Not So Grate!

Most of the Sentinel 7109 articles I've written in this 'blog over the last 8 or so years have been fairly upbeat although I did get frustrated with gland packing not so long ago.

However, not all goes as well as I'd like and I've had a new downer to deal with. I've shown the photo below a number of times to illustrate the how the fire-grate began.

The Fire-Grate as new prior to first steaming in 2016

With an eye on environmental issues, at the beginning of 2019, at Midsomer Norton, we began using a cleaner Welsh coal. All seemed fine for some months and I did the usual half-yearly boiler and fire-box washout in August. However, shortly before the start of the four Santa Specials in December, the centre section of the fire-grate decided to disappear spectacularly as shown below.

Fire-Grate after cleaning at the start of December 2019
(After the first of four Santa Specials)

(This was the reason a diesel shunter was used as banker for the Santa Specials).

Obviously this was not great news and the timing was particularly inconvenient.

I've had to dig deep to figure out how this could have been caused to prevent it happening in the future. I think there are basically two causes, both to do with the coal.

The Welsh coal is clean; it produces very few 'volatiles' (the nice-smelling but smoky stuff) and burns hot. It also tends to disintegrate through agitation and during combustion. In either case, it forms a lot of 'dust' which sits around underneath the coal nuggets. Our nuggets were large, some about the size of three fists.

The dust tends to form into clinker and block the grate in places. Air then has to be concentrated through the remaining unblocked areas and causes hot spots which melt the fire-bars, a bit like a blow-torch. As the year progressed, the coal in our storage bunker became more dust than nuggets and so the amount of grate blockage increased as the year went on and finally precipitated the damage.

Anyway, in summary, that is my interpretation of what happened. All we have to do now is to prevent further damage and replace the fire-bars.

Traditionally, fire-bars have been made from grey cast iron. However, I've had advice that a 20-30% alloy of Chromium and iron is much longer-lasting than plain old grey cast iron.

I've taken this advice and, to be ready for the first 2020 steaming on March 22nd, I rapidly placed an order for a pattern to cast the new fire-bars from Chromium Cast Iron (the pattern has to be specific for the material as the metal would not cool to the right size otherwise). I had to purchase a minimum quantity of 30 fire-bars (which should keep us going for a while!).

The bars arrived just ahead of the delivery date and I am grateful to the staff at Cerdic Foundries Ltd for their help in a time of difficulty.

Quite a car load!

I've not tried a funding appeal before but this is one occasion when I think it is the right thing to do.

Including VAT, the pattern will be £2,400 in round figures - I have bought this.

Including VAT, each of the 30 fire-bars is £120 in round figures.

Please consider donating a fire-bar for Joyce. Donations can be made via PayPal or cheque (preferred as PayPal takes a percentage) by clicking here. I would be more than happy to entertain donors with a cab ride on your next visit.

Go on, you can do it! Thank you in anticipation.

Hooked

As Sentinel 7109 progresses through its new working life, I run into many little irritating operational problems that can be solved quite easily. Filling the water tank is one.

We use a 6-wheeled tanker wagon as reservoir. It's simple to fill the tanker slowly from a domestic supply tap when there is plenty of time. For rapid watering during operations, we use an impeller pump at the tanker to pump along sections of flaccid hose linked by claw couplings to Joyce's tank.

The trouble with a flaccid hose is that it's flaccid. It flaps around merrily in the top of Joyce's tank while filling and is partially blocked by the weight of the tank lid sitting on the hose to prevent it from jet-propelling itself out.

I made a more resilient hose extension to overcome the problem.

Not-so-flaccid hose extension

It neatly hooks over the tank filler rim and doesn't get squashed by the lid.

Simple but effective

Hopefully, we also won't get quite so wet when the tank overflows (which never happens, of course!).

Steam Heating (4)

Following on from Steam Heating (3), Sentinel 7109 had a brief steam test a few days before the start of the 2019 Santa specials. (I'll write about the reason for the brevity in due course).

To the casual observer, the carriage heating performed well although it also showed that the carriages themselves have a number of leaks and cold areas to be attended to. The leaks certainly add to the atmosphere but not always where you want it.

