Failure of Mechanical Seal

FAILURES OF MECHANICAL SEAL SYSTEMS

M.SEALS

FAILURES OF MECHANICAL SEAL SYSTEMSFunction

To provide the seal with a clean, abrasive-free lubricant and carry heat generated at the seal faces.

Used a clean liquid from discharge pump or outside source

Contamination of the pumped product generally makes this type of flush undesirable

If necessary, this fluid flush can be cooled and any abrasive particles removed before it is injected into the seal.

M.SEALS

Seal Flush System

M.SEALS

Seal Flush System (Plan 11)PLAN 11

The flow is from the discharge of the pump directly into the seal cavity This is used only for relatively cool, clean pumpage conditions.

The flow enters the seal chamber at the seal faces, flushes the faces and flows across the seal back into the pump

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This is the reverse flow from plan 11.

Flow from inside the pump is directed outward across the seal faces, out the seal gland and back to the pump suction

This plan is utilised to prevent vapour build-up at the seal faces and is frequently used on vertical canned-type pumps

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Similar to plan 11, this plan takes clean fluid from the discharge of the pump and directs it to the seal faces through a cooler.

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Applied on hot services

This plan utilises an internal pumping ring to circulate the flush fluid across the seal faces, through a cooler and back to the seal cavity.

M.SEALS


Fluids contaminated with particles that are heavier than the fluid itself can be cleaned by using a cyclone separator

This plan takes flow from the discharge through a cyclone separator, where the dirty fluid is returned to the pump suction

The clean fluid is then circulated to the seal cavity, across the seal faces and back into the pump.

M.SEALS

CycloneThe solids content of the pumped fluid should not exceed 10% by weight.2.The pressure-difference ratio (PD) between the inlet and outlet should be from 0.8 to 1.2.

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This plan utilises a flow of clean fluid from an external source Fluid is circulated to the seal cavity, across the seal faces and into the pump

This plan is frequently used when the pumped fluid is contaminated with particles which can not be removed by filter or by cyclone separator.

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In this plan, the flow is directed from the discharge to the seal through a cyclone separator and a cooler.

It is effective for pumping hot fluids contaminated with particles that are heavier than the fluid itself.

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This plan is used with Tandem seal arrangement

This plan utilises a nonpressurised external fluid reservoir with forced circulation provided by an external pumping ring.

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This plan is used with double and dual seal arrangement.

This plan utilises a pressurised external fluid reservoir with forced circulation provided by an external pumping ring.

M.SEALS


This plan delivers an external fluid quench of cooled or heated seal flush liquid, which may be used to prevent build-up of solids at the seal faces

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Pin hole should be countersunk to remove burrs and allow seat to make contact with the seat housing.2. Clearance holes in seat housing on wrong P.C.D. (pitch circle diameter) causing bolts to bind in holes and distort seat housing.3. If there are signs of wear, or the pumped product is abrasive, hard coat the area under the wedge.

M.SEALS

FAILURES OF MECHANICAL SEAL SYSTEMS4. Lantern ring connection (designed to for use with a soft packed pump) is unsuitable for use when pump is fitted with a mechanical seal. If used it will create a pocket of trapped liquid at the seat/face area. Refer also to fault 16.The O-ring groove is over size and the O-ring will not compress when the seat is fitted. Refer to BS 1806 or DIN equivalent.6. Burr on seat housing bore prevents seat/seat housing contact. The burr may cause seal to leak due to cocking.

M.SEALS

FAILURES OF MECHANICAL SEAL SYSTEMS7. Gasket surface area too small. Seat housing will distort when bolts are tightened.8. Bore of seat housing incorrect. There should be clearance around the seat. Refer to appropriate seal bulletin for fitting instructions.9. Contact between back of face and step in sleeve will break carbon face. Check sleeve dimensions and seal setting dimensions.

M.SEALS

FAILURES OF MECHANICAL SEAL SYSTEMS10. No chamfer on nose of spigot.11. Recess should be relieved in corner of seat housing to allow seat to make contact with the seat housing.12. Sleeve should be relieved in the bore to assist fitting cartridge.

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FAILURES OF MECHANICAL SEAL SYSTEMS13. Drive pin ends not chamfered. Pin binding in hole of retainer.No chamfer on seat housing to help when fitting seat. O-ring could be damaged by sharp corner.15. Flushing holes covered by sleeve shoulder.

M.SEALS

FAILURES OF MECHANICAL SEAL SYSTEMS16. Recirculation connection should be in line with face/seat contact area.17. Pin should have chamfer at each end. Pin driven too far into the seat housing preventing seat contacting it. Pin hole P.C.D. incorrect causing pin to bind in hole.18. Check surface finish, should be polished. Check tolerance, should be plus or minus 0.002" or 0.05 mm.

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M.SEALS

FAILURES OF MECHANICAL SEAL SYSTEMSDamage To Rotating And Stationary Elements Caused By Localised Heat Build Up At The Seal Faces.

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FAILURES OF MECHANICAL SEAL SYSTEMSDamage To Seal Faces Caused By Abrasive Particles In The Product

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FAILURES OF MECHANICAL SEAL SYSTEMSDamage To Seal Faces Caused By Sludging Or Bonding.

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FAILURES OF MECHANICAL SEAL SYSTEMSDamage To Seal Faces Caused By Insufficient Lubricant Between Seal Faces (Overloading - Dry Running).

M.SEALS

FAILURES OF MECHANICAL SEAL SYSTEMSIn order to prevent flashing of the pumped liquid between the faces, several causes of action may be taken.A.The injection of pumped fluid into the stuffing box in order to raise the stuffing box pressure.B.The cooling of the liquid in the stuffing box by means of a water jacket.C.A combination of both A and B.

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FAILURES OF MECHANICAL SEAL SYSTEMSCoke Deposits Caused By Solidification Of Seal Leakage To Atmosphere.

Solution - Introduce Quench Liquid To Flush Leakage To Drain.

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FAILURES OF MECHANICAL SEAL SYSTEMSEffects of Gasket Overheating

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FAILURES OF MECHANICAL SEAL SYSTEMSChemical Attack On O-Rings

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FAILURES OF MECHANICAL SEAL SYSTEMSExtrusion - Gasket Distorted Out Of Shape.

M.SEALS

Failure of Mechanical Seal

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