What is a snifter valve????

I recently installed a sound decoder in my HO scale light mike. In the users manual for the decoder it lists the sound of the "snifter valve" as one of the automatically triggered sounds as the loco starts to move. I have never heard of a snifter valve. What is it and what does it do???

Thanks,
Jon

Thank you for the link!

Jon

Guess I can add some additional informations, because coasting of steamers and the methods used, can be very interesting.

First one must understand, why coasting is so problematic in steam locomotives, or in any other steam engine case.
If the driver runs the engine with the throttle open, steam enters the cylinder, controlled by the valve gear, through the steam chest and the cylinder slits or cylinder ports the cylinder space. Here if pushes the piston to the opposite wall. Now the gear switches the ports from inlet to outlet, and the steam can leave the cylinder room to the exhaust. This is supported by steam, which now enters on the opposite side of the piston an pushes it back to the point before, so also pushes the expanded steam through the ports connected to the outlet into the exhaust.
And now the driver shuts the throttle, and the train behind the loco starts pushing the loco further forward. This acts like a giant flywheel, making the pistons still move, but now being moved by the wheels, rods and bars, and not by steam power.
This will result in having a gas tight piston in motion, so a engine will get a pump. So each time, when under steam the steam would push the piston, now as pump the piston would try to draw something in, but there is nothing to aspirate, so the piston starts to generate a more or less high vacuum or negative pressure in the steam chest, the super heater tubes and the main steam pipes up to the throttle valve. So this can lead to serious damage, like dented super heater tubes or a dented main steam pipe inside the boiler. More serious is, the vacuum effects will often relieve the throttle valve, so this may open a little, and this could damage the throttle valve main seal seat, so a general leaking of this adjustable valve would have serious effects in driving the locomotive.
On stationary engines those effects are medium serious, because the engine generated a vacuum, but this will slow down the flywheel, which is usually itself slowed down by the connected power line transmissions, so the slow down effects are rather welcome, than problematic.
In locomotives those vacuum problems with the resulting brake effects become serious, because on downhill ride the braking effect may also harm the engine, as well as disturbing the free coasting of the engine.
So in the beginning of the age of steam on railroads, the engines opened the throttle downhill a little bit. This so called "grease steam" cooler the cylinder bore and piston, as it helped to bring oil to the cylinder liners, preventing the liner becoming deoiled and getting problematic because of increasing friction.
So engineers mounted sniffer valves to the main steam tube or at the steam chest, mainly to locomotives with piston valves. In locomotives with allan-trick-valves the valve body simply lifted from it's lining surface and a pressure balance was given, by quickly drawn in air through the open chimney.
But this resulted in often ash particles and dust particles being drawn into the valve box and thus increasing friction and maybe damaging the liners and lining surface by rubbing on it.
So even here, sniffer valves were mounted, to prevent such problems. First those valves were manually operated. Shutting the throttle and then opening the sniffing valve, to open a bore to the free air, connecting steam chest and open air together. Surely, this lead to further problems, because if the manual open shut mechanism was damaged, the throttle open much steam left through the sniffer valve bores into free air, often the engine wasn't able to go on power.
So self closing valves were the next step of development. the valve was a two part seal: the top part was a valve with a ring seal for the fresh air, the lower valve was a small round lid. If the engine was running under pressure, the throttle open, the lid was hovering on the steam, and was pressed by the steam pressure in the body of the valve to a ring shaped seal seat. Throttle shut, the pressure in the valve decreased and the lid dropped by gravitation to a small seat below, open the channels to the air valves. Small bores helped to overcoming a vacuum effect, but coasting was only able, if the air valve was manual opened.
Later the lid becomes spring loaded and the manual operation now had to open the air channels to the sniffer valve, as to overcome the spring load and pushing the lid to the seat below, opening the sniffer valve for anti-vacuum effects and a free coasting of the engine.
From that point, those sniffer (now called snifter of sniffing valves, because being able so self seal under pressure, making a distinct sound if being shut by streaming steam into the valve body) valves were also opened or closed with pneumatic pressure. Some still mounted on the steam chest, other on the outlet of the superheater throttle valve, or onto the cylinder itself.



