People often install a piping system in a particular size because that’s what they have always done, or because that is what was there. But getting pipe sizing wrong can lead to poor system performance or failure, higher than needed installation costs, or frequent maintenance.
Examples:
These are all common frustrations which could be greatly reduced if more attention was given to getting the pipe sizing correct.
In this blog, we want to share why it is important to get your pipe sizing correct and some tips on how to achieve this.
Asset owners want to know their asset is built right. Engineers take pride in their design work and delivering a working solution to the asset owner. An installer takes pride in their installation and doesn’t want to be called back to a project due to poor system performance.
If you are installing a larger pipe than you need, your material costs will be higher than necessary. Labour costs will likely be higher too. The cost of accessory equipment, such as valving and bracketing, will also be higher.
If your pipe sizing is too small it could result in an increase in energy costs, e.g. power consumption from a pump, which is increasing your operating costs in electricity. You might have to invest in a much larger pump than you need, which will increase capital investment.
You might achieve an initial capital saving for going down a pipe size but this could then mean you have to run larger pumps or run pumps for longer, which increases the operating costs which, over time, can outweigh the capital savings achieved at the time of installation.
The performance of the piping system is important also. For example, if you undersize a pipe you can run into an issue such as water hammer.
Examples:
A meatworks had a large pipe and reduced it down to a pipe 1/3 of the size or less for no known reason. When they went to do their plant cleaning they could only run one hose at a time which made the cleaning process very inefficient. By simply having the correct pipe sizing, they could have had multiple people washing down at once and reduced their washing downtime while increasing production time.
A dairy farm whose cows weren’t getting enough water had cows fighting at the trough for hours after milking. The farmer put a new pump in thinking this would solve his problem and give the cows more water but it didn’t make any difference. In consultation with the installer, the farm water system was changed from 20mm pipe up to 40mm pipe and there was never any more congregating of cows around the trough, the trough was always full with the same pump. Not only did this stop the fighting at the trough, but it improved milk production and reduced ongoing maintenance resulting from broken trough valves and other damage. On top of this, the pump was only running for two hours instead of six to deliver the same volume of water, reducing operational costs.
Some materials, such as copper, are susceptible to erosion when exposed to high velocity and turbulence. Therefore, it is important to get the sizing right to ensure the longevity of the system. Alternatively, if you need to maintain a higher velocity you may need to consider using an alternative material such as stainless steel which is less susceptible to erosion through high velocity and turbulence.
Another consideration, particularly relevant in a commercial plumbing application, is if your pipework is sized too small and the velocity is high, this can create acoustic noise which needs to be minimised in this application.
Firstly, it is important to understand the pressure losses through the system. Increasing a pipe by one size, e.g. from 25mm to 32mm, will reduce your system losses by about 3 times. For example, if you had 30PSI of losses through a 25mm pipeline, through a 32mm pipeline at the same flow rate you would reduce the losses by about a third to approximately 10PSI. It doesn’t take much of a change in pipe size to make a huge difference in system performance and efficiency.
This depends on the application. For example, if it is a wastewater pipeline you have to maintain a certain velocity through the pipework to prevent settling out and buildup in the pipes. In drainage applications, it is recommended to maintain a velocity of 1m/s. In dairy effluent, people think big pipes are best, but there is only a certain amount the pump can put through, and the irrigator can put out. This results in blockages along the pipes.
In general, however, it comes back to a question of economics, is what you are achieving from increasing the pipe size justifying the increase in costs from going with larger pipework?
If you don’t know the flow rate then this would need to be calculated. You would need to know what volume of water is required and at what point in what timeframe.
For example, in a factory washing system, you would need to consider the number of washdown hoses required and the output of each hose at peak demand, as well as their distance from the pump. It is important to design the system for current peak demand and consider possible future expansion of the system.
In an agricultural setting, you again need to know the peak demand. Peak demand on a dairy farm will be different to peak demand on a dry stock farm and, as a rule of thumb, a dairy farm should allow 70 litres per day per cow. They will also need a third of their daily intake in the first two hours after milking, which is often done twice a day.
In comparison, dry stock consumption will peak through the heat of the day but is spread out more. As the temperature increases, the cows will drink more. Therefore, you need to design the system so that it can not only deliver the peak flow rate across the whole day but at the peak demand time.
