Improving Mechanical Improving Mechanical Seal ReliabilitySeal Reliability

William “Doc” BurkeWilliam “Doc” Burke

A.W. Chesterton-ChicagoA.W. Chesterton-Chicago

(800) 244-7325(800) 244-7325

Seals 101Seals 101

Single seals are made of the same 7 Single seals are made of the same 7 pieces: gland, stationary face, rotary face, pieces: gland, stationary face, rotary face, secondary elastomers, drive mechanism, secondary elastomers, drive mechanism, spring face-loader, & gasketspring face-loader, & gasket

Keeping the seal faces together is the Keeping the seal faces together is the main focusmain focus

Proper selection of materials includes Proper selection of materials includes solutions used for cleaning systems!solutions used for cleaning systems!

Pump OperationPump Operation

Most seal problems come from 1 of 2 Most seal problems come from 1 of 2 causes: Pump is not operating near its causes: Pump is not operating near its BEP, or the pump is CavitatingBEP, or the pump is Cavitating

Pumps are often oversized in anticipation Pumps are often oversized in anticipation of future needs, then run against a of future needs, then run against a throttled discharge: this creates Shaft throttled discharge: this creates Shaft Deflection!Deflection!

Oversized pumps have greater NPSHR (Net Oversized pumps have greater NPSHR (Net Positive Suction Head REQUIRED)Positive Suction Head REQUIRED)

CavitationCavitation

Air ingestion is common in WWAir ingestion is common in WW Internal recirculation is often Internal recirculation is often

mistaken as Cavitationmistaken as Cavitation Cavitation is a frequent cause of Cavitation is a frequent cause of

bearing failure & seal faces chippingbearing failure & seal faces chipping NPSHR varies by the square of any NPSHR varies by the square of any

speed changespeed change

Dynamically Balance Rotating Dynamically Balance Rotating AssembliesAssemblies

Dynamic balance of entire rotating Dynamic balance of entire rotating assembly is crucialassembly is crucial

A 14” rim automobile tire has a A 14” rim automobile tire has a circumference of 6.5 feet: it rotates 812 circumference of 6.5 feet: it rotates 812 RPM @ 60 MPH, and we notice the loss of a RPM @ 60 MPH, and we notice the loss of a 1 ounce weight1 ounce weight

Shaft should be within 0.001” Total Shaft should be within 0.001” Total Indicator Runout (TIR) at impeller end to Indicator Runout (TIR) at impeller end to assure good seal lifeassure good seal life

Upgrade Bearing ProtectionUpgrade Bearing Protection Lip seals were designed in the 1940’s for car Lip seals were designed in the 1940’s for car

water pumpswater pumps Pump bearings are designed to provide 30-40 Pump bearings are designed to provide 30-40

years life based on their L10 life!years life based on their L10 life! Contamination, not over-loading, kills most Contamination, not over-loading, kills most

bearings (SKF says 36%)bearings (SKF says 36%) Installation & Removal concerns Installation & Removal concerns (SKF (SKF

says 34%)says 34%) Cool the oil, NOT the bearing, in hot running Cool the oil, NOT the bearing, in hot running

applicationsapplications

AlignmentAlignment Within 0.002” on all 4 planes: vertical angular, Within 0.002” on all 4 planes: vertical angular,

vertical parallel, horizontal angular, and vertical parallel, horizontal angular, and horizontal parallelhorizontal parallel

Couplings transmit torque & resolve thermal Couplings transmit torque & resolve thermal growth: they allow mis-alignment to destroy growth: they allow mis-alignment to destroy much more expensive bearings & seals by much more expensive bearings & seals by transmitting vibration!transmitting vibration!

Buy or Rent a laser, and get training for your Buy or Rent a laser, and get training for your people to use it properly!people to use it properly!

Shoot the couplings with a thermal gun and see Shoot the couplings with a thermal gun and see the wasted HP energy being used!the wasted HP energy being used!

Re-building ProceduresRe-building Procedures Always use new gaskets & o-ringsAlways use new gaskets & o-rings Create & follow a “Pump Repair Checklist” to document the Create & follow a “Pump Repair Checklist” to document the

work done, the parts changed, and changes made off OEM work done, the parts changed, and changes made off OEM specification! Make sure the machinist signs his work order specification! Make sure the machinist signs his work order as a matter of prideas a matter of pride

Use OEM parts wherever possible to assure tolerances/fits Use OEM parts wherever possible to assure tolerances/fits & materials used are correct: stacking tolerances can lead & materials used are correct: stacking tolerances can lead to major headaches! to major headaches!

All materials are readily identifiable from the OEMs, but All materials are readily identifiable from the OEMs, but often are unclear from “pirate/bandit” housesoften are unclear from “pirate/bandit” houses

Be wary of hardened sleeves: make sure you are using set Be wary of hardened sleeves: make sure you are using set screws which can bite into the harder materials!screws which can bite into the harder materials!

Clearances & TolerancesClearances & Tolerances Set impeller clearances by OEM specification: this can be a Set impeller clearances by OEM specification: this can be a

severe problem with component seal designssevere problem with component seal designs Case wear rings typically have a clearance of 0.001-Case wear rings typically have a clearance of 0.001-

0.002”/shaft diameter inch. Change them once this 0.002”/shaft diameter inch. Change them once this clearance doubles.clearance doubles.

Coating the volute or the impeller can be a very good thing, Coating the volute or the impeller can be a very good thing, so long as the impeller & rotating assembly are re-balanced so long as the impeller & rotating assembly are re-balanced and the clearances are not affected!and the clearances are not affected!

Eliminate pipe strain whenever it is identified: no come-Eliminate pipe strain whenever it is identified: no come-alongs or fork lifts should be required!alongs or fork lifts should be required!

Identify turbulence-causing elbows & poor piping Identify turbulence-causing elbows & poor piping arrangements as you move through the plant, & consider arrangements as you move through the plant, & consider flow-disrupters (static mixer in-line)flow-disrupters (static mixer in-line)

Install & Understand Seal Install & Understand Seal Environmental ControlsEnvironmental Controls

Flush: MUST be 15-20 psi higher than Flush: MUST be 15-20 psi higher than stuffing box pressure to workstuffing box pressure to work

Steam QuenchSteam Quench Discharge Recirculation Discharge Recirculation Suction recirculationSuction recirculation Vent vertical applicationsVent vertical applications Be wary of trapped air in stuffing boxes on Be wary of trapped air in stuffing boxes on

horizontal pumpshorizontal pumps