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A Bewilderment of Boilers

Part Eleven

We left the Gresley - Yarrow Water Tube Boiler on the frames, and with the engine about to go out on trial and running in turns. The first known trial run was on 12th December 1929 on a South bound train from Darlington, the second trial was on 29th December 1929 on an up express from Newcastle. No Test Reports have been traced for these runs. The engine was still under the control of the "Works", but presumably doing some work to ensure that it was "run in", and so may have been employed on revenue earning trains to get it to Kings Cross for the Press day on 8th January 1930, and then back to Darlington. A test run was made on 30th January 1930 Darlington to York and return, the schedule for the return journey was 55 mins. Again no Test Report has been traced either for this run or the next test run on 6th February which was Darlington to Doncaster and return, non stop both ways, with a load of 400 tons, scheduled times were out 1 hr 41 mins, return 1 hr 40 mins. One explanation for the lack of Test Reports is that maybe the crews were still learning how to drive and fire this complex machine, and that any data recorded would be of no value until the crews were fully conversant with the engine.

However it must have been deemed that the crews had had sufficient training as a Test Run was made Darlington to Kings Cross on 13th February 1930 and return the next day, with a load of 516.3 tons. To Kings Cross the scheduled time was 5 hrs 7 mins, including stops of 5 mins at Doncaster and of 11mins at Grantham.

The average results are as follows :-    Boiler Pressure 351 lbs per sq in.
High Pressure Steam Chest 297 lbs per sq in.
Low Pressure Steam Chest 54 lbs per sq in.
Steam Temperature in Header 557 degrees Farh.
Smokebox Temperature 590 degrees Farh.

The scheduled time for the return journey was 5 hrs 12mins including stops of 28 mins at Grantham and 5mins at Doncaster.

The average results are as follows :-    Boiler Pressure 281 lbs per sq in.
High Pressure Steam Chest 258 lbs per sq in.
Low Pressure Steam Chest 46 lbs per sq in.
Steam Temperature in Header 547 degrees Farh
Smokebox Temperature 603 degrees Farh

As all the data was recorded at 5min intervals as apposed to mileage it is difficult to pinpoint specific locations. On the return journey the boiler pressure dropped to 195 lbs per sq in. just before Grantham, one can only assume this happened breasting Stoke Summit. The 28 min stop was put to good use as the boiler pressure was up to 280 lbs per sq in. on leaving Grantham. The engine was worked on fixed cut off positions, of 48% H. P. and 40% L.P. all the way from Grantham to Doncaster and the average Steam Chest Pressures were 200 lbs per sq in. H.P. and 50 lbs per sq in. L.P. From the above figures it can be seen that the steam raising capability of the boiler was nowhere near that expected. The steam distribution was also very poor, as shown by the low pressure of the steam in the L.P. Steam Chest.

A further Test Run to Leeds via Ripon & Harrogate and return via York took place on 21st February 1930. The boiler performance was somewhat better, the average results are as follows :-

Boiler Pressure
H.P. Steam Chest
L.P. Steam Chest
Combustion Chamber temperature   
Steam Temperature in Header
Smokebox Temperature
Out To Leeds
325 lbs per sq. in.   
237 lbs per sq. in.
67 lbs per sq. in.
1,390 Deg. Fahr.
525 Deg. Fahr.
584 Deg. Fahr.
Return To Darlington
348 lbs per sq. in.
322 lbs per sq. in.
83 lbs per sq. in.
1,421Deg. Fahr.
555 Deg. Fahr.
584 Deg. Fahr.

