Bulldog valve gear

[steelaxleboxParticipant @steelaxlebox]

[steelaxleboxParticipant @steelaxlebox]

Hello,

A friend with no internet or PC is building a Wilson Bulldog. He has reached the valve setting stage but the ports aren't completely uncovered in full forwards when adjustment is made for reverse. His workmanship is good and to the published drawings. I gather from talking to the gent with the magnificent Bulldog chassis at the 2013 Bristol Exhibition (sorry name forgotten) that one can't expect wonderful things as the valve gear design leaves something to be desired. Has anyone out there information that might help. The friend has a 'phone and would be pleased to talk to other builders.

[Bob YouldonParticipant @bobyouldon45599]

Hello,

The valve gear as designed by Keith Wilson for his Bulldog / Dukedog design is very similar to that of the full size locomotive and I suspect he took the valve gear straight off the works drawings; easy insofar as the full size locomotive was fitted with outside admission piston valves, the design being easily transposed to slide valves. The valve will not open the port fully, probably giving no more than 75% opening, being locomotive links the valve travel will not equate to half the eccentric throw. In full forward gear through to about 15% cut off, the valve events are pretty good, very even, but reverse is a different kettle of fish, much less than full gear, the events go all over the place, a further spanner in the works is the point of suspension, the lifting link being attached to the top of the link. Having had a Bulldog that was built from works drawings including the valve gear and predating the Wilson design by several years, the performance on the track in full gear was impressive and would notch up amost to middle with very even beats in all positions of the reverse gear, in reverse, full gear was again excellent but go to anything below 50% cut off and it would go off song, not too much of a problem though on a continious track. Interestingly having spent time on the footplate of the preserved Dukedog 3217 the performance of the miniature locomotive replicates that of the full size locomotive insofar as the reverse gear valve events are nowhere as good as those in forward gear. Should any correspondent care to put the design through either the Don Ashton or Dockstadder valve gear programes I'd be most interested.

I trust the foregoing may be of some assistance.

Regards,

Bob Youldon

[Bob YouldonParticipant @bobyouldon45599]

Hello,

The valve gear as designed by Keith Wilson for his Bulldog / Dukedog design is very similar to that of the full size locomotive and I suspect he took the valve gear straight off the works drawings; easy insofar as the full size locomotive was fitted with outside admission piston valves, the design being easily transposed to slide valves. The valve will not open the port fully, probably giving no more than 75% opening, being locomotive links the valve travel will not equate to half the eccentric throw. In full forward gear through to about 15% cut off, the valve events are pretty good, very even, but reverse is a different kettle of fish, much less than full gear, the events go all over the place, a further spanner in the works is the point of suspension, the lifting link being attached to the top of the link. Having had a Bulldog that was built from works drawings including the valve gear and predating the Wilson design by several years, the performance on the track in full gear was impressive and would notch up amost to middle with very even beats in all positions of the forward gear, in reverse, full gear was again excellent but go to anything below 50% cut off and it would go off song, not too much of a problem though on a continious track. Interestingly having spent time on the footplate of the preserved Dukedog 3217 the performance of the miniature locomotive replicates that of the full size locomotive insofar as the reverse gear valve events are nowhere as good as those in forward gear. Should any correspondent care to put the design through either the Don Ashton or Dockstadder valve gear programes I'd be most interested.

I trust the foregoing may be of some assistance.

Regards,

Bob Youldon

[julian atkinsParticipant @julianatkins58923]

keith wilson's BULLDOG and DUKEDOG valvegear is fundamentally flawed in that there is insufficient travel for the valves to give acceptable events in anything approaching fullgear.

after some comment at the time keith acknowledged this and suggested builders shorten the lap on the valves – a far from satisfactory solution as this leads to far greater steam consumption and less expansive working and poor events.

i am afraid there isnt an easy way round the problem other than shortening the width of the steam ports or completely re-designing the gear with a greater eccentric throw.

the other well known problem is the lack of clearance with the front bogie and the frames.

cheers,

julian

[Author]

Posts