Page 337 - Water Loss Control

306 Cha pte r Ei g h tee n

Reduced Customer Complaints
Pressure management schemes are designed not only to reduce pressure but also to
provide a constant supply of both water pressure and volume. Some customers experi-
ence periods of the day with low pressures caused by high head losses in the system.
High velocities, some of which may be due to uncontrolled demand downstream of the
customer, cause high head losses. Other customers complain of pressures, which, are
too high and cause either discomfort or damage to equipment in the home. Uncon-
trolled leakage can also cause lack of supply for customers.
Contrary to belief pressure management can increase customer satisfaction.

18.2.2 Potential Concerns
It may seem from the preceding pages that pressure management is the answer to all of
the utility problems! However a poorly implemented program may also cause prob-
lems of its own. When discussing a pressure management scheme for a utility that does
not currently have control or is intending increasing the level of control, the usual con-
cerns are as follows:

• Fire flow concerns
• Loss of revenue
• Reservoirs not filling at night

Fire Flow Concerns
Where fire flows are a concern, sectors can have multiple feeds, controlled by PRVs with
flow-modulated capability. Therefore, if there is a fire, the system has sufficient hydraulic
capacity to maintain pressures and flows for fire fighting, as required for example in the
National Fire Protection Association (NFPA) regulations, in the United States and Canada.
The valves will automatically regulate pressure as determined by the demand requirement
plus the minimum safe operating limit at residual conditions.
Systems, which do not have the benefit of the more efficient flow-modulated valves
often, have a large sleeper valve either in parallel with the operational valve or at a
strategic entrance to the sector. This valve will open when the system pressure drops
due to additional head loss created by the fire flow. In many cases this large valve will
remain closed unless an emergency situation is encountered. The use of a large dormant
valve may in many cases not be cost-effective when calculating against the more mod-
ern efficient demand modulated options, however in some situations the range of
demands dictates that a second parallel valve be used.
The NFPA basically states that systems should have an available residual pressure
of 20 psi while the hydrant is flowing and 40-psi static head. The hydrants are then
coded based on testing as discussed in Chap. 22, as
to their flow capacity at these standard reference
pressures. When setting up pressure
Obviously when setting up potential pressure management zones, fire codes
controlled sectors, these limits along with insurance
must be respected.
regulations for the types of property in the sector,
should be taken into account.
Most countries have some kind of fire code, which should be followed when plan-
ning a pressure management scheme.