39
Zaxis Inc. LLC
801.264.1000
2442 South 2570 West
West Valley City, UT 84119
6.2
Engineering Data.
Converting Pressure to Flow Rate
You can determine the leak rate in ow units (cubic centimeters per minute) based on
the pressures measured by the Isaac. In a pressure decay test, the Isaac holds the
pressure drop on the main screen. The pressure drop is the delta pressure (ΔP) in the
formula.
Delta time (Δt) is the test timer value set in the Isaac’s pressure decay program (provid-
ed the test passes). With this timer being set in seconds, simply divide by 60 to get the
delta time in minutes.
Volume is the part volume plus the Isaac’s internal test circuit (approx. 1cc) plus the
volume of connections between the Isaac’s test port and the product. The total volume
(for our example) must be in cubic centimeters.
Atmosphere is the absolute barometric pressure in mbar (approx. 1000 mbar at sea
level). This number changes with weather conditions.
Leak Rate
(cc/m)
=
ΔP (psi) • Volume (cc)
Δt (minutes) • Atm (psi)
∆P = Decay in pressure, value shown at end of test.
∆t = Test step time in minutes (test time reads in seconds divide by 60).
Volume = Volume of product and leak tester and any xture volume.
Atm = Atmosphere pressure (psia) eg sea level = 14.7 at 68 F. Adjust at elevation is
required.
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