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Bypass Valve
Piston
Inlet
Outlet
Figure 3 Basic Piston Prover
In real-world applications, there are significant dynamics to consider. At the beginning of a cycle, pressure rises rapidly until the piston
accelerates to the speed of the flow stream. Figure 4
is an illustration of a typical Cal=Trak’s internal pressure during a measurement cycle.
A near-maximum flow rate is illustrated to accentuate the pressure variations. The initial pressure pulse, lasting some tens of milliseconds,
reaches a peak of about 0.5 kPa, or 0.5% of its working, near-atmospheric pressure. The pressure settles out to about 0.1 kPa (0.1% of
working pressure) during the timed period. This pressure represents the added pressure due to the weight of the piston. Very small
oscillations continue due to the piston’s under damped nature.
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 100 200 300 400 500 600 700 800 900 1000
Milliseconds
Intracell Pressure (kPa)
Timing
Begins
Timing
Ends
Initial Pressure Pulse
Figure 4 Cal=Trak Internal Pressure