Effect Of Unbalance On Performance Of Centrifugal Pump

Transcription

1 Effect Of Unbalance On Performance Of Centrifugal Pump Sanjay Taneja Abtract: Hydraulic Machine of ome kind are ued in nearly every apect of our daily live; from the pump and machine we ue at home, to the indutrial machinery ued to manufacture, material handling nearly every product we ue on a daily bai. When a machine fail or break down, the conequence can range from annoyance to financial diater, or peronal injury and poible loe of life. For thi reaon, the early detection, identification and correction of machinery problem i paramount to anyone involved in the maintenance of indutrial machinery to inure continued, afe and productive operation..of coure, it natural for machine to vibrate. Even machine in the bet of operating condition will have ome vibration becaue of mall, minor defect. Therefore, each machine will have a level of vibration that may be regarded a normal or inherent. However, when machinery vibration increae or become exceive, ome mechanical trouble i uually the reaon. Vibration doe not increae or become exceive for no reaon at all. Something caue it - unbalance, mialignment, worn gear or bearing, looene, etc. Thi paper focue on the machinery (Centrifugal pump) vibration due to unbalance and the technological effect on it performance. Thi tudy i done to evaluate the performance of the centrifugal pump on different unbalance mae. Some time thee tudie are quite helpful in order to equip better deign of pump o that there hould be minimum effect on it performance due to unbalance. Keyword: vibration, eccentricity, mialignment, hydraulic machine, impeller, reonance, tatic unbalance Abbreviation: ltr-liter, hr-hour, pr-preure 1- INTRODUCTION It i neceary to be intereted in vibration in centrifugal pump becaue it ha a major effect on the performance. Generally, increaing vibration level indicate a premature failure, which alway mean that the equipment ha tarted to detroy itelf. It i o becaue exceive vibration are the outcome of ome ytem malfunction. It i expected that all pump will vibrate due to repone from excitation force, uch a reidual rotor unbalance, turbulent liquid flow, preure pulation, cavitation, and/or pump wear, improper foundation. The magnitude of the vibration will be amplified if the vibration frequency approache the reonant frequency of a major pump, foundation and/or piping component. Generally higher vibration level (amplitude) are indicative of fault developing in mechanical equipment. The ource of vibration in centrifugal pump can be categorized into three type Mechanical caue, Hydraulic caue & Peripheral caue. 1- Mechanical Caue of Vibration The mechanical caue of vibration include Unbalanced rotating component, Damaged impeller and non concentric haft leeve Bent or warped haft Pump and driver mialignment, Pipe train (either by deign or a a reult of thermal growth), Inadequacy of foundation or poorly deigned foundation Thermal growth of variou component, epecially haft, Rubbing part Worn or looe bearing, Looe part, Looely held holding down bolt Damaged part. 2- Hydraulic Caue of Vibration The hydraulic caue of vibration include Operating pump at other than bet efficiency point (BEP) Vaporization of the product Impeller vane running too cloe to the pump cutwater Internal recirculation Air entrapment into the ytem through vortexing etc. Turbulence in the ytem (non laminar flow), Water hammer. Sanjay Taneja Aociate Profeor, Manav Rachana College of Engg. Faridabad, MobL [email protected] 3- Peripheral Caue of Vibration The peripheral caue of vibration include Harmonic vibration from nearby equipment or driver. Operating the pump at a critical peed Temporary eizing of eal face (thi can occur if you are pumping a non lubricating fluid Impeller vane running too cloe to the pump cutwater 56

