housing. A pool pump has a large leaf basket set into a large housing. This does 2 things, it stops large items like leaves, grass, string etc from getting into the pump and causing damage. As the pump inlet always sits at the top of the pump housing, this allows there to be a whole housing of water for the impellor to sit in and this makes it “self-priming”. Self-priming is when the pump is able to suck air and not totally stop as it can draw in water from its housing and start pumping again by itself.
- Easy disconnect couplings. The barrel unions on the inlet and outlet of the pump allow the pump to be easily disconnected to be maintained. Sometimes also the whole housing but also the leaf basket has easy disconnect coupling too so that a small problem can easily accessed an fixed, usually by the owner.
- An open impellor able to handle sand and other debris that passes through the pump.
How does a pool pump work?
A pool pump is designed to recirculate the water in a pool. This keeps the water fresh and clean by distributing pool chemicals, filtering the water and pushing the water through a chlorinator unit. A pump is generally set up at the water level or slightly above and is usually a couple of meters from the pool in an enclosure or shed. The suction for a pool pump generally comes from a skimmer box which is a straining device and water level control at the edge of the pool. It’s designed to let floating material fall into it as the water cascades into a small weir. This captures the heaviest debris and stops it reaching the pump, the water then pools in the bottom of the skimmer and is sucked through PVC pipe across to the pump. Sometimes there is also a drain line set up so the pool can be pumped from the deepest part of the pool as well. This line is mainly for draining a pool to swap out the water or for heavy filtering. The flow between the two lines is controlled by a large valve placed before the pump. As there is generally an amount of sand in the bottom of a pool, then itd advisable to minimise the amount of time sucking from the lower inlet as large amounts of sand can damage a pool pump.
What is a self priming pump?
As a pool pump is self-priming, it can pull water in from the pool with a small amount of prime water. It holds the water in the suction line with a one way flap valve that sits between the leaf basket and the impellor of the pump. The water is pumped through a pool pump by an impellor. This is attached on a metal shaft to an electric motor which spins it a 2800rpm. An impellor is a small round fan like device that when set in a housing, pulls water in from the leaf basket of a pump and then pressurises it and pushes this water out the outlet. Once the pump has started and is primed (all the air is expelled), then the water exits the pump outlet and travels to the filter.
How does a filter work?
At the filter, depending on the position of the valve, the water either is passed through the media, is used to backwash the filter or is expelled straight to the dump line to empty the pool. For the majority of the time, the water is being filtered and this water goes straight back into the pool at the opposite end to where its sucked out from that way the water is recirculated properly. If the pool is a salt water pool and uses a chlorinator unit for chlorine, then once the water has been filtered, it is run through a chlorinator.
What is a chlorinator?
A chlorinator a small electrical unit that is fitted in line with the pool return. The water passes through it and there are a number of metal plates inside the housing. A small electric current is passed from one half of the plates to the other half and this caused and electrolysis reaction. The salt that is dissolved in the water reacts in this reaction to form chlorine which is pushed out into the pool and helps keep the pool water safe and clean. The pool chemistry should be maintained according the Australian standard for pool water and when balanced with a small amount of chlorine being pumped in, the water stays safe to swim in and should not be uncomfortable for people’s eyes and skin.
When working properly, a pool pump should have the capacity to easily turn over the volume of the pool 2-3 times per day.
What is important when you set up a pool pump?
When setting up your pool pump, there are a couple of things you should consider:
- The location of the power supply and the location of the inlets. Sometimes this has already been determined for you and the pipes are already in place. If not then you water to ensure that the power is out of the way and safe and that the suction lines from the pool are simply laid out and as short as possible. You should also ensure that they are a minimum of 40mm but preferably 50mm pipe so that they can handle the water flow properly.
- How high the pump is from the water level. Pool pumps by their design do not produce a large amount of pressure. Because of this, they generally do not have the ability to suck water up from any great height. Because of this, if the pump can be set below or at the water level of the pool then this provides the most efficient operating conditions for the pump. This may even save you money in operating costs as the pump doesn’t have to work as hard.
- The exit pipework from the pump is easy to disconnect and service and where it does to the filter is well supported and simple. This ensures things can easily be fixed and the pump is efficient as possible.
- The chlorinator is set up properly. This means ensuring that the chlorinator is connected to the correct pipe and the pump is run off the chlorinator timer. Also ensure that the chlorinator is set up after the filter as this will stop raw chlorine damaging the filter valve and housing and also mean that chlorine does its job in the pool and isn’t consumed by the organic material in the media.
- The equipment is housed properly. There are 2 main things that are important here, the pump is protected from the sun and rain and that the area is well ventilated and can dry out. By their nature the mixture of moisture, salt, chlorine and electrical gear is not a good mix. If the pump shed or house is well ventilated then fresh dry air helps maximise the life of pumps as it slows corrosion damage.
How do you size a pool pump properly?
The size of a pool pump is determined by:
- The volume of the pool.
- The number of pool users at one time.
- The type of sanitising system being used.
The main factor is the pool volume. A pool’s water should be totally recirculated 2-3 times per day to ensure that its being filtered and sanitised properly. As an example, if the pool volume is 50,000L then you should aim for the pump to pump 125,000L approximately and this should be done over at least 2 x 4-6 hour periods. As the pump needs to run for 12 hours to do 125,000L then the pump should be doing 10,500L/hr or 175L/min. This is a normal flow rate for a mid sized pool pump (1-1.5hp).
What if the pool is used alot ?
If the pool is to be used a lot, especially for entertaining or where there are lots of kids swimming, then you may need to either use a bigger volume pump and filter or run the pump for longer per day. This is because of the large amount of cosmetics and other things worn and also the amount that young people sweat. In addition if there are large spikes in the number of people swimming (15 people swimming in a 50,000L pool) then this needs to be accounted for too.
The other big factor is how the water is sanitised. The most common method that is used is a salt water chlorinator. This unit needs to be run for 6-8 hours per day during summer to ensure that the chlorine levels are maintained in the pool. If there is a large amount of swimmers or the pool water is soiled, then this may need to be turned up temporarily or some liquid chlorine added to spike the water and make it safe. If alternative systems like ozone or peroxide are used, then the pump may need to run at a slower rate but for longer every day to ensure that a good constant dose is being added as these chemicals break down quickly.
This article has talked about how pool pumps work, how they are constructed and how you should select and set one up. When you are next needing some advice on a quality Davey pool pump, filter or Chloromatic chlorinator, please give our friendly sales staff a call on (08) 9721 3577 or send us an email