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Blog · Sourcing guide · 2026-07-24

Marine lubricating oil system spare parts — a sourcing guide for purifiers, duplex filters, coolers and circulation pumps

A vessel's lubricating-oil system commonly includes purification or filtration, cooling and circulation equipment, with the arrangement varying by engine and vessel design. Those are four different worlds to buy from, and the thing that brings someone to this page is usually a symptom of the system rather than of a part. Water in the oil points at the cooler or the purifier; a rising differential across the filter points at the oil or at what is getting into it; a falling oil pressure points at the pump, at the relief valve or at a bearing that is now passing more oil than it did. Naming the symptom alongside the component turns one order into the right order, because the four groups fail in ways that look alike from the control room and nothing alike in the workshop. This guide covers frequently encountered OEM families across four recurring spare-part groups, the data needed to identify each component and the choice between an OEM route and a documented alternative. It does not quote lead times or prices — those depend on the specific unit, vessel schedule and confirmed supply route.

Which OEM families are common on commercial vessels

  • LO purifiers (centrifugal separators for lubricating oil) — Alfa Laval (S, MMPX, MOPX, LOPX, WHPX series), GEA Westfalia (OSD, OSE, OTC series), Mitsubishi (SJ series). See our separators sourcing guide for the full separator identity pattern — LO purifiers share the same bowl components, gravity discs and gasket kit logic.
  • Duplex and simplex filters — Boll & Kirch (Bollfilter automatic and manual duplex), Fleetguard (now Atmus Filtration Technologies, the former Cummins filtration business), Mahle, Hydac, Parker, Donaldson, Cim-Tek. Element codes follow each maker's own format and are printed on the element or its end cap; copy them in full as printed, because a shortened code can match more than one element.
  • LO coolers (plate and shell-and-tube heat exchangers) — Kelvion (including the former GEA Bloksma line), Alfa Laval, Blohm+Voss, Bowman, Serck Como, and coolers supplied with the engine (MAN B&W, Wärtsilä, MaK). On a shell-and-tube cooler the tube stack, tube-sheet gaskets and end covers are the main RFQ line items; on a plate cooler, the plates and the gasket set.
  • LO circulation pumps — Imo (three-screw pumps), Naniwa, Allweiler, Kral, Bornemann, Leistritz. See our pumps sourcing guide for the general pump identity pattern.
  • LO service valves and instrumentation — Klinger, Georg Fischer (GF), Sarco, Yarway. Pressure gauges: WIKA, Nuova Fima, Trerice.

LO purifiers — service kit and gravity disc identity

Service kits, seals and gravity discs recur in lubricating-oil purifier RFQs. One question comes before the parts list: is the machine set up as a purifier or as a clarifier? A lubricating-oil separator can be run either way, according to the separator and the engine maker's recommendation, and a conventional bowl is built for both, with different parts in each set-up. That decides whether a gravity disc is part of the conversation at all, and on an Alfa Laval ALCAP machine it never is, because that design has no gravity disc. Send the following:

  1. Purifier nameplate photo — with maker, model as stamped (for example an Alfa Laval MOPX 205, a GEA Westfalia OSD 18 or a Mitsubishi SJ-G Selfjector) and serial number; the full designation, suffix included, is what separates one bowl build from another.
  2. Service kit level — Alfa Laval sells Intermediate and Major service kits: the Major kit covers the bearings, seals and gaskets of the bottom part, and Alfa Laval notes that a major service also needs the Intermediate kits, so a Major overhaul is more than one kit on the order. Contents still depend on the model. Send the current kit reference or planned maintenance scope. The scope is the more useful of the two, because a kit reference carried forward from a previous order describes what was bought last time rather than what the machine is due for now.
  3. Gravity-disc inner diameter — send the current marking or measured dimension and note the oil specification and operating condition. Do not infer the disc from the separator family alone. On a conventional bowl set up as a clarifier the gravity disc is replaced by a clarifier disc that closes the water outlet; establishing which of the two is in the bowl before the line is written saves the whole exchange.
  4. Bowl and hood gasket set — separate line items from the main service kit on some models.
  5. Application — main engine LO, auxiliary engine LO, or cross-purpose (some vessels share a purifier stand across services).

Duplex filters — element identity and change-over valve wear

Filter elements in the LO line come in two main patterns: pleated paper / synthetic (for example Fleetguard or Mahle) and cleanable stainless steel wire mesh. The mesh pattern is what an automatic back-flushing filter carries, such as Bollfilter type 6.48 on four-stroke engines, and a duplex filter may sit after it, directly in front of the engine, as an indicator filter; say which of the two housings the elements are for. The two are a maintenance philosophy rather than a specification: a disposable element is consumed and reordered on a schedule, while a mesh candle is cleaned and returns to service until it is damaged, so a request for elements against a mesh housing usually means something has gone wrong with a candle rather than that a routine change is due. Whichever is fitted, the instrument that decides the job is the differential pressure across the filter, and quoting the differential the crew are seeing tells more about the order than the element code does. Send the following:

  • Filter maker and housing type as stamped on the housing plate (e.g. Bollfilter type 6.48 for the automatic filter, and the duplex filter's own type if one is fitted); a spin-on filter has no housing plate, and the number printed on the canister is its identity.
  • Element code and micron rating (10, 25, 50, 100 µm are common for LO service).
  • Whether the RFQ is for the element only, the O-ring / gasket set, or the change-over valve internals. The change-over valve is the part of a duplex filter that nobody orders until it leaks. It is worked every time the filter is switched, often under pressure and often against oil carrying whatever caused the switch, and its seats and seals are a separate order from anything in the element chamber.
  • Housing pressure class and design temperature, as stamped on the housing plate rather than taken from a typical range. Where the housing has been in service through more than one oil specification, state the current one: element media are selected against the oil as well as against the rating.

