Advantages of pressure management in the supply network
Controlling and regulating the pressure in the water supply network can provide savings on resources as well as reduce the level of non-revenue water.
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Pressure management is considered the single most beneficial and cost-effective leakage management activity. Most pipe bursts occur not only because of high pressure, but rather due to ongoing pressure fluctuations forcing the pipes to continuously expand and contract, resulting in stress fractures. However, there is a physical relationship between leakage flow rate and pressure. The higher or lower the pressure, the higher or lower the leakage rate. Thus, the pressure should be kept at a minimum without affecting the consumers’ needs.
Water utilities measure their quality, among other things, by whether there is sufficient pressure at the consumer. Therefore, utilities are often using a constant inlet pressure to the individual zones/districts in order to ensure that consumers have sufficient pressure at all times of the day.
Pressure level at the consumers
The pressure at the consumers depends on the friction in the supply line. To compensate for the friction, the inlet pressure is typically higher than the required minimum pressure.
However, the friction depends on the flow rate and therefore, it varies according to the consumption. A constant inlet pressure means that the pressure at the consumers varies during the day. Actually, it means that the pressure at the consumers will be highest at those times where they need the water the least – and lowest when they actually use a lot of water – e.g. in the morning and in the evening.
22 hours with too high pressure?
To ensure that the consumer never experiences too low pressure, the inlet pressure is usually set based on peaks in consumption.
A typical consumption pattern for the water supply shows that consumption is high for only a short time during the day. Of course, there may be exceptions – as if, for example, there is water-consuming industry in the area – but usually, there will be no more than two hours a day with high consumption.
A constant inlet pressure actually results in a pressure that is higher than necessary for 22 hours a day.
A high pressure has a huge impact on the distribution network. This applies to the overall service life of the components and to the number of fractures and pipe bursts. Learn more about the advantages of using control valves.
A lower pressure reduces pipe bursts and leakage – and thus also non-revenue water
There is a direct correlation between pressure and the number of pipe bursts. An international study has shown that a 37% reduction of the average pressure leads to a 51% reduction of the number of pipe bursts (source).
In addition, high pressure also leads to increased water loss through leakages. This is because leakage from holes in the pipeline highly depends on pressure. If, for example, there is a 5 mm hole at a pressure of 5 bar, it will result in a water loss of 11,520 m3 per year. If, on the other hand, the pressure is lowered to 4 bar, the annual water loss will be reduced by 11%, corresponding to 1,267 m3. The reduced water loss achieved by reducing the pressure from 5 to 4 bar also represents energy. Converted to kWh, this corresponds to approx. 461 kWh/year per 5 mm hole in the pipeline. See calculations in the text box at the bottom of the page.
See control valves application examples.
Effective pressure management based on time or flow
It makes sense to reduce the pressure in the distribution network, and this can easily be done without compromising on quality. By lowering inlet pressure during periods with low consumption, an acceptable minimum pressure is maintained at the consumers, while interruptions and inconvenience from pipe bursts and fractures are reduced. Also, the consumers will, in general, experience a more uniform pressure throughout the day.
Installing a control valve at the inlet to a district or zone can help achieve a very efficient control of the pressure based on time or flow. See our wide range of control valves.
Time-based pressure management
Time-based pressure management allows the pressure in the district/zone to be adjusted based on set points. This way, the valve can lower the pressure during periods with expected low consumption and raise it again when consumption increases. Thus, the average pressure can be significantly reduced.
Flow-based pressure management
From the customer’s perspective, flow-based pressure management is a better way of regulating pressure. The regulation uses the signal from a flow meter to adjust the outlet pressure of the control valve according to the current consumption. This will reduce the average pressure, and the pressure at the consumers will be more stable. Such a regulation takes the changes in consumption that falls outside the normal range into account, such as holiday periods, water consumption via fire hydrants and other abnormal consumption patterns.
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Pressure management in the supply network
Energy savings by lowering the pipeline pressure from 5 to 4 bar pressure
∆P (differential pressure in Pa) x Q (flow in m3/sec) = hydraulic effect in Watt
5 bar pressure:
500,000 Pa x 0.0003653 m3/sec = 182.65 Watt
Annual energy use: 182.65 Watt x 8760 hours = 1,600,014 Wh / 1000 = 1,600 kWh/year
4 bar pressure:
400,000 Pa x 0.0003251 m3/sec = 130.04 Watt
Annual energy use: 130.04 Watt x 8,760 hours = 1,139,150 Wh / 1000 = 1,139 kWh/year
Savings:
Annual energy savings.: 1,600-1,139 = 461 kWh/year
