[steamer_ctn]

QJ-6811, on 24 April 2020 - 02:31 AM, said:

Many locomotives have 1 lever operable in the cabin, a second one (if present) can often be manually operated outside.

So are we talking a single blowdown valve with multiple control positions or multiple blowdown valves?

QJ-6811, on 24 April 2020 - 02:31 AM, said:

Subject "automatic blowdown" never heard of? Go and find out how this works, I'm curious.

Have a look at this, and also some googling will shed some light on it.

[QJ-6811]

We are talking about multiple blowdown valves, each with its own operating position

Example (such as China and US), two levers in cabin for blowdown valves left and right separately, steam then blows directly (left and / or right) sideways.
Example Europe, one lever in cabin, steam then blows away between / under the frame in the direction of travel (via damper).
Larger boilers often have a second resp. third blowdown valve, which is occasionally manually operated outside. (really only for blowing "mess out of the front part of the boiler").
Of course there are more variants, depending on the type of locomotive.
( And yes, like the air-operated blowdown valves of German locomotives, there is a second (emergency) lever for manual operation outside. But this is not so interesting for the simulator ... )

[steamer_ctn]

QJ-6811, on 25 April 2020 - 12:05 AM, said:

We are talking about multiple blowdown valves, each with its own operating position

Ok thanks for that.

Why have multiple valves, is it just to give some variation in terms of the steam blast?

In the SIM, I can't see the value in having multiple valves, as most will probably not use the main one anyway.

[QJ-6811]

steamer_ctn, on 25 April 2020 - 12:30 AM, said:

Why have multiple valves, is it just to give some variation in terms of the steam blast?

No, both have the same function. This has to do with the construction of the boiler. A blowdown valve is constructed on the lowest part of the boiler or water level. This is 99.9% of the cases at the bottom of a firebox. (as is known, water is also present around the firebox). Many locomotives (such as US, China, Russian, etc.) have the blowdown valves on the side (bottom point at the bottom ring), both one left and one right. Especially "dirtiness" drops to the bottom, and therefore the lowest point. However, with the firebox you naturally have a left and a right side (after all, inside is the firebox, coal fire) and therefore two blowdown valves are efficient for cleaning.
The "disadvantage" is that the steam (actually the water, but due to the temperature-pressure difference, it immediately becomes steam in the outside air, since the water can be 200 ° C ...) blown sideways with a large jet.
On many European locomotives, they have constructed blowdown valves on the front of the firebox side. (There is often less "free space" here and so as not to blow people off the platforms, clean houses along the track ... etc. :D ) IOW, instead of both sides the water and dirt on the front are drained . These blowdown valves are almost always operable from the cabin.

With longer boilers, the front is only occasionally needed to clean the lowest point / front part of the boiler (debris that does not sink to the back / firebox side)

(For the actual cleaning of the boilers, steam locomotives are brought into the workshop at certain times, to be flushed through "wash hatches" (openings in the boiler))

So in summary, you often have one or two blowdown valves, with the same function, which can be controlled from the cabin.
(similar to the water injectors, you have one or two, but separately they have the same function)