Like Pressure Decay, this method also involves measuring the drop in pressure inside the part over time as a result of escaping material. 

The main difference is that in case of a Pressure Differential test, we measure the change in pressure inside the part compared to the pressure inside a control volume charged to the same pressure as the part. 

This allows us to use differential pressure transducers that can detect very small pressure changes more accurately.

The test typically consists of the following steps:

	Charging the part and the control volume to test pressure
	Isolating the control volume from the part
	Allowing the system to stabilize
	Measuring the change in pressure difference during test

The following illustration shows a typical pressure differential test:

Sensitivity range [std.cc/sec]
Temperature dependence
Operator dependence
Main factors affecting accuracy	Part volume Test time Test media temperature
Test pressure range	high pressure applications
Cost