I'm glad someone asked me that. Perhaps a video clip will help...
I hope you enjoy this.
I guess the answer is... Grate!
Tuesday, 22 September 2020
Thursday, 27 February 2020
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.
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.
(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.
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.
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 |
 |
| Fire-Grate after cleaning at the start of December 2019 (After the first of four 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! |
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.
Tuesday, 7 January 2020
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.
It neatly hooks over the tank filler rim and doesn't get squashed by the lid.
Hopefully, we also won't get quite so wet when the tank overflows (which never happens, of course!).
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.
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| Not-so-flaccid hose extension |
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| Simple but effective |
Thursday, 2 January 2020
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.
To the not-so-casual observer, i.e. me, all was not quite as perfect as I'd hoped.
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!
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!😊
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) |
 |
| Spirax-Sarco PRV on the left |
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) |