What happens when water is pushed through up water pipe

The correct pipe diameter is decided based on the amount  the volume of water being used or the flow through the pipe. When water is pushed along a pipe friction is created. The amount of friction depends on the speed the water the water needs to move along the pipe in order to supply the volume of water at the outlet.  This loss in flow is called friction loss.  There are other factors that will contribute to flow and pressure loss, as an example elbows etc however for this example we will assume a straight run with no connectors

How large is the variation

In the example below we will assume that we are going t be using 2500 litres per hour at the outlet and that the total length of the pipe is 100 metres.  We will assume that our pump is delivering 4500 litres per hour in to the pipe at 5 bar pressure

In figure 1 we are supplying 4500 litres per hour at 5 bar pressure and we have opened the tap to allow 2500 litres per hour to exit.  In order for the 2500 litres per hour to exit the pipe the water will move with a velocity of 1.9 metres per second.  Velocities at over 1.5 metres per second should always be avoided as this can cause water hammer.  Over the 100 metre length we will see a loss of 2.16 bar pressure due to the internal friction of the pipe.  So the pressure at the exit would = 5 – 2.16 = 2.84 bar.

 

In Figure 2 we are supplying exactly the same amount of water at the same pressure however the external pipe diameter is now 32 mm and the pipe wall thickness is exactly the same.  In order to supply the 2500 litres per hour at the outlet the water will need to travel at 1.1 metres per second.  The friction loss in the 32 mm pipe is 0.54 bar over the 100 metre length so our outlet pressure will be 5 – 0.54 = 4.46 bar.  From this we can see that with a slight change in pipe diameter we have a huge energy saving.

If we were to increase the diameter of the pipe to 50 mm we would see a 0.19 bar pressure drop based on the above figures making this the most efficient option however cost wise it would not be the prefered choice, the 32 mm dimeter pipe would be the prefered option.

What size water pipe should I use

You now having an understanding of what happens when you run water through a water pipe.  From this information you can now decide on the diameter required however there are numerous other variable that will change your calculations, for example elbows, turns, type of pipe and wall thickness of the pipe.  Our advice is to email us at [email protected] or call us on 01189736905 so that we can calculate your requirements preventing expensive and time consuming mistakes

 

The correct way to layout a pop up lawn watering system is to arrange the pop ups so that they throw the water in to the middle of the lawn rather than running them down the centre of the lawn throwing water out at 360 degrees.  In other words pop ups should be if possible located on the edge of the lawn as per the diagram below.

 

Pop ups installed in this way water the lawn more efficiently as the area that we want to water receives the water and little or no water is wasted with over spray.  This is even more important with paths and patios as when you spray water repeatedly on to a smooth stone surface  a clear bacteria can develop that forms almost like a think jelly like film which is very slippery.  Over longer periods of time the stone could develop algae or moss and this again would look messy.

 

In the simple examples above we can see that the picture on the left is throwing water in to the centre of the lawn while the picture on the right is an example of central 360 degree rotors that will water the same area.  On the right hand picture we have assumed the patio is at the bottom end and used a 180 degree nozzle as I am sure that at the very least patio furniture etc should stay dry

When watering near a drive  we again want to throw the water away from the drive as water sprayed on to a tarmac drive will encourage moss or if cars are parked on the drive we would soon see streaks for on the cars unless we were using recycled rainwater.

How Close together should we put a pop up

Some companies suggest the 3 or point rules however this put a huge amount of water on per square metre and ultimately adds more zones.  What we think is the best alternative is to use a pop up that applies water evenly to start with like the MP Rotator in a pro spray body and space the bodies at intervals equivalent of the radius of the spray as per the example below.  The pop up in the example has a radius of 5 metres ( the central pop up has a radius of 5 metres and a diameter of 10 metres.  So the pop up bodies are spaced 5 metres apart starting and finishing in the corners at 90 degrees

 

Pumps and Tanks For Large Lawns

A large lawn will need to be watered using a pump with a tank.  The reason for this is so that we can have a reliable higher pressure and a higher reliable flow.  The reason for the higher flow and pressure is so that we can run more pop ups from one zone and cover the area that needs watering efficiently.

There are a lot of thing to consider prior to buying a tank and a pump and this will be covered in more detail later however here is a basic example to give you an idea.

What size tank do I need

Tanks come in many shapes and sizes and prior to buying a tank we would need to know how much water we are using and how quickly we can fill the tank while the water is being used. The example below will give you an idea of the maths used however even this can vary as many timers can have delays programmed in which will delay the start between zones in order to allow the tank to refill.  In the example below we will assume we want to keep the tank as small as is possible

In this example we will have 4 zones watering the lawn.  We will assume the tank is filled by the mans water supply and that it is filling at the rate of 500 litres per hour.  We will assume that each zone will run for 30 minutes

Zone 1 uses 3500 litres per hour

Zone 2 uses 2500 litres per hour

Zone 3 uses 3500 litre per hour

Zone 4 uses 2500 litre per hour

Assumed information

1  The tank is filling at 500 litres per hour

2  Each zone will run for 30 minutes

If zone 1 comes on at 5 am and runs for 30 minutes it will require 1750 litres of water.  In that 30 minute period we know that the tank will receive 250 litres from the main.   In order for zone 1 to run completely without running out of water we would need a tank with a minimum volume of 1500 litres.

