WIXLIB

VWEA16 Rogers Hydraulic Considerations in Pumping System DesignHydraulic Considerations inPumping System DesignVWEA Wastewater Operations Education ConferenceRoanoke VirginiaJuly 14, 2016

Agenda Basics of Hydraulics and Pump Operation Pumping System Design Process Types of Pumps System Curve Development Pump Station Layout Pump Selection Considerations Hydraulic Concerns Case StudiesVWEA16 Rogers Hydraulic Considerations in Pumping System Design Summary Questions

3VWEA16 Rogers Hydraulic Considerations in Pumping System DesignAbbreviations and Acronyms BEP – best efficiency pointBHP – brake horsepowerfps or ft/sec – feet per second (velocity)FM – force maingpm – gallons per minute (flow)H – Head (feet)HP – horsepowern – rotational speedNPSHA – net positive suction head availableNPSHR – net positive suction head requiredpsi – pounds per square inch (pressure)Q – Flow Rate (gpm, mgd, cfs )rpm – revolutions per minuteTDH – total dynamic head

Basics of Pump Operation A pump lifts fluid from one elevation to another Work is needed to lift fluid Work is independent of type Human PowerAnimal PowerWind PowerSteam PowerElectrical PowerVWEA16 Rogers Hydraulic Considerations in Pumping System Design Pump can lift continuously or in increments Take-away: Higher lift requires more work Higher flow requires more work Faster work requires more power

VWEA16 Rogers Hydraulic Considerations in Pumping System Design Pumps deliver fluid against pressure Pressure Force / Area (psi) Head (feet) is commonly used to express pump operatingpressure A 2.31 foot high column of water exerts a pressure equal to 1 psi i.e. Car tires 35 psi 81 feet of head

Closed Conduit Flow (Q) Volume of fluid passing per time (gpm, mgd, cfs ) Q (cfs) Area (ft2) x Velocity (fps) For a given flow, the smaller the conduit the largerthe velocity.VWEA16 Rogers Hydraulic Considerations in Pumping System Design Higher velocity translates into increased frictionalheadloss

TDH is the total amount of head a pump mustoperate against to deliver wastewater to a desiredlocation TDH Static Head Head Loss (HL)VWEA16 Rogers Hydraulic Considerations in Pumping System Design Static Head – exists when pump is on or off Head Loss – exists only when fluid is pumped

For free surfaces: Static Head Discharge Tank WSEL – Suction Tank WSEL Static Discharge Head Discharge Tank WSEL – Pump CLVWEA16 Rogers Hydraulic Considerations in Pumping System Design Static Suction Head Suction Tank WSEL – Pump CLSuction Lift – Negative Suction HeadFlooded Suction – Positive Suction Head

Energy dissipated due to friction andturbulence during pump operation Major Losses (Friction Losses) Due to friction between pumped water and inner surfaceof piping Hf 3.02 L D-1.167 (V/Ch)1.85 (Hazen-Williams Formula)where:VWEA16 Rogers Hydraulic Considerations in Pumping System Design L is length of pipe (feet)D is diameter of pipe (square feet)V is mean velocity (fps)Ch is Hazen-Williams friction coefficient (new up to 140 and old aslow as 80) Minor Losses Due to turbulence at bends, fittings, valves, etc. Hf K (V2/2G) (Headloss factor times velocity head)

NPSHA Atmos. Head Static Suction Head – Suction HL Standard atmospheric pressure 14.7 psi (34 ft. head) Net Positive Suction Head Required (NPSHR) Furnished by pump manufacturer – pump specific Increases with pump flowVWEA16 Rogers Hydraulic Considerations in Pumping System Design NPSHA NPSHR Cavitation Typically occurs in systems with static lift Could occur in flooded suction scenario with extremely longlengths of suction piping Insufficient submergence can lead to vortexing

