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Part built five inch diameter boiler 2011
PYRTE the traction engine and trailer

The front end of PYRTE the traction engine 2011

Heating PYRTE

A trial by fire

Being new to gas firing I first tried a single 5½ x ¾ inch ceramic burner (supplied by a friend) with a number 8 jet in PYRTE thinking it would be big enough to put a fire in her belly, but that barely lifted the needle off the zero on the gauge. Too much heat was being radiated away due to the copper boiler and no insulation around the boiler and firebox at the time.

A second ceramic burner was added (from Forest Classics – who I would recommend you should make a point of steering clear of, 2 months for my burner to turn up; not helpful in the least and court action had to be threatened before it arrived) with a number 8 again, but still not much movement of the needle.

There was lots of yellow flame coming out of the top of the firebox, making me think it was hot enough, surely, but what I found later was that where the heat was needed (around the boiler itself) the flames were what is called lazy – most of the flame’s heat was being wasted above the boiler, owing to the jet sizes being too big and the gas was not being burnt at its best setting.

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At this point insulation was added to the firebox and boiler as a way to try to contain the heat where it was wanted, with a thin steel liner inserted in the firebox, giving around ½ an inch of space at the sides and all around the top part of the boiler with the outer side of this filled with fibreglass insulation material. The bottom was left open to allow the flame to penetrate from down below, with a 4 x ¾ inch gap at the top for exhaust purposes.

The boiler barrel (at the front of the firebox) was surrounded by ¼ inch ceramic lagging (which should really have been used inside the firebox as well, but I had the fibreglass handy) and this was held in place by what is called a cladding sheet (a very thin sheet of steel - can be brass or aluminium, or even hardwood) which is kept in place by brass boiler banding.

With this completed my efforts with PYRTE would barely get steam up to 25 lbs/sq. in. She would run (with no load) for around a couple of minutes, but died a death when the pressure dropped below 15 lbs/ sq. in.

It was strange really...

On air she would run at 10lbs/ sq. inch, but on steam she needed around 20 lbs to make any movement. Possibly the effect of heat on the working parts.

============

In my mind something radical needed doing as the so-called well hyped and fantastic ceramic burners were not doing the job, despite all the thick, sticky gunge being flung around about how good they were.

I purchased a couple of Clevedon Steam’s burners with number 5 jets to give it a try, adding first one to the two ceramic ones and achieved 30 lbs pressure a little more easily, despite the fact the yellow flame was still coming out of the top of the firebox, but I was looking for 50 lbs, and a sustainable 50 at that so that she could be steamed regularly.

With this better heating ability, a second Clevedon’s burner was installed so that with two of the Clevedon’s burners using number 5 jets and two ceramics with 8's, I managed to get up to 50 lbs/ sq. inch under no load, ran her a bit and then had to wait for the dropping pressure to build once more before running her again off and on for a good twenty minutes until my gas cylinder ran out.

Hooray... I was getting there. But the yellow flame at the top of the firebox I didn’t like.

I’d had a bit of email contact with Gerry (the very helpful chap who runs Clevedon Steam, a fellow steam enthusiast) and he told me the yellow flame was because of the number 8 jets.

As this was my first venture into gas heating I explained that I thought the number 8 would give out more heat than a number 5 (but I didn't tell him I'd been thinking in my naive fashion about a number 16, which was bigger still and I thought it would give a better flame because of more gas being available), which he said it would, but the fuel needs to be burnt properly, and my firebox design would need to be taller to achieve this, along with a better through-flow of air.

He said it is simply a matter of balance - the air versus the gas, and I certainly didn’t want to go down the road of changing the size of the firebox as the bodywork on my engine was completed.

============

At this time I was getting very disappointed with ceramic burners (despite the hysteria and hype put out by suppliers of them, along with their stupid raised prices) and decided to go down the route of buying another two of Gerry’s burners (they're almost half the price of those silly ceramic ones), that way burning the gas efficiently and in the right place beneath the boiler.

Having despatched the ceramic burners to the back of my steamshed in disgust and with three of Jerry's installed the result was 50 lbs, although it took a while to get there and would barely sustain that pressure when full throttle was in use (under no load, as can be seen here on Youtube). As cold water was pumped into the boiler the pressure would drop and take a couple of minutes to regain full working capacity, even when not running.

At this time I didn’t realise the flame was too far below the boiler barrel, but had it been closer earlier on, the ceramic burners would have been lighting the sky with their yellow flames.

After his advice I have finally resorted to using 4 of Gerry’s burners, with number 5 gas jets, and PYRTE works great with that. There is a small dip in pressure when cold water is added, but nothing to worry about.

With Gerry’s burners - he makes them for people with Cheddar models, who went bust a few years ago after he worked there (no, not because of him) - the gas fittings thread sizes are ¼ x 32 (Cheddar sizes), with a screw on ribbed cap rather than a nut which gives the impression it should be finger tight rather than pinched up with a small spanner or pliers.

