56xx released.

[Kariban]

When there's no steam passing through you get condensation in the cylinders; water isn't very compressible, so when the pistons move if you didn't empty the water you tend to blow the end of the cylinder off :p. When you open the regulator with the cocks open it blows the water out ( with some loss of steam, you can see that pretty well ), and you get a different sound when you're just blowing steam out so you can shut them again.

It is very, very easy to forget! in fact it does make me wonder why no-one ever made them open automatically.

[alexnick]

I'm afraid it does look a bit like the cylinder . function is backwards in the RSC model. The point was that you could damage a cylinder by not draining water from it.

I was impressed with the soundset though.

AN

[Kariban]

The model is fine, it's just the video

[AndyUK]

When there's no steam passing through you get condensation in the cylinders; water isn't very compressible, so when the pistons move if you didn't empty the water you tend to blow the end of the cylinder off :p. When you open the regulator with the cocks open it blows the water out ( with some loss of steam, you can see that pretty well ), and you get a different sound when you're just blowing steam out so you can shut them again.

It is very, very easy to forget! in fact it does make me wonder why no-one ever made them open automatically.

Some protection is offered by the cylinders being fitted with pressure relief valves (http://www.britishrailways.info/LOCOMOT ... 0PARTS.htm), but I've not been able to determine whether all locos were so fitted. It seems like a very sensible precaution to take, not least in the event of priming when I doubt even the most alert of drivers would be able to open the cylinder cocks in time. In the prototype with pressure relief valves fittted I doubt that not opening the cylinders cocks at the right times is guaranteed to blow the end covers off!

Another reason for opening the cylinder cocks is to prevent pressure building up in the cylinders if the regulator is passing steam slightly when closed, thereby eliminating the risk of the loco slowly steaming off into the distance when nobody is looking.

Andy L

[plewsy2105]

most locos were fitted with relief valves but these wont stop a cylinder from going bang.

and i definitely think the Drain cocks (the proper name for cylinder cocks) are wrong, if you leave the drain cocks open when on the run all that will happen is a little spurt off steam will come out with every stroke of the piston.

plewsy2105

[FoggyMorning]

I'd be inclined to think that Simon at RS has misunderstood the purpose of the cylinder cocks slightly rather than that they have been incorrectly implemented, judging from some of Pete's earlier posts on the subject in the WIP thread

[AndyUK]

most locos were fitted with relief valves but these wont stop a cylinder from going bang...

Why not? Please explain their purpose if not to relieve excess pressure in the cylinders and thus help to prevent damage.

Andy L

[Kromaatikse]

AFAIK, the relief valves are normally in the centre of the cylinder end, and therefore they don't drain all the water out even when they do operate. This means that the hydraulic load can be sufficient to blow a cylinder (or bend a rod) if the piston hits the end quickly enough - as it might well do during starting if slipping occurs. (This may be what happened to Blue Peter, combined with extra water coming over through priming off an over-full boiler.)

The clearance at the cylinder end is deliberately very small to maximise the expansion ratio, similar reason to the compression ratio on IC engines. There is *some* space so a small amount of water can be tolerated, but if there's a lot then not enough can be removed by the relief valves.

The drain cocks tend to get much more of the water out under normal circumstances, not least because they have more time to operate since they can work at atmospheric pressure, but also because they are at the bottom of the cylinders. Some steam inevitably condenses when moving off because the cylinder walls are cold(ish), so the cocks are kept open until the cylinders have warmed up - hence the change in sound that the video mentions.

[plewsy2105]

what i am saying is that they do not always work i.e. if a large lump of ice forms in the cylinder causing the piston to be damaged in one way or another.

relief valves in theory are the same as safety valves in fact they work in a very similar way for example if a steam locomotive has a boiler rated for 200 psi the cylinders would be rated for say around 250 psi this means that the boiler's working pressure can not exceed that of the cylinders maximum pressure. so when the engine is working a train and the boiler reaches its working pressure of 200 psi and for some reason the safety valves don't lift, the relief valves should stop the cylinders from exploding....in theory i might add

There is nothing to stop the cylinders exploding when the engine is working and the boiler pressure is below maximum.

