Why Lentz valve gear?
The first class P2 No. 2001 Cock o' the North was fitted with Lentz rotary cam poppet valves. Most modern steam locomotives used piston valves, where the entry of live steam to and the exit of exhaust steam from the cylinders was controlled by pistons which were driven backwards and forwards by the valve gear. Poppet valves are the type used in internal combustion engines and are activated by cams. Poppet valves can result in higher power, greater efficiency, and reduced maintenance.
Dr Hugo Lenz developed a form of poppet valves where the cams of the oscillating type were driven by conventional valve gear. The original Lentz design was developed to be driven by rotary cams, which in turn take their drive through gear boxes and cardan shafts from the locomotive's wheels. This design was successfully applied to several hundred locomotives worldwide.
However, when proposed for No. 2001, Gresley requested that the Associated Locomotive Equipment Company provided continuously variable cams which provided an infinite number of settings between 10% and 75% cut-off. This fine adjustment was required with powerful locomotives to enable economical operation.
However, on No. 2001 the continuous cams wore rapidly and required replacement after only 10,000 miles, so stepped cams were fitted adversely affecting its economy. Fortunately for No. 2007 Prince of Wales, the Lentz valve gear was further developed by the Franklin company of the USA during the |940s which overcame the wear problems with the cams and other maintenance Issues.
We have been fortunate to obtain details of the Franklin developments and will be incorporating these into the valves and valve gear for No. 2007.
The target for 'The Valve Gear Club' is £300,000, with supporters making donations of £1000 as a lump sum or in monthly installments of £100.
We hope to raise the initial £50,000 in the first half of 2024 to allow for the manufacture of a prototype cam box and test rig, with the intention of the prototype then being fitted to the locomotive. As such we invite our existing supporters to join ‘The Valve Gear Club’ now to get this undertaking off to a strong start. You can sign up at Darlington Locomotive Works on the afternoon of the Convention, or online at your leisure.
Special Benefits for Valve Gear Club members:
- Exclusive Art Deco P2 Poster by Ed Laxton
- Opportunity to buy ticket on No. 2007’s first main line train
- Reasonable access to No. 2007 at all times
- Opportunity to attend ‘The Valve Gear Club Day’ when the prototype is tested.