Accelerated Life Testing of Push Fit Couplings for Climate Control and Fuel Line Applications

Push fit couplings are becoming increasingly popular for vehicle climate control systems due to the simplicity of assembly operations that they allow. An accelerated ageing test has been developed which includes the effect of vehicle vibration and thermal cycles. The couplings include elastomeric seals which after time may age, harden and lose sealing force contact. There can also be some permeation of gas through the seal material although this is usually at a low level which can be calculated provided that the permeation constants for the elastomeric materials have been measured.

A novel test rig has been developed which allows 12 couplings to be tested simultaneously. There is continuous monitoring of the amount of gas that leaks past the coupling seals using sensitive transducers on the gas collection cells. A test sequence has been developed which includes a primary period of several days at 120°C followed by a secondary period of a few hours cooling to between -20 or -40°C. In most cases leakage occurs during the cooling cycle, when the seals are most vulnerable. An overall test sequence of 3000 hrs is used to represent 10 years service conditions. So far several thousand hours of testing has been completed, comparing the performance of different coupling designs and sealing materials for climatic control systems.

For the future it is envisaged to extend this test method to couplings for fuel line applications. More stringent evaporative emission levels, including permeation through the seal, increase the significance of this test approach to fuel line sealing systems.