Allweiler Pump
Spare Parts Requests
Three-screw SN & SNS · progressive cavity · centrifugal units
The Allweiler machines behind most engine-room enquiries
Allweiler builds pumps in Radolfzell, Germany, and is part of CIRCOR, which now publishes the Allweiler product pages and manuals; its marine range reaches ships mainly through three working principles: rotary three-screw pumps for oil duty, eccentric-screw (progressive cavity) units for thick or solids-laden fluid, and standardised centrifugal units for water and general transfer. Each principle wears differently, so each needs different evidence in the request. Series letters describe the build, not the duty: the same series appears on fuel supply, booster, lube oil and hydraulic service, and only the full type designation identifies which execution is in front of you.
SN series — three-screw, fuel and lube oil duty
One driving spindle meshing with two idler spindles, hardened and running in a replaceable liner. Allweiler now presents SN together with SM as one modular system — horizontal or vertical, baseplate- or flange-mounted, built round the same pumping elements — and lists SM for thinner oils than SN. Seen on heavy fuel supply and circulating duty and equally on lube oil service, since the pumped oil is also the film that carries the idlers.
ALLFUEL series — three-screw pumps for marine fuel systems
Allweiler offers ALLFUEL for transfer, booster and burner duty in marine fuel systems and states that it stays efficient on low-viscosity, low-sulphur MGO. The letters on the plate show the build: AFI carries a SiC/SiC mechanical seal, AFM a magnetic coupling, and the -F and -T executions add a filter as a single or twin unit built round a one-piece insert. Seal, filter and insert parts follow those letters, so quote the designation exactly as stamped.
Transfer and bunkering duty
Larger screw frame sizes handle fuel transfer between tanks and bunker lines — high delivered volume at modest differential pressure. Pressure capability comes from the number of sealing chambers along the spindle, so on these frames it is the condition of the flanks and the bore, rather than the driver rating, that decides whether rated capacity is still reached.
Single-helix rotor in a double-helix stator
Allweiler's progressing cavity pumps come as AE (bearing frame) and AEB (block, motor flanged to the pump); the marine catalogue lists them as AE.N and AEB.N. The rotor turns inside an elastomer stator and is driven through a jointed drive shaft. The stator carries twice the rotor pitch and one lobe more, which is what forms the sealed cavities that travel along the axis. The stator is the consumable — and its compound, not the pump size, sets the replacement interval.
Standardised single-stage units
Allweiler builds its NT (bearing bracket) and NB (block) pumps to DIN EN 733 dimensions and rates the NISM in-line pump to the same standard; NI is the in-line block version. Dimensions to a standard do not make the internal parts common, so impeller, wear rings and seal are still matched to the Allweiler type code. The marine-specific centrifugals are sold as ALLMARINE — the MA and MI series, NAM and NIM, NAM-F for fire fighting and the tank-mounted MELO for lube oil — on ballast, bilge, fire-fighting, lube oil and cooling-water duty. State the type code and the actual impeller diameter — these pumps leave the works with the impeller machined down to the ordered duty point, so the trim is not recoverable from the model name.
Pump, coupling and driver on a baseplate
Many shipboard installations are supplied as a mounted set. Coupling elements, guards, baseplate hardware and the driver identity are worth listing separately, since a vibration complaint is often a coupling or alignment matter rather than a pump matter.
Where a three-screw pump quietly loses its pressure
In a three-screw pump the two idler spindles are not gear-driven, and they are not driven through the flanks by the power spindle either. The idlers are rotated by the pressure differential of the pumped liquid acting across their helices, and are held centred in their bores by a hydrodynamic film of that same liquid. They act as rotating seals rather than as power-transmitting members — which is why flank contact loading is low, and why the loss of the fluid film is the failure that matters. That single design fact explains most of the failures seen on board. When the film thins, metal comes closer to metal, and the sealing line formed by the meshing flanks and the housing bore stops holding differential pressure.
The usual trigger on modern ships is fuel. A pump sized and built for heated residual fuel at a given viscosity is then run on low-sulphur distillate at a fraction of that viscosity, sometimes hot from a mistuned viscosity controller. Slip across the sealing line rises immediately; scuffing of the spindle flanks and polishing or scoring of the bore follow over the weeks after. Delivered capacity falls at unchanged speed as slip rises, and once the pump can no longer meet demand this shows on board as falling pressure at the consumers; the pump also becomes noisier, and the relief valve — set for the original duty — starts to influence the delivery it was never meant to regulate.
The second common trigger is what the pump swallows. Weld spatter, tank scale, catalyst fines carried past a bypassed strainer or water slugs after a tank change all mark the flanks and the bore. Because the parts are so closely fitted, a scratch is a leakage path, not cosmetic damage. The third is thermal: a mechanical seal chosen for a given face pairing and elastomer will coke and weep if the pump sits hot and static, and a gland-packed older unit will score its shaft sleeve if the packing is over-tightened to stop a weep.