If zone 2 were to start up straight after zone 1 and our tank was only 1500 litres then it would run out of water straight away.  At this point we could decide to purchase a larger tank or to programme a delay prior to starting zone 2.  To fill the tank the delay would have to be 3 hours in order to completely fill the tank which would make it very awkward  to water all zones at the ideal time of the day which is very early morning.  Because of this we may want to increase the size of the tank in order for us to water zones 1 and 2  this morning one after the other and then  zones 3 and 4 on the follow morning.

If we assume that we will water zones 1 and 2 today and then zones 3 and 4 tomorrow then the calculation for tank sizes is below

 

Zone 1running for 30 minutes will use 1750 litres and zone 2 will run for 30 minutes and use 1250 litres.  So the total amount of water used in the 1 hour ( 30 mins per zone )  is 3000 litres.  In the 1 hour period the tank fill would have supplied 500 litres so would need a tank with a minimum tank size of 2500 litres

The example above is not a true example and only supplied as a guide as there are many other point to consider prior to buying a tank for watering the lawn.  Please do call or email our experts who will be happy to help or as an alternative please do use our free planning service

What Size Pump Will I need

If we look at the example above we can see that both zones 1 and 3 are using 3500 litres per hour.  As these have the highest volumes we will focus on these as the 2 smaller zones can if required have pressure regulators fitted.  So we know we need 3500 litres per hour and we know from the previous article that we need a minimum pressure at the spray head of 1.85 bar however the ideal pressure is 2.5 bar.  Something that we will not cover in detail here is friction so for this example we will assume a friction loss of .5 bar so we will need a pressure at the pump of 3 bar which will give us a pressure at the spray head of 2.5 bar.

All pumps are supplied with a pump performance curve.  This curve will let you know what the outlet pressure from the pump is at a given flow.

In the example above we can see 4 curves which represent various models of this particular pump supplied by the Italian pump manufacturer Dabs.  The horizontal line along the bottom shows the flow and the vertical line at the side shows pressure.  If we put a mark at the 3500 litre per hour mark and draw a straight line up we can see that the smallest model would be totally unsuitable for our application.  However if we follow the red line across we can see that two models fit our requirements and will deliver 3.5 bar at the pump or if we look at the purple line we can see that the larger pump in this family will deliver 4.5 bar when running with a flow of 3500 litres per hour

In this article we have not covered friction related to pipe sizes, fittings, filters, valves etc.  Soe of these will be to complex on very large systems so please do take advantage of our free planning service

Fingers crossed you have read the article that explains how pressure and flow effect the operation of a pop up and how pressure reduces as we use water.  If this is the case then read on if not then go back and read the first article.

We need to know how much water each pop up is using per hour and the amount of water pressure we have from our water source.  In the example below will assume we are fitting a pop up system to a small garden and we are going to run it from the mains water supply.  For large gardens we would probably use a tank and a pump.  This will be covered in a later article when we will explain to you how to decide what size tank you would need and the size of pump.  In the example below we will use a Hunter Pro Spray body combined with an Mp rotator nozzle as these are very cost effective, apply water very evenly and apply water slowly over a longer period of time making them ideal for low flow and low pressure applications which mains water supplies generally are.  On top of this the MP Rotator now accounts for about 85% of our pop up sales because of their leading spray pattern that applies water at 11mm per hour very evenly to the lawn .

Let us assume our water pressure is 4 bar and our flow from the tap is 1500 litres per hour.

lets now put this in to a simple graph

From the example above we can see that in order to maintain 2.5bar at the tap the maximum amount of water we can use per zone is about 550 litres per hour.  There are other pressure loses to consider however this goes beyond the scope of this article.  Please do take advantage of our free planning service if a more detailed plan is required.

Now we know what water we can use we can now see how much our MP Rotators are going to use per hour.  In this example we are going to assume we have a 10 metre by 8 metre lawn

We are using Mp 2000 nozzles set at 90 degrees in the four corners and in the middle we will use one MP1000 at 360 degrees.  From our mp rotator chart we can see that the mp 2000 rotator nozzles are using 74 litres per hour and our Mp1000 at 360 degrees is using 161 litres per hour.  This gives us a total of 457 litres per hour and if we pop this on to our chart we will see that our water pressure at the tap will be close to 3 bar.  From this we can assume depending on the pipe layout etc that we will probably be maintaining 2.5 bar at the MP Rotators spray head so it is well within the scope of pop up operation.  To view the mp rotator water usage guide please click here