Smokebox door fastenings

Dogs/darts, levers/wheels is there any logic to the choices? And why did the Great Eastern go for a supporting ring rather than hinge straps?

Especially oddities like T9s (post super-heat) with dogs round the bottom and darts.

And a subsidiary question. On US engines with Westinghouse pumps etc on the front, and small doors on the smokebox, how did they clean the upper tubes?

Mike

 

Interesting question. I will be interested to read any knowledgeable response.

I wonder how much simple aesthetics and fashion had to do with it. By the time of the grouping there was a split between dogs (Derby, Ashford) and darts (almost everywhere else), with the odd exception like Eastleigh with the combined approach. By 1948 dogs were completely out of favour in the UK. However, in some countries (e.g. West Germany), the trend went the other way, and in the USA darts never found favour.

Given that smokebox doors contributed so much to the character of a locomotive, I wonder if it was an intentional matter of style. In the UK locomotive styling was important to most railway companies, whereas in the USA for the most part a locomotive was just a machine.

 

The centre dart is a simple and effective way to hold a smokebox door tight. However, it does require the door to be closely fitted to its seat. On many locomotives there is a soft packing around the perimeter for the door to close against and make the airtight seal. This requirement for a close fit is not so important with dogs as they pull the door onto the smokebox front at the perimeter and things will distort slightly to overcome any slight gaps that may exist. The disadvantage of this arrangement is that it takes a good deal longer to open and close a smokebox door.

People often think that a good seal is necessary to enable a good smokebox vacuum. It is, but there is another important consideration. Any slight leakage of air near the bottom will cause the char drawn into the smokebox and deposited on the smokebox floor to continue burning in that area, Evidence of air leakage is often shown by burned paintwork on the smokebox. This localised heating can cause distortion of the platework and aggravate the situation. It is one reason why some locos have dogs at the bottom, besides a conventional dart arrangement.

With regard to cleaning tubes, it's not just the door that would get in the way, blastpipes and other bits do too. The usual way would be with a steam or air lance. Tube brushes are generally confined to small boilers; trying to manhandle a 20+foot long rod wouldn't be easy and damned hard work!

 

I am not sure if this meets Tim's "knowledgeable" test, but several observations. I attach an image of the open (standard US) "Master Mechanics" smokebox on a Chinese SY, with part of the self-cleaning components (spark arrestor screens and the rear baffle) removed. Even with a "British"-style smokebox door, it would still present a fairly obstacle-rich environment for getting at the tubes. Most of the rows of tubes are superheater flues, which give rise to the additional problem as they are occupied by the superheater elements. There were various devices for cleaning flues and tubes from the firebox end including sand guns, but I note for instance from the Locomotive Cyclopedia for 1947, that Elesco would sell you a gizmo which fitted over the flue tube ends in the firebox and firstly blew them out first with compressed air and then washed them out with water. For the small tubes, I guess you would similarly attack them from the firebox end.

 

The easy way to clean tubes. Does anyone use these or similar on their boilers?


Notice the beaded tubes. The Americans seem to prefer beading to welding.

 

Ow much?

 

Thanks all. Very informative. Presumably the nore dished shape of the door with a dart is becuase it needs to maintain a shape to fit unlike the door with dogs that can/should be more flexible.

Interestingly, there are some US engines with darts (Lucius Beebe's book Highliners has some images, and they look really odd). Even with a steam lance, cleaning the tubes on something with 2 Westinghouse pumps on each side and a narrow hatch between must have been a sod of a job

 

No idea. I found the video whilst looking for a different type of tube cleaning tool and quite liked it. I was looking for a demo of something like this, available for IBHS (other suppliers and makes are available)
https://www.ibhs.co.uk/smu-tube-clean-machine-1-phase-230v.html
I have used similar on industrial boilers. A complete set up of power unit, flexible drive and tools will set you back about £1500.

 

Pictures of burnt paint on smoke boxes seem more prevalent on pre-grouping photos: I don’t know if that is because the seals were worse, the burns showed up more because of generally better condition paintwork, or whether I simply look at more pre-grouping pictures ...

As for smokebox dogs: I don’t suppose I am the first, nor will I be the last, to curse when, climbing up onto the front of a Maunsell engine at 6am, you discover you have forgotten to take a spanner! Still prefer that arrangement though to a BR standard, which have a habit of being very stiff to open, on account of a slide opposite the hinges.

Tom

 

A supplementary question about the mechanics of the dart. I notice from BR era photographs that the rear-most handle is almost always in the vertical down position, whereas the forward-most handle can be in any position. So presumably one handle is locking into a slot inside the smokebox. Is this right? What does the other handle do?

 

BTW .... the Crosti 9Fs bucked the trend and had dogs. Anyone know why?

 

There is a bar across the middle of the smokebox door opening. This has a rectangular slot in it. The first part of the dart is a flat head which fits through the slot when twisted 90 degrees. To turn that the shaft on the dart has a square section and the first handle fits over this square so you can rotate the dart to pass through the door and hook it behind the cross bar. Usually the handle for this points down when correctly located to shut the door. but it would also work vertically. The outer section of the dart shaft has a thread on it so the second handle can tighter the door up onto the smokebox front and thus can be at any position.

 

Thanks Nigel. Very clear explanation.

So presumably, where there was a wheel (e.g. LNWR), it took the role of the threaded handle, used to tighten the door?

 

Here's a variation on the theme. Dogs with handles! This is a Malayan Railways pacific photographed at Singapore c1960. Each dog had a tightening handle. This was standard on new Malayan steam locos from the 1920s onwards. Seems like a good idea ... no need for a spanner ... but I don't know if this arrangement was used anywhere else.

Update: Looking through photographs I see that Inchicore adopted this approach. Elsewhere there is a similar arrangement in France and Germany, but it looks like it's not a screw-down dog. Instead it's a simple catch with a handle that needs to be jammed into place over the lip oft he smokebox door.

 

To me it looks exactly like those on all the UK locomotives. The only difference is that , instead of a conventional hexagonal nut requiring a spanner, there is a screwed handle to tighten them up. As you say, it avoids having to use a spanner. However, I would suggest that a spanner would produce a much tighter fit - unless you used a length of tube over the handle, that is!

 

The USA tanks on the KESR have short handles on the dogs, at least they did when I drove them. A coal pick was handy for loosening them when some big, powerful person had tightened them.

 

I’ve seen it where there is a wedge shape on the door so you hammer the dog round to tighten it on the wedge.

it’s worth understanding how much vacuum there is pulling on the door. It is not unknown for the vacuum to reach 20 inches of water. 33 feet is equivalent to atmospheric pressure. So a door 4 feet in diameter represents 1809 square inches. As a rough guide 12 inches of water represents 1/2 psi. So there is a pull of 900 pounds on the door. This the says that the dogs or dart are there to establish the seal on the door rather than keeping it closed.

 

That's an interesting thought I've not previously thought about. However, to put it in perspective a 1¼" centre dart when tightened up is easily going to produce a clamping force of 6000 lbf and 12 x ¾" dia dogs around the circumference fully tightened with a correct size spanner would give about 20,000 lbf of clamping force. (I've guessed the screw thread sizes, they may be bigger.)

 

Give it some pain with a battery powered Impact gun.........

 

And make sure have hidden before the bloke who has to undo it comes on scene...

Mind you, if you have an air-braked engine, could you have a take-off for air-driven tools?