an innovate and cost beneficial solution to resolving low
pressure problems for customers at high elevations
by David Flaherty BEng
pumpset - Courtesy of JN Bentley
(Director General 2) is a status where, according to Ofwat, a
customer receives inadequate water pressure generally under 1bar
at their point of connection to the water main. Water companies
are subject to annual regulatory fines for properties on the DG2
register above a threshold. Severn Trent Water arranges its
distribution to cater for as many customers as possible,
providing at least 2bar pressure at the highest point in the
DMA, stripping out the outliers. This results in a pressure of
1.5bar at the point of connection and works for 99% of
customers, but some elevations are too high to set the network
against without causing big leakage problems; particularly in
older (over 100 years) parts of the network. There is a fine
balance between low pressure and leakage when it comes to
distribution; if the pressure is too high leakage increases, if
the pressure is too low then customers at high elevations
suffer. In the absence of operational solutions on the water
network such as DMA rezoning, Seven Trent defaults to capital
schemes (installing pumps and/or pipes). Unfortunately some
properties remain on the register for long periods due to high
cost to resolve.
Though the DG2 small
pumps project covers the whole of the Severn Trent Water region,
this case study focuses on a specific installation currently
ongoing in Stourbridge. The project in its entirety involves
installing 23 (No.) new booster pumps to increase water pressure
to 31 (No.) properties.
A conventional booster
pump includes hard wired telemetry and an outstation to send
signals to the control center via a phone line. Alarms are
visible at a remote location where controllers would monitor and
despatch resources accordingly. It also includes a control panel
for the pumpset.
It was determined in AMP4
that a conventional booster pump costing £90,000 to address
single property pressure was not cost beneficial to the
business. This left Severn Trent with a long-standing problem
for many years. A working group was created and revisited the
delivery strategy to pumped solutions. In late 2015 a brief was
issued to two pump suppliers to design a pumpset that fits
Severn Trentís needs at the lowest cost possible.
The pump companies were
given access to pressure data, flow ranges and site elevations.
Grundfos Pumps won the contract and their standard product
included an assembly inside a GRP kiosk, ready to be piped up to
the network and fixed to a concrete plinth. The kiosk is
supplied by Morgan Marine.
The Grundfos pumpset
Grundfosí pump design was
innovative in that it did not have a control panel telling the
pump what to do; it simply worked off pressure transducers and a
pressure vessel. The pump was designed to combat cavitation and
low flows. At 65db inside the kiosk, noise was not a factor. In
addition to a different type of pump control, Severn Trent also
managed to remove the outstation element on pumps supplying up
to a maximum of 8 properties.
The agreed alternative
was the installation of a pressure logger on a tap-in point on
the discharge pipework inside the kiosk. Pressure loggers have
batteries and send pressure data to the control center via GPS.
These two main changes have resulted in massive savings and made
the project feasible from a cost perspective. The standard
product shown below is costed at £6,800.
Pumpset during construction (Stourbridge) - Courtesy of
Delivery phase and
Once the pump design was
finalised a contractor was sought to take 31 properties off the
register. Design and build contractor Mott Macdonald Bentley
(MMB) won a mini tender competition. Their target price was a
competitive £430k, which was at least 30% less than the AMP5
equivalent. Scottish Power and Western Power Distribution were
the two district network operators. Fisher German was selected
as the land and planning agent to deal with noticing, private
The installation of the
pumpset is straightforward and involves little excavation at the
site. It comes as an electrically safe asset with NICEIC
certification. The pumpsets are fixed onto a 150mm deep plinth,
plumbed into the pipework, powered up, commissioned,
chlorinated, and put into supply.
The pumpset generally
goes onto a service main or on the end of the DMA as this
ensures no disruption to other customers. Severn Trentís
methodology to satisfy the regulator is to provide evidence of
good pressure readings for at least for 10 consecutive days
without issues. Once it is proved that (at least) the minimum
pressure is being supplied, the property is removed off the DG2
First site: Dewsbury
Close in Stourbridge
One particular customer
lives only 2m higher than his neighbour who receives adequate
water pressure. Severn Trent discussed the matter and it was
agreed to site a pumpset adjacent to a wall to the front of his
property. The pump was subsequently installed on his service
main meaning that the installation had no impact on others in
the DMA. A temporary pressure logger was installed in his garden
tap to gather the data.
It took a couple of
efforts to deliver the right pressure because there were massive
headlosses on the service main, but eventually the feedback from
the customer was categorical; he was delighted to receive good
water pressure for the first time in over 24 years.
The effect on the
Operations team in Severn Trent will be negligible. Whilst new
assets are being added to the database, the energy costs are
small and new maintenance is light. The pump is designed to be
replaced if it fails (pump unit price is £500). This is a major
deviation from the standard for non-infrastructure assets.
Without a control panel
the operations team simply needs to isolate power supply in the
metering cabinet to swap out the pump. Most non-infrastructure
assets are complex and require authorisations to work on, but
these are simplistic. It is hoped that power provision is the
next area where Severn Trent will strive for improvements.
Renewable energy might be
possible as the power demand on a 0.55kW pumpset is small (less
than a TV). The kiosk includes a light on the inner wall. It
includes a thermostatically controlled bar heater to combat
temperature to about -20 degrees.
Courtesy of JN Bentley
on plinth (Stourbridge)
Courtesy of JN Bentley
Evidence to date shows that the pumpsets are working as intended
and it will become business as usual for resolving deferred
properties. The anticipated completion date of the programme is
the end of September 2017.
and publishers would like to thank David Flaherty, Programme
Engineer with Severn Trent Water, for providing the above
article for publication.