Lake Monitors Flow Transmitters - Manual (Page 11)

Measuring ranges cover 1.5-12 SCFM through 150-1300 SCFM.
Twenty-four port sizes from 1/8" through 2" in NPT, SAE and BSP can
be ordered to meet specific plumbing requirements. Lake’s pneumatic
meters are also available in alarm and transmitter configurations for
electronic monitoring applications.
Standard Cubic Feet
Lake’s meters are calibrated to measure the
flow of compressible media (gases) in SCFM
– standard cubic feet per minute. A “standard”
cubic foot is defined as a cubic foot of dry air
at standard atmospheric conditions: 70ºF and
14.7 PSIA (0 PSIG) measured at sea level.
When a standard cubic foot of air is
compressed, its actual volume will decrease
proportionally as absolute pressure increases.
For example, a standard cubic foot of air’s
actual volume will decrease by 50% and
density will increase by 100% as the air is
compressed from atmospheric pressure 14.7
PSIA (0 PSIG) to 29.4 PSIA (14.7 PSIG).
See Illustration 2.
There are three factors that affect the Flow
Meter Calibration: specific gravity, pressure
and temperature.Lake meters are calibrated
for air (specific gravity of 1.0) at 70ºF and 100
PSIG. Most low pressure rotameters are
calibrated at 0 PSIG and require corrections
for use at any other pressure.
Lake meters are designed for pneumatic
systems where pressures between 90 - 110
PSIG are used. In these common applica-
tions, a Lake meter with a standard
calibration can be read directly without
applying corrections.
Page 11 / Flow Meters / Lake Manual
14.7 PSIA (0 PSIG)
29.4 PSIA (14.7 PSIG)
58.8 PSIA (44.1 PSIG)
Illustration 2
Illustrates the effect of
different pressures on
the volume of gas.