An Experimental Investigation Into the Response of Disc Valves to Rapid Pressure Changes

The paper describes tests carried out on disc valves of varying thickness and operating on seats of different profile when subjected to sudden changes of pressure across the valve. These changes of pressure were produced in a shock tube SO mm in diameter. The high pressure chamber was 0. 6 m long, while the low pressure chamber was 2.125 m long. A drum camera, synchronised to the pressure pulse, was used to record the response of a particular disc under examination. A quartz piezo-electric pressure transducer was used as the standard against which the displacement of a valve disc was compared. It is shown that an optimum disc thickness may be arrived at when considering the time response of the disc valves to these shock pressure changes. This optimum value of disc thickness is virtually independent of sect profile. It is also shown that valves with large seat area have faster response times to rapid pressure changes than valves operating on sharp-edged seats. A complementary series of tests was carried out in an air compressor where oil was present in the air passing through the valves. These tests showed that the benefits gained by valves whose seats had a large surface area were offset by oilstiction effects. In these circumstances, valves whose seat profile approach knife-edges are recommended. It is hoped that dynamic tests carried out under such controlled conditions will enable parameters such as dynamic drag coefficients etc. , to be derived without the necessity of making assumptions regarding the relative importance of other parameters which affect valve behaviour under normal working conditions in a compressor. Future work will involve an extension of these tests with rates of pressure rise across the valve which are of the s arne order as those encountered in the field. A laser technique which has been used to examine the deformation due to temperature in the diaphragms of pressure transducers is outlined in the paper. This technique will be used to determine the attitude of valves on their seats with a view to obtaining an accurate assessment of surface stresses at impact.