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

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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