Pump principles

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PUMP PRINCIPLES

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Pump principles

  1. 1. PUMPS and PIPING By. Engr. Yuri G. Melliza
  2. 2. PUMPS: It is a steady-state, steady-flow machine in which mechanical work is added to the fluid in order to transport the liquid from one point to another point of higher pressure. Upper Reservoir Suction Gauge Discharge Gauge Lower Reservoir Gate Valve Gate Valve
  3. 3. CLASSIFICATION OF PUMPS 1. Centrifugal: It consist essentially of an impeller arranged to rotate within a casing so that the liquid will enter at the center or eye of the impeller and be thrown outward by centrifugal force to the outer periphery of the impeller and discharge into the outer case. It operates at high discharge pressure, low head, high speed and they are not self priming.  Centrifugal  Mixed Flow  single stage  multi stage  Propeller or axial flow  Peripheral
  4. 4. 2. Rotary:It is a positive displacement pump consisting of a fixed casing containing gears, cams, screws, vanes, plungers or similar element actuated by the rotation of the drive shaft. A rotary pump traps a quantity of liquid and moves it along toward the discharge point. For a gear type rotary pump the unmeshed gears at the pump provides a space for the liquid to fill as the gears rotate. The liquid trapped between the teeth and the pump casing is eventually released at the discharge line. It operates at low heads, low discharge and is used for pumping viscous liquids like oil.  cam  gear  screw  vane
  5. 5. 3. Reciprocating: It is a positive displacement unit wherein the pumping action is accomplished by the forward and backward movement of a piston or a plunger inside a cylinder usually provided with valves.  Piston  Direct Acting  single  duplex  Crank and Flywheel  Plunger  Power Driven  simplex  duplex  triplex
  6. 6. 4. Deepwell Pumps: It is used when pumping water from deep wells. The pump is lowered into the well and operated close to water level. They are usually motor driven with the motor being at the ground level and connected to the pump by a long vertical line shaft.  Turbine  Ejector or centrifugal  reciprocating  Airlift For a final choice of a pump for a particular operation the following data are needed.  Number of units required  Nature of liquid  Capacity  Suction conditions  Discharge conditions  Intermittent or continuous service  Total dynamic head  Position of pump, vertical or horizontal  Location, geographical, indoor, outdoor, elevation  Type of power drive
  7. 7. Centrifugal Pump Reciprocating PUmp Cylinder impeller discharge eye Rotary Pump (Gear Type) Piston Valves Gear
  8. 8. FUNDAMENTAL EQUATIONS 1. TOTAL DYNAMIC HEAD Ht P2 P1 v2 2 v1 2 2g γ Z2 Z1 2. DISCHARGE or CAPACITY Q = Asvs = Advd m3/sec 3. WATER POWER or FLUID POWER WP = Q Ht KW 4. BRAKE or SHAFT POWER BP 2πTN 60,000 KW HL meters
  9. 9. 5. PUMP EFFICIENCY ηP WP BP x 100% 6. MOTOR EFFICIENCY ηm BP MP x 100% 7. COMBINED PUMP-MOTOR EFFICIENCY ηC ηC WP MP ηP ηm x 100%
  10. 10. 8. MOTOR POWER  For Single Phase Motor MP EI(cosθ) 1000 KW  For 3 Phase Motor MP where: 3 EI(cosθ) 1000 KW P - pressure in KPa v - velocity, m/sec - specific weight of liquid, KN/m3 Z - elevation, meters g - gravitational acceleration, m/sec2 HL - total head loss, meters E - energy, Volts I - current, amperes (cos ) - power factor T - brake torque, N-m N - no. of RPM WP - fluid power, KW BP - brake power, KW MP - power input to motor, KW
  11. 11. PIPES and FITTINGS Nominal Pipe Diameter: Pipe sizes are based on the approximate diameter and are reported as nominal pipe sizes. Regardless of wall thickness, pipes of the same nominal diameter have the same outside diameter. This permits interchange of fittings. Pipe may be manufactured with different and various wall thickness, so some standardization is necessary. A method of identifying pipe sizes has been established by ANSI (American National Standard Institute). By convention, pipe size and fittings are characterized in terms of Nominal Diameter and wall thickness. For steel pipes, nominal diameter is approximately the same as the inside diameter for 12" and smaller. For sizes of 14" and larger, the nominal diameter is exactly the outside diameter. SCHEDULE NUMBER: The wall thickness of pipe is indicated by a schedule number, which is a function of internal pressure and allowable stress. Schedule Number 1000P/S where P - internal working pressure, KPa S - allowable stress, KPa Schedule number in use: 10,20,30, 40,60, 80, 100, 120, 140, and 160. Schedule 40 "Standard Pipe" Schedule 80 " Extra Strong Pipe"
  12. 12. FITTING: The term fitting refers to a piece of pipe that can: 1. Join two pieces of pipe ex. couplings and unions 2. Change pipeline directions ex. elbows and tees 3. Change pipeline diameters ex. reducers 4. Terminate a pipeline ex. plugs and valves 5. Join two streams to form a third ex. tees, wyes, and crosses 6. Control the flow ex. valves VALVES: A valve is also a fitting, but it has more important uses than simply to connect pipe. Valves are used either to control the flow rate or to shut off the flow of fluid.
