Pressure Decay / Vacuum Decay

Differential Pressure Decay Leak Test System

Screen Shot 2013-11-17 at 12.25.20 PMPressure decay is an older technology that has existed for many years. It is an indirect leak flow measurement with a leak rate based on decay rate and test pressure. Test volume is calculated for every set up. It is sometimes called “calibration.” Differential pressure decay offers a higher resolution and cost when compared to pressure decay.

Common Issues with Pressure Decay

Pressure decay often gives an indirect measurement when calculating leaks. The changing test volume may give a bias reading. The operator must frequently “calibrate” during a part changeover or the operator can “zero” or mask a leak. Reference volume is required for this method, which is about twice the volume as pressure decay, which means twice the time to fill for each test. A differential pressure transducer is also required. Often, a large (gross) leak will cause an over-range of the differential transducer and damage or destroy it.

The pressure transducer is often not rated for the required resolution and temperature fluctuations can cause errors. For example, an increase in temperature will mask leaks while decreases in temperature will cause false rejects. Both methods are susceptible to these fluctuations and will require frequent “calibration” to overcome drifts. Typically the reference volume must be a “0” leak part. Both systems require extensive maintenance, as well. Consult ATC, Inc. if you are looking to upgrade or replace your pressure decay or vacuum decay leak test system.

IGLS Micro-Flow vs. Pressure Decay

 
IGLS Technology Pressure Decay
Measures direct flow Measures indirect pressure drop
Is temperature insensitive Is temperature sensitive
Is volume insensitive Is volume sensitive
Does not require frequent calibration Requires frequent calibration (high maintenance)
High accuracy Lower accuracy
Higher achievable gage R&R Typically lower or equal instrument cost
Typically 25-35% faster for same capability


Why ATC’s Micro-Flow Test is Faster than Pressure Decay

Screen Shot 2013-11-17 at 12.25.11 PM

IGLS Micro-Flow vs. Differential Pressure Decay

 
IGLS Technology Diff. Pressure Decay
Measures direct flow Measures indirect pressure drop
Is temperature insensitive Is temperature sensitive
Is volume insensitive Is volume sensitive
Does not require frequent calibration Requires frequent calibration (high maintenance)
High accuracy Twice the valves and connections, twice the chance for leaks in the system (high maintenance)
No reference volume required Reference volume (preferred a “zero leak part”) is required for each test part
Higher achievable gage R&R Reference volume must be periodically replaced and verified to be a “zero leaker”
Typically 15-20% faster for same capability Over pressure protection required
Similar cost

 

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