Carriage Warming up and running (Photo: Roger Burfitt)

To the not-so-casual observer, i.e. me, all was not quite as perfect as I'd hoped.

Spirax-Sarco PRV on the left

The Blue Spirax-Sarco Pressure Reducing Valve (PRV) can be adjusted to give the 20-40 psi output pressure range required but it is faced with a very variable load. (For carriage warming, steam is squirted down the steam heating pipe and it exits as steam or water through a series of drip valves after passing through various heat exchangers. There is thus a back pressure from the carriage pipework and hence a 'load' on the steam generator. On initial starting-up, the far end of the pipework is opened to atmosphere to allow the steam through rapidly with much reduced back pressure).

When initially started from cold, the steam is fed into a large cold space. It immediately condenses and this takes place progressively along the two carriages until all is warmed through and steam is exuding from the hose at the far end of the train.

The loading thus initially varies considerably and then will vary yet again depending on how many carriage heaters are switched on and off.

Whilst the PRV can be set initially so that it supplies the right pressure, the changing load then plays with the setting. The PRV also tends to oscillate with a repetitive 'kerr-dunk' noise which I doubt is particularly kind to it.

Setting the PRV to be either on the high side or low side of the pressure range seems to calm down the oscillation. It can also be calmed by limiting the inlet flow using the isolation valve.

I've put a reducing-flow orifice in the inlet steam feed to the PRV which has also helped a little. However, I suspect that if I did the same on the PRV outlet, I would have more success as it will smooth out the load from the carriages. The inlet orifice is easy to fit but the outlet one requires taking it all apart again under the buffer beam.

Adjusting the PRV outlet pressure is also a bind as the PRV is under the buffer beam and not easily accessible.

The PRV does its job well but depends on the loading being more constant than here. More tweaking is required to get this right and make it simple to operate but, according to the Santa Special passengers, it seems to be entirely satisfactory!

Beginning the climb, steam everywhere! (Photo: Roger Burfitt)

In Steam Heating (3), I anticipated that the carriages would be too cold, too hot or somewhere in between. Oddly, I was right so without too many reservations, I declare Joyce's new Steam Heating apparatus to be a success!😊

Steam Heating (3)

Following on from Steam Heating (2), I've fitted the carriage warming equipment to Sentinel 7109 ready for a steam test with a train in a few days time.

I began with the boiler connection and isolating valve.

Isolating valve plumbed into the boiler orifice

Having removed the boiler orifice plug and cleaned out the threads, I checked the 1/2" BSP thread type using a parallel tapping tool. The thread was clearly a parallel type and the BSPT tapered thread of the hex nipple was loose unless tightened firmly. This was as expected so I converted the thread to a tapered type using a tapered tapping tool. Now the BSPT tapered thread of the hex nipple fitted much more positively.

I completed the joint using Rocol steam seal. Total loco unavailable time: about half an hour!

I then fitted the standard buffer beam equipment using the purpose-designed flange.

Standard buffer beam equipment fitted to buffer beam (1)

Standard buffer beam equipment fitted to buffer beam (2)

The blue Spirax Sarco Pressure Reducing Valve (PRV) and Safety valve assembly came next followed by the flexible hose to link the isolating valve to the buffer beam equipment.

Blue PRV and safety valve attached to rear of flange (1)

Blue PRV and safety valve attached to rear of flange (2)

Also showing above is the narrow copper pipe to link the buffer beam outlet pressure to the gauge on the cab's rear panel near the roof on the fireman's side.

Steam Heating Pressure Gauge

The weight of the PRV assembly is supported by a clamp between the PRV and safety valve linked to the footplate above by M10 studding.

Having fitted the buffer beam equipment and attached the hose, I hitched up the hose end using the standard support links. It then became obvious that the assembly was somewhat lower than expected. On examining a MK1 carriage for comparison, the assembly is 6 to 8 inches lower.

Hitched with shortened support linkage

To avoid the end dragging on the ground or catching the rails, by wiring the two end parts of the support links together, I've pulled it up to a safe height above the rails as shown above. A more permanent version will be devised in due course.

Prior to steaming, the first test was to to check that the lower height would not prevent a connection being made to a carriage. As shown below, it is all OK.

