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)