As I was cleaning my porch of all of the winter dust, dirt, bugs, and such with a garden hose, I began wondering how steam is fed into steam boilers. If I don't mind bruising my thumb, I can completely stop the water from flowing out of my garden hose by pushing my thumb against the opening.
A steam locomotive boiler can put one heck of a lot more pressure on something than my thumb. Accordingly, I assume water can't simply "trickle" in or use gravity to go from the tender to the boiler, as the pressure from the boiler would keep it from entering.
How does this process work?Gabe
A remarkable device known as an injector is capable on using steam from the boiler to inject water into the boiler against the pressure in the boiler. Others may be able to offer an exact technical explanation for the leverage mystery of how steam at say 200 psi can force water into a boiler that is holding 200 psi.
There are also other devices that involve mechanical pumps to force the water in.
....Go to Post dated 10-11-03.....How is water injected into working steam engine. {Search}.
Quentin
Injectors are the most common method but the locomotives at Golden Spike NHS also are equipped with cross-head pumps. As the name implies, these pumps are directly connected to the cylinder rod block. When the locomotive is moving, these can pump water with sufficient pressure to add water to the boiler. When the locomotives were first built, there was no pressure relief valve on the high pressure side of the pump. When the boiler check valve failed in closed position, the water pressure in the pump blew out the side of the brass pump casting. For comparison, the boiler safety valve is set for 155 psi and we typically operate at 150 psi. The cross-head pump relief valve is set for about 180 psi.
One problem with cross-head pumps is that they are pumping cold water into the boiler - lowering boiler pressure. Thus, the supply line to the pumps also has steam preheat. The other problem is they only work when the engine is moving. So if you need to add boiler water while stationary - the injector is the only way.
dd
My limited understanding is that a venturi effect is used initially to lift the fresh water column in the cold water feed pipe that gets water from the tender. This is the lifting type of injector. The other, the name of which I forget, gets water from a higher pipe that drains water...I guess.
Once the water is jetting past the steam jet, which is all that the control lever on the injector controls, the steam jet forces water into a chamber where the water cools the steam, causing a severe pressure imbalance between the high pressure injecting steam and the boiler steam pressure against a back-flow valve. This differential forces the water past the boiler check-valve and into the boiler through ports just behind the smoke box bulkhead.
If my rude version is found wanting, please see a much better description below.
http://www.sdrm.org/faqs/boilers/page140.html
Crosshead injectors were a simple mechanical way to inject water into the boiler, the back and forth motion of the piston rod powered a small onw way pump that pushed water into the boiler, later steam powered injectors were introduced and were better able to control the amount of water used. As mentioned the thermal effects of cold water being injected into a boiler led to the invention of the preheater where the water was routed in a way, either thru the smokebox or thru the boiler, to bring the water up to almost boiling where it was then injected into the boiler with no thermal effects on the boiler water, which was far more efficient.
Have fun with your trains
There were also a variety of feedwater heating systems, which included heavy duty steam-powered pumps, either reciprocating or centrifugal.
All modern Japanese locomotives carried (and still carry, those still operating) a rather large reciprocating pump on the fireman's side. I never did a pipe chase to find out whether it pumped cold or preheated water.
Chuck (modeling Central Japan in September, 1964)
Jock Ellis Cumming, GA US of A Georgia Association of Railroad Passengers
jockellis wrote:G'day, Y'all,Didn't the federal government require two crosshead pumps and two injectors as a failsafe to prevent BE, boiler explosion?
IIRC the requirement is for two independent methods of supplying water to the boiler. The engines at Promontory each have two cross-head pumps and one injector for a total of three independent methods. Most water is added via the injector - but each cross=head is operated every day or two to exercise the boiler check valves. Cold water and a cross-head pump can kill 5 lbs of steam pressure in about 1/2 mile of operation. Makes it rough on the fireman.
....The question of why only cold water.....Most tenders had only cold water to supply to the engine.
I have no idea how water was heated in a tender unless there were steam pipes in the tender and steam fed to them from the engine to pre heat the tender water....That would require something flexable in a line from the engine to tender pipes such as high pressure hose or flex metal joints on pipe of some sort.
Some tenders did have steam heat to keep the water from freezing in the colder climates in the winter. Also, steam from the engine was fed to passenger cars for human comfort. The pressure was reduced because of the valve allowing less through to the pipe than was being vented at the other end.
Also, big black tenders can absorb lots of solar energy and make the water quite warm.
For the injector to work the water needs to not be warm... something about a large temperature differential between the water and the steam being necessary, but I don't remember all the physics about it. I do know that sometimes pouring a bucket of water over the injector could cool it off enough to allow the thing to start to work.
The injector is an extremely effecient method of putting water into a boiler and its operation is so counter intuitive to most of us mere mortals as to seem to be magic. The steam that is in the injector comes from the boiler and is actually at a lower pressure than the boiler due to the lengths of pipe to the injector and the valving involved. But that steam being exhausted through a jet and venturi in the injector and hitting the cold water, imparts enough velocity to the water to force the clack valve open and enter the boiler. Even the heat of the steam is returned to the boiler. There is always some loss of water from the tender and steam from the boiler getting it started, but, once the injector starts to work, there is no overflow or loss of steam. They are sometimes refered to as the poor man's feedwaterheater. Very effecient, once running.
