P2 Locomotive Company and related matters

I'm not sure about the design side; the A1 Trust's statement on the details of the cause isn't clear on that. It does say "A4 Pacifics were fitted with a modified ratchet with three pawls ... Tornado now has a three pawl ratchet", which makes it sound like Tornado was built to an original single-pawl design, and they missed the historical 3-pawl update. Overall, they said "we have found four likely contributory factors in the failure. Each one on its own is unlikely to have cause the failure". Some (e.g. the single-pawl thing, and the ring gaps) one would probably class as design/manufacturing; the "oil extracted from the lubricator .. was found to be low in viscosity" could be classed as 'operational', but they said "No firm reason has been discovered for this", so it's not clear if there was no viscosity spec, or if the oil used was not checked to make sure it met such a spec (if one existed).

Noel

 

I'm still can't understand why the A1 Trust decided to pick Lentz valve gear instead of tried and tested Walschaerts. If it works, don't fix it.

 

The trust wanted to build an P2 in its original and distinctive form and this explains 2007 which will represent a P2 as first seen.
The valve gear is Franklin type B rotary cam gear making use of the work carried out by Vernon Smith, being able to access his book "One Man's Locomotive" might prove beneficial here. The Franklin Railway Supply Co. produced a far superior gear to the Lentz type because they had advantages in terms of heat treatments and materials and the Trust hope to take full advantage of any developments made since the 1940s.

 

Indeed. Even in the UK 'Lentz' had not stood still, it being touch and go whether British Caprotti ( as tried out on Black 5's) or Lentz /Reidinger ( as tried out on Horwich Crabs) would be used on the BR Standards

 

Arguably if tried and trusted were the top priority they would have built another Peppercorn A1 and not a P2 at all.

 

Indeed things hadn't stood still. The LNER carried out development work on the Caprotti gear and some tests were being carried out based at Woodford shed. The shed master there was reported to be very keen but unfortunately the records were lost during the WW2.
It has to be admitted that the US locomotive builders were very good at mechanical design and were in advance of the UK in a number of areas.

 

But you know that the A1 was a stepping stone on the way to what they really wanted, a worthy stepping stone but a stepping stone none the less. The P2 would carry out the work asked of it which was beyond the capacity of any Pacific. Works staff at Doncaster were aware of modifications that were needed on the class but were not allowed to put them into practice. Now we can have these improvements and more incorporated into the next member of the class.

 

A Deltic?

 

Tom

 

But ref!!!!

 

Deltic? Poor power to weight ratio compared to what had been achieved with steam.

 

Indeed yes, I believe plans were afoot, to cure the problems/issues. But were put on hold/cancelled, thanks to a certain "Bohemian Corporal" in Berlin and his attempted world tour

 

Just a point of order. I’m not sure this is precisely what was meant, but I’d make the argument that Designers and Engineers on this side of the pond were no less capable than those stateside, just that we are/were more constrained by tradition/we’ve always done it this way/conservatism than those in the states. They would have had more freedom to push the envelope/try new things as evidenced by design choices made on a number of machines.

A far more generous loading gauge also helps.

I don’t think anyone was/is pointing to capability. But I’d hate for anyone to think US Engineers are anywhere near a match for us over here.... *tongue in cheek*

I fully support the valvetrain choice made for the P2. Materials and analysis are light years from where they were when this design was incepted.

Its going to be great to see this machine and I’m sure many of us are interested in the performance. Will the P2 be allowed to haul 14 coaches?

 

Quite so. It also helps when everyone involved in large engineering projects uses the same measurement system, no names [cough - NASA].

 

Their design page indicates that they wanted to build an 'improved and corrected' 2001 (my reading/wording), and since 2001 had originally been built with Lentz, that was the way they went. The news page does say "valve gear to be fitted – choices were improved Lentz/Franklin, Walschaerts or British Caprotti" so apparently they did consider using Walschaerts; apparently the desire to follow 2001 was what led to the Lentz choice.

Noel

 

Have they reached the point of no return on the cylinder / valve gear design? The website refers to the poppet valves being "inevitable" although one senses that the board papers might be rather more analytic. The latest news on line suggests they are still researching the details of the valve gear design and looking for someone to fabricate the cylinders (although the latter task would also presumably also be required for conventional piston valves).

 

The fitting of poppet valves did appear to offer some advantages. 2001 as built did offer some characteristics that were valuable but the limitations imposed by both materials and production methods at the time proved to be impossible to overcome and the modification of the valve gear from continuously variable to one offering a limited range of fixed cut-off positions, or stepped cut-offs, proved to be, well, limiting. The excessive clearance volumes were also the reverse of beneficial.

Chapelon reverted to piston valves, De Casso used piston valves on 232U1 and Porta didn't believe in poppet valves but rather his advanced and more robust piston valves.

So what were the problems? The introduction of a new gear and valve type presented problems to the shed staff. They understood slide and piston valves, Walschaert and Stephenson valve gear, but a new and very different type would demand time and training which implies costs.
Worse the poppet valves were found to leak. Though elastic seats were invented to solve this this expansion problem it appears that the main players moved on and made better use of what was known to work. The valve gear and actuation mechanisms were also seen as lacking sufficient robustness for railway use.

The valves fitted to the Franklin B type of gear take advantage of design and material improvements. The elasticity is in the valve itself. Go to a roadshow, ask a question or two. I mentioned the leakage issue and the elastic seat solution and followed it up. Mr Elliot is very helpful.

As to the situation concerning 2007, just visit the website. The cylinder block fabrication design is progressing well and the valve gear is taking advantage of 3D printing technology to test and finalise the production components. They know the Franklin system works well and have had access to material held by the family of the late Vernon Smith.

 

33hp/tonne? What steam designs were there that provided that kind of power to weight ratio? And, as important, could 22 of them have done the work that the 22 Deltics did?

 

Whether or not there's been any contact between the A1SLT and the owners of Duke of Gloucester I don't know. But, considering that 71000 has a version of poppet gear would perhaps provide some information/experience of this type of valve gear. Which could in turn be beneficial to the A1SLT with regards to 2007.

 

I was just thinking along those lines too. DoG has put in some storming performances over the years, so the valve gear must be pretty good, to effectively use the steam that the excellent boiler produces. DoG is another locomotive that has benefitted from both being restored as per design (ashpan & draughting) and fettling of the valve gear.