While the FSA makes every reasonable attempt to ensure that the information contained in this document is accurate and current, the FSA, its officers, directors, volunteers, and authorized agents are not responsible for any errors or omissions contained therein nor are they responsible for any results obtained from the use of or reliance upon its content. All information is provided “AS IS,” with no guarantee of completeness, accuracy, timeliness or of the results obtained, and without warranty of any kind, express or implied. In no event shall FSA or its officers, directors, volunteers, or authorized agents be liable to you or anyone else for any decision made or action taken in reliance on the information con tained herein or for any for any consequential, indirect, special, or similar damages, even if advised of the possibility of such damages. The informa tion contained in this document is for informational purposes only and does not constitute professional advice. It also includes references to certa in standards that may change over time and should be interpreted only in light of particular circumstances. It is your sole responsibility to confi rm the current state of any referred to standards. FSA reserves the right to modify or update the document content and to modify this Disclaimer at any t ime, effective upon posting of an updated version of this Disclaimer.
This Fluid Sealing Association Knowledge Series training presentation introduces the various configurations of mechanical seals together with an overview of their selection process. A description is provided on:
▪ Seal arrangements – single and dual seals
▪ Dual seal configurations
▪ Piping plans
▪ Seal selection
Mechanical Seal Components
▪ All mechanical seal consist of the same basic elements. These elements may vary in form with different seal types, however the function they provide is the same
Seal Plate (Gland) Gasket
Flexible Element (Spring or bellows/diaphragm)
Seal Plate (Gland)
Stationary Face
Secondary Seal
PROCESS FLUID ATMOSPHERE
Face Pair
Seal Arrangements
Seal Arrangements
Mechanical seals can be grouped into 3 distinct arrangements:
Arrangement 1) Single mechanical seal
A mechanical seal assembly with one pair of seal faces
Arrangement 2) Dual unpressurized mechanical seal
A mechanical seal assembly with two pairs of seal faces. The cavity formed between the two seals is unpressurised and can be filled with a liquid or gas
Arrangement 3) Dual pressurized mechanical seal
A mechanical seal assembly with two pairs of seal faces. The cavity formed between the two seals is pressurized above the process fluid pressure and can be filled with a liquid or gas
Seal Arrangements
Typical arrangement 1 single mechanical seal
Single mechanical seals can incorporate various features to allow the environment on either the process fluid or atmospheric side of the seal to be altered. These include ports (connections) in the seal plate (gland), close clearance bushing or lip seals on the atmospheric side of the seal.
Seal Arrangements
Arrangement 2 and 3 dual mechanical seal
Dual mechanical seals incorporate two mechanical seals in the seal assembly.
These two seal can be arranged in 3 different Configurations (positions of the inner and outer seal relative to each other).
In addition, the cavity that is formed between the two seal can be filled with a liquid or gas that is connected to a seal support system (that controls and monitors the fluid). This fluid cavity can remain unpressurised (Arrangement 2) or pressurized (Arrangement 3)
Arrangement 2 and 3 Configurations
Face-to-Back Configuration
In this configuration, the face of the inboard seal is adjacent to the back of the outboard seal. This configuration can be operated as an Arrangement 2 or 3 seal. Traditionally referred to as a Tandem seal, however this description often implies an Arrangement 2 seal only.
Dual Seal Configurations
Back-to-Back Configuration
In this configuration, the back of the inboard seal is adjacent to the back of the outboard seal. This configuration is commonly used in high pressure Arrangement 3 seals. Traditionally referred to as a Double seal, however this description often implies an arrangement 3 seal only.
Dual Seal Configurations
Face-to-Face Configuration
In this configuration, the face of the inboard seal is adjacent to the face of the outboard seal. This configuration is commonly used in high pressure applications or equipment with high shaft speeds as an Arrangement 3 seal.
Dual Seal Configurations
Face-to-Face Configuration
An alternative Face-to-Face configuration, with the mechanical seal flexible element rotating with the shaft, is commonly used in abrasive chemical applications or pumped fluids with suspended solids.
Seal Environment
Seal Environment
Reliable performance of a mechanical seal is principally governed by the environment that the seal is operating in.
The selection of a mechanical seal type, arrangement and configuration are dictated by the fluid properties and operating conditions.
Piping plans can be selected to alter the environment around the mechanical seal to enhance reliability and safety.
These piping plans are defined in a standard published by the American Petroleum Institute, API-682.
