Pond Solver Articles | How To Choose The Right Garden Pond Pump
Introduction to Garden Pond pump selection
A pump is the one piece of equipment that so many people have difficulty specifying correctly. It is also an area where all too often the retailer or sales assistant is often not much wiser than the consumer.
After reading this chapter you will know far more than most pond keepers and retailers – there is nothing difficult about pump specifications, it is a matter of understanding what you want to do with the pump. Once you know this then the pump almost selects itself.
Why do I need a pond pump?
Without a pump it is almost impossible for a small garden pond to function as anything other than a breeding ground for mosquitoes.
- A pump is the heart within a pond system.
- It circulates life-giving oxygen to biofilter bacteria, to plants and of course to the fish.
- The pump creates the movement we all seek and the soothing sound that we find so attractive.
A pump works in a very simple way: in most cases the pump is submersed in the pond and water is sucked through a strainer after which it enters the centre of an impeller with straight or curved blades … straight blades are normally used on small pumps only.
The impeller is made to turn rapidly by the electric motor driving the pump. As the water enters the impeller it is flung out from the edges of the impellor under pressure into the connecting pipe, which leads the water to the waterfall or the fountain.
As you can imagine the power developed by the electric motor is constant and this determines the fundamental capability of the pump. Think of the power developed by the electric motor being divided into 2 parts as follows:
- Some power is used to create water flow
- Some power is used to lift the water.
The power of the pump cannot be increased so if more flow is wanted then less lift can be obtained and vice versa. This is the most important principle to understand. Grasp this and choosing a pump becomes dead simple.
Click the link to see the Garden Pond Pumps reviewed on this site
Choose a pump wisely – a gentle warning!
Beware of relatively low cost physically large or heavy pumps. These pumps are generally capable of pumping large volumes to heights of around 6 metres or even more yet seem to be reasonably low in cost (big and strong so must be good is the impression given!!!).
Many sales assistants love to sell these because they know they will cover most pond situations and customers will not bring the pump back because it is underperforming. Beware!!!
The reason for the low cost is that they are designed for non-continuous use and are very inefficient in terms of electricity consumption.
Most pumps in this class are specifically designed to pump out sumps or basements and they do a great job of this. They are readily recognized by virtue of their upright stance with the inlet being right at the bottom of the pump to be able to suck up the water or sludge within a sump or basement.
On the other extreme many dealers supply pumps only suited for indoor use in small water feature or aquarium environments as being suitable for ponds. They are not!
This type of pump is easily distinguished from real pond pumps by the short 1.5 metres or maybe 3 meter cable length and small box. It will also tell you by means of a symbol that it is for indoor use only if you look really hard for it. - The symbol is a house with an arrow pointing inside. This will be seen on the pump label and sometimes the box itself.
Critical pond pump selection criteria
In choosing any pump for use in a garden pond take particular notice of the following criteria. They are discussed in more detail below...
- Determine the required flow rate
- Determine the correct head (or difference in height between pond surface and top of waterfall) the pump must be capable of lifting the required volume of water to in order to create the effect you are looking to achieve for your waterfall or fountain. See table later to help in your selection.
- Determine the guarantee and the extent of it. A pump guarantee is important - a minimum of 2 years guarantee should be offered with any pump meant for use in a pond environment.
- Ensure that the retailer is selling you a pump guaranteed for outdoor applications in compliance with your own country’s regulations and that the pump is also suitable for use in a pond environment.
- Check for low power consumption - low power consumption is a hallmark of any good modern submersible pump. Do not use a swimming pool pump unless you know why you need it.
- Look for established and reliable suppliers who support their pumps with a good guarantee.
- A pond pump must be rated for 24 hour continuous running since the biofilter needs oxygen 24 hours per day to thrive and do its job of purifying the pond water. It often makes sense in view of this requirement to use 2 Pond Pumps in a pond.
- In my opinion it is a far better idea to use two smaller rated pumps in parallel to give higher flow rates than to install a sump type pump simply because it can give you larger volume flow. Sump Pumps are very expensive to run and have a short life span.
