×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

The 4 Common Valve Sealing Mechanisms
3

The 4 Common Valve Sealing Mechanisms

The 4 Common Valve Sealing Mechanisms

(OP)
I read with interest a post which asked, "What is the difference in a Position Seated and a Torque Seated Valve"? In reading the answers, I was disappointed that none came close to facts. As such lets start:

There are 4 Basic Valve Sealing Mechanisms:
1) INTERFERENCE FIT
2) PRESSURE ASSISTED SEAL
3) POSITION SEATED
4) TORQUE SEATED


INTERFERENCE FIT:
A Resilient (rubber) seated butterfly valve is an example of an Interference Fit Sealing Mechanism. This is a very technical way of saying that the OD of the Disk is larger than the ID of the liner. Hence, when the disk moves to the closed position, interference is created which seals the valve. Other examples of Interference Fit valves are:
a) Gate Valves (think Wedge Gate)
b) Plug Valves
c) Crusher Seated Ball Valves

Typically, Interference Fit designed valves:
1) Are Bi-Directional
2) Will seal independent of line pressure

PRESSURE ASSISTED SEAL:
A free floating ball valve is an example of a Pressure Assisted Sealing Mechanism. This design uses the line pressure to force the ball, gate or plug into the seat. Theoretically, the higher the pressure (up to the full rated pressure), the better a seal is created. As such, these valves are typically uni-directional, but not always. As in the case of the ball valve, which has 2 seats, and seals bi-directional. One must be careful with application of Pressure Assisted Seal valves for 2 reasons:
1) In low Delta P application, you can see significant leakage!
2) In Flow Up applications, some valves, like Knife Gate Valves, need to be installed BACKWARDS in order to properly isolate.

Other examples of Pressure Assisted Seal Valves are:
1) Knife Gate Valves (single seated, where the seat is on the P2 side of the valve)
2) Single Offset High Performance Butterfly Valves

POSITION SEATED VALVES:
These are valves which simply must be in a specific position in order to seal. Two good examples would be:
1) High Performance (double offset) Butterfly Valves
2) Parallel Disk Gate Valves (high pressure valves used for steam isolation)

In both the above mentioned valves (one being rotary, the other being linear), if they are not in the correct position, they will not seal.

TORQUE SEATED VALVES:
A Torque Seated Valve is a version of a Position Seated Valve which not only must be in the correct position, but also have a specific torque to achieve sealing. The primary example of this valve is a Triple Offset Valve (Butterfly design). The Triple Offset Valve or TOV has a 3rd offset which is the sealing cone. Like a double offset butterfly, both create a cam effect. Unlike the double offset though, the triple can be in the proper position and still leak considerably.

Understanding these various SEALING MECHANISMS is crucial to properly applying any valve. Feel free to send questions as I am willing to help!

I teach a very detailed 8 hour VALVE APPLICATION FUNDAMENTALS Course and this is just one of the topics covered.

Valve APPLICATION FUNDAMENTALS Link: http://valveactuation.com/valve-application-traini...

RE: The 4 Common Valve Sealing Mechanisms

Have you considered posting a FAQ? This would be a useful starting point, and you can add as many as you wish.

RE: The 4 Common Valve Sealing Mechanisms

(OP)
Scotty,

I am brand new to this forum and would love some advice on how to add an FAQ to this. Any suggestions would be appreciated!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources