Jargon Buster

Pump Head

In most pump specifications the pump head will be stated in gallons or cubic meters of water per hour that the pump can deliver to a stated height in feet or meters. As an example a 1HP pump delivering 17m³ of water to a head of 6 meters height. If the height increases you will delivery less volume of water, if the height lowers more water will be pumped as there is affectively less resistance or back pressure holding the water back (see below).

Back Pressure

Back Pressure is the force your pump needs to overcome to produce sufficient flow rate through your pipe work and filter system. The 2 main factors are the effective height and distance if you like your pump will need to lift the pool water to produce the correct flow overcoming along the way what is termed the friction loss. This is the loss introduced by your pipe work, fittings, bends and other equipment such as the filter and heating circuits etc.

As friction loss in your swimming pool increases the back pressure will also increase and the pump will drop its flow rate.

Back Pressure to high:- A major cause of back pressure being to high can be down to an air leak on the suction side of the pump, shown as a higher than normal reading on the filter pressure gauge. Air can be drawn in and pushed through the pipework system and collect within the filter itself severely reducing water flow. If you have an above ground pump and filter system and in some severe cases with below water line installations it can actually cause the pump to lose prime and cause damage if not found in time. Another symptom is a noticeable loss of pressure at the pool jets.

Desirable Back Pressure:- Yes there is such a thing. Some safety circuits particularly in heating and chlorination can have a safety pressure/flow switch that senses the flow of water and if present will allow the equipment to switch on and operate. In the case of heating obviously the flow of water is needed to keep the heater at the correct temperature and not overheat. No water flow would obviously damage the boiler or heat pump and therefore switch off if flow stops. Typical back pressure for this type of safety circuit would be around 0.5/1 bar. Salt Chlorination units would produce to much gas and therefore over pressure, no flow again would switch them off.

Flow rate:- In swimming pools most common equipment types will have a maximum, minimum or desired (optimum) flow rate.

Pumps:- Your pump should be sufficiently sized and matched in most cases to the flow rate of your filter system. Over-sizing pumps does not increase the efficiency of your filter system and in most cases is a waste of electricity.

Filters:- It is desirable to have 3 changes (Turns) of water per day in swimming pools. Depending on the length of time you run your pump, governed by the volume of pool water. A filter and pump match can then be calculated and chosen for the required flow rate. There is no point on having vastly oversized filter when the pump you have can only delivery half the stated flow rate and visa versa.

Combo Pump/Filter Combination:- For simplicity of installation the pump/filter combo has its advantages. In most cases the interconnecting pipework of pump to filter is done for you. Only leaving the flow to the pump, return to the pool and a waste connection ready on its own stand.

Heating:-  The two main types of swimming pool heating in the UK are run from your household central heating boiler either independent or in conjunction with your household central heating timer and air source heat pumps. In the UK solar matting can be useful as an additional heat source but very rarely can be used as the primary method of heating for the obvious lack of sunshine. In most cases particularly for larger pools solar alone is OK for taking the chill off the water and nothing more.

Boiler:- This can be a very simple system controlled by thermostats and timers to maintain the desired temperature. But:- Depending on the time of day(night) etc you are able to run a boiler system will then control the time you have to run your pool pump and filtration. This can be a balancing act between the flow and time required to filter the water correctly and the flow rate of the heat exchanger installed to get enough heat into the pool water. It is desirable in these circumstances to have a separate water pump for heating circulation only.

Air source heat pump:-  This again is a balancing act. Your air source heat pump will have an optimum flow rate. This is the most efficient flow rate that the heat pump can transfer heat to the water on its return back to the pool. To control this flow it is always desirable to have around your heat pump a pipe work bypass circuit, some water going through the heat pump and some around it. You will need to balance the time required to heat the pool with the filtration time requirement. A super sized circulation pump and filter system only requiring a few hours to filter your pool water correctly may not offer enough time to heat your pool water and can therefore be a waste of electricity in extended running times. You can of course have a separate water pump for heating.

Conclusions:-

I hope it is now apparent that pumps, filters, pipe work and equipment’s such as heating and chlorinators need to be correctly specified, sized and balanced for all installations.

 

Recycled Glass Filter Media RGFM

Recycled Glass is now the norm replacing silica sand as the filter media of choice.

How it works

Silica sand is generally spherical in shape, if you think of a grain of sand as a ball. Due to the crushing process recycled glass is generally angular or cube in shape. If you can now imagine a ball of sand of 1mm and a cube of glass of 1mm they will both effectively occupy the same volume but the six sides of the glass cube will have a greater surface area than the ball of the same diameter.

Filtration is dependent on the amount of surface area you have, recycled glass filter media gives you a much greater level of filtration for the same volume kg per kg of silica sand. In addition to a high filtration level the higher surface area also means in certain circumstances you can use up to 15% less media than traditional silica sand.

There are other benefits with recycled glass. It has less micro cracks in its surface compared with Silica glass and therefore reduces bio film formation, in general less algaecide treatments are normally required.

Salt Chlorination

How it works

Starting with clean tap water standard salt is introduced to around 3000 parts per million (3000 ppm). This concentration is around 10% of seawater values and around the concentration of a human tear drop, at this level just has a taste.

By the process of electrolysis and in the normal cycle of the pool water being pumped and filtered the pool water with its salt load passes through an electrolytic cell which splits apart the salt (sodium chloride) into sodium and chlorine gas. The chlorine gas dissolves into the pool water to sanitize the pool. Over a few hours the sodium and gas recombine back into salt, gets split again and the whole process begins again without additional salt.

Super efficient as most chlorinators do not require any additional pumping power, it uses the flow of water during the normal filtration times. Salt does not evaporate and the only loss is by the cleaning and backwash routine, splashing and wet bodies exiting the pool. This minimal loss can be compensated for by adding 4kg of salt per cubic meter of fresh water required in any top up.

Some additional plus points are reduced stingy eyes compared to chemical chlorine, salt is a much nicer product on the skin with greater ph balance.


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