This method involves evacuating the part to suitably low pressure and measuring the increase in pressure caused by test media entering the part. 

Since the pressure inside the part is lower than atmospheric pressure, the temperature dependence is lower. 

Only parts that are able to withstand external pressure can be tested this way (e.g.  thin walled plastic parts can not be tested due to the danger of collapsing)

 

The test typically consists of the following steps:

	Evacuating the part to suitably low pressure
	Allowing the system to stabilize
	Measuring the change in pressure inside the part

The following illustration shows a typical vacuum decay test:

Sensitivity range [std.cc/sec]
Temperature dependence
Operator dependence
Main factors affecting accuracy	Part volume Test time Part cleanliness
Test pressure range	wide range of pressures
Cost