Talk:Gresley conjugated valve gear
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[edit] Edit by 24.4.4.69 regarding cylinder timing and crank angle spacing
Is it possible to get some further documentation on this point? I note that the article previously stated (through several edits) that Gresley 3 cylinder locomotives must have 120 degree spacing of cranks. So was that information factually incorrect for Gresley valve gear equipped locos in general, or merely not true of the UP9000 locomotive which the same user also made reference to in their edit?
My understanding from reading other sources is that the variation in cylinder timing from equal 120 degree spacing relates to the need for the inside cylinder to be angled to clear the leading axle, and the crank spacing will be determined by the angling of the inner cylinder in relation to the outside cylinders for each locomotive, and also the relative size of the inner vs outer cylinders, etc. Because these factors vary by locomotive, so too would the cylinder timing, and as such not all locomotives would share 120 degree spacing, nor would they all share 90/135/135 spacing.
Any comments? Zzrbiker 06:54, 3 October 2006 (UTC)
The suggestion of 90/135/135 spacing is incorrect. In a perfect arrangements the cylinders would operate at exactly 120/120/120 spacing. Where the centre cylinder is raised to clear the leading axle some adjustment may be necessary.--7severn7 19:16, 3 October 2006 (UTC)
Here's a thought. It is arguable the the Gresley - Holcroft valve gear isn't a valve gear per se since it enables a third cylinder to be driven by motion derived from two other valve gears (almost invariably Walchearts). What I mean is it could be used to derive the 3 x 120 degree motion from another valve gear i.e. Stevensons.--7severn7 18:21, 9 October 2006 (UTC)