No, the pump should be sized to suit the application, the system should not be designed to suit the pump.
In a domestic plumbing application, councils will often have the necessary information publicly available for what they allow per day for water consumption as well as wastewater. This type of system will get peak demands that need to be factored in. For example, an apartment building will see peak demand when everyone wakes up for work and has a shower, gets a glass of water, and brushes their teeth. During the day or in the middle of the night this demand will likely drop right down. You have to design the system for the peaks to ensure there is sufficient water available at these times.
This can be done through historic data and needs to be based on fact rather than gut feel. You can work on averages though. Going back to the farm example, you can calculate what the stock usage would be but then you also need to consider other water usages, such as washdown. You also need to consider seasonality. If a cow drinks 70 litres per day, it won’t drink that in the middle of winter, but you need to build in that capacity for when it does need to. In drainage pipework, for example, seasonality could be rainstorms and 1 in a 100-year flood.
Yes. It doesn’t matter what fluid it is the same considerations apply. Other considerations that are also worth considering are:
In considering this you will need to consider the layout of the property to determine if this is a feasible option. In systems where you have a lot of delivery points (for example, a farm water system where you have lateral lines to various troughs or in a factory where you can be running multiple hoses) it does mean you can often use a smaller pipe and get a more balanced delivery at the outlet.
Not really. This impacts the pressure you need to put through the system so more affects the pressure rating of the pipe. As a result, it more comes down to the pump or the fluid delivery system. The pipe will need to be pressure rated to cope with the demands in the system but height doesn’t directly affect the size of the pipe.
This may mean you can vary the pipe pressure rating in a system. For example, in an agricultural setting, you may have a higher pressure rated pipe at the bottom of a hill or at the pump, but if you are pumping up a hill, due to the pressure loss sustained in the system, you may be able to have a lower pressure rated pipe at the top of the hill. This can be one way of achieving installation savings.
Many people think this, but it's not the case. Pressure is created from the source, e.g. your pump, this is what creates the pressure. Putting a smaller pipe in does not in itself create greater pressure.
The performance at the other end is according to the pipe that has been installed and the nozzle or orifice at the end. It’s better to have a bigger pipe to get the volume to your delivery point/s and then install the correct nozzle to achieve the desired pressure or end result than to try and use the pipe diameter to deliver pressure.
It is common to hear of this in domestic plumbing. A small pipe is installed and confusion ensues as to why the shower at the other end of the house doesn’t have the desired pressure. You need to deliver the required litres of water to where you want it then use the shower nozzle, or hose nozzle, to achieve the desired spray effect.
Another thing to consider when sizing a pipe is the fluid which is going through the pipe. If you start putting liquids with higher viscosity or with a high SG, such as molasses, honey, or sludge you will get higher frictional losses.
The type of pipe will adjust the amount of frictional loss. This is known as the roughness factor, or the coefficient of friction. You will see a lower frictional loss in some types of pipe than in others. For example, through a plastic pipe or stainless steel pipe, you can reduce frictional loss over a scheduled galvanized steel pipe because they have a smoother bore.
Example:
A client had a 100mm galvanized steel pipeline running at 3.5 Bar and they wanted to know if they could achieve the same flow rate through a 76.1mm Europress stainless steel tube if the system was operating at the same pressure.
The 100mm galvanised pipe has an approximately 50% larger bore size, so like for like it will still have a lower pressure loss, e.g. if you double a pipe diameter then you have four times the cross-sectional area. The impact a smaller size has will depend on the typical flow rate through the system, as shown in the following figures:
Going to 88.9mm Europress would be a 55% reduction in pressure drop compared to 76.1mm.
Comparing 100mm nominal bore galvanised vs 108mm Europress (actual bore size is almost identical) yet Europress has approximately 23% less pressure loss. This shows how much more efficiency can be gained when comparing like-for-like diameters, just by installing stainless steel over galvanised steel pipe, and this increases exponentially as the steel pipe begins corroding over time.
Need expert advice on your fluid delivery system? Contact the team at Waterworks today. If all you need is industry-leading equipment then download our catalogue to view our product range.