Nostalgia & History > Where is the water coming from?

Where is the water coming from?

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I would guess overflow from the injector.....

I thought that only passenger cars and cabooses had poop shoots.

-E.O.

The injector.

http://en.wikipedia.org/wiki/Injector#Exhaust_steam_injector
Still don't understand it.

flynn Wrote:
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> Still don't understand it.

Yeah. They're sort of a miracle - they shouldn't work! You take steam from the top of the boiler, and form it into a jet which combines with water which it sucks out of the tender to be forced back into the boiler against the very pressure that formed the steam jet in the first place.

I repeat, they shouldn't work. Every time I use one I'm overwhelmed with their simplicity - and the reality that they actually do work.

Here's a schematic of a lifting injector.

B is the boiler, C represents the water tank of the tender. G is the check valve which prevents boiler water from flowing back out of the boiler. O is another check valve, called the overflow valve.

The difference between a lifting injector and a nonlifting injector is simple. A lifting injector is physically located on the side of the boiler at a level above the highest possible level of water in the tender, while a non-lifting injector is located below the cab at a level below the lowest possible level of water in the tender. Otherwise, they're functionally the same.

The control valve S is shown as a screw type globe valve, but in actual practice is usually a lever operated valve which can be opened slowly, or quickly thrown full open, as needed.

When the fireman or engineer decides its time to add some water, he slowly opens the control valve S. A jet of steam forms in the conical shaped (Venturi) tube, "a" in the drawing. It then flows through a second Venturi tube ("b") and fills pipe F. Since it's the same pressure as the water in the boiler on the other side of check valve G, it cannot enter the boiler, but is diverted and lifts the overflow check valve G, which drains to the ground below the cab.

Passing out of jet "a" into the combination tube "b", the velocity of the steam entraps air from pipe E which reduces the pressure in pipe E and causes water from the tender to be forced by atmospheric pressure upwards into the injector where the water itself becomes entrapped with the steam to be dumped to the ground through the overflow pipe. This is the stream of water which your photograph shows dumping below the cab.

The temperature of the cold water from the tender condenses the steam entering the injector, about 380 degrees, and the combined temperature of the overflow is about 180 degrees.

When water appears at the overflow, the operator suddenly throws the control valve full open. This imparts a high velocity to the water which hits the check valve with enough momentum to overcome the boiler pressure! The flow of water through the combination tube "b" creates a reduction in pressure in the overflow chamber and the overflow valve closes. Water ceases to dump to the ground, and the system becomes self sustaining, forcing water into the boiler through the velocity and mass of the water stream

It's a miracle!

-John

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Great explanation! Did you write technical manuals?

Thanks LarryDoyle.

flynn Wrote:
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> Thanks LarryDoyle.


You're very welcome, Flynn.

I should point out that the website you referenced in your search for an explanation seems to overly complicate, and references exhaust steam injectors.

An exhaust steam injector is a more complicated device, but essentially is two injectors combined into a single device. When sitting still, or drifting downgrade, an exhaust steam injector behaves exactly as a non-lifting injector, taking live steam from the boiler to do its work.

When the locomotive is working, however, this clever device automatically switches from use of live steam from the boiler to use of a portion of the exhaust steam from the cylinders - just as a feedwater heater would do, but without feedwater pumps. I've used one and it's really a slick device. Very user friendly.

-John

This time of year, you might find yourself asking how did railroads prevent water in tenders from freezing.

Well, if you haven't wondered you can quit reading here.

But, if you have wondered, or haven't wondered but would like to know anyway, refer back to the drawing above of an injector. Not shown in the drawing is a separate valve handle on the overflow check valve (or a separate valve in the overflow drain pipe) which prevents overflow. If overflow is thus prevented, when the steam valve is opened the steam cannot prime the injector, but will instead pass down through pipe E, and burble back into the tender water, thus warming it. Clever, huh?

A frustrating issue with lifting injectors is that if there is a small leak in the steam valve when it is supposed to be turned off, that steam will condense into hot water which trickles down into pipe E. Then, when trying to start the injector, when pressure in pipe E is reduced by the steam jet the hot water in E will boil rather than being forced by atmospheric pressure up into the injector, and it won't prime. The solution? Simply close the overflow control and blow that hot water back into the tender and allow the supply pipe E to refill with cold water.

-John

-John



Edited 1 time(s). Last edit at 11/25/14 11:40 by LarryDoyle.

Injectors can be tempermental beasts. No two ever seem to work
the same. You need to almost "feel" just when (and how quickly) to
open the valve to full!