Distribution System Pressure Management (2010)

Published: March 25, 2010

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Pressure regulation comes in many forms: surge control, level control, pressure relief, pressure
reduction or pressure sustaining. Pressure reduction, or pressure management (PM) as it is
commonly referred to, is a method that is commonly applied to water distribution networks by
leakage reduction practitioners to reduce water losses. A suite of tools exists to actively reduce water loss. Of these tools, PM has been referred to as “the preventative method par
excellence”1. It is the only tool that can be deployed to existing infrastructure which reduces all types of leakage (background, reported and unreported). In some countries, notably Japan and
the UK, it has been recognized for over 20 years that effective management of pressures is the
essential foundation of effective leakage management. However, recognition of this fact is not
universal. PM reduces leakage levels in two ways:
a) Reducing the flow rate through existing leaks
b) Reducing the frequency of new breaks

The frequency of new breaks is reduced because PM reduces average and maximum
pressures, reduces diurnal pressure variations and can filter out pressure transients.
Pressure managed areas (PMA) are discreet zones of the network that have pressure reducing
valves (PRV) at the inlets. The PRVs can have a basic fixed outlet pressure control or can be
upgraded to have controls applied that typically modulate output pressure based on time,
pressure, flow or remote control. A high efficiency PRV control is based on flow modulation so
that during the night, when demand typically decreases and pressure increases, the pressure
can be reduced further. Maximum leakage levels typically occur at night because of higher
system pressures.

Pressures cannot be reduced arbitrarily. Minimum levels of service to customers as well as fire
fighting capacity from fire hydrants must be maintained.
PMAs are distinct from District Metered Areas (DMA) in that a DMA can function on a temporary
basis. A DMA is a well-established leakage management method for flow measuring a zone
covering around 2,000 customer connections. A DMA can be permanent or can be periodically
established to assess inflow and therefore get a snapshot of the leakage level within a zone.
When an area of higher burst frequency and higher pressure is established as a PMA, then it
should remain under the lower pressure regime as the consequences of breaching the zone and
introducing higher pressures, albeit temporarily, will likely lead to a spate of bursts and certainly higher leakage levels. Once the PMA is established, it should remain so3. For critical PRVs,redundancy may be required in the form of a back-up PRV, on by-pass, so that if the primary
PRV is taken off line, say for servicing or repair, the reduced pressure regime into the zone can still be maintained.

In addition to leak reduction, pressure management will also reduce some types of customer
consumption4 and may therefore negatively impact revenue5. Although this effect can be a
disincentive to pressure management, it can also be positive in terms of managing peak

There are several factors that can contribute to breaks in the distribution network such as low
temperatures, ground movement, traffic loading and corrosion, but further investigation often
seems to show that it is the occurrence of a higher pressure, added to the other adverse factors, that triggers many of the individual failures. This has led higher pressures to be characterized by practitioners as “the straw that breaks the camel’s back”.

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