The Engine must have been immediately dispatched to Scotland, as a further Test Run, Edinburgh to Perth and return was carried out on 23rd February 1930. The stated aim was to test the performance of the engine on heavy gradients, with a load of 408 tons including the dynamometer car. The booked running time was approximately 75 mins. in both directions. The actual was nearer 98 mins. on the way out, and 96 mins. on the return. The explanation of this loss of time was given as being due to the Gateshead driver having to take instruction from a pilot man as he was unfamiliar with the road. The distance travelled was 47.9 miles at an approximate average speed of 30mph both ways. It is stated in the report that a great deal of difficulty was experienced with the high pressure injector, and this caused a considerable loss of water. The average coal consumption for the round trip was 64.2 lbs per mile, and the water consumption was 445 lbs per mile. The other average figures are as follows :-

Average Boiler Pressure
Steam Chest Pressure H.P. Cylinders   
Steam Chest Pressure L.P. Cylinders
Combustion Chamber Temperature
Steam temperature in Header
Smokebox Temperature
353 lbs per sq. in.
314 lbs per sq in.
85 lbs per sq. in.
1,403 degrees Fahr.   
570 degrees Fahr.
624 degrees Fahr.
376 lbs per sq. in.
321 lbs per sq in.
92 lbs per sq. in.
1,449 degrees fahr.
543 degrees Fahr.
633 degrees Fahr.

This was a very comprehensive test with temperature checks front and back on the Right and Left Flues, and also the air temperature left and right entering the ash pan. The maximum draw bar pull was 9.1 tons and the maximum draw bar horsepower was 955.

The above tests and presumably continued "trial" running under the supervision of the works, lead to the following modifications being carried out late March, early April 1930. :-

     (1) The H.P. Injector was increased in size.
     (2) New Superheater Elements 1'-6" shorter were fitted, and triple loop elements replaced the quadruple loops.
     (3) Two new improved Safety valves were fitted.
     (4) The diameter of the Blastpipe was reduced to 4 ¾"

Straying from the Boiler, the Cut Off indicator was operated by means of a "Bowden Wire Cable" this was non too accurate, so alternative schemes were looked at. There is a drawing and correspondence on file at the NRM from Siemens, showing their system as employed on ships, to indicate to the helmsman the angle of the rudder. This system had small indicator lights on the dial and it was suggested that this could easily be adapted to fit the engine . Another similar electrical system was suggested by Vignoles, neither scheme was pursued. Stratford Drawing Office came up with the solution employing Invar rods fitted to the lifting links.

On 16th April 1930 These modifications were tested on a run from Darlington to Leeds via Harrogate and back to Darlington via York. I have not been able to locate a Report for these runs. Again the Engine "disappears" (still under Works supervision, presumably) for another two months and is then released into traffic on 21st June 1930, works for 56 days until 16th August 1930, and then goes back into the works for 155 days until 18th January 1931.

During this Works visit further modifications were carried out as follows :-

  1. An improved Regulator valve was fitted, with spring assisted closure.
  2. The steam supply to the auxiliaries was taken from the Superheater Outlet Header, then passed through the water reservoir on the steam drum, before going through the reducing valve.
  3. The Superheater Inlet Header was altered to get a more even distribution of steam through the Elements.
  4. Another new set of Superheater Elements of slightly reduced diameter was fitted, and the Baffle Plates were moved forward with the intention of diverting more heat onto the superheater elements
  5. A long pipe, perforated at various angles was fitted along the bottom of the boiler, to act as a soot blower.
  6. A Marcotty Tilting Fire Door was fitted, this was in three vertically hung sections, operated by levers to right and left acting on balance weights. Pulling either handle opened the particular side section selected along with the middle section. Pulling both levers opened all three sections. [ As an aside there is a booklet in the NRM file describing the Marcotty Tilting Door and Smoke Consuming Apparatus. Obviously it was intended that the door and apparatus came as one job lot. However looking at the pipework required for the Smoke Consuming Apparatus, it's a good job they only fitted the Door otherwise the bewilderment would have been complete.]
  7. The Brick arch was shortened to 3'-4", probably with a view to getting more heat carried forward.
  8. There was concern that the H.P. Cylinders were doing most of the work, so it was decide to fit liners and so reduce the diameter to 10".

