The International Steam Pages


Improving the Fleet - Front End Redesigns On the Welshpool & Llanfair Railway

The first part was written some time ago by David Mosley latterly a manager of the Welshpool and Llanfair, the second part is a May 2000 update by Nigel Day.


"Back in the mid seventies the locomotive 'Monarch' covered some of the scheduled passenger services. In fact in 1976 it was the mainstay of the loco fleet. Occasionally good, most of its career could however only be described as mediocre. There were a number of reasons for this:

1) The primary firebox being a marine type had very poor primary air intake. A lack of primary air chokes the fire.

2) Because of the virtual non-existence of an ashpan the firebars often became ash locked, thus restricting the air intake even further.

3) The firebox had a firewall in front of the tubeplate. In the fireman's enthusiasm for throwing coal as far down the box as possible a large amount of coal went over the wall and blocked the tubes.

4) Other problems included leaking fire tubes and superheater flues and poor superheater elements which often failed and, as no spares were available, were then blanked off. A reduction in the number of elements reduces the engine's efficiency.

After a brief spell in service the locomotive was sidelined in 1978 awaiting a retube and the fitting of vacuum brakes.

In the mid 1980's the decision was taken to sell the locomotive as its suitability for operating regularly and reliably over the newly extended railway was called into account. Various people and organisations came to view the engine and eventually an offer was made by two members of the Festiniog Railway which was accepted and the locomotive departed to Minfford yard in 1992. At present the locomotive is stripped for conversion to 2ft. gauge and oil firing.

Whilst the engine was being stripped into its component parts Shaun McMahon of the Vale of Rheidol Railway wrote to W & L asking for details of the history of the locomotive whilst it was operating and any problems which had occurred. Shaun and his colleague Nigel Day of the Snowdon Mountain Railway had previously worked together studying locomotive performance and front end design in particular. Shaun had worked on the Festiniog Railway's 'Linda' whilst it was being used as a test bed for various modifications. They studied the problems described with 'Monarch' and came to various solutions, not least of which was replacement and redesign of the blastpipe and the fitting of a liner to the chimney.

When 'Monarch' first arrived at Llanfair it had a spark arrestor chimney fitted from its days in Bowaters paper mill. During some work on the locomotive a replacement chimney was fitted and what is now apparent is that some of the steaming problems could have been cured by a correctly sized chimney that little or no vacuum was created in the smokebox and therefore no draught pull on the fire. Little wonder then that even without the spark arrestor the locomotive was never prone to setting the countryside alight!

Following the 'Monarch' discussions the offer was made by Nigel Day who had designed new Kalpor and Lempor chimneys for the SMR to investigate and offer a remedy to any steaming or performance problems we had for any of our locomotives.

In the early part of the 1993 season we were experiencing problems with our No. 14 in respect of a tendency to throw fire and also give the impression of being rather heavy on coal. (since we measured coal consumption it is interesting to note that whilst not as economical as the superheated No.10 the locomotive is far superior to No.2 of which more anon). As a result Nigel and Shaun spent one of the very few hot days last summer extensively testing No.14, having previously fitted it up with test gear to measure smokebox draught, back pressure in the cylinders and temperatures of the smokebox, exhaust steam and steam chest.

Unfortunately these tests resulted in a large amount of spark emission which caused two line side fires, which resulted in the fire brigade, being called out and the locomotive being banned from future trains until it was modified or the weather changed to rain.

By mid-August had Shaun and Nigel had produced a report and done a redesign of the front-end arrangement. Our own volunteer workshop staff built the new blastpipe with a 4 nozzle top and a liner was obtained and fitted to the chimney. At the same time a new blower was fitted with convergent/divergent nozzles.

At this stage it is perhaps worth explaining about the modifications now made.

Modern steam technology has been little used in Britain to any extent so in certain areas there can be radical improvements, most noticeably in the areas of combustion and draughting. Of all the steam locos in Britain 90% can be described as having poor draughting and another 8% have room for improvement.

The basic aim of any front end is to get the most vacuum for the least amount of back pressure. This is achieved by mixing rather than the effects of moving fluids. With the design being used it is possible to predict and calculate the desired effect. By doing so it removes most of the guesswork associated with such work.

Chronologically the development of front end design was initially through Andre Chapelon and Kylchap in the 1930's followed by Lemaitre and its derivatives by Bulleid. Perhaps the most obvious front end redesign was that of Giesl. Unfairly maligned at first, the design has latterly been tried out on the preserved standard gauge 'City of Wells'. The most efficient, simplest and modern front end designs are those of Kylpor,Lempor and Lemprex systems developed by L.D.Porta and his associates. It is this system that is being used on the W.& L.

In terms of narrow gauge locomotive performance and improvement, the Festiniog Railway led the way in a series of experiments, using the ex-Penrhyn Railway "Linda". The locomotive was the test bed for oil firing in the 1970's and in the early to mid 80's was modified again to burn coal on the Gas Producer Combustion System. At the same time the front end was modified to the Lempor system with a 4-nozzle blastpipe tip and a tapered chimney replacing the original Hunslet design. The reason for the front end re-design was to produce a softer blast which was even across the firebed. Whilst the gas producer system was working reasonably satisfactorily, the reduction in oil prices (the increase of which had led to the experimentation initially), meant it was more feasible to return the loco to oil firing. The front end modifications however remained and now provide an interesting comparison wit the unaltered 'Blanche' in terms of total back pressure against smokebox vacuum. The modified W & L No.14 is some way behind 'Linda' but a considerable technical improvement over its previous performance.

Once the design work was completed the new blastpipe and nozzle assembly were built by W & L's own volunteer staff. A 2-part liner was fitted inside the existing chimney, thus retaining the original outward appearance. A new blower ring was also fitted. Once completed, the locomotive was tested and returned to traffic.

