Setting of pressure and vacuum valves - API 650 tank
Setting of pressure and vacuum valves - API 650 tank
(OP)
I am looking for some guidance for the following situation:
I have a new tank farm with small API 650 tanks for gasoline and ethanol (diameters ranging from 12 to 60ft). I am planning on using pressure/vacuum valves to reduce losses (project is not in the US). Maximum vapor pressure will be 9 psia Reid and max temp will be 100 F.
I would like to know:
- How to determine an adequate set pressure for the pressure/vacuum valves, and what would be typical pressures for this situation.
- How these set pressures are related to the capacities given by manufacturers for their valves, and to the design pressure of the tank (I've seen some confusing info related to using 1/2 of the set pressure to determine capacity of the valves)
I'll appreciate any input.
I have a new tank farm with small API 650 tanks for gasoline and ethanol (diameters ranging from 12 to 60ft). I am planning on using pressure/vacuum valves to reduce losses (project is not in the US). Maximum vapor pressure will be 9 psia Reid and max temp will be 100 F.
I would like to know:
- How to determine an adequate set pressure for the pressure/vacuum valves, and what would be typical pressures for this situation.
- How these set pressures are related to the capacities given by manufacturers for their valves, and to the design pressure of the tank (I've seen some confusing info related to using 1/2 of the set pressure to determine capacity of the valves)
I'll appreciate any input.





RE: Setting of pressure and vacuum valves - API 650 tank
For doing PSV calculations for pressure vessels, this procedure is clear and straight forward. When you are working with "atmospheric tanks", the situation (to me) is much less clear. You need a design pressure for the tank, but you frequently do not have one. If you are buying a new tank, insist on the vendor supplying you with the maximum allowable working pressure for the tank. If you are working with an existing tank, that number is often not available. The only advice I have received in the past is that you must have the MAWP. I guess you need to pay an outside expert to come in, take measurements, then calculate an MAWP if you don't have the in-house ability to do this.
Next you must consider the PVSV characteristics. Unlike "pop action" PSV's, conservation vents START to open at their set pressure but do not reach full relieving capacity until a somewhat higher pressure. You must know or estimate that somewhat higher pressure so you'll have the set point low enough that the full open position is reached before the tank goes. As you can see, the situation is much "messier" than with pressure vessels. When I've previously whined about this, some of the experts like Phil Leckner have jumped in and said, "Sorry, that's just the way it is." So, I'm resigned to this unhappy state of affairs, but hope for the day when the codes will make it mandatory to at least list MAWP on the tank.
Good luck with all this. You'll need it.
Doug
RE: Setting of pressure and vacuum valves - API 650 tank
RE: Setting of pressure and vacuum valves - API 650 tank
My question is more related to the pressure that I should use for the P/Vs. The maximum vapor pressure is 9 psia, so theoretically, any pressure just above atmospheric pressure will be enough for my purpose. Then, should I use 1 oz/in2, 5, 10 as the set pressure? For what I read above, once selected the set pressure of the P/V valves, I need to get the maximum pressure from the manufacturer (based in my relief capacity)which will be more than the set pressure, and design the tanks with an adequate safety margin.
Are there any recommendations for this pressure? I remember seen some info from one oil company, but don't have that information now.
RE: Setting of pressure and vacuum valves - API 650 tank
RE: Setting of pressure and vacuum valves - API 650 tank
If the installation is outside US, you may also have to consider the European PED directiv and the ATEX and CE
regulations for the vessels and the PVSV.
From Europe