  13. 13. DESIGN OF A PIPING SYSTEM The following items should be considered by the engineer when he is developing the design of a piping system. 1. Choice of material and sizes 2. Effects of temperature level and temperature changes. a. insulation b. thermal expansion c. freezing 3. Flexibility of the system for physical and thermal shocks. 4. Adequate support and anchorage 5. Alteration in the system and the service. 6. Maintenance and inspection. 7. Ease of installation 8. Auxiliary and standby pumps and lines 9. Safety a. Design factors b. Relief valves and flare systems
  14. 14. HEAD LOSSES HL = Major loss + Minor losses Major Loss: Head loss due to friction and turbulence in pipes Minor Losses: Minor losses includes losses due to valves and fittings, enlargement, contraction, pipe entrance and pipe exit. Minor losses are most easily obtained in terms of equivalent length of pipe "Le". the advantage of this approach is that both pipe and fittings are expressed in terms of "Equivalent Length" of pipe of the same relative roughness. Darcy-Weisbach Equation Considering Major Loss only f Lv 2 hf meters 2gD Considering Major and Minor Losses hf f (L L ) v2 e meters 2gD
  15. 15. Where; f - friction factor from Moody's Chart L - length of pipe, m Le - equivalent length in straight pipe of valves and fittings, m v - velocity, m/sec D - pipe inside diameter, m g - gravitational acceleration, m/sec2 REYNOLD'S NUMBER: Reynold's Number is a non dimensional one which combines the physical quantities which describes the flow either Laminar or Turbulent flow. The friction loss in a pipeline is also dependent upon this dimensionless factor NR where; ρvD vD μ ν - absolute or dynamic viscosity, Pa-sec - kinematic viscosity, m2/sec For a Reynold's Number of less 2100 flow is said to Laminar For a Reynold's Number of greater than 3000 the flow is Turbulent
  16. 16. Moody’s Chart f D NR where - absolute roughness D - inside diameter /D - relative roughness
  17. 17. VALUES OF ABSOLUTE ROUGHNESS FOR NEW PIPES Type of Material Drawn tubing, brass, lead, glass centrifugally spun cement, bituminous lining, transite Commercial Steel, Wrought iron Welded steel pipe Asphalt-dipped cast iron Galvanized iron Cast iron, average Wood stave Feet Millimeter 0.000005 0.00015 0.00015 0.0004 0.0005 0.00085 0.0006 to 0.003 0.0015 0.046 0.046 0.12 0.15 0.25 0.18 to 0.9 Concrete 0.001 to 0.01 0.3 to 3 Riveted steel 0.003 to0.03 0.9 to 9
  18. 18. For Laminar flow: f 64 NR Centrifugal Pumps 1. TOTAL HEAD Ht = nH where: n - number of stages H - head per stage 2. SPECIFIC SPEED: Is the speed in RPM at which a theoretical pump geometrically similar to the actual pump would run at its best efficiency if proportion to deliver 1 m3/sec against a total head of 1 m. It serves as a convenient index of the actual pump type.
  19. 19. NS where: N Q Q - flow in m3/sec for a single suction pump H - head per stage N - speed, RPM NS - specific speed, RPM 3 0.0194 H 4 3. SUCTION SPECIFIC SPEED S N Q 3 0.0194 NPSH 4 3 NS NPSH S H 4 where: NPSH - Net Positive Suction Head
  20. 20. 4. NET POSITIVE SUCTION HEAD: The amount of pressure in excess of the vapor pressure of the liquid to prevent cavitation. NPSH = Hp Hz - Hvp - hfs , meters where: Hp - absolute pressure head at liquid surface at suction, m Hz - elevation of liquid surface at suction, above or below the pump centerline, m (+) if above PCL (-) if below PCL Hvp - vapor pressure head corresponding the temperature of the liquid,m hfs- friction head loss from liquid surface at suction to PCL. 5. CAVITATION: The formation of cavities of water vapor in the suction side of the pump due to low suction pressure.