Diagnosis matters before ordering, because two very different faults read the same on a gauge. A worn relief valve seat recirculates internally and drops delivery pressure exactly as worn spindles do. Checking and, if needed, renewing the valve cone, seat and spring is far less involved than opening the pump for a rotating set. For that spring, the compression spring calculator gives the rate and the load at the fitted length from the wire diameter, the outside diameter and the coils, for the old spring and the new one alike. Journal bushes on the idler spindles of larger frames, and the bearings locating the drive spindle, give their own signature: knocking, axial movement of the shaft end, or metal in the drained oil. Axial thrust in these pumps is balanced hydraulically rather than carried by the bearing, so a worn balancing bush shows up as axial float at the shaft end and takes the locating bearing with it.
Allweiler pump components that appear on RFQ lines
The groups below follow the order of an Allweiler sectional drawing — rotating set, housing and bore, sealing arrangement, bearings, relief valve — so each RFQ line can carry the drawing item number beside the description.
- Matched spindle sets — drive spindle plus two idlers
- Housing bore liners & insert bushings
- Housing bodies with integral bore, and covers carrying the relief-valve seat
- Balancing pistons and balancing bushes
- Pressure-relief valve cones, seats & springs
- Mechanical seals — component and cartridge type
- Gland packing sets & shaft sleeves on older units
- Drive-spindle bearings — internal and lubricated by the pumped fluid, or external and grease-lubricated, depending on execution
- Journal bearing bushes for idler spindles
- Bearing covers, circlips, shims & lock nuts
- Eccentric-screw stators — standard NBR (Perbunan), Allweiler's ALLDUR compound for abrasive media, or another elastomer chosen for the fluid
- Eccentric-screw rotors & joint assemblies
- Joint pins, sleeves & retaining bands
- Centrifugal impellers, wear rings & shaft sleeves
- Housing-cover joints, shaft-seal O-rings & relief-valve bonnet gaskets
- Flexible coupling elements and lantern housings for baseplate-mounted sets
The stator of an Allweiler progressing cavity pump as a spare part
On an AE or AEB eccentric-screw pump the rotor is the metal helix that turns, and the stator is the elastomer body it turns in; the sealed cavities that carry the liquid exist only while the rubber still grips the rotor. That is why the stator, not the pump, is what wears out and gets ordered.
Three things end a stator's life. Abrasive content in sludge or bilge water wears the elastomer away, so slip rises and delivered capacity falls at the same speed. Running without liquid on the suction side generates friction heat that scorches and tears the rubber, and a stator damaged that way cannot be repaired, only replaced. A compound that does not suit the pumped liquid swells or shrinks, either tightening its grip on the rotor or opening the fit. Each cause points to a different answer: the same compound again, a harder-wearing one, or a different elastomer altogether.
The rotor is judged at the same time. A new stator fitted over a rotor with scoring, pitting or a damaged surface wears out early, so the request should say whether the rotor is being renewed with it or has been inspected and kept.
- Full type designation from the plate, including the size and every letter after it
- Pump number and year of manufacture
- Elastomer marking on the old stator, or the compound named in the original order papers
- Pumped liquid, its temperature, and whether it carries sand, scale or sludge
- Photographs of the rotor surface and of both stator ends
- Whether the rotor, the joint parts and the shaft seal are needed on the same order
Centrifugal pump — general arrangement
A licensed photograph of Allweiler equipment was not available at publication, so this technical reference illustrates the general arrangement shared by this equipment class.
Illustrative technical reference, not a photograph of Allweiler equipment or a Vessel Core installed reference — a licensed photo of this maker's equipment was not available. Vessel Core has no dealership, distribution or partnership agreement with Allweiler; it operates as an independent spare parts supplier.
Turning an SN designation into a quotable line
An Allweiler type designation is a compressed build specification, not just a name. The series letters are followed by a size and then suffix characters; in the type-code key Allweiler publishes for its ALLFUEL three-screw pumps, those characters give the spindle pitch direction and pitch angle, the bearing type, the shaft seal, the material version and the installation type. Two pumps sharing the same size can take different spindle sets because they were built with a different pitch for a different viscosity band, so the full string matters — every letter and digit of it.
- Complete type designation with all suffix characters
- Pump number and year of manufacture from the Allweiler nameplate, photographed square-on — plus the identification number or QR code on the separate digital nameplate that newer pumps such as ALLFUEL carry
- Flow rate and motor speed as stamped on the plate
- Discharge pressure and suction head as stamped on the plate
- Kinematic viscosity from the plate, and the design temperature where the data sheet gives it
- Pumped medium and its temperature in service
- Direction of rotation seen from the drive end, and whether the shaft is sealed by a mechanical seal, gland packing or a magnetic coupling
- Section-drawing item numbers from the pump manual
- Spindle flanks and housing bore photographed under raking light
- Stator elastomer marking on eccentric-screw units
Tools for this equipment: the end-suction pump size reader for the size on the plate, the mechanical seal material code for the seal faces, the flange identifier for the suction and discharge flanges, and the affinity laws calculator when a centrifugal pump runs on another supply frequency. For a seal built to EN 12756 dimensions, the mechanical seal size finder works from the shaft diameter or the measured installation length.