The latest development is the anti-vacuum piston valve.
The piston valve is a rod with two pistons mounted in a fixed distance on the rod. The outer edges open or seal the steam ports to the cylinder.



So the first experiment come from the prussian railways, which build a anti-vacuum piston valve to a prussian tank engine, which was developed by the Vulcan Engine Works in Stettin.
Unfortunately war and the upset of the Deutsche Reichsbahn Gesellschaft during the pre and past WW2 times made this project nearly forgotten.
Also other engineers developed anti-vacuum piston valves, like Mueller and Nicolai. Nicolai was a jew, so his name was erased from the technical drawings and developers list and Karl Schulz was instead named as founder of this anti-vacuum piston valve.
This was a spring loaded anti vacuum piston valve, the later Mueller was without springs, and the last was developed in the former Soviet Republic by the engineer Trofimov.

Let's have a look at the Nicolai and Mueller valve.
As visible in the drawing the piston valve has to bodies, one front and one rear.
With the piston outline the piston valve seal or open the ports to the cylinder.
In the Nicolai valve, the piston valve body was split. So two halves formed the piston body. As steam entered, the two halves were pushed together against the spring load, so act like a common piston valve. Was the throttle shut and the pressure in the steam chest low or absent, the spring pushed the two halves a little bit apart and now both cylinder sides, rear and front were connected together, resulting in a very good idle of the engine, making the loco coast much better.
Broken springs in the Nicolai valve made this Valve often failing, so anti vacuum effect were not good at all, till completely absent, so the Mueller piston valve was the solution. Here the piston body wasn't made of two moveable halves, the two halves were now one body with a ring shaped valve lid on the inner side of each piston body. Under pressure, the lid ring was pressed against the ring seal of the piston body, letting the piston act as a common piston valve. Without pressure in the steam chest, the lid flipped open by the motion of the piston valve itself, and the anti-vacuum effect was given.
Also there are some main backdraws, like difficult anti vacuum lid seal or breaking or bending of the lid, resulting in a complete failure of anti vacuum and improper valve gear function.
This was overcome with the development of the anti vacuum piston valve of Trofimov.



The discussion if his name is spelled Trofimow, Tovimow, or Trofimov is obsolete, because the German Democratic Replublic spelled him Trofimov, and that's how this piston valve is found in the maintenance and construction instructions.
So, as mentioned before, in Stettin the Vulcan company developed a anti vacuum piston valve. This was simple: The bodies of the pistons were no more fixed to the valve rod. Only two carriers were left fixed on the rod.
So under pressure, the bodies of the pistons were pressed to the outside ends of the rod, hit the carriers and acted as a fixed piston valve gear in normal construction design. As pressure in steam chest decreased, the carriers shifted the bodies of the pistons more and more to the inner middle of the valve liner tube, so the ports of the cylinder were finally and complete connected through the exhaust box body and channels.
The valve bodies hat holes, just to prevent the piston bodies to hit the carriers hard by opening the throttle, leading to certain steam leakage problems, but did not really let the valve gear fail. Broken carriers were problematic, but uncritical for the locomotive function and the over all very good coasting made this valve superior.
Trofimov found after WW2 the development and construction drawings, and because knowing of the problems with the Nicolai valve, he used the Vulvan design and improved the construction.
As visible in the picture above, the carrier was removed to a outside, screw locked stopper. The whole valve piston body is loose on the valve rod, with some leading edges.
Under steam, the pressure in the steam chest pushes the piston valves bodies outwards against the stopper. So the piston valves act like a normal fixed piston valve. If steam was shut of, the stoppers pushed the bodies to the middle of the valve liner tube, while the rod was running freely through the piston body central axis. That opened again the full area of the cylinder ports and connected them together, resulting in optimum anti vacuum effect, while also ensuring the possibility to get the gears back to mid gear after anti vacuum.