May be low but fits perfectly.

Now all we need to do is a steam test. I anticipate that the carriages will be too cold, too hot or somewhere in between. If these are the pass criteria, then all should be fine!

Steam Heating (2)

After some pretty hectic weeks, I have most of the sub assemblies ready to fit. Rapid progress has been made possible by Amanda and Rob at South West Engineering Supplies at Bumpers Farm industrial estate near my home in Chippenham. Without them, I'd have been struggling to obtain all the bits and pieces in a short time and they have given me ready access to trial and error items. So a big thank you to them.

Following on from 'Steam Heating (1)', this is how it's developed.

What equipment is needed?

1. High pressure pipework and an isolating valve able to withstand the Sentinel boiler temperature & pressure (212DegC & 275psi).

High Pressure Pipe Fittings and Valve

In the photo above, the steel 'T' fitting's leg links to a 3000psi stainless steel union and thence to a taper threaded hex nipple which will screw into the boiler orifice. This union allows the angle of the 'T' to be set after securely fixing the nipple into the boiler orifice. The plug at the top of the 'T' fitting is to provide another steam outlet for future use.

The second union below the 'T' fitting allows the valve to be orientated appropriately. The valve is a three-part ball valve made by Valtac. I've written about these before. The hex nipple below the valve will connect to flexible braided hose to take the steam down to the buffer beam. Although the nipple in the photo is a steel type, I will be using a parallel threaded hydraulic fitting machined to take a copper washer sealed mating connector.

2. Pipework to carry the boiler pressure steam to the buffer beam apparatus.

Purists might criticise me for using modern flexible stainless steel braided hose instead of copper pipe with braized end fittings. I can order and receive the flexible hose with welded end fittings and a pressure test certificate within a week and be confident in the result. Using copper pipe, I cannot do this. (In fact, the hose arrived in four days!).

I've covered this before in detail here.

3. A pressure reducing valve to take the boiler pressure down to the carriage requirements (about 40psi).

Blue Pressure Reducing Valve (centre) (and one assistant)

Blue Pressure Reducing Valve (and other assistant)

The blue Spirax Sarco PRV is a 1/2" BRV2S with a Green Spring to allow a range of 20-60psi.

Arguably, to reduce the length of high pressure hose, I could have put the pressure reducing valve below the ball valve instead of behind the buffer beam. However the PRV needs to be mounted upright and would have taken up too much space in the cab.

4. A safety valve to prevent exceeding the carriage maximum pressure.

Gunmetal Safety Valve

The safety valve is a 1/2" ART 642 type made by Albion.

Safety Valve Detail including 3 bar setting.

5. A pressure gauge to allow the carriage pressure setting.

3" Steam Pressure gauge

The safety valve has been delivered certified to 45psi (3 bar) so 100psi full-scale is fine. I purchased it new from "thegaugeman61" on Ebay".

6. Heavy duty bracketry to fix the pipework and standard buffer beam equipment to the buffer beam itself.

Flange made to fit the standard buffer beam equipment to the buffer beam

The flange's central hole is tapped to 1.25" BSPT (tapered) to take a 1.25" section of pipe. The pipe section is then held by a Stauff clamp with an additional supporting bar screwed to the bottom edge of the buffer beam. A third bolt fixes the flange through the buffer beam. It is pretty strong and intended to survive heavy handling.

The flange 3-point mounting to the rear buffer beam

The Complete Assembly

I've pre-assembled the 'flat-pack' version of the equipment to show it all together before it disappears out of sight in and under Joyce's metalwork.

Complete 'flat-pack' and assistants

The boiler fitting is at the top. It passes steam via a 'T' fitting to a ball valve and thence to the braided flexible hose. The hose links to the blue PRV which passes lower pressure steam to the safety valve and pressure gauge pipe. Finally the pipe connects to the back of the flange and to the standard buffer beam equipment.

Now all I have to do is fit the kit and test it. Initial fitting will be quite quick for test purposes. I'll clamp the pipework properly when I'm happy it performs satisfactorily. The assistants will not be allowed on site at Midsomer Norton as they haven't passed their Personal Trackside Safety exam (honest!).