DESMI Pump
Spare Parts Supplier
Engine-room pump spare parts supply — NSL · DSL · ESL · modular · ROTAN internal gear · self-priming
DESMI pump builds behind engine-room RFQs
The Danish maker builds its marine programme around a handful of hydraulic platforms that repeat across seawater cooling, ballast, bilge and fire-line service. What fixes the wear-part geometry is the type designation cast or stamped on the pump — not the duty the unit happens to perform on board.
NSL series
Single-stage vertical in-line centrifugal pumps bolted directly into cooling and general-service pipe runs, with the driver carried above the casing. NSLH and NSLV are not high-head versions: DESMI describes them as end-suction pumps, NSLH with a horizontal inlet and NSLV with a vertical one, so they carry a different plate designation and a different casing — read the plate rather than assuming NSL. Requests usually cover the casing wear ring, impeller, mechanical shaft seal, shaft sleeve, motor stool/lantern and the seal chamber components. DESMI builds the range in Monobloc, Spacer and Compact Spacer versions, each with its own manual — state which build is fitted, because the shaft and coupling parts differ.
DSL series
DESMI's DSL is a single-stage, double-suction, vertical in-line centrifugal pump, listed for ballast and cooling-water duty, with bearings and a mechanical shaft seal at both the top and the bottom of the shaft; a version without a bottom bearing has its own manual. A double-suction impeller has an eye and a wear ring on each side, so it is not matched from a single-suction parts list — confirm from the plate and the manual which DSL build is fitted before an impeller, wear ring or bottom bearing is quoted.
ESL series
DESMI's ESL is a single-stage in-line centrifugal pump with a mechanical shaft seal, listed for cooling-water, fresh-water circulation and refrigeration duty, and an ESL Monobloc version has its own manual. ESLH is the end-suction version with a horizontal inlet and a different casing. Seal face pairs, elastomer kits, impellers and rolling-element bearings recur on the line list, but confirm from the plate whether ESL or ESLH is fitted before a wear ring or casing part is matched.
Modular S pumps
DESMI's Modular S is a self-priming centrifugal pump that can handle a mixture of air and liquid, so it evacuates the suction pipe without a foot valve. It is built close-coupled with an electric motor, or with a free shaft end on a base plate for a diesel or petrol engine, and DESMI lists it for bilge, ballast, fire, cooling-water, wash-deck and general-service duty. State which drive is fitted, because the shaft end and coupling parts follow it.
ROTAN internal gear pumps
DESMI's ROTAN internal gear pumps, listed on board for sludge, bilge water and heavy oils and in lubrication systems, where a centrifugal would lose prime or shear the medium. Line items typically cover the rotor and idler set, idler pin and bushings, front cover and gasket, mechanical seal or packing set, and relief valve parts. ROTAN pumps run in either direction and the relief valve spring has to sit on the suction side, so state the flow direction with the request, and say whether the unit is magnetically driven, since that build has no shaft seal.
Self-priming units
DESMI's self-priming pumps — the SA, the close-coupled NSA and the Modular S — and the separate built-on priming pump that NSL, NSLH and NSLV units can carry, on bilge, ballast and stripping duty. Name which of the two is fitted: a self-priming pump and a built-on priming pump are different assemblies with their own parts. Vacuum unit elements, priming valves, non-return components and seal kits are requested as sets.
Seawater cooling service
Seawater pumps serving the central cooler and the SW cooling line, and the fresh-water circulating pumps on the closed jacket and low-temperature circuits. The two duties are built in different wetted materials: for the NSL range DESMI lists cast iron casings for fresh water and bronze, NiAlBz or super duplex casings for seawater, with NiAlBz or super duplex impellers and a duplex stainless shaft. So the circuit must be stated with the pump identity: a bronze or duplex build cannot be replaced from a fresh-water parts list of the same nominal size.
Ballast, bilge & fire line
Ballast, bilge and fire-line installations where suction conditions are harsh and running is intermittent. Seal arrangement, priming provision and driver data must be stated with the pump identity.
A DESMI series name fixes the hydraulic family and nothing else — the same NSL frame size ships with different impeller trims, seal chambers and casing alloys depending on the order. Vessel Core treats the series name as a search key only, and reads the stamped designation before it will call any part a match.
