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Sunday, 19 April 2009

Reversed currents .....

Last week a long overdue repair to a damaged cable for the Abbey's electrical supply was carried out. All seemed fine, but I noticed that the organ's blower motors (there are four!) seemed to be making rather a lot of noise. As this is potentially dangerous and expensive, I went in search of the reason during the 0915 Mass. The Apse Organ blower is the most accessible and seemd to be making the most noise, so, having had a look at it, the duty Verger and I isolated it (It was running at the time!) and opened the bearing cover.

It wanted only a very brief check to tell us that it was running backwards. A swift check on the Tuba Blower revealed it was doing the same .......

Now this may seem strange, but in fact the type of fan used for this will actually "blow" air whichever way it runs, but it is much less efficient in one direction than in the other. Also, with the motor running backwards it isn't being cooled properly so there is a potential for overheating. Now, if two of the motors are running backwards, that tells us that all four are doing it, which means that at least one of the phases in the three phase supply has been reversed! As it is only the organ blower motors that run off the Three Phase supply (415v/45 amp) - everything else is single phase 240v/15 amp - we hope that it is ONLY the blower motors that have been affected. It still means that the Electricity supplier will have to get his team back here PDQ to fix this or face a large bill for any damage to the organs.

Now, a brief explanation is probably due as to why the organ will still run with the reversed phase. First, even if the blower is running at half its normal efficiency the instrument will still get sufficient pressure to play because all the blower does is inflate a "bellows" which is what gives the pressure and the stbility of the wind supply. What would become obvious is if there was a sustained crescendo with the biggest pipes and stops pulled because at half efficiency, the blower would not be able to sustain the wind supply required.

More worrying is that these fans are secured to the motor shaft with a large threaded nut. This is normally tightening itself as the motor runs, but with the motor reveresed, it is probably unscrewing itself and could come off the shaft at any moment. If it does, the force will wreck the fan and could do damage to other parts of the instrument.

Watch this space - especially as we have a visiting choir and organist and the Monk is taking tonights Evensong ......

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