Old organ
Looking at one of Adam Ramets picture on this link I hope http://www.flickr.com/photos/27960849@N07/2787284033/sizes/l/ it shows a pressure guage, with music volume markings, does that mean the organ is variable pressure ?. Is this unusual ?.

I think it is a water pressure glass to measure how much pressure there is in the resorviors. Whites Gavi has one fitted so that you know if something is wrong. Its not un usual, just not common. It just like another way telling you that somethings wrong, or for tuning (getting the working pressure). I may be wrong, but thats what Peter says

Hi there Nick, Jake, The organ shown is an American Organ - or suction-operated reed organ as opposed to a harmonium which is pressure operated. The air reservoir has a linkage which operates the dial. It is unusual as it was a gimmick for that particular organ company so most other organs of it's type don't have these. The brass reeds of reed organs are stable in their tuning at variable wind pressures. If you blow into a harmonica or play an accordion you will know this. A lot of people think old reed organs play at a fixed wind pressure and fixed volume and that, like a pipe organ, you vary the dynamics with stop registration and the swell shutters but this is not so. On these instruments, just like for example a pianola, you can generate a tremendous sweep of dynamics merely by varying the pressure in the instrument as it plays. With experience, just like with a pianola, you get to feel the pressure resistance under your feet as you treadle the bellows / exhausters so the dial in the photo was, as I say, more of a sales gimmick than a practical thing! If you can play a keyboard or piano do get one of these old organs for yourself one day. They are very enjoyable to play and musical once you get the hang of them. Buy one with a large number of stops to get a wide musical range. Each true rank inside usually has 4 stop drawknobs on the front. One rank plays 1/2 and 1/2 each side of the keybaord and also only 1/2 drawn-open on some stops so makers could show 12 stops with only 3-ranks of reeds inside. Add octave couplers and vox humana and that's fifteen stops for not a lot of organ already! These instruments were, like the pianola, made to be played with variable pressure treadling right from day one and this is an important point totally lost to most people these days. Putting an electric blower into one or into a pianola or a player-organ Orchestrelle turns it into a noisemaker rather than an interactive musical instrument. You will find crescendo indicators on Wurlitzer theatre organs and certain other pipe organs. These show the volume of the organ playing into the auditorium but don't work on air pressure calculations but show the number and volume of the individual stops selected at the console plus the positioning of the swell shutters to my understanding. In large fairground organs there are indeed U-tube manometers or liquid column manometers (http://en.wikipedia.org/wiki/Pressure_measurement) fitted to monitor the level of wind pressure feeding from the pump. At GDSF the other week I saw several lurking around the place and would venture that it is more common than not. As the current drawn from the showman's engines is variable the instruments have a rheostat to control the current feeding into the instrument. The manometer shows at a glance whether the current feeding in is too much or too little or indeed whether there is any other fault in the system somewhere. regards Adam