External pressure methods are classified into the pressure decay sensor method and the proximity sensor method. In the pressure decay sensor method, a package is placed inside an enclosed chamber where a pressure is applied to create a pressure differential across the package wall. Gas will flow into the package if there is a leak or a weak seal, because the pressure inside the package (at about 1 atmosphere) is lower than the pressure in the chamber. The decay of pressure inside the chamber is monitored using a pressure sensor (Figure 1). In the proximity sensor method, an open channel is created around the seal of a package by using a clamp system, and compressed gas is applied into the channel. If there is a leak or a weak seal, the compressed gas will enter into the package and cause its upper wall to move. The movement can be detected by a proximity sensor (Figure 2). 

Compared to the external vacuum method, both external pressure methods do not require residual gas to be present in the package. In addition, the compressed gas can easily enter the package even when a channel or a pinhole is plugged up with food particles, whether liquid or solid.

• Package
• A chamber equipped with a pressure decay sensor
• A clamping system coupled with a proximity sensor

1. Put the package into a enclosed chamber or in the clamping system.
2. Apply external pressure to the chamber or the open channel.
3. Monitor the pressure decay or the upper wall movement.
4. Records.

Positive

If the pressure of the chamber decreases or the proximity sensor detect the movement, the package leaks.

False Positive

If the pressure of the chamber decreases or the proximity sensor detect the movement, and the package is good sealed, it may be caused by the unsealed chamber.

Negative

If the pressure of the chamber maintains the same or the proximity sensor do not detect the movement, the package is good sealed.

False Negative

If the pressure of the chamber maintains the same or the proximity sensor do not detect the movement, the leaking channel may be plugged.