Where a seawater-duty pump gives up first
Two failure paths account for most of the DESMI line items that reach a purchasing desk: the mechanical seal loses its face pairing, and the impeller loses metal. Both start quietly, and both are far easier to quote when the buyer records what was measured on dismantling.
Seal faces and face pairing
Seawater carries sand, silt and marine growth straight into the seal chamber. The pairing wears, weeping appears at the seal chamber drain and a salt crust builds on the lantern/motor stool below it. The face material combination and elastomer grade decide the replacement — the seal size alone does not.
Impeller erosion and cavitation
Leading edges thin out and vane suction faces show pitting just behind the leading edge, often carrying into the shroud. Pitting there points to suction-side conditions — strainer, sea chest or NPSH — so a like-for-like impeller alone may not settle the fault. Where a bronze impeller runs in a cast iron casing, the casing and casing wear ring are the anodic parts and lose metal first: inspect the ring bore and casing faces, not only the impeller, and note any sacrificial anodes fitted in the covers and their condition. Record the trimmed diameter that came out, because it rarely equals the nominal diameter of the family.
Wear ring clearance opening up
As the casing ring and impeller neck ring lose their fit, recirculation grows and the pump quietly falls below its duty point while sounding mechanically healthy. Ring bore, ring width and the matching impeller neck dimension should be measured before the RFQ is sent.
Shafts, sleeves and bearings
Fretting under the seal, corrosion at the sleeve shoulder and bearing housing bore wear usually surface together. When a shaft is ordered, state whether the sleeve, key, lock nut and bearing set are being renewed with it.
Casing gaskets and covers
Casing gaskets, cover O-rings and drain plug seals are cheap to include and expensive to omit once the pump is open. They belong on the same RFQ as the rotating parts, listed against the same pump serial.
Coupling elements and alignment
Flexible coupling elements degrade with heat, oil contact and misalignment, and a worn element accelerates seal and bearing wear downstream. Note the coupling make, size and element type — the coupling is frequently not the pump maker's own part.
Line items quoted from a DESMI pump request
Listed in the order the pump comes apart — coupling guard, spacer, seal cover, casing, then the impeller off the shaft taper, with the bearing bracket added where the build is long-coupled. Quoting in that sequence means a missing gasket shows up while the drawing is still open, not after the casing is back on the studs.
- Mechanical seals & seal face pairs
- Seal elastomers & O-ring kits
- Casing wear rings & impeller neck rings
- Closed and semi-open impellers
- Pump shafts & shaft sleeves
- Bearings, bearing housings & brackets
- Seal chamber & seal cover parts
- Gland packing, lantern rings & gland followers
- Casing gaskets, cover seals & plug seals
- Coupling elements & spacer sets
- Internal gear rotor, idler & idler pin sets
- Idler bushings, front covers & relief valve parts
- Priming unit spares & non-return valve parts
- Suction covers & motor stool components
- Shaft keys, lock nuts & fastener sets
- Overhaul sets assembled against one pump serial
Plate data that makes a pump request answerable
A pump spare is defined by hydraulic size, material and sealing variant together. The fields below are what turn a description such as “seawater pump seal, port side” into a line a supplier can actually price.
- Pump type designation exactly as stamped, including the size figures after the letters
- Build: in-line or end-suction (NSL or NSLH/NSLV, ESL or ESLH), Monobloc, Spacer or Compact Spacer, and any built-on priming pump
- Pump serial number & year of build
- Fitted impeller diameter, as measured
- Duty point: capacity in m³/h against head in mlc
- Driver data: rating, poles, frame & mounting
- Wetted materials: casing, impeller, shaft
- Seal arrangement, face materials & elastomer grade
- Position number from the sectional drawing
- Photographs of the plate and the installed unit
Tools for this equipment: 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. Where the pump feeds a fire line, the nozzle K-factor calculator gives the total flow of a number of nozzles at one pressure from their K-factor. Where the relief valve spring is renewed, the compression spring calculator compares the new spring with the old one by rate and by load at the fitted length.
Reading a DESMI plate before anything is called equivalent.
