Steam locomotive valve gears

[steammemories]

I joined the discussion on the West Country and BB Pacific's of the Southern Railway. The discussion rightly referred to the chain driven valve gear on the WC's and BB's and the tendency the engines had to slip. I have seen many different valve gears on steam engines and read much of the views of the merits or otherwise of the different types fitted. I thought it might be the time for a thread on the subject. Earlier last year I visited the Severn Valley Railway and had the pleasure of BR Std class 5 73129 fitted with Caprotti valve gear, indeed the only class five surviving with such. The engine seemed to have a tendency to slip too when getting a heavy train underway. I put it down to the sharper valve events which poppet valves impart to the steam inlet and exhausts. So any views on the issues of valve gears and their merits or otherwise.
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I have put some pictures of the Caprotti valve gear on the blog http://steammemories.blogspot.co.uk/ it would be good to hear others views on the different valve gears incorporated in British steam locomotives. Of course the two most common were Stephensons and Walschaerts. The item came to mind due to a discussion on the thread about the West Country Pacific's and their rebuilds. The added weight of the Walschaerts gear reducing their route availability.

 

[Spamcan81]

I joined the discussion on the West Country and BB Pacific's of the Southern Railway. The discussion rightly referred to the chain driven valve gear on the WC's and BB's and the tendency the engines had to slip. I have seen many different valve gears on steam engines and read much of the views of the merits or otherwise of the different types fitted. I thought it might be the time for a thread on the subject. Earlier last year I visited the Severn Valley Railway and had the pleasure of BR Std class 5 73129 fitted with Caprotti valve gear, indeed the only class five surviving with such. The engine seemed to have a tendency to slip too when getting a heavy train underway. I put it down to the sharper valve events which poppet valves impart to the steam inlet and exhausts. So any views on the issues of valve gears and their merits or otherwise.
--- old post above --- --- new post below ---
I have put some pictures of the Caprotti valve gear on the blog http://steammemories.blogspot.co.uk/ it would be good to hear others views on the different valve gears incorporated in British steam locomotives. Of course the two most common were Stephensons and Walschaerts. The item came to mind due to a discussion on the thread about the West Country Pacific's and their rebuilds. The added weight of the Walschaerts gear reducing their route availability.

IMO the type of valve gear has little or no impact on a locomotive slipping. I have experienced slipping with Walschaerts (including Bulleid's chain driven version), Stephenson, Caprotti, and various proprietary gears on the narrow gauge. Track conditions, load, gradient and heavy handedness of drivers have more effect than the actual type of gear.

 

[341o2]

One feature of the Bulleid valve gear was that the harder the locomotive worked, so the valve did overtravel, thus the locomotive pulled itself along faster until checked. When the MN/WC/BB classes were modified an opinion of footplate crews was that "they might save a bit of coal and water, but don't pull nearly as well as before"

In response to criticism regarding the oil bath and valve gear Buuleid replied that "it was a good idea later seen to have been carried out imperfectly due to a lack of mechanical know how at the time " and "deserves to be developed by my successors"

However, the diesel revolution was now in full swing, and rapid demise of steam inevitable. There was no need for further research and the steam locomotie would retain its inherent simplicity until it was replaced

One of the other aims re the oil bath was that the frequent failure of big end of the inside cylinder connecting rods (This happened to Mallard on its epic run thus becoming the world's fastest steam engine and was replaced by another loco) had virtually been eliminated - only two incidents in 1.4 million train miles

 

[steammemories]

Many thanks for that, as a marine engineer I have little experience of valve gears other than those on steam pumps, on turbines we adjust the nozzles to gain efficiency. I have heard of the problem of over travel and some seem to put that down to the Southern's steam reverser and other to the fact that miniaturisation of the Walschaerts gear magnified any inaccuracies as it warmed up.

