Whistle

[Deleted]

The whistle on my Modelworks Britannia has never worked particularly well and I want to improve it or replace it. It gives a rather feeble strangled sound, particularly at anything less than full boiler pressure. I'd be happy with a good strong single tone - I don't particularly feel the need for a chime whistle, and it would be difficult to find the space for one at this stage.

The whistle is a single tube about 4" long and 1/2" diameter, so is not particularly large. It is mounted under the running board over the right-hand cylinder and is fed by a 5/32" od pipe from the valve in the cab, so there is a fairly long pipe run. The cutout in the whistle is facing downwards, so there should be no build-up of water.

I've removed the whistle and tested it on compressed air, and it gives a good loud clear note at 80psi, but not at 40psi or thereabouts. Is this what would be expected? I noticed that the disk with the flat that lets the air through is fitted about 1mm below the lower edge of the cutout in the whistle body, rather than in line with it - should I file the cutout to line up with the disk? Is there anything else that I can adjust to make the whistle work better at a lower pressure? How should the performance under steam compare with compressed air at the same pressure?

I could shorten the pipe run by mounting the whistle under the rear end of the running board or under the cab floor. Is this likely to improve the note? The long pipe run delays the sound but perhaps also reduces the pressure at the whistle by allowing the steam to partly condense on the way.

Regards, John

[Andrew C]

I was wondering if this location would be a problem.

Currently my Brit also has the whistle near the right hand cylinder.

I had thought of moving it back under the running board by the cab.

Your assumption of drop in pressure over that distance is probably correct. the pipe will take a lot of heat from the steam I should think.

Like you I am very tempted to move it.

Andrew

[Jim]

I'm watching this with interest John and Andrew as I haven't yet decided where best to locate Boadicea's 3 chime whistle, similar to the Polly Models one.

Originally I thought between the frames under the smoke box would be ideal but then moved for ease of access to beneath the footplate on top of the RH cylinder where John has his.

Nearer the cab with less chance for condensation now seems more sensible.

Could your problem John be due to condensate not being able to drain from the whistle?

Slowly getting there
Jim

[Deleted]

On further testing the whistle does in fact work well on compressed air down to about 25psi, so I don't think there's anything wrong with it. So I'm in the process of moving it to a position just forward of the cab, under the right-hand running board. The battery box will enable me to fit a hidden screw to support the front of the whistle. Hopefully the much shorter pipe run will improve things.

Regards, John

[Andrew C]

That's interesting I have just done exactly the same . I intend to do a second steam test this coming weekend. So will keep you posted.

Andrew

[Jim]

It's a funny world. I too got Bodicea's three chime whistle out and tested it on compressed air with the same results as John.
Wherever the whistle is it needs to slope a up to allow any condensate to drain. As an ex brass player water in the tubes makes a great gurgle.

Jim

[Andrew C]

Well I did get Robert Burns steamed on Sunday. Depending on who you talk to it was either a partial success (me) or a complete disaster (my dad)

I got the Safety valves set, the injectors work but the two top clacks need the ball lift increasing to stop the overflow from running. The whistle would work just under the battery box if the whistle weren't blocked and then the valve timing is out by a long way.

So for a first proper steam I think success for having a running engine too soon

Andrew

[jma1009]

hi john,

the languid or disc should NOT be below the bottom of the whistle slot and should be above it by a few thou. so please file the slot to be level with the disc. a 1/2" dia tube isnt generally ok for a range of pressures, depending on the length of the whistle and steam pressure (speed of steam at the disc) and whistle note for which there is a mathematical formulae. a 1/2" dia tube of 4" length, assuming say 3/4" before the bottom of the slot doesnt give ideal proportions... ie the tube is too long for the diameter to give a stable note other than at low pressure. the size of the opening in the tube also has a significant effect, both height wise and width wise.

wrap a piece of shim or card around the whistle and see what happens if the size of the opening is reduced... you might be surprised! if there is an improvement, soft solder some shim round the top of the opening. there is a formulae between diameter and length to give a clear note for a range of pressures/steam speed beyond which the note is either not clear or jumps an octave. this relationship is unfortunately not followed by many makers of commercial fittings. and often the width of the gap between the disc and whistle tube is too much upsetting everything at higher pressures, as is too high an opening in the whistle tube. there is nothing wrong with a flat opening to the top of the slot or the top of the slot having radiused edges, but a 'V' slot should be avoided for a clear note. however if the diameter to length proportion is wrong then the pressure range at which a clear note is produced is seriously compromised, if not compromised completely! the empirical method of checking this proportion is to have a sliding stopper in the end of the whistle to be adjusted to when the note is clearest for a range of pressures, and with a 1/2" dia tube you might find this is an octave above what you would find acceptable.

please experiment and you might be pleasantly surprised at the improvement.

cheers,
julian

[peterseager]

Having spent an amount of time making a whistle for my Manor I would caution against getting too excited because a whistle works on air. Steam, I found, was a different ball game. I read somewhere that when you start to make a whistle you tend to end up going into production to try and make a good one. I tend to agree.

My Simplex has a 4" long 1/2" diam whistle that works a treat. Came with the loco so I don't know where it came from.

Peter

[Deleted]

Hi Julian

Thanks for the ideas. On the principle of only changing one thing at a time, I'll wait to see how it performs on steam with the much shorter pipe run before trying any changes to the whistle itself. I had read that the disc should be flush with the opening or slightly above, so that will be the next thing to adjust if the shorter pipe doesn't solve it. The pitch is higher than I would ideally like, but I can live with it if it's loud and clear.

Regards, John

[Deleted]

I steamed again today, and the whistle sounds much better with the shorter pipe run - it's loud and clear at anything over about 50psi. I suspect that the original long pipe run was causing the steam to be half condensed by the time that it arrived at the whistle.

Regards, John