Vacuum Pumps Common Problems and Troubleshooting

Transcription

1 Vacuum Pumps Cmmn Prblems and Trubleshting Vacuum pumps and systems are ne f the widely used equipment in prcess plants. It is very imprtant t crrectly size and select the vacuum pump as it is t lay dwn the right specificatins. Understanding the fundamentals f vacuum as well as the system and its integratin wuld enable the peratrs t deal with the day t day prblems, which are inevitable. This article highlights varius truble shting guidelines fr sme f the mst cmmnly used vacuum machines like liquid ring vacuum pumps, rtary pistn vacuum pumps, dry vacuum pump, rtary vane vacuum pump and vacuum blwer. Several factrs gvern and influence the perfrmance f a vacuum system. It is imprtant t peridically inspect the vacuum system and all its accessries including the upstream and dwnstream piping and equipment fr leakages as it plays a majr rle in the perfrmance f a vacuum system. Sme f the cmmn prblems faced in vacuum systems culd be n accunt f the fllwing majr factrs: Prcess cnditins and variatins Variatin in utility specs Equipment malfunctin The suctin lad, temperature, leakage rate and ther prcess parameters including the cmpsitin f suctin gas are crucial fr prper functining f a vacuum system. These parameters can be estimated as per the standards f the Heat Exchange Institute and ther standards. These standards can als be applied fr testing the perfrmance f the vacuum system. Once the external step is t evaluate and slve the prblems assciated with the vacuum unit. Sme f the mst cmmnly bserved prblems in different kinds f vacuum pumps alng with suitable truble-shting guidelines are discussed in this article. Liquid Ring Vacuum Pump High Hrsepwer Causes f high hrsepwer can be varius. Cmparing actual data with perfrmance curve is the best starting pint. Prbable causes are: V-belt misalignment and imprper tensining f the belts. Pump is severely verladed with water. Restrictin at the pump inlet r pump discharge Mtr prblem Pump running at a speed abve the required speed. Leakage If the seal water is leaking frm the pump, a careful bservatin f the exact lcatin f the leak and the quantity f the leakage shuld be carried ut. Mst likely areas f leakage are: Gland packing area - It can be reslved by tightening the packing and if leak still persists, replace the packing. Leakage at bdy gasket Trque the bdy blts evenly, if leak des nt stp, then replace the bdy gasket. Leakage at the bdy plugs Tighten the plugs. If leak still persists, check fr crrsin n plug threads and bdy threads. Replace plug if crrsin is severe. Leakage thrugh castings Causes can be ersin, crrsin r insertin f a hard bject int the pump.

2 Nisy Pump Operatin Nisy pump peratin culd be due t: Freign bject trapped int the pump This is a very serius case and is usually accmpanied by erratic nise and vibratin. Pump severely verladed with water Causes graning and hydraulic nise. Cavitatins Sunds like marbles in the pump. Bearing nise Pssibility f bearing failure. Lts f carryver t the pump This is accmpanied by high hrsepwer. Vacuum Prblems Culd be due t: Vacuum surges Surging is ften caused by carryver frm separatrs, r frm lw pints in the line that accumulate water that burp ver peridically int the pump. Lk fr piping prblem in the inlet line. Restrictin in the pump inlet piping This culd be due t clsed r partially clsed valves, bject in the line, plugged inlet screen, etc. This restrictin will cause pressure drp that gives lw vacuum in the system and a higher vacuum in the pump. Check fr crrect seal water flw Excessive r inadequate seal water flw will adversely affect vacuum level. Variatin in seal water temperature If temperature f the seal water is t high, the pump may perate at a reduced capacity. The higher the vacuum level, the mre imprtant it is t have cl water in sufficient quantities. Variatin in pump rpm If rpm is lw, pump will run at a lwer capacity. Check mtr and V- belt. System leaks Surces f leaks can include pen drain valves, blwn gaskets, lse flanges, prly packed valves, inadequate barmetric drp legs n separatr, brken pipes etc. Higher leakage will result in lwer vacuum. Warn pump This is indicated if vacuum lss has been gradual ver a perid f time. Check t see if any befre the vacuum prblem surfaced. Vibratin Prblems Vibratin prblems culd smetimes be due t system prblems but at times culd als be related directly t the pump. They can be bradly classified int tw categries, namely intermittent and cntinuus. Intermittent vibratin Check fr liquid slugs r carry-ver frm separatr. Check fr lw pckets in inlet piping where liquid can accumulate and burp ver int the vacuum pump at irregular intervals. Check fr irregular surces f vibratin riginating. Piping r separatrs can be the surce f vibratin if they are nt prperly secured in place r supprted. Cntinuus chrnic Vibratin Lk fr cnstant carryver and / r excessive seal water t the pump. Lk at discharge piping r level indicatr t be sure that the pump is nt perated when in flded cnditin. Check cupling r V-belt alignment and tensining. Make sure pump is nt started against blank suctin subjecting it t immediate high vacuum. This des nt allw the ring t frm prperly. If the unit is gear driven, make sure vibratins are nt frm gear itself. Check pump munting and alignment. Lse feet, imprper shimming, resnating bases and imprper gruting can set up unwanted vibratins. Check bearings and lubricatin and replace failed bearings. Check the inlet piping fr vibratins. Check pump fr excessive wear.

