2 Outline Intro to Pumping Classifications of pumps Positive Displacement Pump – Examples and ApplicationsCentrifugal Pumps – Examples and ApplicationsPump Curves
3 History of PumpsFirst pumps were driven by water wheels or animal poweredWater was lifted w/ paddles and dumped at a higher elevationOver 2200 years ago in Greece, Persia, the Orient , some still in use todayElectric motor is most common machine in use today, the pump is second most commonAgriculture Automobile Construction Chemical Manufacturing Household Hydraulic Systems Submarines Space Station Zeeland to ZimbabweThe pump is said to be one of the first complex machines in recorded history.
4 Pump ApplicationsUsed to increase the potential and/or kinetic energy state of a fluidLiquid – water, chemical, fuels, coolants, refrigerants, hydraulic fluids, boiler feed, condensate return, etc.Vapor/gas – foams, air, other gasesSlurries – concrete, quarry slurries, mud for drilling, precipitates, sewage, pulp stock, etc.
5 Two Primary Classifications of Pumps Dynamic (or Centrifugal) – Use a spinning impeller to induce centrifugal forces, increasing pressure at the discharge side of the housing.Positive Displacement – Transfers a fixed volume of fluid thru the pump housing with each cycle of operation.Spinning impeller increases the velocity of the fluid w/in the pump housing.The centrifugal forces of the fluid on the pump housing cause an increase of pressure at the discharge side of the housing.As long as there is a path for the fluid to leave the pump housing, more fluid is drawn (forced) into the suction side due to the vapor pressure of the fluid.
6 Classifications of Pumps Overwhelming majority of all pumps are some type of Centrifugal Pump.Lower initial costReduced maintenance costsPositive Displacement Pumps are widely used but for specific applications.Many/most pumping applications use centrifugal pumps.Cent pump impeller spins freely in the fluid with no mechanical surfaces contacting the pump housing.Simple design with minimal wear parts makes for a very reliable device.PD pumps are application specific.
7 Comparison between Positive Displacement and Centrifugal Pumps When viscosities get highWhen you need self-primingWhen you need high discharge pressuresWhen you have a metering application where a specific volume of fluid must be delivered for each rotation of the pump shaftWhen you need constant flow regardless of discharge pressureWhen you want to control flow by controlling pump speed-- use a PD pump
8 Head vs. Flow Comparison between Positive Displacement and Centrifugal Pumps Compare PD with Cent pumpPD has constant delivery regardless of discharge head (pressure)Cent. Pump has high capacity at low head, but flow drops off as discharge head increases.
9 Effect of Increasing Viscosity on Flow for Positive Displacement and Centrifugal Pumps PD pumps have “slip” at low viscosityAs viscosity increases, slip is reduced and flow remains constant throughout range.Cent pump has big performance drop off as viscosity increases above 500 SSU (light motor oil)Can heat fluid to reduce viscosity and still use cent pump
10 Comparison of Efficiency vs Comparison of Efficiency vs. Head between Positive Displacement and Centrifugal PumpsPD pump efficiency is almost constant over operating range.Cent pump will have a single best operating point where efficiency is at a peak
11 Positive Displacement Pump “Family Tree” Many types of PD pumps
12 Types of PD Pumps – Gear Pumps External Gear PumpHigh speedQuiet operationFuel, lubricants, hydraulic fluid power systems, meteringNo solidsInternal Gear PumpNon-pulsating discharge pressureLow NPSHRLow to moderate speedHigh viscosity fluidsExternal gear pumpOne gear is driven by motor, the other is driven by the first.Fluid enters and travels in the cavity between the gear teeth and the pump housing to get to the discharge.Internal gear pumpThe outer cage is driven by a motor. The inner gear is driven by the cage.Fluid travels through two paths.Between the gaps in the cage and the outer housing.Between the inner gear teeth and the crescent shaped divider.
