Mechanical Seal Identification From a Pump Nameplate

Mechanical seal enquiries arrive in two forms. The good ones carry a seal part number. The common ones say "I need the seal for an ISWH 100-200A pump" or "Burgmann seal for a Fristam pump" and nothing else. The second form is answerable, but only through a structured identification process, because a pump model does not determine a seal - the same pump model leaves the factory with different seals depending on the service it was ordered for. This guide sets out how to get from a pump on a plinth to a correct seal part number.

Why the pump model is not enough

A centrifugal pump's seal chamber accepts a family of seals. Which one was fitted depends on decisions made when the pump was specified: the fluid, its temperature and pressure, whether it contains solids or crystallises, whether it flashes, and what the site's emissions and safety requirements were. Two identical pump models handling water and handling hot hydrocarbon will carry different seal faces, different elastomers and quite possibly different seal arrangements.

So the identification path runs through the seal itself and the service, not through the pump model alone. The pump model tells you the seal chamber dimensions; the service tells you the materials; the arrangement tells you the configuration.

The five things that define a seal

1. 01Shaft or sleeve diameter at the seal, in millimetres or inches. This is the single most important dimension and it is measurable with a vernier caliper in two minutes.
2. 02Seal type and arrangement - component versus cartridge; single, double (dual pressurised) or tandem (dual unpressurised); balanced or unbalanced; pusher or bellows.
3. 03Face material pairing - typically carbon versus silicon carbide, silicon carbide versus silicon carbide, or tungsten carbide combinations. This is chosen against abrasives, dry-running risk and the fluid.
4. 04Secondary sealing elements - the elastomer. NBR, EPDM, FKM/Viton, FFKM/Kalrez and PTFE each have a chemical compatibility and temperature envelope, and getting this wrong is the fastest route to a seal that fails in days.
5. 05Metal parts and spring material, usually 316 stainless as a baseline with Alloy C-276 and duplex options for aggressive service.

Reading what is on the machine

Work through these in order; each one may end the search.

• The seal itself. Cartridge seals almost always carry a label or laser marking on the gland plate with a type designation and often a serial. This is the definitive answer. Photograph it before the seal goes in the bin - a surprising number of enquiries follow a seal that was already discarded.
• The pump nameplate. Gives pump make, model, size, serial and often the original order number. The manufacturer can frequently resolve the original seal specification from the pump serial.
• The pump datasheet or the original purchase documentation. In a well-run plant this is in the equipment file and names the seal directly.
• The seal chamber dimensions. If nothing else survives, measure: shaft/sleeve diameter, bore diameter, chamber depth, distance from the chamber face to the first obstruction, and the gland bolt pattern and stud centres.
• The API plan. Look at the piping around the seal - a flush line from the pump discharge, a quench connection, a barrier fluid pot and cooler. The presence of a seal pot tells you immediately that you are looking at a dual pressurised arrangement.

Seal support plans, and why they matter to the order

API 682 seal flush plans define how the seal chamber is cooled, flushed and, on dual seals, how the barrier fluid is managed. The plan in use constrains the seal you can fit and often reveals what the original seal must have been.

• Plan 11 - flush from pump discharge through an orifice into the seal chamber. The most common single-seal arrangement.
• Plan 13 - recirculation from the seal chamber back to suction, used on vertical pumps.
• Plan 21 / 23 - flush through a cooler, for hot service. Plan 23 recirculates through the cooler and is far more thermally efficient.
• Plan 32 - clean flush injected from an external source, for slurries and dirty service.
• Plan 52 - unpressurised buffer fluid on a tandem dual seal, with a reservoir vented to flare or atmosphere.
• Plan 53A / 53B / 53C - pressurised barrier fluid on a dual seal, keeping product out of the atmosphere entirely.
• Plan 62 - external quench on the atmospheric side, typically steam or water, for crystallising or coking service.

If a seal keeps failing, the seal is often not the problem - the plan is. A single seal on Plan 11 in a service that crystallises will fail repeatedly no matter whose seal you fit. Naming the plan in your enquiry lets a supplier tell you that.

Elastomer selection, briefly

The classic and costly error is fitting FKM in hot water because FKM is "the better material". It is not, in that service. Match the elastomer to the fluid, not to a general quality ranking.

