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Vacuum Breakers on Tank Roof

Vacuum Breakers on Tank Roof

Vacuum Breakers on Tank Roof

(OP)
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

Regards,

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.

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Also: If you get a response it's polite to respond to it.

RE: Vacuum Breakers on Tank Roof

LI,

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
device...)


RE: Vacuum Breakers on Tank Roof

TiCL4,

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.

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Also: If you get a response it's polite to respond to it.

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