Organ bellows

[Contratrombone64]

As I contentedly play the lovely Lewis pipe organ where I work, I wonder what the mechanism is that stops the bellows from over filling? Iif anyone has the answer to this sweet mystery, maybe they can share?

thanks

[Soubasse]

I've seen two solutions, one of which consisted of hinged, spring-loaded arms (there's no doubt a better description than that but I certainly can't think of one!) attached to the top and bottom of the external frame of the bellows that eases their rise as they inflate. The other is a simple weight of some sort, ranging from iron girders to slate slabs, bricks or besser blocks (or a combination thereof).

[Contratrombone64]

OK, but that doesn't release build up wind no matter how strong the bricks you put on top, there must be some sort of "back up valve?"

[dll927]

I wonder how many organists worry about what's up there behind the facade.

Years ago I played a pipe organ up in San Jose, CA that was divided on two sides of the sanctuary, in the typical chambers behind walls. The bellows in the Great division had a brick sitting on top.

Assuming that the amount of air in the bellows varies as different combinations are played, the blowers may have some type of adjustment that accommodates that. And what about when the organ is not being played, which is usually a good bit of the service? Something must prevent the bellows from blowing up. The main function of the bellows would be to keep the pressure in the windchests constant. Have you ever heard an organ being played when the power went out? It's rather un-tuneful!!

I would think that just asking any competent organ service man should at least answer the question.

[Contratrombone64]

Yeah, true, when Darrell Pitchford (our tuner/maintenance firm) turns up to tune the beast I'll try and remember to get him to take me inside and show me how this works.

[Krummhorn]

Great question, David ...

I believe that there is a one-way valve in place between the blower and the first reservoir (main regulator). As the organ uses more wind, the reservoir level drops, and as it does, the valve (or flapper) opens to let more air in from the blower.

Found this site on Organ Wind which may be helpful.

A good analogy of this is your cars voltage regulator. It accepts the raw voltage from the alternator and/or battery (usually 13.4 vdc) and regulates it to 12.0 vdc for the rest of the cars electrical system, and discards the rest.

[Contratrombone64]

Lars - amazing and fascinating, thank you. I also watched the couple of little videos relating to that horror, the trumulant.

[Krummhorn]

Yah, the rolling tremulant is quite the marvel, isn't it. Makes me wonder if Leslie got their rotating-cone-over-the-speaker concept from that .

Some tremulants are okay ... I've had mine adjusted at church to be gentle, but with enough amplitude to be noticeable ... a sweet sound with my 4' Gedeckt (metal) on the great division against the swell Gemshorn celeste. I, personally, like them to modulate slowly - I hate those jittery fast trems on classical organs that are akin to the sound a billy-goat makes when their tail is yanked upon .

Theater organs, now that's a different matter - the IV/79 Wurlie up in Mesa (90 minute drive from my home) here sounds wonderful when they pull those on, especially with the Tibia's. I'm an avid admirer of theater organs and that type of music .

I've not seen the Austin Universal Air Chest ... supposedly, in some installations, one can stand inside the pressurized air chest just beneath the pipework. Seems like that would take up lots of valuable space though.

[Soubasse]

I'm sorry to say that I've always found the sound of theatre organs with all trems wobbling away on full to be a singularly nauseating experience, sometimes it's all one can do to actually recognise a tune! A subtle trem on a solo registration on the other hand (a cornet decompose for example) can quite pleasantly lift a piece. That said, I have played too many instruments where the knocking sound of the tremulant is so intrusive it's unusable anyway (and they never knock in time with the piece you're playing either!)

[Ghekorg7]

Hi all !
Tremolo on Theter organs is in most cases overdone and distruct the music played on.
Tibias on the other hand need some, but not full, just light slower tremolo...

In pipe organs I like tremolo on solo stops in Chorals, mostly on Bux works and in slow speed if one can get a well serviced one. Helps melody stand out of the left hand/ped piano accompaniment. I believe it adds to the piece of music played.

[jvhldb]

In one of our local churches the wind chest and blower is located in a passage and I had a look at the regulating mechanism. There is a rope attached to the top of the wind chest, this is then connected over a pully to a flap located inside the wind trunk between the blower and wind chest. As the lid of the wind chest rises, the flap lowers inside the trunk reducing the amount of air going into the wind chest.

There is no such mechanism on our church organ. Apparently it uses the same principle as the jumping castles the children play on, when the air pressure in the chamber reaches a cerain pressure the blower is unable to force more air into it. As the blower has open vanes/blades the excess pressure simply disspates through the blower. If you stand next to a jumping castle blower when the kids get going you can actually hear the air "wooshing" out through the blower, the same happens with the organ blower. The organs working from a compressor normally have an automatic regulator on them keeping the pressure constant.

[Contratrombone64]

Hi all !
Tremolo on Theter organs is in most cases overdone and distruct the music played on.

"distruct"???

[Ghekorg7]

"distruct"???

errrr..... I wanted to say 'make the music played on, sound awfull'

I did a direct translation from what we say in Greece about listening a nice piece of music and being fallen to pieces by, or to destroy it with, a bad/wrong choice of registration/sound colour.....

[Soubasse]

...There is a rope attached to the top of the wind chest, this is then connected over a pully to a flap located inside the wind trunk between the blower and wind chest. As the lid of the wind chest rises, the flap lowers inside the trunk reducing the amount of air going into the wind chest ...

Aha, I've seen those too and now I realise what they're for! And thanks for the rest of your response Jvh, it explains the question that CT64 raised to start with and that in itself was good too. All these years of playing the instrument, knowing only a little bit about the insides of it and David asked one of the most obvious questions that I'd never thought of before!
Cheers

[Contratrombone64]

I have a feeling that the blower for my College organ is hidden under the floor and I know there's a manhole to open for access but it's a precarious drop of about five foot to the floor below (which just happens to be the ceiling as it's on the gallery of the Chapel). I'm too much of a chicken to get into it to check it out, at least not without the aide of a step ladder and stiff drink.