- ▸In multi-spring seals, face pressure comes from a ring of small springs; graphite rings carry point loads — face flatness and spring-seat wear decide pressure uniformity
- ▸The G6 series (-20 to 200°C, ≤ 0.8 MPa, ≤ 3500 rpm) covers industrial, water and sewage pumps and general machinery: unspectacular ratings, messy duties
- ▸Replacement criteria: face wear beyond 1 mm (or a third of face width consumed), through-scoring on the face, spring free length down more than 5%
- ▸Overhaul order: measure sleeve runout and spring-seat wear before pulling the ring — replacing the ring without checking the seat is half a job
- ▸Sewage duty: prefer antimony-impregnated grades with SiC faces; fiber-laden media demand filtration or no graphite ring survives
1. Multi-Spring Design Traits
Mechanical seals divide by elastic element into single-spring and multi-spring:
- Single spring: one large conical spring around the shaft; simple, clog-resistant, suits particulate media
- Multi-spring: a ring of 4–12 small cylindrical springs distributing load through a spring seat to the graphite ring; compact, even force, good for small shafts
The G6 series graphite ring serves exactly this multi-spring cavity. The effects on the ring cut both ways.
Advantage: circumferential force distribution is even, so face pressure is easier to keep flat than with a single spring; fewer local pressure peaks, less edge chipping.
Costs:
1.Each spring transmits force through a small seat area to the ring's back face — a ring of concentrated load points. Graphite is brittle; excessive local back-face stress micro-cracks the ring in service
2.With many springs, one failure drops total spring force 8–25% (by count); face pressure collapses and leakage rises — while the field blames the graphite ring first
3.In particulate media, spring gaps plug up and compensation is lost — multi-spring designs are inherently disadvantaged in sewage and stock service
2. G6 Ratings and Duty Positioning
The G6 series is rated -20 to 200°C, ≤ 0.8 MPa, ≤ 3500 rpm for industrial, water and sewage pumps and general machinery:
| Duty | Suggested configuration |
|---|---|
| Clean/cooling water | Resin-impregnated ring + high-chrome stainless or SiC face |
| Sewage, sandy water | Antimony-impregnated ring + SiC face + suction strainer |
| Light oil, lubricants | Resin or antimony + SiC |
| Weak acid/alkali | Resin + SiC (avoid Al₂O₃ above pH 10) |
| Frequent start/stop | Copper-impregnated (best conductivity, resists startup wear) — banned in ammonia |
Note the 0.8 MPa ceiling: for high-pressure chemical duty move to 120 (M3N, ≤1.2 MPa) or 206 series (≤2.0 MPa) — do not brute-force it with heavier springs.
3. Overhaul Inspection Order
At pump teardown, inspect the ring "outside-in, cause before part":
3.1 Root Causes First
1.Sleeve radial runout: ≤ 0.03 mm (indicator on sleeve OD). Fix the shaft first — a new ring on a bent shaft is wasted
2.Shaft vibration: bearing condition, rotor balance; pump vibration is the seal killer
3.Cavity cleanliness: old gaskets, crystallized media, fiber wads — the new ring's abrasive source
3.2 Elastic Elements Second
4.Spring free length: measure each; replace the set if any is down 5%, cracked or rusted
5.Spring-seat wear: a stepped or unevenly worn seat loads the ring unevenly — replace it
6.Drive/anti-rotation pins: correct position, unworn; single-sided clearance 0.3–0.8 mm
3.3 The Graphite Ring Last
7.Face wear: a third of face width consumed, or wear beyond 1 mm — replace
8.Face defects: through-scoring, edge chips beyond the contact band, spider-web thermal cracks — any one, replace
9.Bore and back face: one-sided bore scoring = pressing/alignment issue; uneven back-face impressions = seat problem
10.Impregnation quality: face blotching, visible through-pores in cross-section — batch issue, contact the supplier
4. Replacement and Installation
- Life mismatch between graphite and SiC is normal: SiC typically outlives graphite 2× or more. Default: replace graphite, keep SiC; replace SiC only for chips or deep scoring
- Replace as a set: ring + O-rings + springs together. Aged O-rings kill compensation; a new ring cannot compensate for them
- Pressing: press rotating rings with a guide sleeve at 2–5 mm/s; check bore roundness after (change > 0.01 mm = excessive assembly stress)
- O-ring lubrication: thin film of compatible food-grade grease; never dry-press (tears the O-ring); ammonia-compatible grease in ammonia service
- Break-in management: the first 2 hours after installation are break-in; a few drops per minute of initial leakage is acceptable. If leakage rises instead of settling, stop and investigate
5. Failure Quick Reference
| Symptom | Root cause | Action |
|---|---|---|
| Leakage growing gradually | Normal face wear; or spring decay | Replace ring; measure springs |
| Sudden leakage increase | Broken spring; extruded O-ring; chipped mating face | Inspect elastic elements and seat |
| Chipped face edge | Excessive face pressure; particle jam | Verify face pressure; add filtration |
| Uneven back-face impressions | Spring-seat wear, off-axis load | Replace seat |
| Axial bore cracks | Pressing interference | Change to push fit; verify tolerances |
| Cavity fouling | Crystallizing/coking media | Change flush plan (Plan 11/32) |
Conclusion
The difficulty with general-purpose rings like the G6 series is never the ring itself — it is the springs, seats and shaft line it lives with. Follow the order "measure runout, check springs, then look at the face" and the same ring's life can vary by more than 3×. Multi-spring designs are inherently disadvantaged in particulate media — for sewage duty, fit the strainer and do not make the graphite ring pay for the missing filter.