Plewsy2105

[AndyUK]

AFAIK, the relief valves are normally in the centre of the cylinder end, and therefore they don't drain all the water out even when they do operate.....

Photographs I've seen have them well below the centres of the cylinders so that they would drain more of the water, they couldn't be in the middle of the 'rear' cylinders as the piston rod would be in the way! Agreed that they can't be relied upon to drain all water and thus guarantee no damage but I was challenging plewsy2105's assertion, which he's now corrected, that the relief valves "wont stop a cylinder from going bang". To me they appear to be a secondary line of defence against cylinder damage in the event of the cylinder cocks not being open when required to drain water, whether from condensation or priming, rather than the first line of defence which is what the cylinder cocks are.

Andy L

[Kromaatikse]

Well, that seems accurate enough. The relief valves probably are adequate in most normal situations, but there are many exceptional things that a steam loco can do.

[SSimon]

I'd be inclined to think that Simon at RS has misunderstood the purpose of the cylinder cocks slightly

Nail ----------> direct hit!

Peter Gillam has kindly pointed out my misleading captions. I've now edited the vid captions and re-posted this on Youtube (sadly there is no way to swap in a new video while retaining the previous url and comments).

http://www.youtube.com/watch?v=dcet-ry_iaQ

Thanks for all your posts on this. It is a great loco, much more involving than driving something like the Black 5 with the Cab Control interface, which allows you to be a bit lazy and look around at the scenery. Having made half a dozen short journeys in it, it is starting to feel more familiar and very enjoyable.

Simon

[Rfairlie]

It is very, very easy to forget! in fact it does make me wonder why no-one ever made them open automatically.

Some protection is offered by the cylinders being fitted with pressure relief valves (http://www.britishrailways.info/LOCOMOT ... 0PARTS.htm), but I've not been able to determine whether all locos were so fitted.

Andy L

Locos fitted with piston or balanced slide valves are fitted with relief valves. In a slide valve loco the valve is held on the face by the steam pressure from the boiler. If water is carried over the pressure in the cylinder will exceed that of the steam chest and the valve will lift off it's face helping to prevent any damage. With piston valves and balanced slide valves the a permanent seal is formed so relief valves are fitted to the cylinder to relive any excess pressure.

Usually the first indicator of a loco priming is a change in exhaust note which gives the driver a chance to open the drains and ease the regulator down before any damage is done. Exhibit A http://www.youtube.com/watch?v=Snyzp3PZ ... ideo_title listen to how the sound changes around 32 seconds in.

Of course the best way to avoid priming is to run with the correct water level.

Running with the drains open will not cause any damage but you are wasting steam and therefore fuel and water.

Some locos such as the Festiniog England locos don't even have cylinder drains, they just a drain on the steam chest.

Tim

[Kromaatikse]

FWIW, the "England" locos referred to above are Prince and Palmerston, with the distinctive all-over saddle tank design. They are very very old locos.

The Hunslets and Fairlies, more often seen on the main line, do have cylinder drains.

[dinmore]

Running with the drains open will not cause any damage but you are wasting steam and therefore fuel and water.

I would disagree with that a little, though I understand where you are coming from. All too common there is a habit of running with taps open for far longer than necessary or opening them even when pausing for short periods. Unfortunately as the cylinders are hot when a loco comes to a rest the oil within the cylinders is thin and soon runs to the bottom of the bores, as soon as the regulator is opened the majority of the oil that should be protecting the cylinders gets blown straight out of the taps. It's something I witness often, a loco has just run round its train and coupled up, cylinders will stay plenty hot enough for condensation not to form in the 10-15 minutes before departure yet many open the taps and pull away for the first few revolutions of the wheels with them open thus losing that precious oil you are depending on to give long piston, ring and bore life.

Mike