Back in traffic for 8 days until 25th January 1931, then back into Works for 9 days, the Marcotty Door had been giving problems, with the bearings on the pivots jamming due to the heat and needed adjustment. The Engine was out for test runs on 4th & 5th February 1931 Newcastle York and Return both days. Then was immediately back in traffic on 6th February 1931 and worked for another month until 5th,6th, & 7th March when it did test runs Newcastle York and return each day. The February and March Test Runs are noted in the Dynamometer car Log Book as Temperature Trials. No Report's on these Trials have been seen. The engine returned to normal duties on 8th March and worked until 23rd March when it was back into Works for 17 days, returning to traffic on 11th April, it then had a sustained period of 59 days of work, before going back into Works on 8th June. This visit to Works lasted 22 days, the Engine being back in traffic on 1st July until 2nd August, it is believed that during this period that the Engine made its last run on The Flying Scotsman on 25th July 1931. This Works visit was to last until 26th November, but it was interspersed with Test Runs on 18th,19th,27th,&28thAugust, Newcastle to Leeds and Return each day.

These runs were noted in the Dynamometer Car Log Book as for Temperature and Carbon Dioxide measurement, I have not traced any reports. A further test took place at Shildon 4th September noted in the Log Book as a Maximum Pull Test, I did see some paperwork on this but due to volume of information I was trying to copy I ran out of time and did not manage to make any notes. Indicating tests were carried out on 19th November 1931, Darlington York and Return .The following day 20th November 1931 double test runs were made Darlington York and Return, noted in the Log Book as Pressure, Temperature, Carbon Dioxide and Water in the Weir Temperature Tests, no reports have been found . The Engine was back in traffic on 26th November and worked the year out.

The Engine was now two years old and it can be seen from the above that quite a lot of the time had been spent in the Works. Most of the trouble seems to have been with leaking tubes and warped casing plates. With 1536 tube ends expanded into the five drums, there was considerable scope for leakage. The casing plates were subject to temperature variations, vibration and shock loading, causing the rivet holes in the seams to tear. Even today the casings on boilers in power stations have problems and they are in a stationary environment. One other point, after the initial confirmation of the fitting of the Marcotty Firehole Door and the trouble with it's bearings, it is never mentioned again. Was it removed at some stage or did it stay until the rebuilding.

Rather than go through a long litany of dates for in and out of Works, and in and out of Traffic, I have hopefully summarised the day to day existence of the Engine throughout from 12th December 1929 to 21st August 1935. There are periods when the Status of the Engine was "not known".

  In Traffic   
In Works
Test Runs etc.
"not known"

It will be seen from the above table that over the period covered, the Engine was only in Traffic 35%, in Works 54%, under Test 2%, and "not known" 9%, of the time. The longest period in Traffic was 198 days from 27thAugust 1932 to13th March 1933,and the longest period in works was 378 days from March 1933 to June 1934, this can be extended to 453 days by adding two periods of "not known" and two days of test runs along with a short period in Works before the Engine officially returned to Traffic on 28th August 1934.

Returning to 1932, the Engine was in Works for Boiler Repairs and the fitting of a new type of Reducing Valve, from 29th March to 28th April. The New Valves still caused problems, so the Engine was back into Works on 9th May . The following modifications were carried out :-

  1. The Vacuum Brake Ejector and the Low Pressure Injector were converted to High Pressure with the steam supply taken from the Steam Drum. This would hopefully reduce the demand through the Reducing Valve and enable it to work as intended.
  2. The Soot Blower was changed to two tubes to give a better cleaning action.
  3. The Superheater Elements were extended by 1'-4" and two extra double loop elements were added.
  4. The Brick Column had its profile altered so as to better deflect the hot gasses away from the ends of the Superheater Elements.
  5. The Brick Arch was shortened to a mere 1'-3"
  6. Extra Baffle Plates were fitted in the Flues to deflect hot gasses onto the forward water tubes.
  7. The water tubes were sprayed with Coal Tar to prevent corrosion. Yarrow's donating the Tar and loaning a spray gun. There is no indication as to whether the inside or the outside of the water tubes were to be sprayed. Outside the tar would have soon burnt off or provided an adhesive surface for the dust and clinker to stick to. Inside it is more than likely it would have emulsified with the boiling water and formed a scum on mixing with any other solid impurities.
  8. The lagging was removed in the air duct between the casings.

