- Air Release Valve Placement
- Air Release Valve Sizing Programs
- Air Release Valve Irrigation
- 2 Air Release Valve Dimensions
Sizing Calculation Air Release Valve Sizing Calculation Air Release & Air / Vacuum Breaker Valve(Including Combination Type) Sizing 1. Air and vacuum Valves should be sized to handle the maximum amount of air to be exhausted or admitted into the pipeline and not exceed an acceptable pressure differential across the valve. For many decades sizing orifices for Air Release Valves has been a mystery. Air entrapped in pipelines is an invisible culprit and no quantitative means exist to determine the precise amount of entrapped air in a flooded transmission pipeline. Groth is the leading Innovator for Pressure/Vacuum Relief Valves, Pressure Relief Valves, Vacuum Relief Valves, Pilot Operated Valves. Sizing Program. Groth Corp manufacturer of pressure/vacuum relief valves. Groth Corporation is committed to providing innovative solutions, quality products and comprehensive service to improve the.
Sample Problem Statement
Design a pressure relief valve for the following service.
Protected equipment : Separator vessel
Relief service : Fuel Gas
Reason for relief : Blocked gas discharge
Relieving Rate : 10,000 kg/hr
Gas Density : 4.1 kg/m3
Ratio of specific heats for the gas (CP/CV) : 1.35
Compressibility factor of gas = 0.95
Relieving temperature = 200C
Set pressure : 5 barg
Accumulation : 10%
Back pressure at relief valve discharge : 0.5 barg
Type of relief valve : Conventional
Solution
This sample problem for relief valve sizing calculation can be solved in following steps, which are based on pressure relief valve sizing procedures described in API RP 520 Part I. The first step is to determine whether the gas flow type is critical or sub-critical.
Step1
The first step is to determine if the flow conditions are critical. For this purpose the critical flow pressure (Pcf) downstream to the relief valve has to be calculated using the following equation from API RP 520 Part I,
P1 : Relieving pressure upstream to relief valve in bara
P1 = 6.51 bara (including 10% accumulation)
k : Ratio of specific heats of the gas .. (CP/CV)
k = 1.35
Pcf : Critical flow pressure for the given flow conditions in bara
Pcf = 3.5 bara
If the pressure downstream or back pressure of the relief valve is lower than the critical flow pressure, then the flow is said to be of critical type. In this case, the actual pressure downstream to the relief valve cannot fall below the critical flow pressure even if much lower pressure exists further downstream to the valve. Mass flow relieved cannot increase any further, for the given set of flow conditions upstream to the valve.
In the present case, back pressure (1.5 bara) < Pcf (3.5 bara). Hence the flow is of critical type.
Step2
Next step is to use the relief valve sizing procedure given in the API 520 part I for critical flow type gas relief valve. The following equation is used,
... (1)
A : orifice are requirement in mm2
W : flowrate in kg/hr
W = 10,000 kg/hr
T : Temperature in Kelvin
T = 273.16 + 20 = 293.26 K
Z : compressibility factor of gas
Z = 0.95
Air Release Valve Placement
C : coefficient for fire case as a function of k (CP/CV) as per following equation,
Here, C = 351.6
P1 : Relieving pressure upstream to relief valve in bara
P1 = 6.51 bara (including 10% accumulation)
Kd : Coefficient of discharge
Kd = 0.975 for gas service
Air Release Valve Sizing Programs
Kb : capacity correction factor due to back pressure
Kb = 1 (for conventional relief valves with near atmospheric backpressure)
KC : combination correction factor for use of rupture discs
KC = 1 (for absence of rupture disc upstream to the valve)
Plugging this data into equation (1), the minimum required orifice area for the relief valve is calculated to be,
A = 22.0 cm2
Step3
Air Release Valve Irrigation
The next higher available orifice area should be selected for the pressure relief valve to be actually installed. Referring to the table of standard orifice sizes given in EnggCyclopedia's relief valve sizing calculator,
2 Air Release Valve Dimensions
Next high available orifice area is selected to be A = 23.20 cm2 and the corresponding designating letter is 'M'. Available valve size is '4M6', which correspond to different nozzle sizes for suction and discharge nozzles of the pressure relief valve. For a '4M6' valve suction nozzle is of 4' size and discharge nozzle of 6' size.