The Perfect Joint (1)

Sentinel 7109 works at 275psi, a higher pressure than most steam locomotives, waggons and traction engines. Many steam industry suppliers have off-the-shelf items for up to around 180 psi but, for Sentinels, more specialised items need to be sourced, in particular jointing material.

For the steam fittings to the boiler and piping to the engines, I've chosen a robust 1.5mm jointing sheet made by Klinger and sourced from Seddon & Black (now Craftmaster Steam Supplies). Identified as PSM/AS, it is a tanged stainless steel sheet sandwich with exfoliated graphite either side (instead of bread!). It is certainly up to the task but it presents a challenge of its own.

Safety valve flange adaptor (1)

The tanged stainless steel sheet makes the material difficult to cut. Tin-snips are fine for outer edges where the curvature is slight; however, inside edges of smaller radius cannot be done this way. Small holes can be cut with hole punches so long as there is a solid backing of just the right hardness for the punch to cut through to. The best combination I've found is to use a chunk of heavy paving stone and a length of old oak from an ancient desk.

In the photo above, I used hole punches for the stud holes, tin-snips around the outside and a chisel for the centre hole - which is clearly not too tidy!

Safety valve flange adaptor (2)

Wandering off-subject for a moment, this is what it looked like before it was removed from the boiler. EN3B studs have been used to replace the originals.

Before removal from the boiler!

The standard type of Sentinel safety valve manifold, similar the one pictured below, would be fastened to the four-hole flange.

Sentinel Safety Valve manifold

I had to buy half a square metre of the PSM/AS sheeting which was more than I wanted just for the boiler fittings' joints. As it had seemed pricey to use large copper washers for the steam pipe joints, I pondered whether there was a way of making the washers using PSM/AS. This would of course mean cracking the problem of cutting holes with diameters of around an inch or two and only a quarter inch total material width.

There are gasket punch sets available but, as they come at a price and don't claim to be able to cut the tanged sheet sandwich materials, I'm looking to find a better alternative.

Hole Cutters

A hole cutter looks possible but, without care, could easily tear the material surface away from the inner tanged sheet.

I've an idea how to do this effectively but some R&D is needed to perfect the technique and the outcome of that will have to wait for the next article!

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!

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.

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!

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!