Yarrow's had a Technical Assistant (a Mr. Horwill) at Darlington from April to the end of August, 1932, he seems to have been tasked with sorting out, the gas flow through the flues, number and position of baffles, the effect of lagging etc. on air flow and internal and external casings. There is an extensive correspondence file, as it seems it was deemed necessary for him to report almost daily, to Yarrow's, also enclosing a drawing of his latest proposals.

A scale model of the boiler was set up and Gresley, Robson (Darlington Works), and Horwill (Yarrow) each had their suggested baffle layout tested. Yarrow's had sent some chemically treated compressed paper blocks that were to be ignited to provide smoke to blow through the model to gauge the effectiveness of the various baffle arrangements. As the Boiler model was made of wood the smouldering paper was likely to set fire to the model, so sawdust was blown through instead. It is not too clear, who if anybody, was adjudged to have had the best baffle layout and the layout adopted in (6) above is probably an amalgam of all three schemes. Horwill reported to Yarrow at the end of July that he did not think there was anything more he could do at Darlington, Yarrow's do not seem to have agreed on this point and he remained at Darlington until 27th August, when the Engine returned to traffic.

The above modifications seem to have done the trick as the Engine embarked on it's longest period of revenue earning service, 198 days, including 5days of test running. There is a slight doubt as to whether the length of this period is correct, as after the 1st test run on 17th October further test runs were delayed until 31st October due to a leaking mud hole door on one of the Water Drums. The repair was done on shed, and the Engine remained in traffic until the next test run.

The Test runs with the Dynamometer Car were held over 4 days 17th Oct. 31st Oct. 1st Nov. 2nd Nov. and 3rd Nov.1932, hauling scheduled trains, Out 11-10 am ex Newcastle, and return 5-10 pm ex Edinburgh, distance 124.5 miles each way, each day. Described in the Log Book as Flue Temperatures and Coal and Water Measurements, a summary as follows :-

 Boiler Pressure 
412lbs/sq in
402 lbs/sq in
418 lbs/sq in
434 lbs/sq in
418 lbs/sq in
418 lbs/sq in
409 lbs/sq in
411 lbs/sq in
388 lbs/sq in
404 lbs/sq in
411 lbs/sq in
 Av Speed 
51.2 mph
45.7 mph.
53 mph.
47.6 mph
49.5 mph
47.9 mph
48.9 mph
48.7 mph
44.6 mph
47.2 mph
48.4 mph
 H.P. Cut off 
 L.P. Cut off 
 274 lb/m 
280 lb/m
265 lb/m
311 lb/m
281 lb/m
288 lb/m
299 lb/m
283 lb/m
304 lb/m
315 lb/m
290 lb/m
44.1 lb/m
44.3 lb/m
42.4 lb/m
44.2 lb/m
46.0 lb/m
44.2 lb/m

It has been suggested that a 4" dia Blastpipe Top was tried during the above test runs, there is no mention of this in the Test Report, so it may or may not have happened.

In the Test Report the following conclusions are drawn :

  1. The Steam Chest Pressures are higher due to the feed to some of the auxiliaries not being taken from the main steam pipe.
  2. The larger Superheater has resulted in an increase in the steam temperature of approximately 40 degrees Fahr.
  3. Due to the removal of the internal lagging, a greater volume of slightly cooler air is flowing through the air ducts to the ash pan. In consequence it is possible to run for long distances with the front damper shut and maintain steam pressure.
  4. It was noted that there was considerable differences in the flue temperatures and that if oil firing had been employed a definite relationship between flue temperatures and boiler demand could probably have been established. Due to the large volume of coal on the grate and the variations in heat output due to hand firing it was not possible to establish a relationship.