Today the Trofimov at many museal locomotives is used, and improved constructions are available, making the valve going into anti vacuum position much better and returning to operation position much earlier than the elder constructions.



So how was that in the US? Are there anti vacuum piston valves ? Which function and design? Of are there still sniffing valves used?

Are you sure that the term is "snifter" ? I think you might be refering to drifter or "drifting" valves. I read an article
many years ago in Railroad magizne about the orgin of drifting valves. The jist of the article was that with the advent of
superheated steam, the lube oils of the time were not up to the high temps from the superheated steam. When the
engine was working all was ok, as the combination of steam and cylinder oil would keep things working. The article said
that the trouble happened when steam was shut off, as when drifting down hill etc. The lack of steam in the cylinders was enough to let the high heat of the cylinder walls "flash" burn the oil resulting in little or no lubrication and scoring of cylinders etc. To overcome this valves were installed at the steam chests to admit air to keep temps down. I dont know if
this intentionaly or by defalt had any bearing on adverse cylinder pressure when locomotives were drifting, but not working
steam. It would seem i think that when drifting as rule the cylinder cocks are opened to relieve any build up of water and or
pressure in the cylinders, at least that has been my experience. As to any "sound" made by these valves, i dont know. I
suspect that what is refered to re: the" model sound system" may well be ment the sound of the open cylinder cocks which
do create an exhaust sound when an engine is working steam. Hope this is of some help......

Hello trapper,
let's clarify some parts out together...

trapper wrote:Are you sure that the term is "snifter" ?

Yes, Snifting from the word "to snif" as a dog does...
It's a part of the anti-vacuum-installation for coasting

I think you might be refering to drifter or "drifting" valves. I read an article
many years ago in Railroad magizne about the orgin of drifting valves.

Consider please: Not all engines had drifting valves! As far as I knew, many locomotives in GreatBritain and France don't have such valves, they were simply unknown. Also in Germany, not all locomotives could get drifting valves, because of their different constructions and task they had to do.
So most of germany four cylinder compound engines don't have drifting valves, but have snifter valves.
Also in the time before the increased use of drifting valves, the engines got snifting valves on each side of the valve cylinder, which could be operated by compressed air from the cab. On idle or coasting the engineer set those valves open, to admit air into the valve cylinder and into the main cylinder.
Also our little ELNA has a snifting vavle:

In the picture you can see our 0-8-0 Tank locomotive 184 DME, build by Henschel in 1946.
Behind the stack or chimney there is the snifting valve. Our ELNA has a self-operating drifting unit by Winterthur, which is a pipe to both valve cylinder endes, to connect both exhaust steam chests. In the middle of the pipe a self closing valve, the winterthur valve, is mounted. It is shut if the engine runs under steam, and opens by gravity if the engine is coasting with steam shut off. It has nothing to do with the piston valves itself.
Usually now the cylinder volume can be pumped by the piston from one side to another, because both sides are connected by the winterthur drifting unit, but in many cases this was improper - because of condensation and less piston volumes or open drain cocks - which as a result haven't enough diameter to act as a good air inlet to have a smooth and really free drifting or coasting on idle.
To overcome this, the winterthur drifting unit was improved with a self closing snifting valve, which is mounted behind the stack. It closes if steam enters the cylinders, and opens by gravity when the throttle is closed. Thus air can enter the main steam pipes to the cylinder and so into the pistons, so with this no pumping effect of the waving piston is given, no compression or aspiring process is retarding the wave of the piston, so nothing retards the free drift of the engine.
Usually we once tried "mid gear drifting" which works fine, but the better is drifting with the drifting units - and drifting with winterthur is better than with snifting valves only, drifting with Nicolai drifting valves is better than with winterthur, and drifting with Trofimov valves is superior to drifting with Nicolai valves.

