The Pioneer of Modern Leak Testing

Pressure Rise Leak Testing

This month I’d like to discuss leak testing of a fuel regulator.

There are several potential methods that could be used for this device and it therefore makes a good candidate for a discussion around the pros and cons of each.

The fuel pressure regulator is an engine management component that is found in one form or another on virtually all internal combustion engines. It is a component of the vehicle’s fuel system, and as its name implies, is responsible for regulating the pressure of the fuel flowing through the system. Different engine operating conditions will require different amounts of fuel, which can be metered by changing the fuel pressure. Many fuel pressure regulators use vacuum operated mechanical diaphragms to change the pressure, though there are vehicles that are equipped with electronic fuel pressure regulators. Because the fuel pressure regulator plays a direct role in the distribution of fuel to the engine, any issues with the component can potentially cause performance issues and other problems for the vehicle.

The test parameters for fuel pumps are in the range of 0.2 sccm to 2.0 sccm with the test pressure ranging from 40-90 psig.

Lets’ look at the leak testing methods that we could choose from:

Direct methods of air leak testing:

Pressure decay

 Mass flow

Differential pressure decay.

Indirect methods:

Pressure increase

 Helium mass spectrometry

Pressure decay.

This is the simplest method but it lacks some sensitivity and has generally the longest cycyle time.

Differential pressure decay

Faster cycle time, better sensitivity than simple pressure decay

Mass flow

Higher cost than the two pressure decay techniques, better choice for large volumes.

Helium mass spectrometry

Highest sensitivity but highest cost. Not necessary for this type of assembly

Pressure increase

High sensitivity, high repeatability, fastest overall cycle time and lowest cost. This is the technique most suitable for this application.

As the name implies this is the reverse of pressure decay leak testing. The first step of the test involves the evacuation of the test part. The leak tester will then monitor for an increase in pressure as air from outside the part ingresses through any leak path. This test is preferred over the pressure decay test because it is not subject to the difficulty encountered with pressure decay of measuring small changes in pressure in a high pressure system. The pressure increase test cannot have a pressure rise if greater than one atmosphere. There may be some non-linear measurement at the beginning of the test due to outgassing but a visual plot can quickly show when a real leak is being observed.

Joe Pustka

Director Applications Engineering

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