The Engine went into Works for repairs on 14th March 1933, was out on 18th May 1933 worked for 11days and then was back in the Works for it's first General Overhaul on 29th May 1933 and was not back into traffic until 28th September 1934. The Overhaul did not start immediately, in July the Engine was piped up to the Dynamometer Car and the boiler was subjected to static testing to determine the temperature of the water and steam, and the effect on evaporation rates These tests, like the initial tests at Yarrow's, showed that the boiler was capable of producing an adequate volume of high pressure steam, but these were "ideal" conditions, and the boiler was not subject to fluctuating demands and benefited from a constant firing rate.

During the General Overhaul the Blast Pipe Top was reduced to 4 ¼" dia. The Steam Reversing gear had given trouble during the Oct./ Nov. 1933 test runs, so it was removed and a Screw Operated system was fitted. ( this sounds simple, but in actual fact the layout of the required shafts and gearboxes was fairly complicated). Chapelon recommended that a new intermediate Superheater be fitted to resuperheat the exhaust steam from the high pressure cylinders before it's reuse in the low pressure cylinders. To achieve this Thirty Two single length elements were fitted to each of the right and left flues. The inside of the outer casing to the air duct was reinsulated with "Alfol" foil. It is believed that once the static testing was complete the overhaul commenced in late July and carried through to 13th June 1934. This seems along time, but it has to be realised that, this was a unique engine, there was no spare boiler, Darlington did not build the boiler so they were working in the dark so to speak as to the repairs required (they should have been very familiar with the boiler the number of leaking tubes they had dealt with over the past 3 years). Say replace 5 tubes per day that takes up 5 months, so one can see that the time soon ebbed away. The front and back water drums were connected to help water circulation.

One point here that I have not been able to resolve, the high pressure cylinders were reduced to 10" dia in January 1931, Gresley instructed Darlington to revert to the original 12" dia in July 1932, but I have not seen evidence as to when the change took place.

The Engine was allegedly back into traffic on 13th June 1934, there is a period of 12days that I cannot account for, from this date, the Engine being back in Works again on 26th June until 10th July, another unknown period of 5 days before the Engine is back into works on 16th July. This time the Engine stays in the Works until it is released in traffic on 28th September 1934, but just make sure, Test Runs were undertaken, with Dynamometer Car and Counter Pressure Loco Nº756 Darlington - York via Ripon and return York - Darlington via Ripon on 22nd & 23rd August 1934. No Test Reports have been seen for these runs.

There now followed a reasonably long period of running until 4th January 1935, when the Engine went into Works for minor repairs and was back in traffic on 10th January 1935. A cracked Steam Chest forced the Engine back into works on 24th January 1935.

Gresley wrote to Thompson on 6th March 1935 enclosing copies of the Drawings for the Kylchap Exhaust system and instructing Thompson to "Kindly arrange for Engine Nº10000 to be modified in accordance with these drawings". The Drawings were listed as follows:-

General Assembly
Arrangement of Double Blast Pipe
Divide Cylindrical Petticoat Pipes with supporting brackets
Alternate blast pipe top to that shown on Drg. Nº378/2

The latter drg was include in case all the four differing blast pipe tops shown on Drg. Nº378/2 were unsuitable. The designers were hedging their bets here as they were at pains to point out that " In the case of all engines of a special type, such as Engine 10000, it is not possible to determine the principals of the "KC" Blast Pipe equipment as accurately as is the case with a normal type locomotive."

