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

    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