1 ME444 ENGINEERING PIPING SYSTEM DESIGN CHAPTER 6 : PUMPS 2 LAST SESSION 1.PIPING SYSTEM DESIGN PROCEDURE 2.PIPE THICKNESS 3.PIPE SIZING AND SYSTEM PRESSURE DROP 3 CONTENTS 1.Fundamental of Pumps 2.Operating Point 3.Pump Selection 4.Pump Installation 4 1. Fundamental of Pumps When source pressure is not enough to provide desired output, pump is utilized. SOURCEPIPING SYSTEMEND USERS 5 Pump output Flow rate and Pressure rise. Flow rate 6 Pump input and output Output = Flow rate and Pressure rise. Flow rate Input energy 7 Specific Speed 8 Pump performance Dynamic pump Positive displacement pump 9 Pump performance range 10 Performance curves = 0.57 (N s = 1,550) = 3.66 ( N s = 10,000) 11 Steep vs. flat curves Flat curve for closed loop system with variable flow rate Steep curve for high head and constant flow rate 12 Affinity law Impeller DiameterImpeller Speed 13 Example of performance curves 14 Example of performance curves 15 Speed of induction motor polesSynchronous speed (rpm) Possible Operating Speed (rpm) 16 Standard motor size hpkW 1/ / / / / / hpkW 17 Effect of Fluid Viscosity 18 Net Positive Suction Head 19 Net Positive Suction Head Required At low pressure, water can become vapor, causing cavitations. Temperature T ( o C) Vapor Pressure (kPa)** Suction pressure must be maintained above NPSHR to avoid cavitation 20 Net Positive Suction Head Available z Suction lift Vapor pressure Pressure drop in suction piping MUST Maintain NPSHA > NPSHR 21 2. Operating Point Pump performance curve System pressure drop curve Operating point 22 Filling a tank from bottom Pump performance curve 23 Filling a tank from bottom vs. from top Which way fill faster? 24 Throttling the discharge valve Pump performance curve Fully open valve Throttled valve 25 Variable speed drive vs. valve throttling Pump performance curve N1 Throttled valve Fully open valve Pump performance curve N2 Feedback signal 26 VSD for pressure control Valve 1 and 2 open Pump performance curve N2 Pump performance curve N1 Pressure set point All valve open Pressure signal 27 Limitation of VSD Cannot reduce speed System curve Feedback signal 28 Parallel and Serial Connection 29 Response to Parallel Connection 30 Parallel Connection of Pumps with Different Size 31 Utilization of Pressure Tank Pressure Switch Pressure Tank Air Water time Pressure in tank Pump operate Pump stop 32 3. Pump Selection Best Efficiency Energy cost is far beyond the pump cost 33 Example 6.1 Select the suitable pump for Example m.WG. 34 Example 6.1 (2) 200 lpm m Possible selections: NM12 and NM25/20 35 Example 6.1 (2) Select NM12: Trim Diameter to 198 mm 36 Example 6.1 (3) Select NM12: Trim Diameter to 198 mm Pump has efficiency of 49.5% Power consumption 3.2 kW Max power consumption 4kW Select Motor size: 5.5kW Note: follow standard motor size 37 Example 6.1 (4) hpkW 1/ / / / / / hpkW 38 Example 6.1 (5) Dimension of NM12 39 Example 6.2 Back to example 5.3, if two identical pump of the following curve is installed, predict the operating point. 40 Example 6.2 (2) 23.1m.WG. = 21.6m.WG Variable with flow rate m. WG. Elevation Constant 41 Example 6.2 (3) 2 pumps in parallel Single pump 42 3. Pump Installation 43 Typical Installation 44 Suction Lift More suction lift = Less NPSHA Cavitation 5 Meter lift is the maximum possible value Foot Valve Submersible pump 45 Pumping from Tank Vortex prevention plate Drain Mak-up Vent Overflow 46 Eccentric Reducer INCORRECT CORRECT 47 Installation photos 48 Installation photos 49 Homework Exercise 6.1 and 6.2 50 Case Study