LO coolers — tube stack and gasket identity

An LO cooler is either a gasketed plate cooler or a shell-and-tube cooler, and which one is fitted is the first line of the identification: a plate cooler resolves to plates and a gasket set, a shell-and-tube cooler to a tube stack, tube-sheet gaskets and end covers. On a ship with central cooling the main-engine LO cooler is cooled by the low-temperature fresh-water circuit rather than by sea water, which changes the material question. Before the parts, one diagnostic point decides the scope. A tube leak moves whichever way the pressure difference pushes it, so oil appearing in the cooling water and water appearing in the oil are not the same fault: the first is usually a running leak with the oil side higher, the second often shows only when the engine is stopped and the oil pressure falls away. Saying which one was observed, and at what condition, changes whether the order is a tube stack, a set of gaskets or a pressure test first. Send:

  • Cooler maker and type as stamped on the nameplate or frame (a Bloksma cooler may now be supplied under the Kelvion name), plus the drawing number where the plate is unreadable.
  • Duty side (oil vs sea water vs fresh water) and design pressure.
  • Tube material — copper, brass (CuZn), CuNi 90/10, CuNi 70/30 or titanium where specified by the original cooler design and duty.
  • Tube count (from vessel documentation or a tube-sheet photo).
  • Whether the RFQ is for the full tube stack, individual tubes, tube-sheet gaskets, or end-cover gasket set. Add the sacrificial anodes on any cooler with sea water on one side. They are a routine consumable, they are what protects the tube material once the cooler is back together, and they are almost never on the enquiry that renews the tubes.

LO circulation pumps — screw pump identity

Electrically driven LO circulation pumps are often screw pumps: three-screw on Imo units, with Kral, Bornemann and Leistritz also met in this duty. Read the pump type from the plate rather than assume it from the duty, and if the engine carries its own engine-driven LO pump, say whether the line is for that pump or for the electric one. These pumps almost always run with a standby alongside them, and after some years of separate repairs the two are frequently no longer identical. Say which of the pair the line belongs to and whether the other has already been renewed, because a spare bought to match the wrong one of a pair is a common way to end up with two different pumps and one set of spares. The identity evidence is:

  • Pump maker and full type designation as stamped (for example an Imo ACG frame, or a Kral K-series unit with its size code), plus the serial number.
  • Rated flow (L/min), rated pressure (bar), rated speed (rpm).
  • Rotor set material — steel, hardened, or hardened + coated for high-pressure duty.
  • Mechanical seal specification and shaft-seal type (mechanical seal, lip seal, or packing).

OEM route vs verified alternative

For purifier service kits, duplex-filter elements, gasket sets and standard O-rings, a documented alternative may be considered when material, dimensions, duty, warranty and class requirements allow it. Gravity discs, bowl parts and cooler tube stacks require closer review of geometry, balancing, materials and traceability for the exact unit. On the cooler in particular the tube material is chosen against the water on the other side rather than against the oil, so a tube stack cannot be assessed from the cooler designation alone. Vessel Core records the proposed route for each RFQ line.

What we cannot promise before the RFQ is reviewed

Vessel Core does not quote lubricating-oil spare-part prices, lead times or supply route before the specific unit, application and identification data are confirmed. Every quotation is prepared for the specific request. A gravity-disc quotation remains preliminary until the current inner diameter and operating context are known. The same applies to a filter element quoted without the housing model, and to a tube stack quoted without the water side, because in both cases the component that fits is decided by something the part number does not carry.

How to send the RFQ

Use the RFQ form. Attach a clear nameplate photo and add the one fact for that group that the plate does not carry: for a separator, whether it runs as purifier or clarifier and the current disc marking; for a filter, the housing the elements go into and the differential the crew are reading; for a cooler, which fluid was found in which; for a pump, which of the pair it is. Use the RFQ evidence checklist to review the fields item by item.

Frequently asked questions

What identity detail is often missed in LO purifier RFQs?

The gravity-disc inner diameter is often omitted. It is selected for the separator model, oil density and operating condition. If the oil specification has changed, recheck the selection and send the current disc marking or measured diameter with the RFQ.

What is the difference between paper/synthetic and stainless mesh filter elements?

Pleated paper or synthetic elements are normally replaced according to the maintenance plan, while some stainless wire-mesh elements are designed for cleaning and reuse. Confirm the element code, micron rating, material, differential-pressure limit and housing compatibility rather than choosing by construction alone.

What identity evidence does an LO cooler need?

Cooler maker and model (Bloksma, Blohm+Voss, Bowman, Alfa Laval Aalborg), duty side (oil vs sea water vs fresh water), design pressure, tube material (copper, CuNi 90/10 or 70/30, titanium for sea water side), tube count, and whether the RFQ is for the full stack, individual tubes, or gaskets.

Are aftermarket gravity discs safe?

A documented alternative may be considered for seals, O-rings and some service-kit gaskets after material and dimensions are confirmed. A gravity disc must match the separator model, internal geometry and operating condition; choose the OEM route or another option supported by the required technical documentation.

What about LO circulation pump identity?

Screw pump identity follows the general pump pattern (see the marine pumps guide). Imo ACG series, Kral K-series and Leistritz L4/L5 series are the common families; Bornemann pumps also appear. Rotor set material and pressure rating are the identity anchors.

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