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Hauraki Plains Gazette, Volume XXXIII, Issue 4388, 10 March 1922, Page 3

The account of the stoppage of the Main Trunk express at Te Awamutu. on Tuesday, as reported in the daily paeprs, must have been somewhat difficult for the lay person to understand. It read in part: "Inquiries made by the police and railway offi-i cials led to the theory that an impact with an obstruction, which probably fell from the engine itself, caused the steam valves to relax, giving „the impression that, there had been an explosion.” In explanation of this it may be 'stated that an obstruction falling on the valve gear may certainly have caused a temporary relaxation of the steam pressure in the slide-yalve chest. The ordinary slide valve is a flat, grid-dron piece o? metal, which automatically cpvers and uncovers the steam ports. If the steam is Shut off the valve, which is loosely held on the valve rod passing across the centre of its Lack, falls ■ away somewhat from the steam-port faces. Should the steam be turned on suddenly again the pressure sends the valve forward against the steam ports with a bang, and it is quite conceivable that ifl a pressure of 2001 b to the square inch, or a ton and a quarter to the/Square foot, were let instantaneously into an empty valve chest the valve would be driven up •against the port-face with such ter-i rifle intensity that the ■ noise’ would resemble that made by a loud explosion.