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Engineering Data
Converting pressure to flow rate.
The leak rate can be determined in flow units (cubic centimeters per
minute) based on the pressures (P-1 less P-2) measured by Sprint LC. In a
pressure decay test, Sprint LC holds the pressure drop on the main digital
readout: large numerals in the center of the LCD. The pressure drop is the
delta pressure (ΔP) in the formula.
Delta time (Δt) is the test timer value set in the pressure decay program
(provided the test passes). Because this timer is set in seconds, merely
divide by 60 to get the delta time in minutes.
Volume is the part volume plus the internal test circuit (generally between
5.0 cubic centimeters and 15.0 cubic centimeters depending on model)
plus the volume of connections between the test port and the product. The
total volume (for our example) must be in cubic centimeters.
Atmosphere is the barometric pressure in pounds per square inch (roughly
14.7 psi at sea level). This number changes with weather conditions.
ΔP
Volume
Leak Rate =
Δt
atm
psig
cubic
centimeters
cc/m =
minutes psi
*
*
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