The difference in performance was immediately apparent. In its unmodified state the locomotive was normally restricted to 5 units (30 tons) up the 1 in 29 out of Welshpool, but with the modifications the locomotive easily managed 6 units with a reduction of around 5% in coal consumption. Regular crews were reporting reductions in coal consumption on normal trains of around 10%. The cost of the materials used in the modifications were recovered within 30 days' running.

Ironically the spark emission still remained high and the fitting of a fine mesh spark arrestor was to follow in the early part of the 1994 season.

Alterations in the method of firing the locomotive also help in the reduction of spark emission. In traditional firing practice all the combustion air is admitted below the grate. This causes the lighter and some of the heavier particles to be drawn through the boiler tubes and ejected. To reduce the emissions the primary air is kept to a minimum (about 30% is sufficient to prevent the firebed from going dead) and secondary air from the fire hole door burns the liberated gases given off from the firebed. Using this technique clinker is less likely to form. The front damper should be kept shut at all times and a minimum amount of back damper used. Too much air will cool the combustion gases and reduce the steam output.

Following the ongoing success of the design on No.14, Shaun and Nigel turned their attention to No.2 'The Countess'. Never a particularly good steamer, it was noticeably heavier on fuel than the other locomotives. It was therefore considered an ideal candidate for conversion and immediately after the season ended Nigel produced some drawings and the modified front end was made.

Using the existing blastpipe base the top was modified to a 4 nozzle pattern similar in external appearance to No.14 but differing internally. A liner was also fitted to the chimney reducing the choke size. A new blower ring and rerouted ejector exhaust were also provided.

It was not possible to test the locomotive immediately after construction owing to other work being completed, most notably its wheels were away at the Festiniog Railway being reprofiled.

Problems with 'Sir Drefaldwyn' led to 'Countess' re-entering service earlier than expected and it ran for the first time in its modified state a week before Easter 1994. Its first run showed that all was not well and further investigation was required.

It soon became apparent that the ejector exhaust was obstructing one of the nozzles and that there was an alignment problem with the blastpipe itself. Once these minor problems were rectified the loco was tested again and the difference in its performance was outstanding.

The locomotive is still not as efficient as No.14 in terms of coal and water consumption part of which can be attributed to the ex GWR ejector used, but further improvements may be gained from altering the valve gear. However its improvement at present has led certain people to eat their words that the boilers of the two original engines were at the limit of their steaming capacity.

During the winter of 94/95 the Austrian 0-8-0 'Sir Drefaldwyn' also received front end attention with new exhaust pipes and a modified Lempor blastpipe top. It was due to enter service in the early part of the season but mechanical problems delayed its appearance. Its eventual usage will make interesting comparisons with the other two engines bearing in mind that as a superheated engine it was far more efficient in terms of coal and water, anyway.

Looking ahead, the eventual overhaul of the W&L's No.15 will be a chance to put some of the lessons learned from the previous conversions to good effect. A large engine, the possibility of converting it to run on the Gas Producer Combustion System has not been overlooked, and as the loco needs a replacement firebox, any necessary alteration should be easily completed."


Update - May 2000 By Nigel Day

"Since the article was written the Earl has been rebuilt and now has a Lempor similar to that fitted to the Countess and all reports are that it is doing well. The loco had a nozzle made to the drawings of No.14 which is smaller than that of the Countess and the Earl the result was that the blast was too strong. Once the correct drawings had been found for the correct nozzle had been found and made as stated the result is highly effective.

The Tubize has also had its rebuild including a new firebox and has been under test again and very predictably the steaming is very satisfactory.

The W&L is a case of using modern technology to help solve a problem within the preservation movement where the technology is only applied to a minimum level. This is shown by the fact that the Lempors are fitted inside the existing chimney.

This means that the whole of the operational fleet of locomotives has now been fitted with improved draughting with many benefits, just like the Snowdon locomotives. The result is that a number of other locomotives have received attention from me on other UK railways. These include a number of standard gauge tank engines based at Embsay, Caledonia on the Isle of Man. The are others on the way.

Although Snowdon is mentioned here it is relevant to the fact that the resent conversion of #4 Snowdon to oil firing by myself uses Lempor technology to solve one of the problems which helped kill previous attempts at oil firing on the SMR. This was the lack of high draught rates which is essential at the evaporative rates these locomotives work at.

Although the technology used on the W&L is standard Lempor technology I have changed the manufacturing techniques to that which suit the available equipment. The main difference is that of having the nozzles machined from round bar. This means no formers are necessary and the resultant nozzle is robust. Some, which are now over ten years old still have the machining, marks on the out side. The correct dynamics are maintained by keeping to the correct de larval sections.

In first deciding to re-draught the Snowdon locomotives in the 1980's as a result of not being able to keep up with the new upstart Diesels it was extremely difficult to find any information on design data on front ends. Such things as test gear have been constructed out of pipework from the coca cola machine and a low reading pressure gauge out of a water works bought for a fiver at a car boot sale. Such simple equipment can teach you a lot of what is happening in a locomotive's body. It took over two years to design the first chimney, which did not work, and it was only after several modifications was success achieved. In doing so a lot of research has been cried out to try to find away of further developing a next generation of draughting, some of which has been tested on SMR locomotives with interesting results. I give due credit to those who have gone before me on this subject, as it becomes progressively harder to find a new idea, which has not already been tried. There is still much to do yet to get near the ultimate draughting device but that is the challenge.

By the way the new 1996 rail car cannot keep up with my modified 1896 steam locomotive such is progress. "


Click here to return to the modern steam locomotive developments page.


Rob Dickinson

Email: webmaster@internationalsteam.co.uk