- When you look at the packaging a pump is supplied in you must be able to understand what the pump is capable of doing. If you cannot get this information easily be wary of buying the pump no matter what the price is. Good information on the outside of the box should be mandatory.
Correct Flow Rate Specification
Well this is the first time you come across the need to know how much water is in your pond.
As a basic rule of thumb a pump should pump the total volume of the pond around and through the biofilter circuit every 2 hours. In this way the contents of the pond are circulated 12 times a day. At this flow rate there is a good balance between the needs of plants, fish and the biofilter in a pond system.
The flow rate is such that debris can also settle to the bottom of a pond rather than be churned up continuously making the water cloudy. This is another good reason for limiting the height of a waterfall, i.e. to avoid churning in a small pond.
Koi keepers often prefer this flow rate to be doubled so the water is turned over every hour or 24 times per day. The choice is yours. More water means more cost always.
Click my Pond Calculators to obtain help with working out pond requirements and specifications
Correct Head Selection
What is this word head? It normally refers to the pressure that a pump must develop to do the duty required of it.
For our practical purposes at this stage it simply means the height difference between the water surface in the pond and the outlet point of the pipe attached to the pump (normally the top of the waterfall). Pond Pump Head is a fancy word for indicating how much pressure a pump must generate to get the correct amount of water to this height. Another term is lift.
Consider the following...
If the outlet pipe from a pump was lifted 50 cm above the pond surface then a certain amount of water would flow out of the pipe (this could measured by those inclined by timing how long it takes to fill a 10 litre container for example).
If the pipe was then lifted to 1 meter above the surface of the pond then a reduction in flow would be seen (if you do not believe this take your 10 litre container and see how long it now takes to fill it - it will take longer without any doubt).
What we now understand is that the higher the head for the pump then the lower is the amount of water pumped. This is because the pump has to generate more pressure and can only do this by reducing the water flow; in simple terms more flow equals less pressure from same pump.
This is a very important observation, which can be critical when selecting a pump.
For your interest and coming back to the words maximum flow seen on all pump boxes we can now see that the maximum flow is the amount of water the pump can pump when the height difference or head is ZERO above the pond surface. Now you can see how impractical this figure is. I do not know anyone who has a waterfall 0 cm high.
In practice many ponds have a waterfall. By measuring the vertical distance from the pond surface to the inlet to the waterfall we are actually measuring the head we need to be able to pump against. This is an important and practical consideration when choosing a pump.
While we are talking about head and poor information there is another impractical bit of information displayed on most pump boxes. This is maximum head.
This bit of information means at that head or height difference between the water surface and the waterfall the flow from the pump will be ZERO litres per hour - i.e. there is zero flow.
Such a flow would make an impressive waterfall don’t you agree?
To summaries you can almost ignore Maximum Flow and Maximum Head. In practice ask yourself the following the following:
- How much water do I want to pump in litres per hour (or gallons per hour)? This is also governed by need for a waterfall or not as you will see.
- To what height do I want to pump that amount of water - I measure this height difference from the water surface in metres remember and NOT from the bottom of the pond?
What length and diameter of pipe is required for optimum performance? This can be important in selecting the correct pump but in most cases for small ponds is of relatively minor importance. For those inclined to want to know why it is important because power is needed to overcome friction in the pipes through which the water flows. This “friction loss” reduces slightly the power available to lift the water volume required.
Click my Pond Calculators to obtain help with working out pond requirements and specifications
The Pond Pump Guarantee
A pond pump with a 2 years guarantee or more essentially tells the customer that the design is good, the performance good, and that the manufacturer stands behind his products.
A pond is a very harsh environment in which a pump has to run 24 hours a day 365 days a year. When you see a 2-year guarantee on a pump from a reputable company you can buy with total confidence.
Pumps fail mainly because of impellor breakages often through poor handling when cleaning the pump. The solution is to replace the impellor.
