How can you improve leak testing precision and throughput?

Various methods have historically been used to check leaks in systems and components—from bubble tests to rotameters and pressure loss detection. While these traditional methods have their place, they each have serious drawbacks in accuracy, throughput, and automation. You may be faced with more demanding situations that call for more effective techniques. This note outlines a method that can more quickly detect and accurately measure leaks at controlled differential pressures. Furthermore, it enables automation (including data capture) and cycle-time efficiency.

Objectives

Method

In addition to the delay, the pressure differential across the flowmeter creates an uncertainty in the actual test part pressure. This problem is made worse by the fact that the uncertainty is greater for large leaks. For these reasons, it is essential to use a flow meter designed to operate with a very low pressure differential.

Instrumentation Choice

The recommended mass flow meter is the Hastings HFM 300. It is chosen for its ability to accurately measure flow to within 0.75% of Full Scale while operating with extremely low pressure differential. Whereas typical mass flow meters require 4 inH2O pressure differential to operate, the HFM 300 only requires 0.25 inH2O. For your leak test, 16 times less pressure differential means 16 times faster! This is demonstrated in the actual test case below.

Another important consideration when selecting the proper instrument is avoiding what is known as “fold-over”. This problem arises in some typical flow meters when they actually misreport a very high (over-range) flow as a normal flow and allow a bad part to pass. The HFM 300’s sensor design correctly interprets over-range flows; its output signal will not come back on scale. The HFM 300 will not report false acceptable readings.

Test Case