Reference 8-41
8.14 Pneumatics Operation
The tester employs electrically controlled pneumatic valves to supply compressed
air (or other gas) for leak testing a component.
The valves operate in a programmed sequence to pressurize a test component and a
reference component or chamber. The test and reference components are then
isolated from each other and a differential transducer is used to monitor the
pressure difference between the two ports. A leak in the test component results in a
pressure change, which is used to decide whether a leak in the test component is
within a specified tolerance.
8.14.1 Key Components
The illustrations on the following pages show the pneumatic operation in the steps
of a typical pressure decay test using a differential pressure decay tester. The key
components shown in the diagrams are:
Combination Valve (also called a Combi-Valve)
The Combination Valve comprises the Fill/Vent and Equalization valves.
Fill/Vent Valve:
The Fill/Vent valve has 3 states.
A: Fill, selects the pressure regulator to pressurize the test component.
B: Isolate, locks or holds the pressure within the test component.
C: Vent, vents the pressure within the test component to the atmosphere.
Equalization Valve:
The Equalization valve has 2 states.
A: Open, provides a flow path from the Fill/Vent valve to the test
component via the test and reference ports.
B: Closed, isolates the individual test port, reference port, and Fill/Vent
valve from each other.
Differential Pressure Transducer
Monitors the pressure difference between the test and reference ports during
the measure step and is used to determine the magnitude of leakage of a
component connected to the test port.
Gauge Sensor
The gauge sensor transducer measure the test pressure applied to the test
component and is used to check the pressure is within the preset tolerance.
Regulator
An electronic or manual regulator supplies the required test pressure.
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