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This article outlines Labour ideals and values, and demonstrates the tensions between egalitarian and meritocratic imperatives for the reform agendas Labour governments pursued in office and the educational settlements reached. It challenges 'common sense' interpretations of elites and elite education and fixed 'ability' thinking, and promotes the key principle of human educability, helping to show the importance of historical memory for understanding how unfair educational separation entrenches inequality. In so doing, it seeks to advance an agenda for action to develop an alternative to the current institutional forms of schooling, one which would establish community comprehensive education for everybody .

During the operation of reciprocating compressors, the flapper valve opens and closes under fluid pressure and flow. As it closes, it strikes against the valve seat, generating stresses and noise. This cycle of loading produces bending and impact fatigue stresses in the reed. This load pattern is repeated billions of times during the service life of a compressor and it defines the service life and reliability. The goal of this study was to calculate the impact fatigue strength of the Flap-X and the SS 716 grades and, to provide the compressor manufacturers with the information they can use to specify a steel grade to be used in their compressors, for reliable service. Impact fatigue tests were conducted on a custom-built impact fatigue test rig that used air pulses to produce movement of the reed valves manufactured by a major European compressor manufacturer Nidec Global appliance GmbH, at a frequency of 315 Hz and pulse width of 2.2 milliseconds. The testing was conducted according to the staircase test method detailed in the International Standard SS-ISO 12107:2012. The impact fatigue strength of the Flap-X and SS 716 steel valves was calculated in terms of the impact velocity according to the modified staircase test method in the standard. The test results and their statistical analysis showed that the impact fatigue strength of the Flap-X grade was higher compared to the SS 716 grade. The calculation and testing of the impact fatigue strength of the flapper valve steel grades could help the compressor designers to select the optimum material for their compressor designs, to provide reliable service. The higher impact fatigue strength of the Flap-X grade, lower failure rate and longer impact fatigue life will allow the compressor manufacturers to design thinner valves, as Flap-X can sustain higher impact fatigue stresses reliably for longer time and, at the same time help reduce noise, as thinner valves produce less noise for a given pressure and frequency.

Impact fatigue is a phenomenon that is the main cause of failure of reed valves in compressor systems. This phenomenon occurs in compressors due to repeated opening and closing of reed valves during suction and exhaust cycles of compressors. When the valve opens it creates bending fatigue stresses in the body of reed valve; when the valve closes it strikes against the valve plate creating impact stresses. This reed valve movement and impact is repeated billions of times. This cyclic movement influences the impact fatigue life of the reed valve and, hence, the performance of a compressor. The valve movement can be defined in terms of valve frequency, valve lift, valve velocity and impact velocity. Inside a reciprocating compressor, a number of parameters including the valve design, valve material, compressor operating frequency and suction/exhaust pressure influence the reed valve movement. In this paper, we studied the valve movement parameters for three different suction reed valve designs manufactured from Flap-X – a martensitic stainless steel grade developed for reed valves – tested in a custom-built impact fatigue test system. The valves were excited into movement using compressed air pulses varying in frequency up to 300 Hz and varying pulse width. The valve displacement and frequency was recorded by a laser sensor at 10 000 frames per second. Before starting each test, the operating conditions such as the operating frequency and the air pulse width were pre-set in the impact fatigue test system’s control software while the applied pressure was kept constant during the test. The valve response was measured to be different for the different valve designs tested in this study. The reed valve design influenced the important reed movement parameters such as the valve lift, valve velocity, impact velocity and the frequency of valve vibrations. The valves were not tested to failure as the focus of this study was to collect the dynamic data of valve movement. However, for a practical impact fatigue testing of the reed valves intended to achieve fracture of valves, the testing should be conducted at higher frequencies to reduce test times as well as for a stable amplitude of vibration and impact velocity as shown in this study. The information obtained from this study shows the applicability of the presented impact fatigue test system to study the reed valve movement as well as their impact fatigue characteristics.

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