It is so effecient that some people have advocated that only an injector is needed to maintain the boiler's water level, but then they find out about the persnicketyness of an injector and realize that some other method is necessary, too. If all methods fail, dump the fire, stop the train, and evacuate the cab!
Semper Vaporo
Pkgs.
....Absolutely, evactuate the cab....!! I saw a sizable {B&O} steam engine first hand that blew up back about 1943 and there was nothing remaining but the cast frame, and cylinders and rods and wheels & axles, etc...All above that was gone....!
We see a noticable difference in injector performance between now (average ambient 55 degrees) and August (average ambient 85 degrees). The biggest difference will be the minimum boiler pressure with which the injector will prime and operate. When we start the injector - the first thing we do is to prime it. This gets the air out of the lines and cools down the injector with a fresh flow of water from the tender.
Modelcar: I have a book that documents a boiler explosion similar to what you describe. Impact evidence on the ground indicated that the boiler left the frame, traveled something like 270-ft forward, BOUNCED once and went OVER some trees and a set of utility wires, and came to rest about 350-ft ahead of the point of the explosion. The brakes on the train were applied as soon as the air pipe was severed as the boiler left the area, but the train continued down the track and came to rest against the boiler laying across the tracks. No passengers were injured, but three in the cab were killed.
DD: is your injector classed as Lifting or Non-Lifting?
CSSHEGEWISCH wrote:A question about injectors. In Dan Ranger's article in TRAINS about cab-forwards, he mentions a situation where the water in the tender tank was hot and the injectors were unable to pick up the hot water to feed the boiler. Why do injectors only pick up cold water?
This could be two questions rolled into one.
In one version I interpret the words "pick up" to mean pulling water from the tender to the injector. I believe that, if the water is too hot and any kind of a pump, injector or mechanical, tries to draw it (pull on it), then the water will simply boil and the pump will suck steam instead of water. Worse yet, I think the mechanical pump will permit "water hammer" to occur when the vapor rapidly condenses between strokes of the pump. The shock and vibration of water hammer can overstress all the equipment.
In the other version I interpret the words "pick up" to mean the internal operation of the injector. As previous posts and several Internet reference pages have pointed out, operation of the injector depends on the steam condensing when it comes into contact with the water. So, I think that the water boils instead of the steam condensing, if the water coming in is too hot.
Either way, the injector won't work because the water is turning into steam instead of the steam turning into water.
I looked at a table of water vapor pressure vs. temperature. Between 130 deg F and 180 deg F the vapor pressure goes from low to about half what it is at the boiling temperature. This means that you can only pull about half as hard on the water in a pipe at 180 deg F as you can pull at 120 deg F without getting evaporation.
The extremely loud roar the injector makes comes from thousands of miniature water hammers occurring in the condensing process inside. This happens whenever you inject steam into water.
Nice explanation, thanks!
I think I now understand why sometimes pouring water on the injector fails to cure a problem. I have read several accounts of it working and/or not working and this misunderstanding is probably the cause. Pouring water on the injector could cool it enough to cool the incoming water such that it would start working. If the incoming water is warm enough then it might not help. If the water poured on the injector happens to run down the outside of the feed pipes then maybe that would cool the incoming water enough. Someone not fulling understanding it all may have only heard to pour water on the injector and repeated applications is all they ever figured out to do. Maybe, eventually, enough water is poured on it and it starts working and the injector is just labeled as persnickity. It the water they are using is warm water from the tender then it may not help at all or could make it worse. Again, blame is laid on the injector, not the lack of knowledge.
Semper Vaporo wrote: Modelcar: I have a book that documents a boiler explosion similar to what you describe. Impact evidence on the ground indicated that the boiler left the frame, traveled something like 270-ft forward, BOUNCED once and went OVER some trees and a set of utility wires, and came to rest about 350-ft ahead of the point of the explosion. The brakes on the train were applied as soon as the air pipe was severed as the boiler left the area, but the train continued down the track and came to rest against the boiler laying across the tracks. No passengers were injured, but three in the cab were killed. DD: is your injector classed as Lifting or Non-Lifting?
Both engines have lifting injectors - even though the position of one of the injectors is low enough that water will siphon through it if the celler valves in the tender tank are not closed when not injecting. You can put a lot of water on the ground that way.
Great information so far. What is the difference between an injector and a siphon? I seem to recall a discussion about siphons being used in later model steam locomotives...
Erik
An injector puts water into the boiler.
A siphon is used to help the water circulate in the boiler. A siphon, or "Thermic Siphon", is a pipe that runs from near the bottom of the boiler, "through" the firebox, to the crownsheet. This helps get "cool" (relatively) water from the bottom of the boiler into the area of the fire, up to the top of the boiler atop the crownsheet. If you could see inside a boiler in operation with siphons you would see the water actually mounding up at the top opening. This action was thought to actually help keep the crown sheet covered in low water situations.
Designers had to be careful that the connections for the water gauge did not get into this flow as it could severely corrupt the reading; either making it appear too high due to flow being directed toward the lower fitting, or too low because the flow might be across the end of the lower fitting causing a suction effect.
Often the siphon was used to support the firebrick of what is called the "arch"... a device used to force the fire to take a longer route from the bottom of the firebox to the flues, which helped with complete combustion of the fuel and maximized the heat transfer to the water.
There are a whole bunch of truely "High Tech" inventions in a steam locomotive that are hidden from view and generally unknown by the average citizen.
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