Cylinder Drain Cocks

May someone with greater knowledge than myslef please explain the correct procedure for using drain cocks?

From my own education from a former LNER/BR fireman they are to be opened at start after significant periods of rest, 20 mins or more and left open for 1-2 cycles of the piston. Leaving them open for longer is wasteful and unnecessary as any condensate is cleared quickly once steam is being admitted. Often the water is cleared sitting stationary.

I see videos online of them being left open for a lot longer, like 10+ cycles which I suspect is for "dramatic effect" and to be honest, it really gets my goat...

What are your thoughts here? Is the correct procedure written down somewhere?

 

I imagine the potential consequence of not using the drain cocks enough could be expensive. Much more than several goats.

 

The official BR "Handbook for Railway Steam Locomotive Enginemen", published by BR/BTC in 1957, reprinted by Ian Allan in 1977 and on other later dates, says that steam cocks should be left open when the engine is standing or "at any time there is an indication of water in the cylinders." But it gives no indication of how long to keep the cocks open when moving off. There is reference to a BR Permanent Notice 32709/1 which apparently gave further information about the cylinder cocks, although this may relate to safety precautions when preparing a locomotive from the context in which it is mentioned.

 

well, what are the consequences of leaving them open too long, and what are the consquences of not leaving them open long enough? In which direction should one err?

 

Indeed, a bit of wasted steam versus the chance of blowing the end off a cylinder!

 

The purpose of the taps was to clear condensed water from the cylinders. This occurs if the engine has been standing for some time and a certain amount of steam has leaked past the regulator valve into the cylinder. But it also occurs when steam enters the main steam pipes, valve chests and cylinders before they have reached a sufficient temperature by which this will not occur. It takes time for the mass of the cylinder block in particular to warm to this extent, and until it does - certainly much longer than '1 - 2 cycles of the piston' - then condensation back to liquid water will occur. As a liquid, water is not compressible and any trapped between the piston and cylinder cover is likely to cause damage, sometimes very expensive damage.

An experienced driver will know when condensation is no longer happening and will close the taps then. Premature closing of them can be very expensive indeed.

 

Peter Townend wrote that one Scottish ex-LNER shedmaster referred to the drivers of a neighbouring ex-LMS depot as 'the hydraulic gang' due to their disdain for using the drain cocks. Dealing with over-strained cylinder cover studs was apparently not his favourite recreation.

The drain cocks can also give a bit more control on starting, because pressure clears from the cylinder that bit quicker when the regulator is closed.

 

Running with the drain cocks open is noisy, uses steam and restricts forward visibility, so I doubt most drivers would wilfully choose to have them open for longer than they consider prudent.

Bear in mind though that immediately on starting is a period of high workload for a driver (checking behind the train; ensuring the loco doesn't slip and being ready to deal with a slip if it occurs, maybe starting to notch up) so closing the cocks may not be the immediate highest priority task. It is also possible that, if the loco has been standing for a while and the fireman has slightly misjudged their build up, the water may be a bit on the high side and more liable to be picked up, so keeping the cocks open a bit longer would be prudent until you can see that the exhaust is nicely clear above the chimney. Then there is the issue of cab ergonomics - how many controls can you simultaneously operate, or at least be responsive to, on starting? If you've got one hand on the regulator and are leaning out, the drain cocks may be hard to reach.

As others have said, prudence with shutting the cocks tends to be primarily in one direction.

Tom

 

Yes my goat too to ,I've seen this happen numerous times ,it seems to have started excessively some fifteen /twenty years ago .The temperature in the cylinders of loco's running say ,London to Peterborough, which stopped for a few minutes in the station must be well above what would evaporate any water immediately. There were thousands of excellent photo's taken in steam days of trains leaving stations ,including terminal ,where a train engine would be standing for some time ,that never would have been taken if the train had left in a cloud of steam.

 

I have the impression, from videos posted here in the last few years, that the drain cocks tend to be left open considerably longer on some locos, particularly Bulleid pacifics. Might that be due to the cab ergonomics?

 

Mainly down to having a large steam circuit. Takes a long time to warm the system through and expel any condensed steam.

 

Interesting to see people suggesting that they are being left open for longer. My impression is that they seem to be used considerably less than they were on rail tours (and at Didcot where we visited a lot) in the 80's when they seemed to be opened every time a new movement started, irrelevant of how long the locomotive had been standing?

 

I doubt that he's saying that but is saying that people often leave them open far longer than necessary. Personally I shut them as soon as I think it is OK. When that is is going to be very dependent on the loco but it is unlikely to be more than a few revolutions when it is on a train because the loco will have run light from the shed and that will have started to warm the cylinders. Drain cocks open whilst the loco is stood, yes but if it has only been stood a few minutes and is 'hot' then I shut them before setting off.
A couple of other points about drain cocks not appreciated by many.

• Slide valve locos don't need drain cocks because any water trapped in the cylinders will force the slide valve off its seat. I know of quite a few industrial locos that don't have them fitted, simply a single steam chest cock. The downside of this is usually dirty water being blown out of the chimney when starting off so, if they are fitted, it is better to use them. With a slide valve loco once warmed up I rarely open the cocks during the day unless I'm getting off the loco.
• Some locos tend to accumulate water in their exhaust passages which, again is ejected up the chimney. This is especially true of BR standards and no amount of drain cock use will prevent this because the water is on the down side of the steam circuit. People often point to this happening and say the driver has shut the cocks too soon.
• A prime reason for opening the drain cocks when stationary is to safeguard against inadvertent movement due to pressure build up. However, a leaking reg has the advantage of warming the cylinders meaning that there is less need to open them when starting.
• If a piston valve loco is priming then it is very necessary to open the cocks to prevent damage and also take steps to stop the priming.
• Using the cocks does tend to put oily water onto the railhead which is not the best thing for adhesion. Not to bad when running in reverse but a nuisance when running forwards.

On the NYMR we have the problem when leaving Grosmont that people are stood by the crossing and the steam emitted from cocks can and does lift stone ballast and this can hit people so we are not encouraged to leave with the cocks open but to warm the cylinders first by whatever means you can. This could mean running up and down the shed headshunt.
At the end of the day, it is down to the drivers discretion. And experience.

 

No,I,m saying they should only be used if necessary , eg not after a longish run. I don't think drivers in the 50s/60s were much bothered whether there was anybody photo'ing or not.

 

An attempt to reduce the chance of slipping

 

Or just hide the slip altogether...

Sent from my Moto G (4) using Tapatalk

 

See my previous comments re leaving them open. They tend to put oily water on the rails, especially on cooler days of spring, autumn & winter.

 

Porta referred to adhesion as 'The Kingdom of Railway Stupidity'