How To Repair Internal Leakage Of Roots Vacuum Pump Unit
Roots vacuum pumps are widely deployed in chemical, metallurgical, powder‑processing and other industrial sectors. Long‑term operation under dust‑laden steam or corrosive‑media conditions may trigger internal‑leakage failures. Different from external air leakage via flanges or housings, internal‑leakage faults are concealed and hard to detect in early phase. It continuously deteriorates vacuum indexes and pumping speed and brings unstable batch‑production quality. Drawing on overhaul‑service experience of domestic and overseas projects as a roots vacuum pump manufacturer, this article distinguishes internal‑leakage from external‑leakage, describes typical fault symptoms, step‑by‑step location methods, on‑site repair workflows for valve‑seat components, disposal solutions for multiple internal‑leakage causes, as well as maintenance safety rules, post‑repair acceptance criteria and regular preventive‑maintenance suggestions.
Distinguish Internal‑leakage And External‑leakage, Identify Typical Symptoms
Faced with insufficient vacuum performance, most operation‑maintenance staff check flange‑and‑pipeline external‑leakage first, ignoring gas back‑flow inside pump housing. Obvious differences exist between the two fault types.
‑ External‑leakage: Ambient air infiltrates from external points including pipelines, flanges and shaft seals. When the roots pump body is isolated, vacuum still drops rapidly in pressure‑hold test.
‑ Internal‑leakage: Mating failure of internal pump‑chamber components causes gas back‑flow between high‑pressure and low‑pressure cavities inside pump. When the roots pump is tested in isolated status, ultimate vacuum obviously fails to reach name‑plate specifications, and no leak points can be detected on all external sealing surfaces.
When internal‑leakage occurs, units usually deliver several warning signals:
Ultimate vacuum persistently fails process set‑points. Backing‑pump performs normally yet overall pumping speed decays sharply.
Under equal process load, pump‑housing temperature rises, vibration intensifies and power consumption per‑unit‑product increases.
For steam‑ or dust‑handling service, internal‑leakage accelerates corrosion and wear on rotors and pump‑chamber, and faults get progressively worse.
Recommended troubleshooting sequence: Complete full external‑leak inspection first. Disassemble pump body only after confirming no external‑leakage exists and faults are attributed to internal pump leakage.
Common Root‑causes Of Internal‑leakage
Internal‑leakage does not stem from single component failure. It mainly falls into three fault categories.
Damaged sealing‑surface of bypass / relief valve group (original‑document fault source)
Erosion by dust particles, medium corrosion and frequent opening‑closing impact produce pits, grooves and deformation on valve‑seat and valve‑core sealing surfaces. Valves cannot fully close and create internal gas return passage, which ranks as a frequent fault for aged equipment.
Excessive rotor‑related clearance
Foreign‑object impact, long‑time abrasion, thermal‑cycling deformation or phase offset of synchronizing‑gear enlarge gaps between rotor‑to‑rotor, rotor‑to‑housing and rotor‑to‑end‑cover, resulting in gas return flow via clearance gaps.
Failed static seal inside pump chamber
Aged or broken inner gaskets of end‑covers, bearing‑housings and partition plates lead to cross‑chamber gas cross‑leakage and further internal‑leakage.
Fault Location: Sectional Isolation Test Method
Prior to disassembly‑repair, perform sectional‑isolation tests to lock fault categories and reduce unnecessary disassembly work.
Close main process valve, isolate vacuum vessel and test ultimate vacuum of complete unit separately.
Disconnect inlet‑and‑outlet ports of roots pump and test performance of backing pump alone. If backing‑pump indexes are qualified, faults are located at roots main pump.
Before roots‑pump disassembly, manually turn coupling, feel rotor‑rotating resistance and check for jamming or friction noise to preliminarily judge rotor‑gap status.
Open pump‑end‑cover and visually inspect relief‑valve assemblies, check valve‑seat sealing‑surface for erosion, pits and deformation traces to judge whether faults belong to valve‑group‑caused internal‑leakage.
Some overseas factories lack professional machining resources. After fault location, evaluate whether to carry out on‑site repair or purchase replacement spare‑parts. Direct valve‑group replacement is recommended for heavily eroded valve‑seats instead of on‑site welding‑and‑grinding.
Complete On‑site Repair Workflow For Valve‑seat‑sealing‑surface Internal‑leakage
For valve‑seat‑valve‑core erosion‑deformation, on‑site repair can be performed with lathe, welding and grinding resources (original‑document repair process supplemented with safety and pre‑process requirements).
Pre‑repair Safety Requirements
Shut down complete unit, cut‑off motor power and implement lock‑out‑tag‑out. Fully depressurize pump chamber and purge residual process media inside.
Fully disassemble valve‑group components, take photos and mark parts to record assembly orientation and prevent mis‑assembly during reassembly.
Thoroughly clean all components to remove rust, dust and old welding‑slag.
