Storage tank breather vent valve

[handee]

Hi, we're desigining a 5000 gal SS atmospheric storage tank for non-flammable liquid. Well be filling it at about 100 gpm and draining it at about 30 gpm. I simply need a breather vent to let the air out when filling, and let the air in when draining (its a little smelly so we'll be venting it to the roof).

My supplier has specified a $500 53-lb Crispin dual vacuum and pressure air release valve that looks awufully complicated to me for the required duty. Does someone have experience with a simpler breather vent valve?

Thanks!

Fran McConville

 

[BenThayer]

i'm not real familiar with Crispin's systems but have seen many devices like these from Protectoseal at

http://www.protectoseal.com/18540chart.html

but the $500 price tag does not sound very expensive for something you are referring to as complicated.

also, the 30 gpm sounds like too small a number for withdrawal from a tank that size. make sure you are looking at all scenarios and not just the normal withdrawal rate. often overlooked scenarios for an atmospheric tank are draining after the flushing/washing or leak testing.

A 2" or 3" nozzle wide open when full will pass much more than 30 gpm. Also, if you have two tanks in parallel and you want to balance between the two tanks via a pump suction line, you can move a lot of liquid very fast!

most of these types of mistakes are caused by failing to look at how we commission and operate equipment at other than the design steady state..

 

[JStephen]

It could just be a "free vent", a gooseneck or mushroom-type vent with screen, no pallets.

On a tank that small, check the maximum pressure it can handle. That may help reduce the vent size if you do use a P/V vent.

Tyco/Varec, Shand&Jurs, Groth are some other names to look up for P/V vents.

 

[sailoday28]

As BenThayer (Chemical) has stated, the drainage flow, if unrestircted could be much higher than 30 gpm. Therefore check maximum vacuum of tank design and resulting dp across vent when drainage occurs.

 

[EGT01]

FXM,

Is this the Crispin valve you are referring to?

http://www.crispinvalve.com/dualair.htm

Unless it is a "bullet" style storage tank that is being supplied, I would have some reservation for using this valve on a tank built to API-650 or API-620.

Determine the code to which you tank is constructed and follow the typical relief guidelines accordingly.

 

[JimCasey]

I have no experience with the Crispin valve but it appears to made for water or sewage. You mentioned that your process fluid is smelly..So if your stuff is sewage, this might be the best valve particularly since they mentioned an AWWA code conformance for vacuum breakers and air release valves.

I DO have a lot of experience with Groth and Protectoseal conservation vents and they are as reliable as gravity. The moving disc that opens and closes is called a Pallet. Base cracking pressure is about 1/2 ounce/sq in. Adding weight discs to the pallets raises the set pressure. The sealing member is a thin TFE sheet, that flexes to shed ice and contaminants.

 

[handee]

Thanks for all of your advice, folks, and for the warning to pay attention to non-standard operations. Yes, that was the type of Crispin valve our supplier recommended, but I think one of the Protectoseal or Groth models will do better, or even the free vent idea. However, I will check with the tank manufacturer for guidance on the relief guidelines in API-650, the applicable design code.

Fran McConville

 

[TD2K]

API 2000 is the guide for relief requirements for tanks.