Piping Plans
Basic Types of Piping Plans
Piping plans can be grouped into 3 types. These types relate to which part of the mechanical seal environment the piping plan effects
Piping Plans can be connected to:
▪ Process fluid side of the seal
▪ Atmospheric side of the seal
▪ Barrier or buffer cavity of a dual seal
Process Fluid Flush Plans
Process Fluid Piping Plans change the seal chamber conditions by:
▪ Changing temperature
▪ Changing Pressure
▪ Creating flow to remove debris
▪ Removing trapped vapor
Process Fluid Piping Plans Can be used on all seal Arrangements
Process Fluid Flush Plans
Common Process Fluid Piping Plans :
API Plan 02 Provisions for heating/cooling jacket around the seal chamber and/or seal plate (Gland plate)
API Plan 11 Recirculation of fluid from the pump discharge to the seal chamber
API Plan 13 Recirculation of fluid from the seal chamber to the pump suction
API Plan 14 Plan 11 and 13 together
API Plan 21 Plan 11 with an inline heat exchanger
API Plan 23 Seal chamber fluid circulated through a heat exchanger
API Plan 32 External flush fluid injected into the seal chamber
Atmospheric Piping Plans
Atmospheric Piping Plans change the environment around the mechanical seal by:
▪ Changing temperature
▪ Cleaning to remove debris
▪ Displacing atmosphere (oxygen or humidity)
▪ Monitoring leakage
Atmospheric Piping Plans Can be used on all seal
Arrangements
Atmospheric Piping Plans
Common Atmospheric Piping Plans :
API Plan 51 Dead-ended vessel providing an atmospheric quench liquid.
API Plan 62 Quench fluid (liquid, gas or steam) injection at the atmospheric side of the seal
API Plan 65A/B Leakage detection (detected by leakage flow)
API Plan 66A/B Leakage detection (detected by leakage pressure)
Dual
Seal Piping Plans
Dual Seal Piping Plans Barrier/buffer cavity Piping Plans change the environment between the inner and outer mechanical seal by:
▪ Changing temperature
▪ Providing a safety buffer or barrier
▪ Providing an alternate fluid to lubricate the seal faces
Dual Seal Piping Plans Can only be used on Arrangement 2 and 3 seals
Dual Seal Piping Plans
Dual Seal Piping Plans :
Arrangement 2 (Unpressurized dual seals)
API Plan 52 Liquid buffer stored in a reservoir and delivered to the mechanical seal
API Plan 55 Liquid buffer delivered to the mechanical seal from an external system
API Plan 72 Gas buffer delivered to the mechanical seal from a gas control panel
API Plan 75 Condensing leakage detection used with Plan 72
API Plan 76 Non-condensing leakage detection used with Plan 72
Dual Seal Piping Plans
Dual Seal Piping Plans :
Arrangement 3 (Pressurized dual seals)
API Plan 53A Liquid barrier stored in a reservoir and pressurized by a gas blanket
API Plan 53B Liquid barrier pressurized by a gas bladder accumulator
API Plan 53C Liquid barrier pressurized by a piston accumulator
API Plan 54 Liquid barrier delivered to the mechanical seal from an external system
API Plan 74 Gas Barrier delivered to the mechanical seal from a gas control panel
Seal Selection
Seal Selection
The process of selecting a seal involves:
▪ Reviewing the operating conditions in the seal chamber
▪ The process fluid physical and chemical properties
▪ Any hazards the process fluid may present to personnel and the environment
▪ Reviewing industry or user specifications and requirements
▪ Reviewing federal or local mandated specifications
* Contact your seal vendor for more detailed guidance in the seal selection process
Seal Type Selection
The selection of seal type is determined by the pumping conditions and pumped fluid properties. This can be generalized as:
▪ If the pumped fluid has a low specific gravity (density) or has a low vapor pressure at the pumping temperature, dual seals should be selected (arrangement 2 or 3)
▪ If the pumping temperature is outside the limits of elastomers (O-rings), then a metal bellows with non-elastomeric secondary seal should be selected
▪ If the pumped fluid has a moderately low specific gravity, then a pusher seal should be selected
* Contact your seal vendor for more detailed guidance in the seal selection process
Seal Type Selection
Contact your seal vendor for more detailed guidance in the seal selection process
Selecting the seal Arrangement
Is the process fluid:
▪ Very hazardous or a poor lubricant or abrasive
▪ Hazardous
Non-hazardous
Arrangement 2
Arrangement 1
* Contact your seal vendor for more detailed guidance in the seal selection process