What to send with a seal enquiry

1. 01The seal part number from the gland plate if it exists, photographed.
2. 02Pump make, model, size and serial number, from the pump nameplate, photographed.
3. 03Shaft or sleeve diameter at the seal, measured.
4. 04The pumped fluid, its temperature, suction and discharge pressure, and whether it contains solids.
5. 05The seal arrangement - single, dual pressurised, dual unpressurised - and the API plan if you can identify the piping.
6. 06Photographs: the pump nameplate, the seal area with piping visible, and the failed seal faces if the seal has been removed. Face wear patterns tell an experienced engineer why it failed.
7. 07Quantity, and whether you want a like-for-like replacement or an upgrade to address a recurring failure.

On genuine seals

Seal faces are precision components. A counterfeit seal with an out-of-specification face flatness or a substituted carbon grade looks identical, installs identically, and fails in weeks - typically taking the pump bearing with it when the leak reaches the bearing housing. We supply new and genuine OEM seals with manufacturer documentation and traceability, and where a like-for-like is discontinued we will identify the OEM's own current equivalent rather than substituting an unbranded part.

Reading a failed seal: what the faces tell you

Before discarding a failed seal, look at it. The wear pattern on the faces is diagnostic and will often tell you why the seal failed, which determines whether a like-for-like replacement will simply fail again.

• Even, polished wear across the full face - normal end of life. Replace like for like.
• Heat checking, visible as fine radial cracks on the hard face - the seal ran dry or with inadequate cooling. Address the flush plan, not the seal.
• Deep scoring or grooving - abrasive particles in the fluid. Consider a harder face pairing or a Plan 32 clean flush.
• Chipping at the outside diameter - mechanical damage, often from cavitation, vibration or a hydraulic shock event.
• Blistering on a carbon face - fluid absorbed into the carbon then flashed. Points to thermal problems or an unsuitable carbon grade.
• Uneven wear on one side of the face - misalignment, shaft deflection or excessive run-out. The seal is reporting a machine problem.
• Elastomer swollen, hardened or cracked - chemical incompatibility or temperature outside the material envelope.

Photograph the faces before the seal is discarded and send the photographs with your enquiry. A supplier who can see the failure mode can advise whether a different face pairing, a different elastomer or a different flush plan is the actual answer.

Shaft and machine condition: the seal is not always the problem

Mechanical seals are precision components installed on rotating machinery, and they are unforgiving of conditions the rest of the pump tolerates. Repeated seal failure on the same pump almost always has a mechanical root cause.

1. 01Shaft run-out at the seal - excessive run-out forces the seal faces to track a moving target and they cannot.
2. 02Shaft deflection under load, a function of shaft stiffness and how far the pump operates from its best efficiency point. A pump running far off BEP deflects more.
3. 03Bearing condition - worn bearings allow shaft movement the seal must absorb.
4. 04Coupling alignment. Misalignment loads the bearings and moves the shaft.
5. 05Pipe strain transmitted into the pump casing, distorting it and moving the seal chamber relative to the shaft.
6. 06Cavitation and operation at low flow, both of which produce vibration and thermal effects at the seal.

A seal that fails in weeks rather than years is reporting one of these. Replacing the seal without correcting it buys a few more weeks at the cost of another seal.

Installation practice that determines seal life

A correctly specified seal installed badly fails as reliably as a wrongly specified one.

• Working length. Component seals must be set to the manufacturer's working length. Cartridge seals arrive set, but the setting clips must be removed after the gland is bolted and before rotation - leaving them in destroys the seal on start-up, and removing them before bolting loses the setting.
• Cleanliness. Seal faces are lapped flat to a fraction of a light band. A fingerprint, a dust particle or contact with a hard surface ruins them.
• Lubrication on installation - the correct lubricant on elastomers, and never a petroleum lubricant on an elastomer that is not compatible.
• Gland bolting must be tightened evenly in sequence to avoid distorting the gland and the stationary face.
• The seal chamber must be vented and flooded before start-up. Starting dry destroys the faces in seconds.

Upgrading rather than replacing

A seal that has failed repeatedly is an invitation to change something. The options, in rough order of cost:

• Change the elastomer, where the failure evidence points to chemical or thermal attack on the secondary sealing elements.
• Change the face pairing - moving from carbon against silicon carbide to silicon carbide against silicon carbide addresses abrasive wear and dry-running risk at modest cost.
• Convert from component to cartridge, removing installation setting error from the failure population.
• Change the flush plan - adding a cooler, a clean flush or a quench addresses the environment the seal operates in rather than the seal itself.
• Move from single to dual seal where emissions, safety or product loss justify it, accepting the barrier fluid system that comes with it.
• Address the machine - alignment, pipe strain, bearing condition, or operating point - which is often the real answer and the one nobody wants to hear.

The right sequence is to establish the failure mode from the faces first, then choose the intervention. Upgrading blind is expensive and frequently addresses the wrong thing.