So the snifting valve is the valve, which let air enter the cylinder with the waving piston in it, to support a free idle and a better drifting. Snifting valves have a dinstinct sound, in our prussian G8 - a 0-8-0 light freight engine - the snifting valves do a dinstinct kling-klang-kling-klang sound during drifting, which is really good to recognise, because of the modified snifting valves to support a better drifting ability.
On ELNA the snifting valve is a silent, but if you know about and what to listen for, a dinstinct noise of aspiring and rushing air during the drifting... I consider on other engines, this noise is quite more and better to hear, depending on size and type of snifting valve and drifting arrangement.

The jist of the article was that with the advent of
superheated steam, the lube oils of the time were not up to the high temps from the superheated steam. When the
engine was working all was ok, as the combination of steam and cylinder oil would keep things working. The article said
that the trouble happened when steam was shut off, as when drifting down hill etc. The lack of steam in the cylinders was enough to let the high heat of the cylinder walls "flash" burn the oil resulting in little or no lubrication and scoring of cylinders etc.

Hm, maybe there is a missunderstanding. Let's see:
The oil problem is not because if idling or drifting, the main problem is the high steam temperature. Saturated steam at 232 psi has a temperature around 400° F. For many cylinder oils this temperature isn't difficult to handle, so the oil doesn't get to hard emulsified by the hot steam, thus a good and proper oil film can be estimated due the wave of the piston, to reduce wear and friction.
If we start talking about superheating, we start talking about getting higher steam temperatures. In Germany we can assume that fpr most steamers in proper condition the temperature will reach 680° F up to 710° F on coal fired engines and up to 790° F on many oil fired steam locomotives.
Common cylinder oils can't deal with those temperatures, thus a special oil has to be used.
If we use common cylinder oil on superheater locomotives, this oil will quickly emulsify, thus wear and friction will increase, damage to cylinder and piston valve liners will occour, as the piston rings will get damaged thus the sealing betwen the cylinder and valve sides will break down, the engine will work improper and maybe completely fail.
Also, the common cylinder oils can deal with the high temperatures, and build up a layer of burned oil which itself is sticky, very adherend to the piston and liners, and thus no good lubrication is given on those points...
This is not a problem on idle or drift, this problem occurs if the engine is working under steam.

But this might be also a kind of different oil applications to the cylinder, but even with the british form of pre-emulsifing the oil by atomiser units, the hot cylinderwalls won't flash burn the oil, because if steam is shut off, the cylinder walls tend to cool down and the cylinder walls seldom get as hot as the steam itself... and oil what can deal with the superheater steam won't get in trouble with hot cylinder walls.

On a downhill ride, the oil supply has to be given and because the cylinder itself cools down, the temperatures aren't the problem anymore. If you get temperatures in the cylinder that high, you should watch friction and wear - because your piston might be damaged, the rings might have a problem, because: If friction causes temperatures that high, that oil resistant to more than 680° F will burn or fail as lubricant, the friction must be really worth to think about and take immediately care about!
On a downhill ride, one has to spend a little drifting steam time by time, just to emulsify the oil and help to prevent oil accumulations on piston and liners, also to increase the temperature a little bit, to make the very viscid cylinder oils more fluid and help to get a good lubrication film on the liner surface.

To overcome this valves were installed at the steam chests to admit air to keep temps down. I dont know if
this intentionaly or by defalt had any bearing on adverse cylinder pressure when locomotives were drifting, but not working
steam.

