Question ? … what are blowdown drains ? … eg. The MR’s guide to Locomotive servicing terminals … page 61 …
All help will be greatly appreciated … thanks
There are a couple of drains on steam engines for blowing down an engine. One is to remove sediment, scaling and rust from the boiler. The fireman opens a hand valve in the cab that allows the steam pressure to clear gunk from the bottom of the boiler. This is discharged through a pipe that is aimed at the ground generally under the cab alongside the firebox. There is another valve on each steam chest to remove condensate when starting. Water in cylinders can be very dangerous since 1 volume of water generally make about 968 times that volume of steam. Excess water in a cylinder can expand blowing the head off the cylinder. By opening a valve a portion of the steam is discharged directly to atmosphere under the cylinders clearing any water accumulation. The more general definition of a blow down drain is the first one.
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The blow down drains or mufflers are used to relieve the steam pressure in the boiler. If the hogger is lucky or very skilled, blowing down a boiler will loosen the scale that had crusted for better heat transfer. I believe it was an FRA rule for boiler washing. Most boilers were washed down at least once a month then again at every scheduled service and in for class repairs. Some rail roads had real bad water and locomotives would require more frequent blow downs and washes. Another time a boiler is blown down is when the water would foam up. If the water glass shows foam then the engineer or the fire man would blow down the boiler to try to rid the foam.
Pete
There were two types of blowdowns.
The first was more commonly called blowing the mud ring. Sediments from the water settled to the bottom of the boiler and were blown out by opening a valve that allowed steam to blow out the side of the boiler. Most videos I have show the steam blowing straight out the side, not down, when they blow the mud ring. Needless to say, this was always done out in the open countryside where no one was in harm’s way.
The second type was e blowdown that could be used in confined areas such as engine terminals that did not blow steam with as much force as blowing the mud ring. These drains blew the steam straight down through pipes and could be connected to hoses to blow the steam up into the air to relieve boiler pressure is preparation for engine servicing.
1 volume of water generally make about 968 times that volume of steam.
actually; depending on the disolved mineral content, altitude and a number of other factors; water converting to steam will seek to occupy a volume 1620 times the water volume at 0 psi.
blow down valves are usually located in the boiler’s water leg, next to the firebox. Often they are located in the side or front of the water leg, you would never blow straight down. the resulting hail of rocks stones and dirt would be most unpleasant. the crew must also be careful (when blowing down) that nobody is in a position to be hit by the stream of steam, it can be fatal.
One would not use the blow down to relieve pressure in the boiler. that is the job of the safety valve. if it is necessary to lower the pressure (such as to keep from lifting the safety valve in the station) the crew would use the injector.
The blow down valve on our (1910 davenport) locomotive is in the front of the water leg. the fireman uses a long handle to engage the valve and the steam is directed forward underneath the boiler where it can’t burn or scald anyone. we blow down an inch of water as measured in the water glass and then the fireman closes the valve. we blow down twice a day. in the morning, as soon as full operating pressure has been reached, and at night last thing before putting her away for the night. the purpose, as stated above, is to remove impurities, scale and disolved gunk from the boiler.
some engine terminals had small structures resembling dog houses into which the stream was directed when blowing and engine down. they had open grates in the floor for the water to escape and drain away. this kept it from flying everywhere and these were adjacent to the track usually near the ash pit.
grizlump
My understanding was that the problem was the water was not compressable, not that the water would flash to steam. Steam on the power/ intake side would push the piston, and try to compress the condensate on the exhaust side. Either the piston would not travel the full stroke, or blow the head off.
Phil
when a steam locomotive stops the large cylinder casting cools rapidly. when restarting or when running with steam shut off (such as down hill, or coasting into a station) there are valves called cylinder cocks one on each end of the cylinder which are opened from the cab (some locomotives have spring loaded cylinder cocks which open on their own) this allows the non compressable condensate to be ejected from the cylinder.
the problem in blowing a cylinder head off is not the presence of water in the cylinder per se, it is that before the end of piston travel is reached the distribution valve (in the steam chest) starts to move from the exhaust postion to the admission position- trapping the condensate in the cylinder. (if the exhaust valve were still open the water would be sprayed “harmlessly” out through the exhaust passage and up the stack [{it can be done both accidentally and intentionally} a situation called puking the engine -a most unpleasant experience for nearby spectators since the