 

[341o2]

valve overtravel on the Bulleid's was intentional to provide extra torque. It also meant the locomotive was more likely to slip under less than ideal conditions As I have mentioned elsewhere the design was originally conceived around an eight coupled locomotive which would have meant a greater proportion of its weight being avaliable for adhesion

the steam reverser on these locomotives did tend to creep. Usually in service this was not too important an issue, but it was when 35022 was sent to LM for tests including the stationary plant, this hampered accurate testing so special clamps were made up to hold the reverser in place

 

[steammemories]

I have to admit that I have never seen City of Wells slip leaving Keighley and it has a stiff grade out of the station. Could well be drivers who know the engine well. I remember in one of the British Steam Railway DVD's Richard Hardy talking of a trip on Wells when it was working the Golden Arrow. The driver had offered him the regulator for the trip down to Dover and so he offered the fireman a break on the return, her said he found Wells impossible to get to steam well and it near broke him by the time they got back to Waterloo. He was shed master at Stewarts lane at the time.
I have just got back from Haworth and Oxenhope where BR Std class 4 75078 is running in, another superb engine. I have put some video's on the blog at
http://steammemories.blogspot.co.uk/2015/02/75078-moves-off-shed-for-oxenhope.html
Can I upload video here, does anyone know how?

 

[341o2]

I would not take into account the opinions of one locomotive crew. Regarding diesel and electric traction basically you operate the controls and the locomotive responds accordingly.

With steam there is something akin to horse and rider. Even modern steam locomotives can behave differnently. Different crews have their own individual apprroaches and can either praise an individual locomotive, or refer to it as a (deleted) old camel

 

[MarkyT]

One of the other aims re the oil bath was that the frequent failure of big end of the inside cylinder connecting rods (This happened to Mallard on its epic run thus becoming the world's fastest steam engine and was replaced by another loco) had virtually been eliminated - only two incidents in 1.4 million train miles

The recurring meme of frequent middle big end failures with Gresley conjugated valve gear did not reflect the post war experience of my father who looked after three cylinder locomotives at Top Shed in the late 1950s through to the end of steam, although clearly maintenance procedures had been tweaked by then to intervene before wear became a problem. It should be noted that those additional measures were not expensive nor did they take the locos out of traffic any more frequently than required for other necessary overhaul work. In addition to the famous A3s and A4s this gear was also used on the large fleet of 184 V2 locomotives as well as a number of smaller classes, and the V2s were sometimes used interchangeably on express diagrams at speeds of up to 90MPH, where their smaller wheels would be moving the various conjugation levers even faster than those of a larger wheeled pacific at a similar speed, yet there is no great history of the V2s failing en masse with big end problems, even through the rigours of wartime austerity during which they became famous for prodigious haulage feats albeit at much lower speeds!

The big advantage of the gear was it's simplicity and accessibility beneath a hatch in front of the smokebox, leaving no cranks, rods and levers in between the frames to inspect and oil save the main connecting rod linkage and it's bearings. It was a very simple means to gain the smooth pulling power advantages of three cylinders without the disadvantages of placing much equipment between the frames, something the Bullied gear clearly did in spades whilst generating many new problems of its own.

A spate of 'headline' failures such as on the Mallard run seems to have portrayed the conjugated gear in a very poor light not long before Gresley's untimely death in 1941. He was thus unable to defend or improve the technology, a fate from which it never recovered as Thompson literally wielded a gas axe to his predecessor's front end design. It can be argued that the supposed unequal power at high speed was not actually a problem if correctly compensated for in design, and for balance and ride it certainly seems preferable that any small increase in effort insofar as it existed was exerted in the middle cylinder rather than on one side. The Gresley pacifics featured a larger plain bearing area for the inner big end than for the two side rods, and further measures such as roller bearings for these components might have been employed.

BTW i'm definitely not criticising Bullieds ingenuity, but introducing something so radically different, complex and untried as his chain drive miniature valve gear during wartime was perhaps ill advised on what was otherwise an excellent series of locomotives.

 

[Bevan Price]

From the performance point of view, the Caprotti valve Class 5 4-6-0s (LMS & BR) seemed to have poorer acceleration and hill-climbing ability than the rest of the class, but they were very free-running once they (eventually) reached their maximum speed.