2 Internal recirculation Air entrapment into the ytem through vortexing etc. Turbulence in the ytem (non laminar flow), Water hammer. 2-LITERATURE SURVEY Pump component and rotor unbalance have been crutinized in recent year by both uer and manufacturer. While it may appear that more retrictive (lower) unbalance level may automatically reult in lower vibration and longer machine life. Nelik and Jackon (1995) indicated uch wa not the cae but their reearch howed that hydraulic unbalance contribute much more ignificantly to vibration than mechanical unbalance. ISO 1940/1 (1986) pecifie balancing quality grade (G level) for variou type of rotating equipment. For pump general recommendation i G-6.3 but ome uer and manufacturer pecify G-2.5 for better performance of fan in pump. and will vary with the load even at contant peed. In the horizontal direction, a phae hift of 90 will be oberved. 3.3 Bent Shaft When a bent haft i encountered with a pump, the vibration in the radial a well a in the axial direction will be high. Axial vibration may be higher than the radial vibration. The pectrum will normally have 1 and 2 component, a hown in Figure 2. If the: Amplitude of 1 rpm i dominant, then the bend i near the haft centre Amplitude of 2 rpm i dominant, then the bend i near the haft end. The phae will be 180 apart in the axial direction and in the radial direction. Thi mean that when the probe i moved from vertical plane to horizontal plane, there will be no change in the phae reading. Fig2 3-EFFECT OF UNBALANCE In thi paper covering iue i only unbalance effect on the performance of pump out of all mechanical caue explained above. Although it i eential to dicu all mechanical caue to get ome poitive concluion. 3.1 Unbalance Vibration caued by ma imbalance in rotating machinery i an important engineering problem. The objective of balancing i to reduce rotor vibration to a practical minimum. Reducing rotor vibration generally increae the ervice life of the rotating machinery. The fundamental difference between a centrifugal ewage pump impeller and thoe of it clear water couin i it ability to pa olid material that would normally clod later. Due to the unbalance in the impeller, vibration occur and lead to decreae in fluid velocity and local preure which may caue an undeirable turbulence and poible cavitation. Hence, to remove the unbalance in rotor i neceary. Fig Eccentricity Eccentricity occur when the centre of rotation i at an offet from the geometric centerline, and thi may happen if the pump impeller i eccentric due to a manufacturing or aembly error. In the vibration pectrum, the maximum amplitude occur at 1 rpm of the eccentric component, 3.4- Pump and motor mialignment There are baically two type of mialignment that can occur between the motor and the pump: Angular mialignment the haft centerline of the two haft meet at angle Parallel mialignment the haft centerline of the two machine are parallel A hown in Figure 3, angular mialignment primarily ubject the motor and pump haft to axial vibration at the 1 rpm frequency. A pure angular mialignment i rare, and thu, mialignment i rarely een jut a 1 rpm peak. Typically, there will be high axial vibration with both 1 and 2 rpm. However, it i not unuual for 1, 2 or 3 to dominate. Thee ymptom may alo indicate coupling problem (e.g. looene) a well. A 180 phae difference will be oberved when meauring the axial phae on the bearing acro the coupling, a hown in Figure 3.Parallel mialignment reult in two hit per rotation; and, therefore a 2 rpm vibration in the radial direction. Parallel mialignment ha imilar vibration ymptom compared to angular mialignment, but how high radial vibration that approache a 180 phae difference acro the coupling. A before, a pure parallel mialignment i rare and i commonly oberved to be in conjunction with angular mialignment. Thu, both the 1 and 2 peak will typically be oberved. When the parallel mialignment i predominant, 2 i often larger than 1, but it amplitude relative to 1 may often be dictated by the coupling type. When either angular or parallel mialignment become evere, it can generate high amplitude peak at much 57

3 higher harmonic (3 to 8 ) or even a whole erie of high frequency harmonic. reciprocating force can often generate vibration at frequencie of 2x, 3x and ometime higher multiple of RPM. Fig-3 4- SIGNIFICANCE OF VIBRATION FREQUENCY To illutrate the importance of vibration frequency, aume that a machine, coniting of a fan operating at 2400 RPM and belt driven by a motor operating at 3600 RPM, i vibrating exceively at a meaured frequency of 2400 CPM (1 x fan RPM), thi clearly indicate that the fan i the ource of the vibration and not the motor or belt. Knowing thi imple fact ha eliminated literally hundred of other poible caue of vibration. Typical 1 x RPM vibration can be attributed to: Unbalance Eccentric Pulley Mialignment Bent haft Looene Ditortion - oft feet or piping train Bad Belt - if belt RPM Reonance Reciprocating force Electrical problem Determining that the frequency of exceive vibration i 2400 CPM (1 x fan RPM) ha reduced the number of poible caue from literally hundred to only ten (10) poible caue. A little common ene can reduce thi number of poible caue even further. Firt, ince the vibration frequency i not related to the rotating peed (RPM) of the drive belt, belt problem can be eliminated a a poible caue. Secondly, ince thi i not a reciprocating machine uch a reciprocating compreor or engine, the poibility of reciprocating force can be eliminated from the remaining lit. Finally, ince the frequency i not related to the drive motor in any way, the poibility of electrical problem can be eliminated. Now, the number of poible caue of exceive vibration ha been reduced to only even (7) by imply knowing that the vibration frequency i 1 x RPM of the fan. Vibration analyi i truly a proce of elimination. Additional tet and meaurement can be taken to further reduce the number of poible caue of a vibration problem. However, it hould be obviou that knowing the frequency of vibration and how the frequency relate to the rotating peed of the machine component i truly the firt tep in the analyi proce. Of coure, not all machinery problem will generate vibration at a frequency equal to the rotating peed (1x RPM) of the machine. Some problem uch a looene, mialignment, reonance and 5-OBSERVATIONS Experimental rig i hown in figure 4. Initially Obervation are taken in normal condition and Final obervation are taken after introducing unbalance on fan of a centrifugal pump. Experimental et up include Make-Crompton greave Self priming moonet pump (Made in India) Kw/hp-0.37/0.5 Voltage-220±6% Speed-2780 rpm Current-2.8 amp Capacitor-10µF,440V Type-Mini win-п Size-25x25 mm Duty-S1 Head-6/28.5m Dicharge-2600/570 lph 1 phae-ac-50hz Inulation B cla Specification of preure gauge Vacuum gauge mm Delivery gauge-0-7 kg/cm² Temperature degree centigrade Collection of water i meaured by beaker of capacity 2000ml. Time i taken by top watch Initial obervation Temperature of water= 29.5 degree centigrade Table-1 S.N RP O. M SUCTIO N PR. in mm of hg 130 mm 130 mm DELIVE RY PR. in kg/cm² DISCHA RGE ltr in econd ltr in econd DISCHA RGE PER minute ltr ltr Average of and come ltr per minute Dicharge per hour will be x60= ltr. 58