Work A force does work when it actson a body over a distance Units of foot pound (ft-lb) Wastewater pumps do work tomove the wastewater PowerVWEA16 Rogers Hydraulic Considerations in Pumping System Design Rate of work done (ft-lb/s) Wastewater pumps most oftendo work by using electricmotors Motors are commonly rated byhorsepower (hp) 1 unit of hp is equal to 550 ftlbs/s

12VWEA16 Rogers Hydraulic Considerations in Pumping System DesignThe Pumping System Design Process Collect informationDetermine type of pump to be usedDevelop station layoutDevelop system curvesSelect pumps that match the system curvesWrite your specificationCoordinateFinalize the design

13VWEA16 Rogers Hydraulic Considerations in Pumping System DesignCollect Information What – type of fluid is to be pumped? Fluid properties: density, viscosity, solidscontent, temperature From where to where? System characteristics: friction and minorlosses, suction lift, static head, other pumpsoperating simultaneously How much – what are design flowrates?

14Determine Type of Pump Flow and head requirements Type of fluid, solids content Site conditionsVWEA16 Rogers Hydraulic Considerations in Pumping System Design Footprint and headroom constraints Subgrade conditions Elevation constraints Suction and discharge inverts Suction head availableMore than one type may work - what’s best for the specificapplication and owner preference?Fairbanks-Morse

15Types of PumpsPump TypesCentrifugalSingle suctionDouble suctionRadial FlowMixed FlowAxial FlowKineticPeripheral/RegenerativeSpecialVWEA16 Rogers Hydraulic Considerations in Pumping System f-primingOpen impellerSemi-open impellerClosed impellerJetGas liftHydraulic DiaphragmVaneGearLobeScrewPistonHoseHydraulic Institute

Types of Pumps Kinetic (Rotodynamic) Pumps Energy is imparted to the fluid by a rotating impeller which increasesthe flow velocity and converts to a pressure increase upon exit. Can be safely operated under closed valve conditions (for shortperiods of time). Three Types: Radial-flow pumps (Centrifugal Pump) - higher pressures and lower flow rates thanaxial-flow pumps. Axial-flow pumps - lower pressures and higher flow rates than radial-flow pumps. Mixed-flow pumps – A compromise between radial and axial-flow pumps - operate atVWEA16 Rogers Hydraulic Considerations in Pumping System Designhigher pressures than axial-flow pumps while delivering higher discharges than radialflow pumps. Positive Displacement (PD) Pumps PD pumps physically displace fluid Closing a valve downstream can lead to continual pressure build up andfailure of pipeline

Positive Displacement PumpsLobe PumpHose PumpVWEA16 Rogers Hydraulic Considerations in Pumping System DesignHP Reciprocating Triplex PumpProgressing Cavity Pump

Progressing Cavity PumpsVWEA16 Rogers Hydraulic Considerations in Pumping System Design Flowrate fixed to speed Capable of pumping highly viscous stream Commonly used in sludge and slurry pumpingapplications Operates at high pressures Must avoid running pump dry Provide safety features on discharge

Centrifugal PumpVWEA16 Rogers Hydraulic Considerations in Pumping System DesignA centrifugal pump lifts fluid from one elevation to another by continuouslyadding kinetic energy (accelerating the fluid) using a rotating impeller

20Common Types of Centrifugal Pumps forWater and Wastewater Horizontal Split Case Pumps Vertical Turbine PumpsVWEA16 Rogers Hydraulic Considerations in Pumping System Design End Suction Pumps Closed impeller Non-Clog pumps Submersible non-clog pumps

Horizontal Split CaseApplications Water treatment: Raw Water High service pumping Transfer pumping Wastewater treatment:Characteristics Wide flow range Heads to 500 ft. for single stage,higher for two-stage High efficiency (85-95%) Ease of maintenance Flat curveVWEA16 Rogers Hydraulic Considerations in Pumping System Design Reuse filter feed Reuse distribution Treated effluent pumpsConfigurations Horizontal motorVertical motorSingle or two stageDual diesel / electric driveHorizontalVertical