13 Other Common Types of PD Pumps Lobe PumpNo metal to metal contactCan handle solids without damaging themApplications are found in food processing, pharmaceutical, personal care, etc.Diaphragm PumpLobe pumps are “timed so that there are no contacting parts.Each lobe has a shaft sticking out the back side of the pump housing.The shafts have meshing gears installed outside of the housing.One shaft is driven by a motor. The gears keep the two lobes in the same relationship with each other.Diaphragm pumpsCan be mechanically driven or air driven. Air driven pumps can be installed in hazardous environments without concern for electrical sparks igniting a combustible atmosphere.
14 Centrifugal Pump “Family Tree” PumpsCentrifugalPositive DisplacementSingle StageMulti-StageHorizontalVerticalOpen ImpellerClosed ImpellerThe other side of the pump story…Most common centrifugal pump is the single stage, horizontal shaft, w/ a closed impeller.
15 How a Centrifugal Pump Works Pump housing must be primedImpeller rotates, imparting an outward velocity to the fluid – kinetic energyFluid velocity reaches maximum at the outside diameter of the impellerFluid enters the volute where it is channeled to the dischargeHousing must be filled with water for the pump to operate – “prime”Fluid reaches a maximum pressure at the discharge side of the pump.In the volute, velocity decreases, causing an increase in pressure.Pressure is highest at the discharge.If the downstream piping isn’t blocked fluid will flow.The “cut-water” is the point where the impeller is closest to the housing.Resistance to flow, starting at the volute, reduces velocity creating pressure energyVapor pressure of fluid causes new fluid to be drawn into the eye of the impeller
16 A Centrifugal Pump/Driver Installation Discharge lineElectric MotorPump HousingCouplingBuffalo Forge pump from UO Lab showing all pump partsBearing SupportSuction lineExternal CoolingStuffing Box and Packing Gland
17 Single Stage, Horizontal Shaft, Closed Impeller Flowserve Pump Co. Cut-away shows good view of bearing support, packing, housing/impeller clearances
18 Horizontal, Split Case, Single Stage Fire Pump Patterson Pump, Div Horizontal, Split Case, Single Stage Fire Pump Patterson Pump, Div. of Gorman-RuppNote the pressure gages on the upstream and downstream side of pump.Handwheel valve.Split case pump has bearings on both side of impeller, where previous picture shows cantilevered design.
21 Types of Impellers Closed vane Open vane Open vane, cut impeller Closed vane gives highest discharge headOpen vane handles solidsCut impeller allows you to use the same pump for a wide range of applications (where the maximum flow and head is below that of the full-sized impeller.
22 Pump Curve for a Goulds Model HSC centrifugal pump at 3500 rpm When selecting new pump or changing capacity of existing pumps:Capacity for 6 impeller sizesNPSHRReq’d horsepowerEfficiencyPump curve shows:Head vs flowReq’d HP vs flowEfficiency vs flowNPSHR vs flow – all at a specific RPMSingle pump curve shows data for all impellers that are available for this pump.
23 Pumping Affinity LawsUsed for estimating pump performance when changing impeller size or RPMQ1/Q2=N1/N2H1/H2=(N1/N2)2P1/P2=(N1/N2)31-2-3 Affinity Laws:Flow is proportional to RPMHead is proportional to the square of RPMPower is proportional to the cube of the RPM
24 Pump Efficiency Overall Efficiency PP, Pump Input power, BHPPW, Pump Output PowerConsider the efficiency of a pump/motor package.Measure the electrical input powerMeasure the water horsepower – the rate of work being done to the fluid.To measure the pump efficiency you need to measure the torque on the pump shaft and the shaft RPM – Prony brake.Then measure the water horspower.PMOT, Driver Input Power
25 Pump Maintenance Seals Shaft packing vs. mechanical seals Monitor for leaksBearingsOverhung vs. double supportMonitor vibrationWetted parts corrosionCavitationmonitor suction-side pressurelisten for rattling