4 Fig-4 on previou page (7) how experimental rig. Fig-5 (unbalance weight on fan of pump) 59

5 Obervation after introducing unbalanced ma on fan ide of centrifugal pump S. N O RP M UNBA LANC ED MAS S SUCTI ON PR. IN mm 5 gm gm gm DELIV ERY PR. IN kg/cm² DISCH ARGE ltr in econd ltr in econd 6870 ltr in14.56 econd DISCH ARGE PER minute ltr ltr ltr Dicharge in firt cae (5 gm unbalance)=29.51x60= ltr per hour Ditance of unbalanced weight from centre of pump=5.2 cm (Unbalance in gm cm=26) Dicharge in econd cae (10 gm unbalance)=28.79x60= ltr per hour (Unbalance in gm cm=52) Dicharge in third cae (20 gm unbalance)=x60= ltr per hour (Unbalance in gm cm=104) 6-CONCLUSION AND FUTURE SCOPE Hydraulic power i proportional to multiplication of dicharge and head, it mean if by introducing unbalance on the machine any of thee parameter increae by any no of time, power will alo be decreaed by that no of time. P α Q H P=POWER Q=DISCHARGE H=HEAD It i clear that after introducing unbalance there i almot negligible effect on uction and delivery preure head but Effect on dicharge i quite ignificant. Actual dicharge of pump i 1787 ltr per hour. After introducing unbalance there i a coniderable reduction in Dicharge and in cae of 20 gm unbalance it come 1698 ltr per hour. It mean dicharge i reduced by 90 ltr in one hour which i a quite ignificant. It clearly how power of pump will be reduced by 5%. 5.1 Future cope: Everything that rotate need to be in a tate of balance to enure mooth running when in operation. Preciion balancing i eential to the manufacture of rotating equipment and to the repair and renovation of intalled machine. A machine peed increae, the effect of unbalance become more detrimental. Modern technology allow for accurate balancing to be performed both in the field and in the workhop. Further area of thi tudy can be extended for analyzing the effect of unbalance on everal type of hydraulic machine of different nature uch a machine of different application in hydro power generation and rotating part a mixer, grinder, axle in automobile etc. It will alo be immenely helpful in the area of increaing life of critical machine uch a power generation machine (turbine and other moving part), dental drill, hydro machine, turbo charger etc. Sometime thee analyi are alo providing important tip for changing the deign Of pecific machine.(uch a changing the bearing poition inide the houing) to minimize the effect of unbalance. Now it can be undertood by thi analyi that there i a ignificant impact of unbalance on performance of a hydraulic machine(pump) o ometime it i eential to equip/modify deign in uch a way o that better performance can be achieved by keeping minimum unbalance.(with in leer quality grade) REFERENCES [1]. Shiyu Zhou and Jianjun Shi, Active Balancing and Vibration Control of Rotating Machinery: A Survey, The Shock and Vibration Diget, July 2001, Vol. 33, No. 4, [2]. Ing. G. Manni, Balancing Theory and Application, CEMB S.p.A. Via Riogimento, Augut 1999, Rev [3]. Val S. Lobanoff & Robert R. Ro, Centrifugal Pump deign and application, Jaico publihing houe 2 nd edition [4]. Igor J Karaik & Ray Cartor, Centrifugal pump, Tata McGraw Hill Book company- 2 nd Edition, [5]. Paul R. Donavin, J. J. Patel, Herbert L. Miller & Curti G. Sterud Feed pump dicharge line vibration olved at Byron tation unit 2 preented at the American Power Conference, Chicago, Illinoi; April 13 15, [6]. Entek IRD International Introduction to vibration technology Edition I, Jul 1984, Tata McGraw hill [7]. INTRODUCTION TO VIBRATION TECHNOLOGY Denni H. Shreve Director of Marketing IRD Mech analyi, Inc. Columbu, Ohio November 1994 [8]. Corneliu Scheffer Pump Condition Monitoring Through Vibration Analyi Pump: Maintenance, Deign, and Reliability Conference, [9]. Paper Ref: S1163_P0437, 3 rd International Conference on Integrity, Reliability and Failure, Porto/Portugal, July 2009 [10]. VIBRATION AND NOISE IN CENTRIFUGAL PUMPS - SOURCES AND DIAGNOSIS METHODS Ravindra Birajdar [1], Rajahri Patil [2], Kedar Khanzode [3] Kirlokar Brother Ltd., India 60