Monday, 25 June 2012

Superheater Inlet Manifold (No Leek here (yet)!)

With the arrival of the specialised nuts, screws, washers and bolts etc., I've been able to start preparing some of the sub-assemblies for fitting.

This one is the superheater's steam inlet manifold which sits at the top front of the boiler. It takes the single boiler outlet and splits it into four for connecting to the four superheater 'rings'.

Superheater Inlet Manifold Top View (1)
The new engineering studs are a little on the long side but to no avail. They are made from EN8 which is an unalloyed medium carbon steel with good tensile strength and satisfactory for attaching a steam fitting (as you will know from a previous article on the subject!).
Superheater Inlet Manifold Top View (2)
There are two narrow-bore steam outlets, one at each side of the manifold. One of these will be used to supply the pressure gauge; the other to feed the whistle valve.

Looking from below (or it will be below when eventually mounted on the boiler), there is a spare steam outlet which has not previously been used and has merely been blanked off as in the second picture below.

Bottom View showing spare steam outlet
Bottom View - spare steam outlet closed up
This spare boiler outlet will be ideal for supplying a vacuum braking ejector!

If you are struggling to come to terms with the spelling of the heading, click here!

Friday, 22 June 2012

Preventing a draught (1)

I decided it was time that the fire-hole door was smartened up a little.
Bright and Shiny, almost new looking
I don't suppose it will stay like this for long!

One point of interest surprised me and that was that the cast item in the picture is Aluminium and not iron or steel. It is thus quite a manageable weight to lift open. There is also a steel plate hidden behind which covers the fire-hole and prevents the Aluminium from melting.

The arm on the right is to latch on to a bracket to hold the door closed.

In use, when the door is closed, air is prevented from being pulled in through the fire-hole above the fire. Whilst a small amount of top air will reduce smoke, it also bypasses the air path through the fire grate and will reduce the heat output.

Tuesday, 19 June 2012

Steam Brake Cylinder Completed (Again!)

In my previous article about the steam brake cylinder, I claimed the cylinder was complete and ready for installation. Honest, I thought it was but then I found that it really needed some tidying up and finishing off.

The previous paint used on the cylinder had been a type of red oxide but it is not specified to be able to stand up to the high temperatures encountered when pressurised steam is involved. I thus did some investigation and found a coating made by T&R Williamson Ltd who for many, many years have specialised in supporting the railway and other industries. They come well recommended and were very helpful on the phone.

New finish with the piston retaining ring in place
The chosen coating was a siliconised paint capable of withstanding 350DegC and able to be applied directly to metal. Its ability to iron out all brush marks and set with a silky smooth finish is amazing. I'll not mention the price!
Side view with condensate drain valve disassembled
I also mentioned previously the condensate drain valve which had had to be unblocked before it could perform its job again.
Valve ball and housing...
...with a view into the valve chamber
The appendage at the bottom of the cylinder body (it is normally mounted on a vertical surface) has a hole from the bottom of the cylinder into its chamber. A ball sits in the chamber and is held in slackly by a tapered screw-in plug with a small hole through it.
Screw-in plug with hole through it
When there is no pressure in the cylinder, the ball sits at the bottom of the chamber so that steam or air can pass by it and out through the hole in the screw-in plug. Excess condensation is blown out.

When steam or air is allowed into the cylinder under pressure, the ball is blown on to the tapered hole in the plug and prevents the steam or air from escaping. This maximises the force on the cylinder's piston and the loco's brake. (Also on YouTube).

Listen carefully to the video clip; when the piston is pushed fully out, the hissing through the condensate valve increases until the ball clicks over the hole. I hope this will work satisfactorily; it may need tuning with a different size of ball in practice.

When the pressure is released again the ball drops back into the chamber to open the hole again and allow condensate to drain.
 (Also on YouTube).
Again listen carefully; as the pressure falls, there is a pronounced Tick as the ball falls back into the chamber.

So that's how it works, I hear you say!

Post script 22nd June 2012: I tried a 0.75" ball instead of the 0.625" ball used in the videos. 0.75" is too large such that it blocks the outlet when the screw-in plug is tightened. I don't have a smaller ball to try so 0.625" it is. In this case, clearly, size matters!

Friday, 15 June 2012

Nut Screws Washers & Bolts!

I've been struggling for some time to place an order for the various nuts, screws, washers and bolts plus engineering studs for holding Sentinel 7109 together. The struggle has been to discover the correct type of steel required in each case.

For run-of-the-mill purposes, the material from which these items are made does not matter; however, when the items being fixed are steam fittings supporting 275psi pressure, I (and the boiler inspector) have to get this right.

Boiler shell fixing studs (EN3B)
As an example, the photo above shows some of the specially made EN3B studs required for holding the boiler together. EN3B is a bright mild steel with properties that enable tighter tolerance threads to be cut and hence provide a stronger engagement between the stud and nut threads. It is not particularly strong in a tensile manner. I'd assumed earlier that it was the tensile strength which was to be important but it seems not. More information on EN3B properties can be found by clicking here.
Outer shell in place with fittings & blanking plates
(for hydraulic testing)
Some of the boiler fittings and blanking plates used during the first hydraulic test are shown above. From this experience, I assumedthat EN3B fixings would be needed everywhere that a high pressure steam joint had to be made. However, on trying to purchase EN3B studs, nuts, screws & bolts, it was apparent that these were not commonly available and that there was some inconsistency in recommendations depending who was being asked!

After some considerable amount of searching, I came to the conclusion that the fixings' material required for steam fittings is more to do with what should be avoided rather than what precisely should be used. The material to be avoided is 'leaded' mild steel such as EN1A. Whilst EN1A is easily machined and welded, it is not for this application. This therefore answers why some suppliers of engineering studs do not specify the precise mild steel their stock is made from; hopefully it is safe to assume that they are fit for purpose and will not be made from EN1A!

Nut and Bolt Inscriptions
Restoration of Sentinel 7109 has not failed to expose gaps in my knowledge. One gap that is not so empty now is the meaning of the inscriptions on nuts and bolt heads. I hadn't until recently noticed that the inscriptions could vary from bolt to bolt; however, they do and they indicate the tensile strength capability. I'm not going to attempt to include a dissertation on the subject here but there are some good references such as this one from 'Bolt Science'.

The '8.8' bolt head and compatible '8' nut pictured above are a medium grade metric type suitable for pulling together steam pipe joints; they are easily available off the shelf.

I think I've got to the bottom of these fixing requirements now and have at last placed an order for 11kg of them. So shortly reconstruction of Sentinel 7109 will be able to commence!
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