Contact US

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!

*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

Vacuum Breakers on Tank Roof

Vacuum Breakers on Tank Roof

Vacuum Breakers on Tank Roof

Dear All,

I am trying to understand the root cause driver behind the requirement to activate the vacuum safety valves on the floating roof tank rood when the roof lands on the tank's bottom, is it due to the sudden displacement of the liquid and the risk of tank's implosion due to the depletion of the liquid from the tank once it lands. Any reference to the same in API 650 or 620?

Thanks alot


RE: Vacuum Breakers on Tank Roof

Basically, Yes

Once the floating roof hits the floor with its legs it becomes, in essence, like any other type of fixed roof tank and all the normal requirements apply.

Just when you want the roof seals to leak they will seal tighter than a ducks ar8se on you....

There nothing specific in API 650 on this I think other than if you don't you'll exceed the external pressure and collapse the tank.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Vacuum Breakers on Tank Roof


I'm not familiar with floating roofs. Are they given a vacuum rating in initial design in the fully empty position to which a vacuum relief can be designed? During normal operation vacuum wouldn't be an issue, but the floating roof becoming a fixed roof now requires a design pressure for the scenario.

RE: Vacuum Breakers on Tank Roof

The floating roof should have vents to allow for vapor expansion and contraction beneath the roof when it is landed.Typical application, is to install PV valve to provide venting capability.

This is copy and paste from API 650 Appendix C

(C.3.9 Vents
To prevent overstressing of the roof deck or seal membrane, automatic bleeder vents (vacuum breakers) shall be
furnished for venting air to or from the underside of the deck when filling or emptying the tank. The Manufacturer shall
determine and recommend the number and sizes of bleeder vents to be provided based on maximum filling and
emptying rates specified. Each automatic bleeder vent (vacuum breaker vent) shall be closed at all times, except
when required to be open to relieve excess pressure or vacuum, in accordance with the Manufacturer’s design. Each
automatic bleeder vent (vacuum breaker vent) shall be equipped with a gasketed lid, pallet, flapper, or other closure

RE: Vacuum Breakers on Tank Roof


Basically it goes back tot he design of a normal 650 tank, i.e. vacuum of about 1 inch water column is all it is good for.
API 650 tanks really really don't like negative pressure.

Hturk has it spot on.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close