The Engine was theoretically back in traffic 11th May 1935, and then back in works 22nd May for checking over and then out doing Test Runs with the Dynamometer Car and the Counter Pressure Loco Nº761. Leeds - Hull and return, 30th, 31st May and 4th, 5th, 6th June 1935. Instructions were given that two sets of men from Neville Hill were to be sent to Darlington to bring the test train back to Leeds, via Ripon and Wetherby,(on the 29th May) he same men to remain with the engine throughout the tests. Some testing of cut off combinations was tried en-route from Darlington but were found to be impracticable.

The stated aim of the tests was to find out the effect of the differing blast pipe top configurations, and to try and determine the relationship between smoke box vacuum, back pressure and steam temperature. An attempt would also be made to find the maximum power output at constant speed for different cut off positions. In the event only two sets of blast pipe top arrangements were tried, with the Nº1 bars giving an area of 16.9 sq ins through the blast pipes equivalent to a dia of 4.65 ins for a plain single blast pipe. The Nº3 bars gave an area of 21.8 sq ins. equivalent to a dia of 5.27 ins.

It is impossible to give a summary of the results as they are all tabulated to relate to the fixed cut off positions and then graphs were drawn up to determine the relationships given above. The Speed was kept at or near 60mph., the boiler pressure was maintained at about 440lbs per sq in. on average the lowest pressure was 410lbs per sq in. and the highest was 470 lbs per sq. in !!! The highest drawbar horse power with the Nº1 bars was 1470 and with the No3 bars 1702. The highest draw bar pull was 4.67 tons with the HP cut off at 50% and the LP at 55% with the Nº1 bars,and with the Nº3 bars the pull was 5.02 tons with the HP cut off at 50% and the LP cut off at 55%.

The Report states that with the Nº3 bars high power outputs were obtained, with an average horsepower of 1400 at 60.5 mph being maintained for 9 miles, followed by an average of 1520 at 60 mph for 8 miles. It was concluded that it would not have been possible to obtain these power outputs with the original blast pipe,due to the high back pressure that would occur. To avoid trouble with steaming on light trains the Nº1 bars should be used, they also cleared the smoke better. Finally it was stated that the engine steamed better and was easier to fire when worked hard.

The engine went straight back into traffic until 14th June when it went into Works and was fitted with a cowl between the side wings forward of the chimney to hopefully lift the smoke clear of the cab. New improved firebars were fitted that increased the air flow through the grate to 56% of the area, an increase of 26%.

The Engine returned to Leeds on 10th July and the next day ran Leeds to Newcastle Via the Coast route and returned the same route, hauling the dynamometer car and Counter Pressure Loco Nº761. Returning straight to traffic the Engine worked until 21st August and then went into Works for repairs. Whilst awaiting a decision on various "improvements", the order was received to cease all work until further notice. The Cass A4 Silver Link made its spectacular high Speed debut on 27th September 1935 and that sounded the death knell for Nº10000. As a Locomotive it must be said that Nº10000 was only marginally acceptable and must have been the bane of the shed staff's lives.

The boiler was an example of trying to get a quart into a pint pot, the finished product was at the limits of the loading gauge for height and width. It may also have been more of a success if the front part of the boiler had been of the normal fire tube layout, as per the Delaware & Hudson H.P. boilers. At it's inception it was a bold effort to try to provide an economical boiler for the fleet of Pacific's, but in the end it failed to make the grade. Even if the boiler had performed better than the normal Pacific Boilers, the likely maintenance costs and time out of traffic, repairing all the leaking tubes would rule against it becoming the standard boiler for future express engines.

The Engine remained in store for over a year until13th October 1936, when the Engine travelled, under it's own steam to Doncaster, the journey of 76 miles is reported to have taken 15 hours.

The Engine was Rebuilt with a similar boiler to Diagram 108, but with thicker plates. But that is another story-------


HP boiler

Researched and written by Mel Haigh,
Education Officer, Sir Nigel Gresley Locomotive Trust Ltd.
First published in Chime 141, Autumn 2006
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