Most pumps that do fail permanently and just refuse to wok suffer the problem early in their lives. This is generally a result of electrical failure. Such a failure is rare but does happen. In the event of electrical failure the pump cannot be repaired – the motor is normally totally encased in a special water resistant resin for safety reasons.
A 1-year guarantee on a pump recommended for pond use (not small water feature pump for indoor use) indicates that there is probably a design point that is weak or the pump is designed for non-continuous use and therefore it is designed to last only for a certain running period measured in hours.
If a pump is designed to run for 8000 hours this is only about 1 year on a continuous running basis. However if the pump runs only 2 hours per day it will last 12 years. I am not therefore saying the pump is a bad pump only that it is a bad choice for a pond.
Click the link to see the Garden Pond Pumps reviewed on this site
Pond Pumps For Indoor and Outdoor Applications
Pond pumps are designed to operate in harsh outdoor environments. In practice this means the water in which they reside becomes polluted with all sorts of foreign bodies including soil, plant material, small stones, fish waste and so on.
These foreign objects find their way into the pump moving parts and can do damage if the pump is not designed to withstand these rigors. Also it is normal to encounter wet, hot, freezing and other weather conditions outside not normally associated with an indoor or aquarium feature.
Ponds also tend to be big enough for people to even fall into which brings into play the safety factors associated with water and electricity.
For all these reasons the design and therefore cost of a true pond pump is very different from that of an indoor pump.
Government bodies in most countries of the world recognize in particular the safety problems associated with outdoor pumps.
Pond Pumps and Electricity Consumption
The majority of retailers who sell pumps will never mention the advantages of low power consumption pumps yet this is a very important part of a purchasing decision. I would go as far as to say that the concerns over running costs should outweigh those concerning the cost price.
In countries like the UK, Germany and the USA running cost is the prime decider on pump model chosen such is the expense of ongoing electricity consumption.
Always think seriously of Installing 2 Smaller Pumps instead of a single large one. Two smaller pumps can be far more economical than one larger pump. Do this today and you will save far more than this book cost you.
One can be used to power the biofilter and the other one to power a waterfall. At night you can switch off the pump supplying the waterfall. You must never switch off the pump supplying the biofilter.
A further advantage of this 2-pump system is that the biofilter does not have to be higher than the waterfall and this can make it much easier to hide.
Click my Pond Calculators to obtain help with working out pond requirements and specifications
Pipe Diameter and Length Considerations
If you build a large pond or need to pump high volumes of water (say more than 2,000 litres per hour then you certainly need to understand a bit more about pipe size selection.
When water flows through a pipe it loses some of its energy because of friction along the pipe inner surfaces. The faster the water is traveling in the pipe the more energy is lost due to higher friction losses. You can imagine in a thinner diameter pipe that the water would have to flow much faster for a constant water flow rate in terms of litres or gallons per hour.
The calculation of friction loss is very complex and is a function of flow rate, pipe diameter, density, other variables and empirically determined factors.
The clear message is do NOT use small pipe diameters if you want to get the most out of your pump.
Always use the widest diameter pipe and shortest length to get the best out of your pump.
Any doubts then go for a bigger pump.
Manufacturer and Distributor Reliability
Look for manufacturer's pumps for which the appointed distributor has a good track record of offering reliable and consistent service, innovation and fairness.
The distributor is responsible for guarantees and marketing the pumps and protecting the reputation of the manufacturer.
Do not deal with companies who have no infrastructure to support the products. You need service in 3, 4 or 5 years time remember and you need replacement parts occasionally.
Click my Pond Calculators to obtain help with working out pond requirements and specifications
Information on the Pond Pump Packaging
If there is a lack of information on the box then you should not buy the pump. It is as simple as that. How can anyone be expected to buy a pump when he cannot tell quickly the flow rates at different heads, the guarantee and the power consumption as well as the cable length, and whether it is for outside or inside use?
Click the link to see the Garden Pond Pumps reviewed on this site
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