MECHANICAL SEALS FOR WATER / WASTEWATER … Seals_TimSullivan.pdf · packing vs mechanical seal?...
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Transcript of MECHANICAL SEALS FOR WATER / WASTEWATER … Seals_TimSullivan.pdf · packing vs mechanical seal?...
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MECHANICAL SEALS FOR
WATER / WASTEWATER
INDUSTRIES
AWWA / MWEA
FEB 5, 2014
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SINGLE STAGE SPLIT CASE
PUMP
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Various Pump Types
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PACKING VS MECHANICAL
SEAL? PACKING
LOW INITIAL COST
HIGH MAINTENANCE
COST
LEAKAGE
ADJUSTMENT
SHAFT WEAR
HIGH FRICTION
HIGH ENERGY USAGE
SEAL
HIGHER INITIAL COST
LOW MAINTENANCE
COST
NO LEAKAGE
NO ADJUSTMENT
NO SHAFT WEAR
LOW FRICTION
LOW ENERGY USAGE
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Component Seal
Low cost
Installation settings are critical
Fit in limited space pumps
Do not allow impeller adjustment easily
Default OEM design
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BASIC UNBALANCED MECHANICAL SEAL
GLAND
GASKET
STATIONARY
FACE ROTARY
FACE
SPRINGS
SET
SCREWS
DYNAMIC
O RING
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Set Screws Rotary Face Stationary Face
Wave Spring
Dynamic O Ring
SINGLE COMPONENT SEAL
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Component Seal Installation
Measure shaft size - +.000, -.002
Disassemble pump & repair as needed
Reassemble pump WITHOUT seal
Adjust impeller clearance
Mark position on shaft of stuffing box face
Disassemble pump, install seal, reassemble pump
Lubricate shaft o ring
Slide seal onto shaft
Install gland with stationary face
Install environmental control
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Single Cartridge Seal
Most common type
Simple installation
In plant repairs
Allows for impeller adjustment without
disassembling pump
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SINGLE CARTRIDGE SEAL
HEAVY DUTY
GLAND
GASKET
FLUSH PORT
QUENCH PORT
LOCK
RING
SPRINGS
SEAL SLEEVE STATIONARY
FACE ROTARY
FACE
DYNAMIC O RING
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Single Cartridge Seal
Installation
Measure shaft size - +.000, -.002
Disassemble pump to gain access to shaft
Lubricate shaft o ring
Slide seal onto shaft
Adjust impeller clearance
Tighten gland bolts, either 2 or 4 bolts
Tighten lock ring set screws
Remove centering clips
Install environmental control
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Split Seal
No need to dis-assemble pump
Installs in about one hour
Can be installed on worn shaft/sleeve
In plant repairs
Not intended for low emissions service
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GLAND
GASKET
ROTARY
HOLDER
SPLIT MECHANICAL SEAL
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Split Seal Installation
Measure shaft size - +.000, -.002
Adjust impeller clearance
Install rotary holder, O ring & faces
Rotary holder position is important!
Install gland
Tighten gland bolts, either 2 or 4 bolts
Install environmental control
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STUFFING BOX PRESSURE
If you are going to flush a mechanical
seal or packing you need to know the
stuffing box pressure
Flush pressure should be 15 psi above
stuffing box
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STUFFING BOX PRESSURE
SINGLE STAGE END SUCTION PUMP
DISCHARGE PSI MINUS SUCTION PSI
DIVIDED BY 4 PLUS SUCTION PSI =
STUFFING BOX PSI
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End suction pump stuffing box pressure
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SINGLE STAGE SPLIT CASE
PUMP
STUFFING BOX PRESSURE =
SUCTION PRESSURE
STUFFING BOX IS LOCATED IN
SUCTION FLOW PATH
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SINGLE STAGE SPLIT CASE
PUMP
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Environmental Controls
There are many ways to control the
environment that the seal operates in
The seal or the process fluid can be
heated, cooled OR cleaned
Some methods will dilute the process
fluid
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Vertical Turbine Seals
Installed after the pump is mounted
The motor is mounted
Impellers are adjusted
Seal Sleeve is tightened to shaft and mounting clips are removed
Install vent line
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STUFFING BOX PRESSURE
IN MANY APPLICATIONS THE
STUFFING BOX MAY BE UNDER A
VACUUM EVEN THOUGH THE PUMP
DISCHARGE PRESSURE IS HIGHER
THAN ATMOSPHERIC PRESSURE
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What Can Make a Good Seal
Leak?
Wrong materials of construction
Excessive face movement
Face hang up
Excessive heat
Abrasive damage
Wrong environmental control
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Materials of Construction
Metal parts, o-rings and faces must be
able to withstand the temperature,
pressure and corrosive nature of the
chemicals being sealed
This can usually be determined by a
combination of chemical listings and
plant experience
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Excessive Face Movement
Face movement is caused by several
factors
Shaft deflection and vibration are the
most common causes
Excessive face movement is inherent to
many seal designs
Springs on stationary face and self
centering lock rings significantly reduce
face movement
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Face Hang Up
If the seal faces are not free to move
easily at their interface with the o-rings
they will hang up, the result of this
hang up will be faces that open
allowing leakage and abrasive damage
The best seal designs have o-rings
that ride on clean, highly polished
surfaces
As the faces wear the o-rings should
travel to a clean surface
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Excessive Heat
The most heat sensitive part of a seal is
the o-ring
Excessive heat can be caused by high
pressure, process fluid temperature or
friction from the seal itself
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Excessive Heat
If heat damage occurs consider the
following:
Reduce the stuffing box pressure
Cool the process fluid or the seal either
internally or externally
Use a seal design, or faces, that
generate less frictional heat
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Abrasive Damage
In most cases abrasive damage to
seal faces occurs only after the faces
are allowed to open
Most abrasive particles will not fit
between the faces when they are
closed
Flush systems and various box
bushings can reduce abrasives
Using seal designs that limit face
movement will reduce abrasive failures
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