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Thanks for all those interesting replies. Unfortunately, I was not referring to inboard Schwimmers but rather a reservoir (remote from the soundboard) having a floating pan instead of ribs - one often sees older double rise bellows converted to this type, presumably because it is less expensive than re-leathering the original. My original question in regard to this was in relation to calculation of size. I have seen quite small reservoirs of this type supplying quite large divisions, although with internal disc valves controlling the input of wind from the blower - presumably because these are faster acting than an external roller blind or guillotine.

Sorry if I didn't make myself clear in the previous post.

PM

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Thanks for all those interesting replies. Unfortunately, I was not referring to inboard Schwimmers but rather a reservoir (remote from the soundboard) having a floating pan instead of ribs - one often sees older double rise bellows converted to this type, presumably because it is less expensive than re-leathering the original. My original question in regard to this was in relation to calculation of size. I have seen quite small reservoirs of this type supplying quite large divisions, although with internal disc valves controlling the input of wind from the blower - presumably because these are faster acting than an external roller blind or guillotine.

Sorry if I didn't make myself clear in the previous post.

PM

 

Thanks for the additional explanation. You sound as if you're discussing a particular case, or a project maybe?

 

I think there's nothing much wrong with these (I think they're called 'membrane reservoirs') provided

1. they have sufficient rise and fall (see below)

2. in terms of efficacy, you should remember that they are the equivalent of a single-rise bellows

The double-rise bellows so beloved of all our great firms was adopted so generally because it gives such a uniformly steady (as opposed to solid, unyielding) supply of wind. The additional, inverted fold layer helps greatly with this (?was it referred to as Cummings's improvement?) Builders were concerned to achieve this equalisation of pressure because of their reliance upon hand-blowing. A single rise (if fed by a decent-sized trunk and controlled by a well-adjusted valve or pallet) gives steady enough wind IMHO.

 

You ask about size, well it's just a question of capacity (i.e. difference between rise and fall of the top board). I hope others will rush in to correct or confirm what I say, but I would reckon so long as the volume of the pallet-box is not larger than the volume given by the rise and fall, you would be fine in all eventualities. This presumes that there is not too great a distance between the reservoir and the chest, and that the trunk to the chest is adequate. Having said that, some historically-informed builders have gone back to using relatively narrow trunks at this point in order to achieve the old effect! [We're back to 'living, breathing' wind again!]

 

P.S. I forgot!

If these are small (i.e. 3' long or less, and for some reason oblong ones work better than square ones), you may have a problem with their speed of reaction. I've known them to be sluggish to respond and refill after sudden demands unless the pressure is obtained by a combination of weights and springs. Don't ask me why! Someone here will know!

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Thanks for the additional explanation. You sound as if you're discussing a particular case, or a project maybe?

 

I think there's nothing much wrong with these (I think they're called 'membrane reservoirs') provided

1. they have sufficient rise and fall (see below)

2. in terms of efficacy, you should remember that they are the equivalent of a single-rise bellows

The double-rise bellows so beloved of all our great firms was adopted so generally because it gives such a uniformly steady (as opposed to solid, unyielding) supply of wind. The additional, inverted fold layer helps greatly with this (?was it referred to as Cummings's improvement?) Builders were concerned to achieve this equalisation of pressure because of their reliance upon hand-blowing. A single rise (if fed by a decent-sized trunk and controlled by a well-adjusted valve or pallet) gives steady enough wind IMHO.

 

You ask about size, well it's just a question of capacity (i.e. difference between rise and fall of the top board). I hope others will rush in to correct or confirm what I say, but I would reckon so long as the volume of the pallet-box is not larger than the volume given by the rise and fall, you would be fine in all eventualities. This presumes that there is not too great a distance between the reservoir and the chest, and that the trunk to the chest is adequate. Having said that, some historically-informed builders have gone back to using relatively narrow trunks at this point in order to achieve the old effect! [We're back to 'living, breathing' wind again!]

 

P.S. I forgot!

If these are small (i.e. 3' long or less, and for some reason oblong ones work better than square ones), you may have a problem with their speed of reaction. I've known them to be sluggish to respond and refill after sudden demands unless the pressure is obtained by a combination of weights and springs. Don't ask me why! Someone here will know!

 

Thanks for that considered reply. Yes, it could well be for a particular project, where space is tight. I have made them in the past and used them successfully, utilising weights, and the results have been good. Your 'rule of thumb', relating the volume of the rise to the volume of the pallet box presents a sort of logical relationship, so thanks for that also.

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Thanks for the additional explanation. You sound as if you're discussing a particular case, or a project maybe?

 

I think there's nothing much wrong with these (I think they're called 'membrane reservoirs') provided

1. they have sufficient rise and fall (see below)

2. in terms of efficacy, you should remember that they are the equivalent of a single-rise bellows

The double-rise bellows so beloved of all our great firms was adopted so generally because it gives such a uniformly steady (as opposed to solid, unyielding) supply of wind. The additional, inverted fold layer helps greatly with this (?was it referred to as Cummings's improvement?) Builders were concerned to achieve this equalisation of pressure because of their reliance upon hand-blowing. A single rise (if fed by a decent-sized trunk and controlled by a well-adjusted valve or pallet) gives steady enough wind IMHO.

