ENG421 (3c) – Pipes, Valves, Pumps Pump characteristics Distribution Boosting Pumping Installation

Pump Characteristics (1 of 12) characteristic differences between centrifugal, mixed-flow and air-lift pumps depends on : - speed - output - head conditions for all three pumps, flow increases as head decreases

Pump Characteristics (2 of 12) Specific Speed defined as speed of ideal pump geometrically similar to actual pump enables comparison of pumps by reference to specific speed helps to specify pumps that are more efficient Ns is specific speed (dimensionless) n is pump rotational speed (revolutions per second) Q is flowrate (m³/s) at the point of best efficiency H is total head (m) per stage at the point of best efficiency g is acceleration due to gravity (m/s²)

Pump Characteristics (3 of 12) Specific Speed (cont)

Pump Characteristics (4 of 12) Characteristic Curves for roto-dynamic pump : quantity of fluid pumped varies directly as speed of rotation head varies as square of the speed power consumption varies as cube of the speed design point - pump operates at maximum efficiency

Pump Characteristics (5 of 12) Characteristic Curves (cont)

Pump Characteristics (6 of 12) Power Input required by pump

Pump Characteristics (7 of 12) Selection of Pumps choice of pump depends on : type of use flow velocity head requirements specify complete range of duties not just “normal” operating conditions supplier/manufacturer will be able to advise for full output of large pumping station single pump is rarely used to ensure continuity of supply use standby pump(s) two pumps – each 100% of duty three pumps – each 50% of duty

Pump Characteristics (8 of 12) Selection of Pumps (cont) Horizontal Centrifugal Pump suitable for all water works duties except - large volume against low head - pumping from wells and boreholes advantages : cheap great variety of designs (meet wide range of pumping conditions) for high-lift pumping : fixed speed, multi-staged horizontal centrifugal pump is most economical Submersible Pump suitable for pumping from wells and boreholes including from well to high level tank specifically preferred in wet conditions

Pump Characteristics (9 of 12) Prime Movers pumps are driven either by - direct-coupled electric motors - internal combustion engines petrol, diesel, oil, gas good for remote locations infrequent duty demand

Pump Characteristics (10 of 12) Prime Movers (cont) Electric Motors generally more economical, both capital and operating costs unless - power is not available at the site - pumping only required at infrequent intervals e.g. storm, sewage, and surface water pumping flood control works preferred due to : very good for unattended operation (un-manned) very suitable for automatic control reliability efficiency quietness in operation have diesel back-up for power failure

Pump Characteristics (11 of 12) Automatic Control of Pumping electronic, automated control eliminates need for 24 hour per day manned attendance additional cost for control equipment repaid many times by savings in labour costs usually only for grid-fed electric motors (not diesel driven pumps) programmable logic controllers (PLC) start/stop conditions (level, time, pressure) remote control remote monitoring

Pump Characteristics (12 of 12) Automatic Control of Pumping (cont) protection for various devices in pumping systems

Distribution Boosting (1 of 5) any pumping arrangement that increases the pressure or flow of water though an existing pipeline system Addition of fixed extra flow or pressure - for extra flow install additional pump in parallel to existing pump add flows for a given head consider extra flow increases frictional losses causes drop in delivery head

Distribution Boosting (2 of 5) Addition of fixed extra flow or pressure (cont) - for extra pressure install additional pump in series to existing pump add heads for a given flow consider extra pressure increases internal forces in pipe causes failure of pipe

Distribution Boosting (3 of 5) Addition of fixed extra flow or pressure (cont) effect of boosting flow in a rising main to a reservoir

Distribution Boosting (4 of 5) Maintenance of a given pressure common use of booster pump is to increase pressure of water over distribution system especially at times of high draw-off during low demand (e.g. night time flow) pressure at end of distribution mains may satisfy pressure requirements for high demand times increase pressure by : - laying additional distribution mains (expensive) - booster pump at times of high flow

Distribution Boosting (5 of 5) Maintenance of a given pressure (cont) effect of boosting pressure of water directly into distribution systems

Pumping Installation (1 of 2) Several possible layouts for a pumping station site may be set by technical requirements consider : - amenity of locality - accessibility for construction - accessibility for maintenance - suction and delivery pipework to each pump control valves to be installed - provision of one or more reserve (standby) pumps facilitates maintenance on other pumps - electrical switchgear, instrument paneling, pressure gauges, flow measurement devices - water hammer protection

Pumping Installation (2 of 2)

References Nemerow, N.L. et al, 2009, Environ Eng : Water, Wastewater, Soil and Ground, 6th ed., John Wiley and Sons, New York (TD430 .E58 2009), pages 231 - 240 Twort, A.C. et al, 2000, Water Supply, 5th ed., Arnold, London (TD345T98 2000), pages 559 - 612 Viessman, W. et al, 2009, Water Supply and Pollution Control, 8th ed., Pearson, Upper Saddle River, pages 179 – 189