Matched components ask more of an enquiry than loose parts do.
Screw pump geometry is unforgiving in a way that a bearing or a gasket is not. The parts are finished against each other, so the request has to describe a set and a fit, not a shelf item. What follows is how those two facts — a rotating set finished as one, and idlers carried by the fluid rather than by gears — change the questions asked before any Allweiler item is quoted.
Spindles quoted as a set
Drive and idler spindles are treated as one line item unless the manual for that frame size says otherwise. Requests that name a single idler are queried back before any supplier outreach, because the answer changes both the specification and the outcome on board.
Viscosity band before pitch
Spindle pitch follows the viscosity the pump was built for. The medium, its service temperature and the viscosity figures on the plate are asked for early, since they decide which execution of a given nominal size is the right one.
Bore condition assessed with the set
New spindles running in a scored bore recover only part of the lost pressure. Where the housing carries a replaceable liner, that liner is put on the same enquiry; where the bore is machined into the casing, the choice between reconditioning and a new casing is raised openly.
Relief valve checked first
Because a worn valve seat and worn spindles look identical on a discharge gauge, the valve internals are raised as a separate, much smaller line before an assumption is made about the rotating parts.
Seal execution stated, not assumed
Face materials, elastomer grade and whether the pump carries a cartridge seal, a component seal, gland packing or a magnetic coupling are confirmed from the drawing or a photograph. On SN and SM pumps a return line connects the seal chamber to the suction side, so the seal works against suction pressure rather than discharge pressure. Hot standby service and distillate service point to different seal executions on the same pump.
Elastomer chosen against the fluid
On eccentric-screw units the stator compound decides service life. Sludge, waste oil, chemical dosing and hot water each argue for a different grade, so the fluid and temperature are confirmed before a stator is specified.
Allweiler pump enquiries — recurring questions
Can a single worn idler spindle be replaced on an Allweiler three-screw pump?
Normally not on its own. The drive spindle and the two idler spindles are finished and paired as a set, and the running clearance between the spindle flanks and the housing bore is what limits internal slip. Mixing a new idler with worn mating flanks usually restores neither the sealing line nor the hydraulic balance, so RFQs for screw pumps are quoted as a matched spindle set unless the pump manual states otherwise for that frame size.
What nameplate data is needed for an Allweiler SN pump enquiry?
The complete type designation including all suffix characters, the pump number and the year of manufacture, and the flow rate, discharge pressure, suction head, motor speed and kinematic viscosity shown on the plate — Allweiler's own manuals ask for pump type, pump number and year of manufacture with every spare-parts order. Direction of rotation and the pumped medium matter as well, because the same nominal size is built in more than one spindle pitch for different viscosity bands.
Why does an Allweiler fuel pump lose discharge pressure after a change to low-viscosity distillate?
The idler spindles in a three-screw pump are carried hydraulically by the pumped fluid rather than by gears. Thin, low-lubricity distillate reduces the film between the spindle flanks and the bore, so slip across the sealing line rises and flank or bore scuffing can begin. Delivered capacity falls at unchanged speed as slip rises, and once the pump can no longer meet demand this shows on board as falling pressure at the consumers; a worn relief-valve seat reads the same way on a gauge and should be checked before a spindle set is ordered.
Can Vessel Core identify Allweiler progressive cavity parts without a part number?
Often yes. For a progressive cavity unit the pump type designation, the serial number, the elastomer grade marked on the stator, the pumped medium and clear photographs of the rotor, joint assembly and stator ends are usually enough to begin identification. Section-drawing item numbers from the pump manual remove most of the remaining ambiguity.
How is the right stator identified for an Allweiler AE or AEB pump?
From the complete type designation on the plate, including the size, together with the pump number and the elastomer marking on the old stator. The compound matters as much as the size: a stator of the right geometry in the wrong elastomer can swell, shrink or wear early, so the pumped liquid and its temperature are stated on the same line. Photographs of both stator ends and of the rotor surface show whether the rotor should be renewed at the same time.
Why does a new stator on a progressing cavity pump fail early?
The usual causes are dry running, a compound that does not suit the pumped liquid, or a worn rotor left in place. Friction heat from running without liquid scorches the elastomer, an unsuitable compound swells or shrinks, and a scored or pitted rotor wears the new rubber from the first hours of service. Which of these applied decides whether the next order is the same stator, a different elastomer, or a stator and rotor together.
Is Vessel Core connected to Allweiler?
No, and there is no agreement of any kind. Vessel Core holds no dealership, distribution, representation or partnership agreement with Allweiler, and quoting a component against one of its designations implies no approval by the maker and no claim of interchangeability.
Send the nameplate and the measurements.
List the pump type designation, works number, medium and viscosity, the components required and the port. The spindle set, the relief-valve internals and the stator are then quoted as separate lines, so the ship can decide what to open now and what to carry as a running spare.