==============

When I was arranging the four burners on the bottom plate of the fire box, I failed to tighten a couple of these fitting tight enough. I installed the burners in PYRTE and took her out for a trial run on a local car park. With a flame to the underside, she popped (the gas lighting) and I sat back with a brew to wait for the pressure to rise.

It seemed to be taking for-ever; the pressure would barely get above 15 lbs/sq. inch. There was heat above the top of the firebox. I hadn’t overfilled the boiler. It wasn’t windy, which can slow down the heat-up, and I could hear the gas burning and I had a new bottle of gas, along with a spare one just in case.

So the question was, what was I doing wrong?

I swapped the gas bottles over, thinking it may have been a duff bottle of gas, but still the pressure didn’t rise.

After about twenty minutes and still at just about 15 lbs, upon closer inspection (my eyes aren’t that good these days), I saw that the bottom of the firebox had the paint peeled off and there were flashes of yellow flame showing at the joints at the bottom, so in disgust the gas was shut off and I let her cool down.

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With her back on my bench at home with the complete burner and bottom plate assembly sat in my vice with the gas pipe coupled up, I tried to light the gas above the burners once again to see what had happened and found they would not light. I could smell the gas, so it was getting through, or so I thought. I could hear it escaping, so I checked the screwed pipe connections with a flame (naughty of me, I know).

What had happened was that the seal at the gas pipe joints hadn’t been tight enough and the gas had escaped there, burning the seals away, making the gas escape worse. The yellow flame was neat gas burning before it had even reached the burners.

So before re-assembly (and repainting and much cursing at my stupidity) I made a point of making sure these connections were tight enough.

============

A further point is that on my early attempts at steaming PYRTE, I had the burners sat too low. The best position so far is with the burners at ¾ to ½ inch from the outer shell of the boiler barrel and pointing towards its centre, although this is a little awkward to get right owing to the fact that you cannot see any flame inside the firebox. It has to be judged approximately and packed up to raise the burners to the correct height as can be seen in my picture.

Please ignore the erratic shaping of the piping as this was taken after an awful lot of fancy snake charming had occurred.

With this new height and after re-assembly, I boiled the kettle, topped up the tender tank and began pumping the water into the boiler.

Once I had around a teacupful in the boiler, I lit the gas at the top of the firebox, underneath the steam take-off tube and she popped, then popped again as all four burners were lit in pairs.

More boiling hot water was added to show just a little in the sight glass and then I lubed her up properly.

I shall have to make the pump a little bigger as it seems to take forever charging the boiler up at the start.

Inside two minutes I could hear the water boiling, with water and steam being pushed out of the drain at the cylinder base (which is left open at start-up). Thirty seconds later a full jet of steam was showing there and the drain tap was turned off, although water dribbles and wisps of steam continued to escape. This is normal as the various parts on an engine need to be up to temperature and pressure to become steam tight.

A further five minutes saw the pressure up to 25 lbs, with small amounts of steam escaping in various places, so I set the flywheel in motion, opening the regulator a little to get the engine turning over, that way warming her up a bit quicker and also evenly.

Fine, the pressure dropped, but not by too much as I ran her slowly for around half a minute, then shut off the regulator and stopped her.

By this time the pressure was down to 20 lbs because of the leaks and the engine running, but with another five minutes under her belt she was showing 45 lbs and very few leaks were evident in the last phase of the heat-up. It's this last phase, when the leaks are sealed, that the pressure rises quite quickly. She was near enough ready for action.

All in all, there needs to be around 30 lbs showing on the gauge before the regulator shuts off properly when the engine is first built. This will improve as the regulator slide beds down onto the top of the cylinder block. I now find that the pressure builds up much quicker because of the better sealing after a few years of action.

============

As an aside, it is best for a heat engine to be warmed up thoroughly before work commences, and for that reason I like to see these leaks in the warm-up, especially if there is a small amount of steam coming from the exhaust (the chimney in this case). At least that way you know your cylinder and valve gear is being warmed up evenly.

 

After running your model steam engine, dare I say it, having your way with her, getting your steam fix, it is simply a matter of opening the boiler drain-off tap, once the gas is turned off, to allow any pressure in the boiler to push the hot water out and onto the floor while you have a natter or a brew with your friends.

Half an hour later, PYRTE can be moved, although she will still be very warm to the touch. Heavy gardening or welding gloves are the order of the day here with moving hot steam engines.

Also, the gas consumption has improved no end with Gerry’s burners, compared to the poor disposed-of ceramic variety, and I highly recommend them as they do the job brilliantly (and just in case you are thinking I'm plugging these a bit too much, there is no commission involved here - I'm just a very happy customer).

 

George



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