Overflow pipe verses venting.

[darthsoilsguy2]

There is a overflow/overfill line inside a API 650 tank built in 2004 that i'm looking at.

It's intake is about 2' below the roof the fixed roof. The 8" pipe comes down the inside, elbows towards the wall, penetrates the shell, and elbows down outside the tank. The tank roof has a 4" pipe vent with pressure/vacuum conservation vent attached.

Here's my question:

Do overflow pipes come with some sort of check valve that prevents the pipe from venting air in or out, but will allow product to discharge? Or is it likely that the conservation vent is doing nothing?

 

[IFRs]

It's likely that the overflow pipe allows air in and out and the vent is there to protect the tank if the pipe becomes clogged. You'd see a check valve if there was one - it is unlikely to be inside the tank. There might be a float type cover on the inside pipe but I doubt it.

 

[darthsoilsguy2]

All I could see was a large opening sized screen on the top.

The Owner is a public university and they had installed an aftermarket gas collection system on the outlet end of the conservation vent. I'm guessing to make other 'stakeholders' at the campus happy.

 

[MJCronin]

Thank God for "stakeholders" and all engineering preformed by non-engineers.

Lets talk about purposes....

An overflow serves to direct flow to a safe place in the event of a filling error. It is a device used to prevent possible tank structural damage and an uncontrolled spill. The overflow sized is based on a maximum filling rate and it can act as a vent.

A conservation vent is a necessary device that has nothing to do with overfilling the tank. It functions to prevent overpressure and underpressures during normal tank activities (including filling)

In properly designed systems, one would expect to see a vent pipe that was equal to or smaller than a fill pipe. Similarly, in properly designed systems, one would expect to see an overflow that was one or two pipe sizes larger than the fill pipe.

Whats in the tank ??

 

[Duwe6]

And yes, you need a device on the Overflow Pipe to force the 'breathing' to go thru the Pressure/Vacuum Conservation Vent. It is called an Overflow Valve. Go to *Protectoseal* or *Shand & Jurs* and buy an Overflow Valve. They both have good websites. Conservation Vents and Overflow valves are old technology, work well, and you REALLY need an Overflow Valve. It should have been installed at the same time as the Conservation Vent was.

Otherwise, throw away the Pressure/Vac Conservation Vent device. It is not being allowed to work.

 

[darthsoilsguy2]

@mjcronin
#6 heated fuel oil. Funny how clean the conservation vent is though.

@Duwe6
There was definitely nothing like what i saw on S&J or Protectoseal's site going on at that pipe. We shouldn't throw it away. it's practically new off the shelf with some UV damage to the lid and wingnut/washer corrosion.

I've seen a lot of tanks with the overfill serving as a vent, and a bunch of tanks without overfill pipes that have conservation vents. 1st time i've seen both when i posted OP..... but now i've seen two more tanks with similar worthless vents at the same campus.