Whistle problem

[Dennis RaynerParticipant @dennisrayner52782]

[Dennis RaynerParticipant @dennisrayner52782]

I have just finished machining up the bell whistle for Elidir (the ¼ scale Hunslet from Reeves) and I am very disappointed with the result. I have read all the previous threads on this topic on this forum and looked at various Youtube videos and "whistle" websites. I've learnt a lot but these sources are all strong on "how to make" and a bit weak on "what to do if it doesn't work"

Basically, when testing on air, my whistle whistles reasonably OK at 100 psi but with some "whoosh". As the pressure goes down the whistle sound disappears at 70 psi to leave ONLY whoosh. One thing I have noticed is that the whistle valve needs to be fully depressed to get any whistle at all.

Any advice or comment would be very much appreciated

Dennis

[Rob keevesParticipant @robkeeves73950]

Whistles behave differently with steam, due to the denseness of steam. sorry i cant help anymore. Rob.

[BazyleParticipant @bazyle]

What's more it may perform differently on steam. Mine needs to warm up. You will find more useful advice looking on organ related websites – they have the same problem.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Dennis ,

Fault could be one of many things but the most common one is due to mismatch between flow areas of whistle steam slot , through bore of valve when open and any pipework .

Very complex but basically whistle steam slot has to have the controlling orifice in the whole steam flow system .

Its all about pressure drop of the steam – what you want for an effective whistle is for the entire pressure drop to occur at the whistle .

This means in practice that through flow area of valve and pipework has to be larger than through flow area of steam slot .

If valve or pipework are too small pressure drop occurs in these and nothing at whistle . Under these conditions 'whistle' will probably be weak and cut off all together at lower steam supply pressures .

Regards ,

Michael Williams

[julian atkinsParticipant @julianatkins58923]

hi dennis,

please dont look at organ pipe principles…they work at 2-4 psi and dont conform to steam whistle principles.

i have made a bit of a study of this subject over the years.

i would be inclined to play around with the opening ie the gap between the bell and the bottom part, and suspect that a smaller opening (ie lowering the bell ) will effect some improvement. additionally a slot no more than 1/64" between the disc/ languid and bottom fitting is quite sufficient… no more is required.

there is a relationship between diameter and height of the bell (as well as the height of the gap). if you can provide more details of diameter and height of the bell i might be able to help further.

michael william's comments about pressure drop are very relevant… it's the speed of the steam as it emits from the disc that is important. if the whistle valve and pipework isnt properly proportioned and big enough then the whistle is compromised.

i hope the above comments are of help, from one terrier builder to yourself with your wonderful completed terrier!

cheers,

julian

[Dennis RaynerParticipant @dennisrayner52782]

Many thanks for the replies – I hope to try it on steam within a month but Youtube videos suggest it should perform reasonably well on air hence my concerns.

I have followed the drawings exactly. The whole thing is machined from 1" OD brass rod – the bell is bored out to 15/16" diam. and the base to 7/8"diam. The bell depth inside is 1¼" and it sits 5/16" above the base. The disc in the base is 13/16" so, sitting in a 7/8" hole, I calculate the annula area to be 0.336 sq in. Now we come to what is being suggested as the root of the problem. The passage through the whistle valve and into the base of the bell is 1/8" OD which is a cross section area of 0.050 sq in. (ie Just 15% of the annular area). Within the existing external shape I could open up the passage to 5/32" (=.076 sq in.) and increase the disc diam. to 27/32" giving an annular area of 0 .172". This would incease the ratio to 40%. Still way short of the 100% being recommended but do you think this would help? It all seems a classic example of being able to scale the externals but not the internals.

Regards Dennis

[The Merry MillerParticipant @themerrymiller]

test post

[julian atkinsParticipant @julianatkins58923]

hi dennis,y

yes please do try increasing the cross-sectional area through the valve and pipe, and reduce the annulus to 1/64".

if the gap between bell and base is adjustable from the 5/16" specified, reducing it gradually on air may produce a clearer note.

the bell of the whistle seems a bit squat to me. without getting too technical proportions of 1:2 and also 1:5 of diameter to bell length work well at the pressures of our miniature locos. you therefore may not get a clear note and avoid the 'whooshing' or jumping an octave etc.

i spent much time experimenting with a very similar whistle 2 years ago.

cheers,

julian

[Dennis RaynerParticipant @dennisrayner52782]

I've opened up the passageways as much as I dare (which is not a lot as I said before) and I've lowered the bell more towards the annulus. The gap is now about about 1/4" (down from the 5/16 specified). The changes have made a significant improvement with the whistle (on air) working from 100 PSI down to 50 PSI. I think I'll refrain from any other changes until I've managed to try it on steam using the complete steam pipe run.

Many thanks.

Dennis

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