3 Rtary Pistn Vacuum Pump Excessively High System/Pump Ultimate Pressure This culd be due t: Faulty prcess equipment faulty r imprper functining f the vacuum pump Check pump perfrmance. Prcess equipment cntaminated by high vapr pressure material Clean equipment with acetne r alchl, r either Pump dwn with vacuum pump vernight. Prcess equipment leaks Check prcess equipment fr leaks. Imprper flw f vacuum pump il Clean il ducts. Cntaminatin f vacuum pump il Change pump il, Discharge valves malfunctining Check valves per Discharge Valves. Vacuum pump leaks Check pump fr leaks Vacuum pump shaft seal malfunctining check shaft seal Internal parts wrn r damaged Disassemble pump and inspect internal part. Oil flw blcked Clean il lines. Excessive Pump Nise at Lw Pressure Culd be due t: Hydraulic nise f pump discharge Open gas ballast valve. Pump Stalls Pump stalls culd lead t prductin lss. Prbable causes culd be: Electrical pwer lss Check pwer at pump. Pump malfunctining. Pump il cntaminated r pump is insufficiently lubricated. Pump discharge line blcked Clear pump discharge line, check il mist eliminatr element fr blckage. Pumps des nt Start Electrical failure Check fr pwer supply at pump Check mtr. Pump flded with il Clear il frm pump by turning ver manually r disassembling the pump. Excessively lw temperature Heat pump t recmmended minimum starting temperature. Oil Discharged frm Oil Mist Eliminatr Excess il n discharge side f il mist eliminatr Unscrew il mist eliminatr and pur il thrugh the discharge fitting back int the pump, r reduce pump inlet pressure belw certain set pressure t allw cllected il t drain back thrugh the integral check valve in t the il mist eliminatr. Dry Screw Vacuum Pump Insufficient Pumping Capacity Prbable causes: Suctin filter r strainer is clgged Clean r change it T much Clearance Check clearance Overlad n Electric Mtr Prbable causes: Freign matter culd be caught in the pump Adjust r replace the screw and casing Pressure lss in piping increases Check the pressure difference between inlet and utlet Interference between screws Adjust side clearance, clearance between screw and casing larger Discharge prt r line is clgged & back pressure is increased Drain and clean discharge prt and line

4 Overheat Overheating f the pump culd be due t: Excessive lubricant in frnt end cver check il level High temperature at vacuum pump inlet Reduce inlet temperature High cmpressin rati Check suctin and discharge pressure Interference between screw and casing Search fr the cause f interference Prblem with cling water flw Clean cling water line Discharge prt r line is clgged and back pressure is increased Drain and clean discharge prt and line Kncking Prbable causes: Incrrect psitining between timing gear and screw Repsitin the system. Imprper assembly Reassemble Damage n gear due t verlad r imprper lubricatin Replace timing gear Damaged Bearing r Gear Prbable causes: Imprper Lubricant Change Lubricant Lubricant level lw Refill lubricant Rtary Vane vacuum Pump Pump des nt start Cnnect the pump crrectly, if nt cnnected prperly Set mtr prtectin switch prperly, if incrrectly set If perating vltage des nt match with mtr, replace mtr Replace mtr if mtr is malfunctining If il temperature is blw 12 C, Heat the pump r pump il r use different grade f il If il is t vicius Use apprpriated il grade Exhaust filter / exhaust line is clgged, replace filter r clean exhaust line Pump des nt Reach Ultimate Pressure Gauge is unsuitable Use crrect gauge External leak pipe fittings may be lse. Check and tighten all fittings Flat valve des nt clse Repair the valve Inadequate lubricatin due t unsuitable r cntaminated il clgged il filter r clgged il lines Change il replace filters r clean Oil line ad casing. Vacuum lines are dirty Clean vacuum lines Pump capacity is t lw Check required pump capacity, and replace the pump if necessary Pumping Speed is t Lw Dirt trap in the intake prt is clgged Clean the dirt-trap. Make sure that dust filter is installed in the intake line. Exhaust filter is clgged Install new filter elements Cnnecting lines are t narrw r t lng Use adequately wide and shrt cnnecting lines Anti-suck back valve is hard t pen Check spring fr free length. After Switching ff Pump under Vacuum, Pressure in System Rises t Fast System has a leak and shuld be checked Malfunctining f the anti-suck back valve Repair the valve. Vacuum Bsters Kncking r Rapping Unit ut f time due t wrn bearings r gears Replace wrn parts.

5 Rtrs tuching each ther due t excessive temperature Reduce temperatures by lwering differential pressure. Excessive Operating Temperatures Pressure differential t high Reduce pressure acrss bster by lwering cut in pressure. Als check blank-ff pressure f fre pump and system fr leaks Lack f Vlume Wrn clearances Re-establish clearance Reduce speed Check mtr Abnrmal Bearing and Gear Wear Lss f Oil Cnclusin Inadequate lubricatin Maintain crrect il levels, imprve frequencies f il change and initiate il sampling prgram Wrn seals Replace seals A step-by-step prcedure, adpted in trubleshting vacuum pump and / r system helps in easily lcating the prblem and in finding apprpriate slutin. In general, the first step is t cmpare the riginal design cnditins with the existing cnditins. Any change in design cnditins including utilities may have a direct impact n the perfrmance f the unit. Once it is ascertained that external factrs are nt respnsible fr malfunctining f vacuum system, truble shting f equipment shuld be dne. Reference Bk: Chemical Industry Digest Vlume- XX.9 September, 2007