How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
(OP)
I have a tunnel compressed air system that delivers air to to my facility at 120 psig. I have a compressed air work station with 1/2 inch piping and an R12 Norgren pressure regulator that drops the 120 psig air pressure to 30 psig. Cv is 3.6 for the regulator. Downstream of the Norgren Air regulator is a 1/4 inch diameter kunkle model 548 relief valve set at 30 psi with 48 SCFM capacity.
HOW do I calculate the flowrate in the 1/2 inch diameter pipe at 120 psig ? and How do I know if the Relief valve is sized correctly ?
HOW do I calculate the flowrate in the 1/2 inch diameter pipe at 120 psig ? and How do I know if the Relief valve is sized correctly ?
Joseph Muniz
Facility Engineer





RE: How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
http://www.engineeringtoolbox.com/air-flow-compres...
The 1/2" compresses air line will deliver 50-60 SCFM.
RE: How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
Note that a lot of the charts and simple equations work on the principle that the gas (air) is essentially incompressible. Once your end pressure starts to be less than 90% of the inlet pressure they become more and more unreliable as the expansion of the air takes place generating significant additional velocity.
Flow capacity using CV is easy to calculate - search for gas CV equation.
If max volume in exceeds relief valve flow out then it is undersized.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
Joseph Muniz
Facility Engineer
RE: How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
Now, what is the source of the pressure into the relief valve? (The "proper" size of the relief valve is one size that can release at least as much, if not more, than the maximum pressure coming into the pressure vessel. Your relief valve needs to be large to continuously release all of the 120 psig air coming through that 1/2 line that is ????????? long?
RE: How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
If you don't like the chart, use the app at the bottom of the page:
"Related Mobile Apps from The Engineering ToolBox
Compressed Air Pipe Lines App"
The app shows 14.8 psi pressure loss over 100 feet when compressed air is flowing at 40 SCFM
Another calculator:
http://us.kaeser.com/Online_Services/Toolbox/Press...
RE: How do I Calculate Flowrate , Q, for a one half inch pipe diameter air line using 120 psi gauge ?
Also you can estimate the maximum flow by assuming a perfect frictionless orifice (= minimum port size of regulator valve) at critical flow (sonic) conditions and use the ideal gas flow equation PV = mRT to calculate the estimated ideal flowrate (actually mass flowrate to be solved for here). Where P = critical sonic flow pressure PSIA x 144 (approx. 0.5 x upstream absolute pressure for air) V = volumetric flow rate cu. ft./sec. (= Velocity x Area of port = sonic velocity ft/sec x area ft. sq. = <SQUARE ROOT gkRT> times area of port PI(D2)/4 ft. sq., where g=32.2 gravity constant, k=1.4 ratio of specific heats for air, R=1545/29 universal gas constant for air, T sonic flow temperature = T upstream times 2/k+1, degrees Rankine = deg F + 460), m = mass flow rate lbs/sec(unknown to be calculated), R = 1545/29, T = T upstream x 2/k+1 = Sonic flow temperature deg. Rankine. Solve for mass flow rate then use ASME/API relief valve equations with calculated mass flow to size relief valve based on 44.7 psig inlet pressure. Make sure all the units you use in the equations are consistent (ft., Lbs, sec, deg R, ft sq. PSIA x 144 to PSFA, etc.