  21. 21. CAUSES OF CAVITATION  Sharp bends.  High temperature  High velocity  Rough surface  Low atmospheric pressure EFFECTS OF CAVITATION  Noise  Vibration  Corrosion  Decreased capacity 6. CAVITATION PARAMETER 4 δ NPSH NS H S 3
  22. 22. 7. IMPELLER DIAMETER D 60 2gH πN meter where: - peripheral velocity factor whose value ranges from 0.95 to1.09 8. AFFINITY LAWS OR SIMILARITY LAWS FOR CENTRIFUGAL MACHINES a. For Geometrically similar pumps Q ND3 Power N3D5 H N2D2 T N2D5 b. For pumps with Variable Speed and Constant impeller diameter Q N Power N3 H N2 c. For pumps at Constant Speed with Variable impeller diameter Q D Power D3 H D2
  23. 23. RECIPROCATING PUMPS Specification: Ds x Dw x L where: Ds - diameter of steam cylinder Dw - diameter of water cylinder L - length of stroke 1. VOLUMETRIC EFFICIENCY ηV Q VD x 100% where: Q - discharge , m3/sec VD - displacement volume, m3/sec
  24. 24. 2. DISPLACEMENT VOLUME  For Single acting 2 VD L(D W ) Nn' m 3 4(60) sec  For Double acting without considering piston rod 2 VD L(D W ) Nn' m 3 4(60) sec  For Double acting considering piston rod VD LNn' 4(60) 2 2D W - d 2 m 3 sec where: N - no. of strokes per minute L - length of stroke, m D - diameter of bore, . d - diameter of piston rod, m n' - no. of cylinders n' = 1 (For Simplex) n' = 2 (For Duplex) n' = 3 (For Triplex)
  25. 25. 3. PERCENT SLIP % Slip = 100 - where: hs - enthalpy of supply steam, KJ/kg he - enthalpy of exhaust steam, KJ/kg ms - steam flow rate, kg/hr WP - fluid power, KW V 4. SLIP Slip = VD - Q 5. THERMAL EFFICIENCY e 3600(WP) m s (h s he ) x 100% 6. FORCE PRODUCED and ACTING ON THE PISTON ROD 2 Fs D S (Ps 4 Pe ) KPa where: Ps - supply steam pressure, KPa Pe - exhaust steam pressure, KPa Ds - diameter of steam cylinder, m (Ps - Pe) - mean effective pressure
  26. 26. 7. FORCE TRANSMITTED TO THE LIQUID PISTON Fw e m Fs 2 Fw (Dw) (Pd Psu ) 4 Ds (Pd Dw e m (Ps where: em - mechanical efficiency Psu - suction pressure of water cylinder, KPa Pd - discharge pressure of water cylinder, KPa KPa Psu ) Pe ) 8. PUMP DUTY: Work done on the water cylinder expressed in Newton-meter per Million Joules Pump Duty 9.81m w (H d H su ) x 10 1000m s (h s - h e ) 6 N-m Million Joules where: mw - water flow rate, kg/hr Hd - discharge head of pump, m Hsu - suction head of pump, m
  27. 27. 9. PUMP SPEED V = 43.64(L)1/2(ft), m/min 2 VD (D W ) Vn' m 4(60) where: ft - temperature correction factor L - length of stroke, m 3 sec 10. TEMPERATURE CORRECTION FACTOR ft = 1 For cold water = 0.85 for 32.2 C water = 0.71 for 65.5 C water = 0.55 for 204.4 C water 11. For Indirect Acting pumps N 907 f t L
  28. 28. Example no. 1 A mechanical engineer of an industrial plant wishes to install a pump to lift 13 L/sec of water from a sump to a tank on a tower. The water is to be delivered into a tank 105 KPa. The tank is 18 m above the sump and the pump is 1.5 m above the water level in the sump.The suction pipe is 100 mm in diameter, 8 m long and will contain 2 - standard elbows and 1 - Foot valve. The discharge pipe to the tank is 65 mm in diameter and is 120 m long and contains 5 - 90 elbows, 1 - check valve, and 1 - gate valve. Pipe material is Cast iron. Determine the KW power required by the pump assuming a pump efficiency of 70% and motor efficiency of 80%. Other Data = 0.001569 Pa – sec = 1000 kg/m3
  29. 29. At Suction At Discharge
  30. 30. Using point 1 and 2 as reference point P1 = 0 gage P2 = 105 Kpa Z1 = 0 Z2 = 18 m HL = 0.71+45.634 = 46.34 meters Pump efficiency = 70% Motor efficiency = 80% Overall Efficiency = 0.70(0.80)=0.56
  31. 31. A centrifugal pump design for a 1800 RPM operation and a head of 61 m has a capacity of 190 L/sec with a power input of 132 KW. What effect will a speed reduction to 1200 RPM have on the head, capacity and power input of the pump? What will be the change in H, Q and BP if the impeller diameter is reduced from 305 mm to 254 mm while the speed is held constant at 1800 RPM. Neglect effects of fluid viscosity. Given: N1 = 1800 RPM N2 = 1200 RPM H1 = 61 m H2 = Q1 = 190 L/sec Q2 = BP1 = 132 KW BP2 = For N1 = N2 = 1800 RPM D1 = 305 mm ; D2 = 254 mm
  32. 32. FROM AFFINITY LAWS OR SIMILARITY LAWS FOR CENTRIFUGAL MACHINES a. For Geometrically similar pumps Q ND3 Power N3D5 H N2D2 T N2D5 b. For pumps with Variable Speed and Constant impeller diameter Q N Power N3 H N2 c. For pumps at Constant Speed with Variable impeller diameter Q D Power D3 H D2
  33. 33. PREPARED BY: ENGR. YURI G. MELLIZA XAVIER UNIVERSITY ATENEO DECGAYAN

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