Production line leak detector

Most analytical techniques have been designed to achieve detection of the tiniest leak possible with minimum design complexity. They are capable of detecting a leak rate below a certain allowable level. The new generation of leak testers from Furness Controls are designed to achieve these level of detection reliably with fast, easy and simple operations.

Using absolute pressure transducers, the detection of a very fine leak in the range of 1:50000 is possible. When taking zero-drift phenomena into account as occurred in practical situation, this value may reduce to 1:10000. In industrial environments where long term use is favored, the resolution would further reduced to 1:1,000. Taking these into account, Furness Controls design modern leak testers that are suitable for fine leak detection and long term stability operation in production line environments. Instead of measuring a drop in the overall pressure, a differential pressure system was developed to measure the loss of air pressures.

In a typical differential pressure system, the product is filled with air through the system. The system categorizes the product into two regions. One half is held as a reference, while the other half is connected to the test item. The differential value is taken across the system; thus any leak in the test item will cause a drop in pressure, which is shown as a reading in the instrument. A pass or fail signal is given at the end of each test cycle.

Using differential pressure measurement system, the effect of instrumental problems such as zero drift, temperature drift is minimal as they only directly affect the test pressure and not differential pressure. For example: a 1% drift on an typical leak testing instrument recording a charge pressure of 60 psi is 0.6 psi. However, in the differential pressure system, a 1% drift on an instrument reading 60 psi is only 0.00014 psi. An extremely low sensitivity in the order of micro-scale can also be achieved with reliable long term operation.

A number of different systems have been developed to enable efficient product inspection in the production line for a wide range of products.

The product to be tested is connected to the leak testers and it is charged to a test pressure. At this stage, leak can be identified when pressure loss occurs. The results can be shown as the rate of pressure loss, as value of pressure loss or, if the volume of the test item is known, as a flow rate (through calculation). A reference cell may be charged simultaneously in order to save overall cycle time by achieving an system equilibrium sooner.

Flow detection measures the flow of replacement air (gas) directly from the reference cell into the leaking cell by means of a laminar orifice.

Continuous leak testing method is developed as means to allow operator to identify the effect of any adjustments made on the tested product. This is necessary for large scale manufacturing of domestic appliances and other larger assemblies part where faulty components are to be rectified, not discarded. The continuous flow leak testers constantly charge the test item while simultaneously measure the flow required to do so. When the operator has repaired the leak and the flow falls below the acceptable leak rate, a pass signal is given.

A tightly-sealed container is placed inside a sealed chamber and charged to a test pressure. Leak can be detected through measuring the pressure rise in the outer chamber This technique can be used when the object test pressure exceeds the testing capability of the leak testers.

All of the above-mentioned techniques are not suitable if the test item cannot be pressurized. In such cases, pressure dump test is the preferred option. The test item is initially placed inside a container which is later charged with pressure and filled with a specific volume of air. it is often possible to place the item inside a container and to charge the container with a specific volume of air. If the test item does not leak, the resultant pressure within the container will be dependent on the free volume of the container (container less volume of test item), the charge pressure and the volume of the air. However, if the test item does leak, the effective volume of the container will be the full volume of the container less the solids within the test item, i.e. a larger volume. Consequently the resultant pressure within the container will be lower.