Machining‑and‑welding Repair Procedures
Grind valve‑seat sealing‑surface with portable grinding‑machine to eliminate erosion pits and grooves and restore circular geometric precision.
Position original valve‑core shaft‑passing‑hole center by four‑jaw chuck on lathe and perform hole‑expanding machining to correct deformed hole position.
Keep shaft‑center unchanged, assemble valve‑core through‑shaft in‑place and complete spot‑welding fixation.
Carry out surfacing with D547 Mo hard‑alloy welding‑electrode. Bake welding‑electrode as‑specified, control overlay layers and thickness to reduce welding‑crack risk. Machine valve‑head sealing‑surface matched with grinded valve‑seat hole.
Trial‑assemble components and run red‑lead coloring sealing‑test, check sealing‑surface fitting rate to guarantee tight sealing‑pair closure.
Important note: This repair relies on lathe‑, welding‑ and grinding‑competence. Overseas sites without supporting machining capacity shall purchase complete replacement valve‑group spare‑parts directly. Forced on‑site surfacing‑repair easily causes re‑failure within short operating period.
Disposal Solutions For Other Two Kinds Of Internal‑leakage
Internal‑leakage Caused By Excessive Rotor‑clearance
Disassemble pump body, measure actual gaps of rotor‑to‑rotor, rotor‑to‑housing and rotor‑to‑end‑cover with feeler gauge and compare with factory technical‑specifications.
For rotors with scratches or abrasion, polish or replace rotor parts subject‑to‑damage‑severity.
Recalibrate synchronizing‑gear phase, lock locating‑pin and adjust all clearances back to factory‑standard range.
After assembly, manually turn coupling to confirm smooth rotor rotation without friction or jamming.
Internal‑leakage Triggered By Failed Inner‑gasket Static‑seal
Disassemble corresponding end‑cover and bearing‑housing assemblies and remove all old gaskets. Clean seal‑grooves and mating‑surfaces and clear rust and residual‑adhesive.
Re‑select gasket material matching process‑medium for corrosion‑resistance and temperature‑resistance.
Tighten bolts evenly in diagonal multi‑pass sequence to avoid local insufficient compression which brings repeated cross‑chamber leakage.
Acceptance‑verification Work After Repair
Never put unit into process‑production directly after assembly‑repair. Complete three‑level validation to avoid re‑work.
Manual‑turning inspection: Manually rotate coupling. Rotor shall turn smoothly without friction or jamming throughout full‑cycle rotation.
No‑load single‑unit pressure‑hold test: Isolate external‑process‑system, run vacuum‑extraction and pressure‑hold test for roots‑host alone. Record pressure‑rise rate, confirm internal gas‑back‑flow is restrained and ultimate vacuum returns to design‑specifications.
Loaded trial‑run: Connect backing‑pump and run loaded test simulating real‑world working‑conditions. Record motor current, pump‑housing temperature‑rise and vacuum readings. All parameters shall fall within factory‑reference range.
If pressure still rises rapidly in pressure‑hold test, re‑open end‑cover and re‑check sealing‑surface fitting status and gap values instead of forced commissioning.
Routine Maintenance To Reduce Internal‑leakage Risks
Most internal‑leakage comes from medium erosion, over‑differential‑pressure operation and insufficient filtration. Component‑damage can be delayed via regular maintenance.
‑ Install intake‑side dust‑removal filters. Hard‑particle ingress into pump‑chamber acts as main inducement for erosion‑wear of valve‑seats and rotors. Inspect and replace filter cartridges periodically.
‑ Strictly follow differential‑protection‑settings. Prohibit long‑time over‑differential‑pressure operation of roots pump. Avoid sharp frequent working‑condition fluctuation and mitigate thermal‑cycling impact on components.
‑ Build parameter‑inspection log‑sheets. Record ultimate vacuum, motor current and pump‑housing temperature regularly. Stop unit for troubleshooting at early parameter‑degradation instead of waiting for full‑scale faults.
‑ For steam‑laden or corrosive‑gas processes, deploy front‑end condensation and neutralization pre‑treatment to lower erosion‑corrosion impact on internal metal‑components.
From the perspective of vacuum pump total cost of ownership, proper front‑end medium‑pre‑treatment plus periodic inspection greatly reduce pump‑housing overhaul frequency and avoid heavy loss from unplanned production‑shutdown.
Conclusion
Roots‑pump internal leakage shows little visible external damage and only brings gradual vacuum‑performance drop. Do not disassemble the pump blindly; locate faults via leakage check and sectional tests first. Choose repair or part replacement according to on‑site machining conditions and complete turning, pressure‑hold and loaded‑test acceptance. Dust‑and‑steam‑caused erosion cannot be fully eliminated, yet filter maintenance and pressure‑monitoring reduce inner‑part wear. Maintenance teams shall track vacuum data in daily checks to eliminate hidden risks and avoid unexpected shutdowns.