22Vertical TurbineApplications Water treatment: Raw water pumps Groundwater pumps(submersible) Membrane feed pump Filter backwash pump High service pumps Transfer pumpsVWEA16 Rogers Hydraulic Considerations in Pumping System Design Wastewater treatment: Reuse filter feedReuse distribution pumpsTreated effluent pumpsVTSH (vertical turbine solidshandling)Characteristics Wide flow range Wide head range – addstages for higher head Steep curve Very compact footprint Prone to vibration Difficult to serviceConfigurations Can-type Wetwell-mounted Submersible

End SuctionApplications Water treatment: Booster PumpingFilter BackwashMembrane FeedChemical FeedRaw water Wastewater treatment(non-clog impellers):VWEA16 Rogers Hydraulic Considerations in Pumping System Design Sewage lift stations Raw sewage pumpsCharacteristics Low to Medium flow High head - add stages Curve shape variesConfigurations Vertical - save space or to mountmotor above flood elevation Horizontal - provides goodaccess and saves head room Close-coupled (singlepump/motor shaft) Direct coupled (motor shaftconnected to the pump shaft bya shaft coupling) V-belt drive Extended shaft Submersible

24End Suction Pumps – WastewaterVWEA16 Rogers Hydraulic Considerations in Pumping System Design Heads to 250 ft. for a single stage Best efficiencies 70-75% Impeller options:Channel ImpellerVortex ImpellerSemi-Open Impeller(recessed impeller)(enclosed, 1-3 vanes)Sewage lift stationtypical applicationGrit and sludge pumpingtypical applicationsSolids handling performance improvesHydraulic efficiency increases

25Pump Type Selection Example – Griffith RWPSSelected horizontal split-case pumps – why? Had available land area and suction head Rock subgrade Suitable curve shapeVWEA16 Rogers Hydraulic Considerations in Pumping System Design Owner preference Ease of maintenance

Centrifugal Pump Summary Larger impellers - Greater flow and head Greater Speed – Greater flow and head Larger, slower impellers are more efficient but cost more Pumps in parallel - more flow at same headVWEA16 Rogers Hydraulic Considerations in Pumping System Design Pumps in series - higher head at same flow Generally, power increases as flow increases to run out Best efficiency point (BEP) is at max of efficiency curve

Centrifugal Pumps - Points to Watch Rotational speeds 1,800 rpm Non-clog in particular Flooded suction - no priming needed Curve shall continually rise to shut off Steeper pump curves are best for VFDsVWEA16 Rogers Hydraulic Considerations in Pumping System Design Duty point to be 75% Qmax, close to BEP Aim for efficiencies 75% single stage Size motor HP for “run out” or maximum power NOT duty point

28Station Layout - Where to Start? Resources Hydraulic Institute (HI) Standards, other references Consider constraints – site, budget, etc. Collect/develop information needed to create systemcurvesVWEA16 Rogers Hydraulic Considerations in Pumping System Design Elevations of suction, pump room floor, high points, dischargeFor retrofits, survey/measure existing elevations, testexisting pumps for flow and pressure Develop piping system layout, list of minor losses

29Station Layout Considerations Provide sufficient work space between pumps Use largest pump and motor dimensions (now or future) Allow for expansionVWEA16 Rogers Hydraulic Considerations in Pumping System Design Think through process of installing/removing pumps and valves Size crane and openings for heaviest / largest single item in the station Ensure crane can reach everything it needs to lift Consider need for portable hoists or truck access, etc. when selectingpump spacing, sizing hallways Involve operations and maintenance staff early

30Layout - Hydraulic Institute Standards American National Design Standards for Pump Intake and CentrifugalPumps Wetwells - different designs for clear and solids-bearing liquids Provide steady, uniform flow with minimal flow disturbances Keep solids entrained Piped intakes – recommended piping configurations, velocity limitsVWEA16 Rogers Hydraulic Considerations in Pumping System Design Canned vertical turbine pumps – geometry and velocity specifications No flow disturbing fittings within 5 pipe diameters of suction Long-radius bends and full-port valves are not considered flow disturbing