Pink engine?!

I think I have spoke about this before ,I had a fusible plug go on a loco with about a 10 square foot grate area ,the fire, quite large ,was out in a mater of minutes.
Leaking tubes on the rear tube plate ,bottom row were nothing unusable ,we would wait until the weekend before replacing or trying to expand ,if they weren't burnt away to much. If a tube was blowing a fair amount we had (job to describe )a long rod about 3/8 round and four foot or so long,with a plate 5 or 6 ins square welded on one end ,the rod would be shoved up the afending tube ,the plate would divert the steam/water down on to the fire, not towards the fire hole door. Quite often the leaking tubes would seal up when out working.No brick arches were fitted to the locos.

 

That may open up a whole new discussion. The GWR were happy with just one safety valve, the LNER two but the LMS insisted on four for their Pacifics

 

In My 'Road Steam' life I've seen a fire on a 6 square foot grate literally doused by a plug dropping, just giving the engine enough time to get off of the road.(Into a pub carpark). I'm guessing that Stratfords reluctance to fit fusible plugs probably goes back mto the small boilers used on the Eastern Counties Railway, whereby a dropped plug on Brentwood Bank would put the locomotive out of action, and therefore if singleheading the whole train would have to stop, whereras a scorched crown, provided that it hadn't ruptured MAY get over Ingrave summit and allow the loco to be changed at Shenfield

 

Swindon actually used two valves. I was a bit surprised by the comment (amongst others...) about Barclays only having one, but I guess as there's just a single spring it can be interpreted that way.

 

Forgive my ignorance of anything that’s copper capped! I didn’t know that

 

Yes ,I worked with four Barclays ,all had two, they were 14 and 16 inc cylinder loco's.

 

I was careful to state "reduces the temperature", it certainly would not put out a deep hot fire. The reaction of steam on hot coal or coke is endothermic, absorbing heat, cooling as in the water gas cycle which used coke to get producer gas - principally carbon monoxide - by passing steam through coke. This was intermittent: first blowing air through the fire to get the coke up to temperature and then steam to get what you wanted until everything had cooled down and the reaction tailed off. In a gas producer fire box one of the effects is that by introducing steam under the grate you lower lower the firebed temperature which gives a considerable effect in mitigating clinkering.

(Weeping tube ends in the firebox tube plate affect the performance of the boiler surprisingly little - I have known a locomotive give a remarkable performance with something approaching a sheet of water running down under the tubes.)

 

Back in the day, safety valves were set to the required pressure in the works using the steam from the works boiler and MPD's were not allowed to touch them, only change them. Thus, with individual pop valves, it would be pot luck which valve blew first. Nowadays the heritage movement doesn't have that luxury and valves are nearly always set on the loco, in which case you can choose which valve blows first, although, as the second/third valve should blow at the red line, any valve blowing earlier has got to be below that pressure. Inspectors usually accept an accumulation pressure of 5 psi above the red line, especially with spring balance valves.
Two valves has been accepted as requirement on steam boilers since the 1850's and was a legal requirement under the Factories Act. The reason for more valves, as found on the larger locomotives, is almost certainly down to standardisation. The railways would have standard valves of a few different sizes and, if you really needed a larger valve, it made sense to fit more of a standard design. Valve height also played a part. The bigger the physical size of the valve, the taller it must be and height becomes critical on the larger locos built to the limits of the loading gauge.

 

The 'Stipulations and Conditions' of the Rainhill Trials, 1829, stated:
"There must be two safety valves, one of which must be completely out of the reach of the Engine man, and neither of which must be fastened down while the Engine is working."

So it goes back even further than that.

 

"Modern H&S gone mad" etc.

RPSI, FfRS, TRPS, RERPS, RHDRA, WLLRPC

 

One oddity I've found is the Wantage tram Shannon. The current boiler, which dates from 1896, only has one valve, and replaced the 1857 original which had two!

Oh and to spice things up a bit more, it only has one injector.