The Practical Pumping Handbook

Transcription

1 The Practical Pumping Handbook by Ross Mackay ELSEVIER

2 Contents Acknowledgements Dedication About the author xv xviii xix Centrifugal Pumps The pump Applications Pump cases Diffuser casings Back cover arrangements Mounting feet The impeller Specific speed Open and closed impellers Double suction pumps Materials of construction Nonmetallic pumps 13 Pump Hydraulics The pressure-head relationship Pressure terminology Pumping pressure Total dynamic head Performance curve Efficiency Net positive suction head The composite pump performance curve The best efficiency point (BEP) 22

3 Contents Pump run-out Minimum flow point Affinity laws Change of electric motor for performance change Other changes Pump performance on special liquids Impeller hydraulic loads Radial thrust Shaft deflection System Hydraulics Pump limitations Liquid flow in pipes Specific gravity Pressure in a static system Pressure in aflowingsystem Changes in an existing system The effect of capacity change on friction The effect of head change on flow rate Pipe size changes in a system Basic elements of pump system design Gravity and static head Friction losses and friction head Velocity head Total head System curve The effect of operating performance Static head changes Batch transfer system Pressurized system Closed loop system Friction head changes System controls Restrictions in piping Recirculation systems Pump speed changes Series and parallel operation Series operation Parallel operation VI

4 ent 3.6 Pump system analysis Example Example Example 3-A Example 3-B System curve revisited Suction Conditions General Vapor pressure Cavitation Net positive suction head NPSH required by the pump Increase the eye area of the impeller Install a suction inducer Use a double suction impeller Use a slower speed pump Use lower capacity pumps Use a booster pump NPSH available from the system Static head (Hs) Surface pressure (Ha) Vapor pressure (Hvp) Friction losses (Hf) Sample NPSHA calculation Suction specific speed Confusing conditions Suction recirculation Discharge recirculation Air entrainment Similarities and differences Priming Self-priming pump layout Centrifugal pump with priming tank Air ej ector system Submergence Pump selection and purchasing Pump selection factors Operational experience End user data sheets Svstem ODeratine considerations

5 Contents Closed loop systems Batch transfer system Multiple destination systems Price evaluation Traditional pricing negotiation Value based purchasing Factors involved in mechanical suitability Mechanical seals Seal environment Bearings Lubricant protection Rotational speed Shaft slenderness ratio Maintenance hours Downtime and lost production The results 85 Stuffing Box Sealing 6.1 Shaft sealing 6.2 Packing 6.3 Mechanical Seals Match the seal to the service The seal faces Seal flexibility options Fretting seals Balanced or unbalanced seals Outside seals Split seals Cartridge seals Double seals 6.4 Environmental controls Seal flush Reverse flush Seal quench Barrier fluid systems 6.5 The seal chamber Pump Bearings 7.1 Pump bearings 7.2 Bearing loads 7.3 Ball bearings 7.4 Other types of bearing VIII

6 Cylindrical roller bearings Journal bearings The total bearing arrangement Oil lubrication Static oil lubrication Constant level oiler Oil ring lubrication Oil mist lubrication Grease: lubrication Shielded bearings Bearing life Lubricant protection Sealed bearings The lip seal The magnetic seals Bearing isolator.ontent! Special Applications 8.1 Slurry pumping Industrial slurries Municipal waste Pipelines and mines Recessed impeller vortex pumps Diaphragm pump Progressive cavity pump Solids and slurries - useful formulae Abrasive wear 8.2 Paper stock Air in stock Excessive discharge throttling Filters and additives Paper stock pumps Medium density stock pumps High density pumps The fan pump Determination of pump performance Example Example 2 Special Pumps 9.1 Sump pumps Vertical sumo oumo IX

7 Contents ^^mmm^mmmmmmmi^mmm^mmmi^^mmmmma^m Submersible pump Priming the pump Air operated double diaphragm pump Horizontal centrifugal pump Self-priming pump Vertical turbine pumps Vertical pump bowl assembly Vertical pump column Pump discharge head Vertical pump performance Vertical pump sump requirements Vertical pump design considerations Magnetic drive pumps Pump bearings Temperature considerations Decoupling Failure costs Positive displacement pumps The piston pump The diaphragm pump The gear and lobe pump Screw pumps Progressive cavity pump Pump Installation and Piping Installation Location Receiving Handling Foundation leveling Mounting the baseplate Cement based grouting Epoxy based grouting Pregrouted baseplates Piping considerations Location Pipe size Suction elbows Straight pipe Air pockets Suction source design Pipe strain 172

8 .ontent: Pipe fittings 10.3 Alignment Shaft couplings Shaft offset and angularity High temperature corrections Typical acceptance values Run out Soft foot Alignment methodology C-flange adapter 11 Troubleshooting 11.1 Skill and experience 11.2 Operational problems Cavitation problem solving Uncurable conditions 11.3 Reliability problems 11.4 Failure analysis Speed of problem occurrence Excessive power consumption Frequency of problem occurrence Hydraulic imbalance in a double suction pump Undersized shaft in an end suction pump 11.5 Failure modes Impeller Wear rings Shaft Sleeve Bearings Packing Mechanical seal - general Mechanical seal - seal faces Pump Maintenance The strategy Economic considerations Preparation for pump dismantling Removing the back pull-out assembly Inspection checks on cast parts Casing and wear rings 205 XI

9 Contents wma^mmmmi^mmmmmmmmki^mma^mmmm^mmi^mm 12.6 Dismantling the back pull-out assembly When packing is fitted When a mechanical seal is fitted Dismantling the bearing housing Inspection checks The back cover The frame adapter The bearing housing Lip seals The shaft Mounting bearings on the shaft Check shaft condition Assembling the back pull-out assembly A packed stuffing box Installing the impeller with a packed stuffing box Packing procedures Installing with a mechanical seal Installing the impeller with a mechanical seal Installing the back pull-out assembly Fluid Properties Properties of water at various temperatures Effect of altitude on pressures and the boiling point of water Viscous liquids Viscous performance correction for small pumps Viscous performance correction for larger pumps Friction Loss Tables Friction loss for water in pipe Typical resistance coefficients for valves and fittings Materials of Construction Materials of construction for pumping various liquids Material selection Material classes for centrifugal pumps in general refinery services 249 XII

10 jntent: 15.4 Material; 3 for pump parts 15.5 Material specifications for pump parts 16 Conversion Tables and Formulae 16.1 Conversion tables Length Area Volume Velocity Capacity Pressure or head Energy, work, heat Power Mass 16.2 Useful formulae Bibliography Index Head-pressure relationship Power calculation The affinity laws Pressure in a static head system Pressure in aflowingsystem The effect of capacity change on pipe friction The effect of head change on the flow rate The effect of changes in pipe diameter on the friction in a system The effect of changes in pipe diameter on the flow rate in a system Total head in a system Net positive suction head available from a system Impeller specific speed Suction specific speed Calculation of grease service life L-10 bearing life calculation Slurry specific gravity XIII