Pressure Decay Testing
Elements Involved In Electronic Pressure Decay Leak Testing
- FTI leak testing systems use Air Pressure, Electronics and Pneumatic components to perform leak tests.
- Air pressure and/or vacuum are the media used to test for leakage on all FTI systems
- The electronics control the timing of each step in a leak test and monitor the pressure in the test part.
- Pneumatic components control where the pressure goes and convert the pressure in the test part to an electrical signal.
System Components
- Precision Regulator: Usually available in a variety of sizes and have precision diaphragms for precise pressure adjustment
- Precision Valves: Normally poppet style with small orifices designed for zero leakage. Spool valves are not used as they do not seal adequately enough for precise leak tests.
- Electronic Pressure-Decay Transducer: Hyper sensitive device capable of measuring to the nearest .0001PSI or better by converting pressure to an electronic signal. NOTE: Transducers are sensitive to temperature changes
Leak Tester System Resolution
| Theoretical Resolution using 16 Bit Processor | |||
|---|---|---|---|
| Pressure (PSI) | Transducer Range (Volts) | Bits | Pressure Resolution |
| 0-5 psi | ± 10vdc | 32767 bits | .000076 psi / bit |
| 0-100 psi | ± 10vdc | 32767 bits | .0015 psi / bit |
| 0-1000 psi | ± 10vdc | 32767 bits | .015 psi / bit |
NOTE: The minimum pressure drop (decay) of .01 -.02 psi is required to assure a reliable and repeatable test.
Principles of Pressure Decay Leak Testing
Gas Law: PV = nRT or P = nRT/V
P = Pressure
V = Volume
n = number of moles (atomic wt of the gas)
R = Universal gas constant
T = Temperature (in Kelvin's)
- T= tc + 273
n stays constant for non leaking parts
n decreases for leaking parts