Mechanical Seal FAQ: 50 Questions Buyers Actually Ask

Fit and Selection

Q: How do I know which seal fits my pump?
A: Send the pump brand and model, shaft diameter, bore size, media, pressure and temperature. We cross-reference and confirm the fit before you order — a seal sized on the pump model alone is a guess.

Q: What if I only have the old seal part number?
A: That works too — the number identifies the design, size and materials. We match an equivalent and confirm the shaft and bore against our records before shipping.

Q: Single or double seal?
A: Single for clean, non-hazardous duty; double for toxic, flammable or abrasive media, or where a leak must not reach the atmosphere. Your media and safety requirements decide.

Q: What is the difference between a mechanical seal and gland packing?
A: A mechanical seal uses two flat faces running against each other with a thin liquid film between them; packing is compressed braided material around the shaft. Seals leak less and last longer on most services; packing is simpler and cheaper on some older pumps. Converting from packing to a seal usually requires the bore to be machined to a seal chamber — check that before you buy.

Q: Can the same seal fit different pumps?
A: Yes — standard seals are sized by shaft and bore, not by pump brand. A 35/60 seal fits any pump with a 35 mm shaft in a 60 mm bore, which is why we ask for dimensions, not just the pump name.

Q: My pump has a shaft sleeve. Which size matters?
A: The sleeve diameter where the seal rides. Measure the sleeve, not the bare shaft — the seal seals against the sleeve surface.

Q: What is a cartridge seal and do I need one?
A: A cartridge seal arrives pre-assembled with gland, sleeve and faces set, so installation is simpler and spring-setting errors are avoided. It costs more; it is worth it for hard-to-reach pumps or less experienced installers.

Q: What does DIN 24960 mean on a seal?
A: It is the standard that defines common seal sizes by shaft/bore pairs, like 35/60. A DIN 24960 seal is a standard-dimension seal, interchangeable with other makers' DIN seals of the same size.

Q: Can you cross-reference a competitor's part number?
A: Yes — send the number, a photo and the shaft/bore dimensions, and we will match an equivalent from our range.

Materials and Lifespan

Q: How long does a seal last?
A: There is no honest single number. On clean water duty, a well-installed seal often runs 3-8 years; on abrasive or flashing services it can be months. Installation quality and operating conditions matter more than the seal itself, which is why we ask about your duty before promising anything.

Q: SiC or tungsten carbide faces?
A: Silicon carbide suits water and most chemicals and runs well against carbon. Tungsten carbide handles abrasives and thermal shock better. We recommend based on your media — send the details.

Q: Can you help with material compatibility?
A: Yes — send media, temperature and concentration, and we will confirm face materials and elastomer. Getting the elastomer wrong is one of the most common causes of early failure.

Q: Which elastomer should I choose?
A: NBR for water, oils and general service; EPDM for many chemicals and hot water; FKM for higher temperatures and aggressive media. The media decides — never guess on chemicals.

Q: Why did my last seal fail so quickly?
A: Common causes: wrong material for the media, a damaged shaft, dry running, or an installation error. If we can see the failed seal — send a photo — we can usually name the cause.

Q: What is the maximum temperature a seal can handle?
A: Standard elastomer seals are comfortable to roughly 100-150 °C depending on the elastomer; special constructions like metal bellows go higher. Hot services also need flush to cool the faces.

Q: Does running dry damage the seal?
A: Yes, quickly. The faces are designed to run with a liquid film between them; without it they heat, crack and wear in minutes. A seal run dry is usually destroyed.

Q: What is a carbon face and why is it common?
A: Carbon running against silicon carbide or tungsten carbide is the classic face pair: carbon wears preferentially, keeps a smooth mating surface, and is economical to replace. It suits most clean services.

Q: How can I extend seal life?
A: Correct installation, clean flush, no dry running, proper alignment, and fixing pump problems like vibration and cavitation when they appear. A seal rarely fails alone — it fails because something else changed.

Ordering and Delivery

Q: What is your MOQ?
A: No hard MOQ on standard sizes — one piece is fine, and many customers start that way before moving to volume. For custom seals we discuss minimums based on the tooling involved.

Q: What is the lead time?
A: Standard sizes typically 7-15 days depending on material availability; custom and OEM projects are quoted individually, usually 2-4 weeks after sample approval. We confirm the date in writing with the quotation.

Q: Do you accept sample orders?
A: Yes — 1-10 pieces at factory-direct pricing, so you can test the fit and performance before committing to volume. Sample orders ship by courier.

Q: What payment terms do you offer?
A: T/T for standard orders; other arrangements for larger or repeat business. We confirm all terms in the quotation before you order.

Q: Do you ship internationally?
A: Yes — by courier such as DHL or FedEx for small orders and by sea freight for volume. We quote the shipping method and cost with your order.

Q: How are seals packed?
A: Individually protected so faces stay clean and undamaged, in export cartons with part numbers marked on each package. Faces travel protected, never loose, and cartridge seals ship with their installation sleeves in place.

