Badger Meter QuikSert - Manual (Page 16)

In this equation, the pressure (P) is absolute pressure, that is, the observed gauge pressure plus the atmospheric pressure .
The commonly used domestic unit of measure for absolute pressure is pounds per square inch absolute (psia) . Atmospheric
pressure is considered to be 14 .73 psi . Therefore, Absolute pressure (psia) is the sum of the gage pressure plus 14 .73 .
Absolute Pressure = Gage Pressure (psig) + 14 .73
The absolute temperature in the equation (T) is expressed in degrees Rankine, which is calculated by adding 459 .67 to the
temperature in ° F .
Absolute Temperature = Observed Temperature (° F) + 459 .67
Effects of Changing Pressures
For applications where the pressure does not remain constant and “Standard” units of measure must be determined, the
degree to which changing pressures affect readings must be known . Relatively small changes in pressure can produce large
errors in the calculation of standard volumes, especially at low ambient temperatures .
OTEE: N The effect of changing pressure is much greater than the effect of changing temperature . The overall effect of
changing temperature and pressure is the algebraic sum of the individual effects .
Effects of Changing Temperatures
For applications where the temperature does not remain constant, it may be desirable to compensate for large fluctuations
in temperature . In many applications, temperature changes will not produce serious measurement errors and can be
disregarded . In situations where temperature changes are more extreme, for example seasonal temperature changes from
winter to summer, reading accuracy can be adversely affected if the measurement is not adjusted for temperature effects .
Fixed Pressure and Temperature Conversions
Generally, gas volumes are reported in standard cubic feet but are measured in actual cubic feet .
OTEE: N Standard cubic feet and actual cubic feet are equivalent for gases at standard conditions of 0 psi and 60° F .
Simple conversions between Actual and Standard measurements are easy if the system pressure and temperature are known .
The general conversion formulas are:
Standard Cubic Feet =
Actual Cubic Feet x P
P
x T
a s
x T
s a
Actual Cubic Feet =
Standard Cubic Feet x P x T
s a
P x T
a ss
Where:
P
a
= system pressure in psia (14 .73 + gage pressure)
P
s
= standard pressure in psia
T
a
= system temperature in ° R (system temperature in ° F + 459 .67)
T
s
= standard temperature in ° R (standard temperature in ° F + 459 .67) = 519 .76° R
Example 1
One actual cubic foot at a pressure of 90 psig and 85° F is equivalent to how many standard cubic feet?
Standard Cubic Feet = =
104.73 x 519.67
14.73 x 544.67
=
54,425
8,023
= 6.784
1 x (90+14.73) x 519.67
14.73 x (85 + 459.67)
This example shows that there are 6 .784 standard cubic feet of gas in 1 actual cubic foot of gas at a running pressure of
90 psig and 85° F .
Turbine Flow Meter, B142 Gas QuikSert
Page 16 June 2014