Well, I don't know the article, but I guess there is a huge misunderstanding of oil supply, oil function and the whole thing about. Maybe the article refers to a fact, when engineers use oil for lower steam temperatures on suberheater locomotives... maybe then this would work, but I would never recommend to do so or to think this is worth to guess about.
If you have high superheat steam temperatures up to 780° F - please go ahead and tkae an oil which can deal with those temperatures. If you need, I will show you certains oils which can do!
German, and most other locomotives in Czech republic, France, Switzerland and Austria I know had special oil containers and oil pumps only for oiling the steam engine parts which get in contact with steam.
I don't know if the US have such, but... I don't know locomotives which don't have... Because you can't use the grease for bearings of axle and rod for cylinders, or use the same oil for axle and rod for the cylinders...

The valves I know, which let air drain into the cylinders and valve cylinders or steam chests are there, because to support drifting! And not for cooling down! I swear!

It would seem i think that when drifting as rule the cylinder cocks are opened to relieve any build up of water and or
pressure in the cylinders, at least that has been my experience.

Yes, indeed, but: If you have drained water, only small drops will be there, not a big problem is you drift... because the piston works now like a water pump and will press the water into the exhaust.. water hammer will only occur, if water is present in the cylinder and you open the throttle and adjust a cut off... because now you get more steam by compression or water hammer, because water can't be compressed - thus the drain cocks help to prevent this situation and should be opened allways prior the opening of the throttle and shut, it all water might be flushed out.
But the drain cocks have a small diameter, they won't work properly as air sniffer valve for idling, as high air speed through the small bore of the drain cock openeing will occur... Thus this will retard the free waving of the piston during drifting and retard the free run of the engine. Your engine won't drift freely... the reterds depends on how good and free the piston can wave... remember my posting on Riggenbach dynamic brake for steam locomotives...
You can give this a try:
Take two locomotives of the same type, remove in the front one the piston valves and let the valve cylinder lids open. Now go with the second locomotive behind the other and: Speed up both locos by pushing the front one to about 12 mph... now close the throttle and do what you might have to do for drifting, but keep the throttle shut... if both locos have the same drifting ability, thus the same free run, both will stay together. If the wave of the piston on the last locomotive will do any retard, the front engine will get loose and move further, as the pushing engine does... and it's amazing how the distance can be, betwen two locomotives... even if you only compare two different drifting units, like the winterthur and the trofimov drfting valve... this can be more than a whole locomotive lenght and a straight, flat track!

As to any "sound" made by these valves, i dont know. I
suspect that what is refered to re: the" model sound system" may well be ment the sound of the open cylinder cocks which
do create an exhaust sound when an engine is working steam. Hope this is of some help......

Well, the sound of snifting valves is strange often. It's often a load, dinstinct noise, like a something sniffing... hence the name.

Hello Steffen. Yes, you sure know your way around a steam engine. No doubt about that. However lets not let terminology
confuse things. I believe the orignal post was in regards American locomotives and a model. Given that, i have never in
my experience here in the states have come across the term "snifter" in regards a drifting valve. Given that the orignal
post was about a model locomotive, i suspect that the manufactuer of the steam engine model was refering to open cylinder cocks: a totaly different appliance. I realy think the model manufactuer got his terms mixed up....

trapper

I am sure it's not the cylinder cocks. My guess is that the sound is in fact drifting valves. The sound reffered to in the instructions is a quick "shhhick" noise just as the engine begins to move. The decoder does not have the "hiss-hiss" of open cylinder cocks.

Thanks to all for the replies. There is a wealth of information contained in these posts. Thanks to all for sharing this information!

Jon

Maybe snifter valve is to drifting valve as shunter is to switcher???

I finally got around to doing some looking into this; it's a term I'd never heard before. I have Loco Cycs from 1906, 1922, 1925, 1930, 1941, and 1947 (full title: Locomotive Cyclopedia of American Practice, published by Simmons-Boardman). The first chapter of each is a dictionary of terms; I didn't find any mention of a Snifter Valve in any of them. (Note the 'American Practice' in the title).

The only online references I could find in a quick search (including the earlier Wikipedia link) seem to indicate it was a European (mainly Britain and Germany) term for a valve to break vacuum in the cylinders of a coasting locomotive- as Steffen explained. Not used on this side of the pond, and apparently not much used in later superheating.

