I’m currently tuning the sound functions on the Grizzly Northern’s 1st sound equipped locomotive, a Spectrum 2-8-0 and am puzzled by the “snifter valve”. I hear it making a short phssht-like sound on changing direction. In the case of the Tsunami-equipped 2-8-0 the snifter valve function is automatic and not controlled by a function key, unlike the boiler blowdown, only the sound volume is adjustable, via CV141.
In real life does the snifter valve automatically clear condensate from the cylinders? I thought that clearing the cylinders via the cylinder cocks was manually controlled by the engineer. In the case of the model is this a design compromise?
The snifter valve worked in one of two ways. It either equalized pressure across the cylinders so a leaky main valve wouldn’t allow a locmotive to creep away or it vented the leaking steam for the same purpose.
The explanation I’ve always heard about it was that it was an anti-vacuum device on the smokebox, to prevent too great a vacuum being formed by the steam through the blastpipe. That’s how it is on British locomotives, anyway - it’s the small valve behind the chimney.
Nick - you’re not thinking of the cylinder drain cocks are you? The snifting valve is automatic, the drain cocks are manually operated (although most engines, particularly those with piston valves will have an automatic pressure relief valve mounted on the same boss as a drain cock, to prevent damage in the event of priming).
Snifter valves prevents the valve chest creating a vacuum when drifting, drawing smokebox gasses and cinders into the valve chest. They are open to atmosphere when drifting or the regulator/throttle is closed, and close when the regulator/throttle is opened. They are very common on slide valve engines. They do not offer any protection against cylinder damage due to priming.
Modern US practice favoured the use of by-pass/relief valves - popular makes were Prime and Viloco. These performed the same function as snifting valves, but offered the additional advantage of allowing the engine to drift with the throttle completely shut without losing compression or lubrication. They also function as relief valves to protect against priming, and to prevent the engine from wandering off on it’s own if the throttle didn’t fully seat closed.
On some UK locos the snifter valve was mounted on the superheater header, as mentioned, but in many early examples the header was fitted with a relief valve, as UK practice at that time was to have the regulator in the dome, upstream of the superheater elements.
Thanks for the correction Mark. I had it explained to me when I was about 10, clearly I’d misremembered the precise details of it, and my experience with real steam engines is limited to engines small enough not to need one!
Incidentally, I wasn’t referring to the snifter valve as preventing priming, but the cylinder pressure relief valves that are often fitted at the ends of the bores, along with the cylinder drains.
No worries Eddie, I could see from your post you knew the difference. Here on the NSW railways the relief valves were known as Cardew valves, after the CME who designed them.
My family owns a Fowler A4 traction engine from 1905, and a Garrett steam wagon of 1926. My grandfather had a very early (1868), very interesting ploughing engine, but he sold that some time ago. Of course, since I moved to the US my contact with the steamers is much reduced, but I try and keep my hand in as much as possible.
I’ve also been on quite a few of the railway engines over at the Middleton Railway in Leeds (the oldest working railway in the world, dating back to 1758). I did a very small amount of work on their Cockerill 0-4-0VBT (a very interesting loco with a thimble tube vertical boiler), and I’ve been up and down the line on several of their little shunting locos.
What steamers have you worked on, and do you currently work on any? It’s always interesting to see the different working practices around the world. For example, isn’t it the case that every engine in Australia must have two safety valves?
One post of yours from a few days ago that I thought was interesting was you commented about using hot water for the boiler hydraulic test - when we’ve done them we’ve just used cold, as the only ones I’ve actually done were with a brand new boiler and a boiler with a new firebox, so there was no risk of grooving or anything like that due to injecting cold water, but is there another good reason to use hot, in your experience?