Q: Can I mix sizes in one order?
A: Yes — mixed sizes and mixed materials are routine. Each line is quoted and packed separately with its own markings.

Q: What if a seal arrives damaged?
A: Photograph the packaging and the seal immediately and send it to us; we replace damaged goods. Inspect shipments on arrival — damage claims need the photos.

Support and OEM

Q: Do you provide installation support?
A: Yes — written guides, installation videos and engineering support by message with every order. For volume customers we can join a call for specific questions.

Q: Can you make custom seals?
A: Yes — from a drawing or a sample, with a prototype to sampling to production workflow. Custom projects start with a clear spec of size, materials and duty.

Q: Do you support private label?
A: Yes — with consistent QC and documentation on request. We mark products per your specification and keep records for traceability.

Q: Do you provide drawings?
A: For standard seals we provide dimension drawings; for custom seals you approve the drawing before production starts. Drawings are part of the package, not an extra.

Q: Can you match an OEM seal exactly?
A: We match the dimensions, materials and performance. Exactly is a strong word — no two manufacturers make identical seals — but an equivalent that fits and performs is the standard goal, and we say so plainly rather than overpromising.

Q: What warranty do you offer?
A: We stand behind manufacturing defects — replace or refund. We cannot warrant seals against misapplication or bad installation, and neither should any honest supplier.

Q: Can you help troubleshoot a leaking seal remotely?
A: Yes — send photos and the operating details (media, temperature, pressure, run time) and we will work through the likely causes with you.

Q: Can you supply spare parts separately?
A: Yes — springs, sleeves, O-rings and gland components for many standard seals are available as spares. Tell us the seal type and what you need.

Installation Questions

Q: Do I need special tools to install a seal?
A: Basic hand tools plus a puller for the old seal, fine abrasive paper, lubricant, a torque wrench and ideally a dial indicator. A proper installation sleeve comes with most cartridge seals.

Q: Can I replace a seal without removing the pump from the line?
A: Often yes — most end-suction pumps allow seal access by removing the coupling and the back cover. If the seal sits behind the impeller, the pump head must come off; check the pump manual. A mechanic with the right procedure can do most standard pumps in a couple of hours.

Q: Should I lubricate the seal during installation?
A: The elastomers, yes — with the recommended lubricant, clean water or soap solution for water service. The faces, never: faces must stay dry and clean.

Q: How tight should the gland bolts be?
A: Follow the drawing: typical gland bolts run 15-40 Nm for common sizes, tightened evenly in a cross pattern. Firmly by feel is how glands get cocked.

Q: How do I set spring compression?
A: Measure the installed working length against the drawing with a depth gauge or calipers. Most seals need only 1-2 mm of compression from free length — do not guess; too much compression causes heat and early wear, too little causes leaks.

Q: My new seal weeps slightly at startup. Is that normal?
A: A very slight weep in the first minutes while the faces seat is common. A steady drip after 30 minutes, or any leak once hot, is a fault — investigate.

Q: Can I reuse a seal that has been removed?
A: No — once the faces are separated and the elastomers have taken a set, a used seal almost never re-seals properly. Always fit new.

Q: Which way does the rotating face go?
A: Follow the drawing — most seals are directional. If the seal has markings or a drive collar, they indicate orientation. When in doubt, ask before installing; fitting a directional seal backwards guarantees a leak.

Troubleshooting Questions

Q: My seal leaks after a few months. What causes this?
A: Look first at the faces: heat cracks mean dry running; a worn flat pattern means abrasives; a chipped face means installation damage or cavitation. The failure pattern names the cause, and a photo of the faces tells us more than any description.

Q: The seal squeals when the pump runs. Why?
A: Squeal usually means the faces are running dry — not enough flush, the pump is cavitating, or the spring compression is too high. Check the flush line and the suction conditions first.

Q: Seals fail repeatedly on the same pump. What should I check?
A: The pump, not the seal: shaft runout, bearing wear, misalignment, cavitation and vibration all kill seals. If the third seal fails the same way, the first two were probably fine.

Q: My pump vibrates after seal replacement. Is the seal the cause?
A: Usually not — vibration comes from misalignment, imbalance or bearings. A seal feels it and fails from it, but it rarely causes it. Check the coupling alignment before anything else; it is the usual culprit after a rebuild.

Q: Why do I smell burning rubber?
A: The elastomer is overheating — dry running, high face pressure or a blocked flush. Stop the pump: a burning elastomer means the seal is already damaged.

Q: The seal leaks only when the pump is stopped. Why?
A: Static leaks point at the elastomers or the stationary seat, not the faces. A set O-ring, a loose gland or a poor bore seal will hold pressure only while running.

Q: Why did my seal fail after running dry?
A: Dry running generates heat the faces cannot shed; the faces crack and the elastomer cooks. This is the most common cause of sudden, early failure — and the most preventable.

Q: When should I replace the seal versus repair the pump?
A: If the shaft is worn or the runout is high, repair the pump first — a new seal on a sick pump is a short life. When in doubt, measure runout and check bearings before ordering the seal; the measurement costs nothing and saves a repeat job.