 

You ask about size, well it's just a question of capacity (i.e. difference between rise and fall of the top board). I hope others will rush in to correct or confirm what I say, but I would reckon so long as the volume of the pallet-box is not larger than the volume given by the rise and fall, you would be fine in all eventualities. This presumes that there is not too great a distance between the reservoir and the chest, and that the trunk to the chest is adequate. Having said that, some historically-informed builders have gone back to using relatively narrow trunks at this point in order to achieve the old effect! [We're back to 'living, breathing' wind again!]

 

P.S. I forgot!

If these are small (i.e. 3' long or less, and for some reason oblong ones work better than square ones), you may have a problem with their speed of reaction. I've known them to be sluggish to respond and refill after sudden demands unless the pressure is obtained by a combination of weights and springs. Don't ask me why! Someone here will know!

 

On a double rise reservoir the inverted ribs are there because those that poke out from the reservoir tend to cause it to collapse from the pressure inside, while those that poke into the reservoir tend to cause it to inflate. Use both, join top, bottom and the centre frame with the 'z' hinged brackets you will find on all double rise units, and the two effects cancel each other out. Pressure is maintaned with weights. The big problem with this type of reservoir is that if a large demand is removed (taking ones foot off the pedal with the Open Wood drawn for example) the pressure will jump because of the large mass of the top plate - often very audibly.

 

Single rise reservoirs use springs to maintain pressure. The reason is that as the reservoir opens, the effect of wind pressure on the ribs, causing them to try to turn inside out, increases, and the pressure reduces. As springs exert more force as they stretch, they compensate for this effect. However, they also have a problem, as the lightness of the top board of the reservoir means that it can be made to vibrate. Sometimes some of the springs are replaced with bellows weights, as the resulting increased mass of the top plate is less likely to vibrate, although wind pressure is not so constant as the reservoir rises and falls with demand. Nothing is perfect!

 

Regards to all

 

John.

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On a double rise reservoir the inverted ribs are there because those that poke out from the reservoir tend to cause it to collapse from the pressure inside, while those that poke into the reservoir tend to cause it to inflate. Use both, join top, bottom and the centre frame with the 'z' hinged brackets you will find on all double rise units, and the two effects cancel each other out. Pressure is maintaned with weights. The big problem with this type of reservoir is that if a large demand is removed (taking ones foot off the pedal with the Open Wood drawn for example) the pressure will jump because of the large mass of the top plate - often very audibly.

 

Single rise reservoirs use springs to maintain pressure. The reason is that as the reservoir opens, the effect of wind pressure on the ribs, causing them to try to turn inside out, increases, and the pressure reduces. As springs exert more force as they stretch, they compensate for this effect. However, they also have a problem, as the lightness of the top board of the reservoir means that it can be made to vibrate. Sometimes some of the springs are replaced with bellows weights, as the resulting increased mass of the top plate is less likely to vibrate, although wind pressure is not so constant as the reservoir rises and falls with demand. Nothing is perfect!

 

Regards to all

 

John.

 

Hi

Interestingly, the chamber organ here (c.1820 - but possibly built by an amateur copying an earlier instrument) has a 2-stage reservoir - but the intermediate frames both "poke out" - so in effect, it's a weight-controlled single-rise reservoir. Most of the time the wind is stable enough - not rock solid, but enough variation to give some character without the organ sounding wrong or out of tune. In extreme cases - repeated bass chords on full organ for example, it is possible to set the reservoir "bouncing" - producing almost an unintended tremulant effect.

 

Every Blessing

 

Tony

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Hi

Interestingly, the chamber organ here (c.1820 - but possibly built by an amateur copying an earlier instrument) has a 2-stage reservoir - but the intermediate frames both "poke out" - so in effect, it's a weight-controlled single-rise reservoir. Most of the time the wind is stable enough - not rock solid, but enough variation to give some character without the organ sounding wrong or out of tune. In extreme cases - repeated bass chords on full organ for example, it is possible to set the reservoir "bouncing" - producing almost an unintended tremulant effect.

 

Every Blessing

 

Tony

 

On this and other posts above:-

 

I occasionally deputise at a church with a west-end extension organ high up on the wall, and detached console. The case is very shallow below the chests, and not very deep from front to back. It often displays an attack of the 'wobblies' if one plays anything involving staccato cords on full organ, and the distressing effect, sounding like an excessive tremulant, is never in keeping with the performance. The Widor is guaranteed to set it off!

 

The organ's builders have explained that this is due to the limited room, and the inability therefore to supply wind via a conventional reservoir, etc.

 

CP

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Oh, jelly bags. Yuck! I don't like the wind they give - a brittle, teeth chattering sort of bouncy, rather than a fluid one. That's my least favourite feature of the Oxford Metzler.

 

 

The Belfast Cathedral Harrison has jelly-bags for the Positive Organ. They seemed perfectly satisfactory except when one blew out and the entire C# side went out of tune....

 

I'm sure there's some awful ones around, though.

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