Sounds like a cross-cultural (trans-pacific?) translation misunderstanding in the manual development, perhaps?

steamfan6325 wrote:My guess is that the sound is in fact drifting valves.

Suppoerted!

The sound reffered to in the instructions is a quick "shhhick" noise just as the engine begins to move.

Well, this sound refers to a common air snifter valve, but also can be a sound of support valves, which added extra steam to the steam chest, to promote extra power to pull on...
But sniffing valves were drifting valves, no doubt in this. And they were used only in drifting, so opened if the main throttle is closed... and most sniffing valves do no noise during drifting... only if the engine is working under pressure, throttle opened, that sniffing valves makes this shhhick noise, because it's closed by steam pressure.
But the noise can also appear, if the drain cocks of the cylinder are open and the throttle is opened to move on. Now steam hisses out from the drain cocks, and after some turns the engineer closes the drain cocks - resulting in nearly the same noise.
But: This isn't a snifting valve...

The decoder does not have the "hiss-hiss" of open cylinder cocks.

This noise only comes if the engine is moving under pressure and the steam changes from from to rear drain cocks....

Can you ask your sound decoder manufacturer about the noises? This would stop any speculations about what and where the noise may come from ;o)

@Marty:
We talk not about something alive... we talk about a model. And if the decoder manufacturer delivers this decoder to british model train users... they usually use sniffing valves. Also, if the decoder can or should be used for european locomotives, even here this noise would be needed...

So, this is to speculative... just to guess that american locomotives do not have, so this sound from the decoder could not be a snifting valve...

I am certain that the instructions simply used the wrong terminology. The "shhik" noise is consistant with drifting valves that are normally open and are forced closed by steam chest pressure when the throttle is opened. The alternating hiss of open cylinder cocks is simply not in the decoder's "sound files".

I have seen one engine under steam that is equipped with what I now know are drifting valves. This decoder makes the same noise that the drifting valves on the real engine (an 0-4-0T switcher) made.

Just to avoid confusion the decoder is meant to represent medium sized american engines.

To all who took the time to research and reply to my question: THANK YOU! I have learned a lot about the operation of, and reason for, drifting valves. Or if you prefer, snifter valves...

Jon

Hello Jon,
don't mind about.

Consider, that drifting is a major concern in operating a steam engine, because to safe fuel many engineers speed up the train, then close the throttle and let the mass of the train keep up drifting, as long as the speed drops below a threshold. The throttle is opened again, and the train speeds up again.

So in common steam engines if the throttle is closed, the piston works like a rod driven air compressor, which reduces the free idle very roughly. And if you need to drift and speed up, drift and speed up - as usually done - you will encounter with closing the throttle serious and very dominant 'brake' effects by the moving piston during drifting, so the moment to reopen the throttle for speeding up is much more early compared to an engine with a drifting equipment.

Usually most engines without drifting equipment are set in drifting via valve controls mid gear and throttle closed. But: Serious developments and test had been undertaken to get better drifting abilities, which lead to snifting valves on the corners of the valve gear box - so called corner valves. They were manually operated by air, an permit extra air inlets for better drifting and reducing of the air compressing effects in the cylinders.
The next step was the self closing drifting valve constructed by the swiss locomotive works in winterthur, the so called winterthur drifting valve. In GB and France this winterthur drifting valve was reworked and got a single sniffing valve, usually mounted behind the stack and operated by life steam from the main steam pipe - and if throttle closed, this valve was opened and admitting air to the cylinders via the main steam line.
The most reliable drifting equipment was the drifting piston valve. Usually small flap-valves within the valve piston surface established the overall good drifting ability, later moveable pistons on the piston valve rod made the race and are today considered as the most genuine drifting equipment - the so called Trofimov or advanced Trofimov piston valves...

And with those, the sound of a sniffing valve will be completely absent...