How can I calculate the line size of a vent for an atmospheric tank?
How can I calculate the line size of a vent for an atmospheric tank?
(OP)
Hi All,
I have to design an atmospheric tank with a vent (goose neck type. The tank is being field to almost 2/3 of its height with flow rate of 194 gpm. How can I calculate the size of vent I need?
194 gpm = 26 CFM
if I choose 3/4" SCH40 vent then velocity of air will be 141 ft/sec. does it mean that in this case air inside the tank will be compressed during filling stage and pressure develops(or vaccume happens during discharge), or it only means air will be discharge at high speed with noise but without developing pressure inside?
I have to design an atmospheric tank with a vent (goose neck type. The tank is being field to almost 2/3 of its height with flow rate of 194 gpm. How can I calculate the size of vent I need?
194 gpm = 26 CFM
if I choose 3/4" SCH40 vent then velocity of air will be 141 ft/sec. does it mean that in this case air inside the tank will be compressed during filling stage and pressure develops(or vaccume happens during discharge), or it only means air will be discharge at high speed with noise but without developing pressure inside?





RE: How can I calculate the line size of a vent for an atmospheric tank?
Oh, and where there's flow, there's always pressure differential (or head difference).
RE: How can I calculate the line size of a vent for an atmospheric tank?
what are the dimensions of the tank and what product is to be stored in it?
RE: How can I calculate the line size of a vent for an atmospheric tank?
Size the vent for twice the maximum fill rate and/or 30 fps, but take DLite's comment into consideration and don't make it any less than 4".
What's the motivation for a 3/4" vent. Are you trying to set the Guiness record for the smallest tank vent ever installed?
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: How can I calculate the line size of a vent for an atmospheric tank?
RE: How can I calculate the line size of a vent for an atmospheric tank?
MAN! Real engineering. 8<)
RE: How can I calculate the line size of a vent for an atmospheric tank?
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: How can I calculate the line size of a vent for an atmospheric tank?
RE: How can I calculate the line size of a vent for an atmospheric tank?
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: How can I calculate the line size of a vent for an atmospheric tank?
RE: How can I calculate the line size of a vent for an atmospheric tank?
-Captain Obvious
RE: How can I calculate the line size of a vent for an atmospheric tank?
I have found good correlation with the Darcy-Weisbach equation for low pressure systems provided the relative pressure drop does not exceed say 10-15%. Of course in compressible flow with high line speeds and large pressure drops I would not use this equation, but we are talking about free venting. Clearly his vent is undersized with those velocities.
I do as 1gibson suggested select a pipe size and schedule, then verify it meets the calculated minimum pipe size. I am not suggesting using the Darcy-Weisbach equation will suit all design conditions but am open to suggestions that would work better. BigInch, can you supply some reference links that show this method provides large error over my stated operating range? And what other equations would you recommend using over D-W?
Cheers
RE: How can I calculate the line size of a vent for an atmospheric tank?
The more filling flow rate, the more air volume needed to be vented outside. so by increasing the filling rate, the flow rate in the vent pipe increases as well till you get chocked flow at the vent pipe. This is what you should avoid. chocked flow for a pipe with a know diameter and atmospheric pressure on discharge can be calculated. Compressible adiabatic flow equation for air flow through an orifice can be used. However, we know that sonic flow will occur when discharging air at a pressure exceeding 1.9 times the outlet pressure. So the maximum capacity of your vent pipe will be achieved if the tank pressure gets to 28 psia (13 psi gage). if you consider a discharge coeff of 0.7, then you can use the following equation:
This is how you can calculate the max capacity of your vent with a know diameter. You will see that a smaller sized vent have the capacity you are looking for, but do not overlook the practicalities.
RE: How can I calculate the line size of a vent for an atmospheric tank?
A useful article, with a spreadsheet to do the calculations, is available at http://we
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: How can I calculate the line size of a vent for an atmospheric tank?
"An undefined problem has an infinite number of solutions" Can I add ... "None of them good."
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: How can I calculate the line size of a vent for an atmospheric tank?
Although I don't generally subscribe to the notion "if some is good then more is better" when it comes to having big vents on tanks it might actually be true.
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: How can I calculate the line size of a vent for an atmospheric tank?
Special thanks to WATERPIPE, BIGINCH and ENGADDICT for their great tips. Also thanks to KATMAR, DLITE30 and 1gibson.
:)
RE: How can I calculate the line size of a vent for an atmospheric tank?
If you really want to thank them, click the little purple star under their posts where it says "thank ___ for this valuable post". Make their day.
RE: How can I calculate the line size of a vent for an atmospheric tank?
Hello All,
2nd question:
Is weep hole in the reinforcement pad of the nozzle, lugs or attachments, an ASME SEC VIII mandatory requirement? or they are better to have by ASME? or not at ASME at all? I could not find a requirement in UG-36 or UW-16. If you know where to find it could you please let me know?
Thanks