 

[Spamcan81]

One feature of the Bulleid valve gear was that the harder the locomotive worked, so the valve did overtravel , thus the locomotive pulled itself along faster until checked. When the MN/WC/BB classes were modified an opinion of footplate crews was that "they might save a bit of coal and water, but don't pull nearly as well as before"

In response to criticism regarding the oil bath and valve gear Buuleid replied that "it was a good idea later seen to have been carried out imperfectly due to a lack of mechanical know how at the time " and "deserves to be developed by my successors"

However, the diesel revolution was now in full swing, and rapid demise of steam inevitable. There was no need for further research and the steam locomotie would retain its inherent simplicity until it was replaced

One of the other aims re the oil bath was that the frequent failure of big end of the inside cylinder connecting rods (This happened to Mallard on its epic run thus becoming the world's fastest steam engine and was replaced by another loco) had virtually been eliminated - only two incidents in 1.4 million train miles

I would be very interested as to where you obtained this info. Speaking to a leading light in the Bulleid world and he disagrees with the statement.
--- old post above --- --- new post below ---

valve overtravel on the Bulleid's was intentional to provide extra torque. It also meant the locomotive was more likely to slip under less than ideal conditions As I have mentioned elsewhere the design was originally conceived around an eight coupled locomotive which would have meant a greater proportion of its weight being available for adhesion

the steam reverser on these locomotives did tend to creep. Usually in service this was not too important an issue, but it was when 35022 was sent to LM for tests including the stationary plant, this hampered accurate testing so special clamps were made up to hold the reverser in place

I would be very interested as to where you obtained this info also. The same leading light in the Bulleid world disagrees with this statement too.

 

[341o2]

Would you identify this "leading light" and his credentials as after all he is doing the critisising

so we are saying that unrebuilt Bulleid pacifics were not prone to slippnig unless handled with care?

I base my comments on half a centuary of railway enthusiasm including those that did their research when both OVSB & John Click were alive and both the MN and WC/BB intact

 

[steammemories]

I read an article some days ago which referred to the London Tilbury and Southend Railway Tank engines which stated that the valve gear used was a direct lift from the Somerset and Dorset 2-8-0's. It seems feasible as both engines were designed at Derby though of course the LTSR engines were three cylinder engines. I have put several photographs on http://steammemories.blogspot.co.uk/. Does anyone know of this or the details of such, I would welcome members comments.

 

[Spamcan81]

Would you identify this "leading light" and his credentials as after all he is doing the critisising

so we are saying that unrebuilt Bulleid pacifics were not prone to slippnig unless handled with care?

I base my comments on half a centuary of railway enthusiasm including those that did their research when both OVSB & John Click were alive and both the MN and WC/BB intact

I will let the gentleman concerned identify himself if he joins the forum and the debate. He is a long time active member of the Bulleid Society and has dealt with the John Clicks, Harry Friths etc. of the world and as such he disagrees with you regarding your remarks about over travel of the valves being designed into the system. Yes Bulleids could be tricky on starting but then again so could those Pacifics fitted with conventional valve gear.
--- old post above --- --- new post below ---

I read an article some days ago which referred to the London Tilbury and Southend Railway Tank engines which stated that the valve gear used was a direct lift from the Somerset and Dorset 2-8-0's. It seems feasible as both engines were designed at Derby though of course the LTSR engines were three cylinder engines. I have put several photographs on http://steammemories.blogspot.co.uk/. Does anyone know of this or the details of such, I would welcome members comments.

Are we talking about Stanier's 2500 class?

 

[steammemories]

I will let the gentleman concerned identify himself if he joins the forum and the debate. He is a long time active member of the Bulleid Society and has dealt with the John Clicks, Harry Friths etc. of the world and as such he disagrees with you regarding your remarks about over travel of the valves being designed into the system. Yes Bulleids could be tricky on starting but then again so could those Pacifics fitted with conventional valve gear.
--- old post above --- --- new post below ---


Are we talking about Stanier's 2500 class?

Yes we are, do you have knowledge or a view? I am doing a bit of digging about these engines. They seem to have developed a very self sustaining thread of continuing development right through to the BR std class 4 tank we all know so well from many preserved railways.