Pump requests are reviewed against the plate reading, the measured wear items and the material record of the installed unit. Where a pump has no legible plate left — common on a seawater unit that has sat in a bilge-splash corner for fifteen years — the how we work page sets out the fallback sequence from casting marks and flange dimensions.
Wear Ring Bore, Not Series Name
Seal face diameters, wear ring bores and shaft sleeve lengths taken from the dismantled pump carry more weight than a family name. Where measurements are unavailable, the plate reading and drawing position number are used as the starting reference.
Seals and Bearings Have Their Own Makers
DESMI fits bought-in mechanical seals and rolling-element bearings whose own manufacturers publish the specification, so those items can be reviewed on the component maker's reference when the installed specification is documented. Impellers, wear rings and shafts stay tied to the DESMI serial and the casing alloy.
Material Context for Salt Water
Bronze, cast iron and duplex builds of the same nominal hydraulic size are not interchangeable in service. The wetted-material record is checked before an item is treated as equivalent, and any uncertainty is put back to the buyer.
Requests Without a Part Number
A plate photograph, a description of the removed item and its measurements are enough to open a review. See preparing an RFQ without a part number for what to capture while the pump is still open.
Handover Planned Around the Open Casing
A pump overhaul is a fixed window: the unit is off the line, the coupling is broken and the casing is open. Vessel Core asks when the casing is due to close, not just when the vessel berths, because a wear ring that arrives after the impeller is refitted has missed its job entirely.
Estonian Company, Checkable Details
Reg. 17028043, VAT EE102773714, Tallinn. The registry entry is public and the company verification page links straight to it.
What buyers ask once the pump is open
What DESMI pump data is needed before a quotation can be prepared?
Send the pump type designation exactly as stamped on the plate, the pump serial number, the fitted impeller diameter, the duty point in cubic metres per hour against head in metres liquid column, and the motor data. Wetted materials and the seal arrangement matter as much as the designation, because the same hydraulic size is built in different material and sealing variants for seawater and fresh-water duty.
Can a DESMI pump part be identified without a part number?
Often yes. A nameplate photograph, the position number from the sectional drawing in the pump manual, and measured dimensions of the removed item — seal face outer diameter, wear ring bore and width, shaft sleeve length — are usually enough to begin identification review. Vessel Core confirms the reading back to the buyer before any supply route is quoted.
Which DESMI pump components appear most often in RFQs?
Mechanical seals and seal face pairs, casing wear rings, impellers, shafts and shaft sleeves, bearings and bearing housings, casing gaskets and coupling elements. On ROTAN internal gear units the request usually covers the rotor and idler set, the idler pin and bushings, the front cover and its gasket and the relief valve parts; on self-priming installations it covers priming unit components and valve parts.
Can Vessel Core review OEM-route and alternative supply routes for DESMI pumps?
Yes, once the paperwork behind the item exists. For a seal that means the face-material code and elastomer grade taken from the pump's own seal drawing rather than from a catalogue table. For the casing and impeller it means the alloy recorded on the order confirmation. For a wear ring it means the bore and the impeller trim measured at dismantling, not the figure printed in the family table. Where that record is missing, the gap goes back to the buyer before anything is called equivalent.
Is Vessel Core connected to DESMI?
No, and there is no agreement of any kind. Vessel Core holds no dealership, distribution, representation or partnership agreement with DESMI, and quoting a component against one of its designations implies no approval by the maker and no claim of interchangeability.
How the manufacturer is named here
DESMI A/S of Nørresundby designs and stamps the pumps described here, and is named on this page only as the manufacturer of equipment a buyer may need identified. Type designations are quoted so a casting can be matched to a parts list, never to signal an appointment. Maker names help identify equipment and prepare an RFQ. They do not imply that Vessel Core holds authorised-dealer, representative or partner status with the manufacturer.
Send the plate reading and the measured wear items.
Send the pump type designation, serial number, impeller diameter, duty point, wetted materials and the line items you need, together with the port of call. Vessel Core reads the type designation against the impeller diameter actually fitted, checks the wetted-material record for the seawater or fresh-water build, and returns the line list quoted position by position from the sectional drawing.
