Tuesday, 25 November 2014

A new blind for The Great Wheel at Quarry Bank Mill

Last week the Norfolk Millwrights were at Nether Alderley Mill, as described in the previous post. This week they are at our parent National Trust property, Quarry Bank Mill in Styal, Cheshire. Quarry Bank is home to The Great Wheel.

The original Great Wheel was designed by Thomas Hewes and installed at Styal in 1818, replacing three earlier wheels. It was over twice the size of its predecessor, developed around 100 hp, and powered Quarry Bank Mill until 1904 when it was replaced by a water turbine which worked until the mill closed in1959.

In 1980 the Quarry Bank Mill Trust restored the mill, and replaced the turbine with a new Great Wheel. This came from Glasshouses Mill in Pateley Bridge Yorkshire and was almost identical to Styal's original Great Wheel. It required a great deal of restoration including casting of a new main shaft. The new wheel had been designed by William Fairbairn, Hewe's apprentice at the time the original Great Wheel was installed. It has operated at Styal since the early 1980s but recently its blind has developed leaks and needed to be replaced.

The blind is the device which controls the amount of water allowed onto the wheel to fill its buckets. It is rather like a large version of a window blind; attached to a rack mechanism it can be raise or lowered between the pen trough and the wheel (which is of the breast shot type) to vary the water flow into the wheel's buckets. Back when the wheel powered the mill machinery the power required would vary depending on the number and type of machines in use at any time, and the blind, controlled by a governor, enabled it to maintain a constant speed irrespective of  loading. The new Great Wheel no longer powers the mill, and we use the blind simply to turn the water supply to the wheel on or off by raising it to cut off the supply, or lowering it slightly to allow enough water onto the wheel to cause it to rotate.

Recently the wheel has taken to running for short periods even when the blind was up. This is because the blind has started to leak and despite being 'up', sufficient water was getting through to slowly fill the buckets and start the wheel turning. The Norfolk Millwrights were therefore engaged to manufacture and install a new blind. I am a volunteer at Quarry Bank and went along there this morning on my little Honda C90 to see what progress was being made.

As ever, please click on any picture for a larger image.

 The last leaves of late autumn hang over Quarry Bank mill meadow this morning. The weir forms the mill pond behind it to power our Great Wheel, the water reaching the wheel through a series of leats and sluices, to the head race which runs under the mill yard. When the water drops off The Great Wheel, having done its work, into the bottom of the wheel pit, it is considerably below river level. It cannot therefore flow back into the river at that point, but follows a tail race tunnel of about 1/3 mile in length which allows the water to re-enter the river at a lower level, further downstream. 

From November to February the mill is closed to the public on Mondays and Tuesdays, hence the deserted mill yard and closed main reception. The Norfolk Millwright's van and my Honda C90 are the only vehicles in the yard this morning.

 A poster explains to visitors to the mill why the Great Wheel is temporarily out of action (click on the picture to make the text legible)

Inside the wheel chamber the millwrights work in the pen trough, drained of water of course. The blind is in two halves which operate together as one continuous blind, and by this morning the old left hand blind had been removed. The replacement, still rolled up, can be seen above the head of the millwright behind the ladder. 

A millwright positions the rolled-up left hand blind prior to installing it 

Here's a view of the front side of the wheel, which normally rotates left to right in this picture, so the buckets (which fill with water, whose weight turns the wheel) are upside down at the left of the picture and on their sides at the top of the picture. By the time they have rotated to the front of the wheel, they will be right way up to receive water from the pen trough past the blind.   

The inside of The Great Wheel. This picture shows how it's a suspension wheel, just about the peak of water wheel design; they didn't get any better or more efficient than this wheel. 'Suspension' means the wheel and its buckets are suspended from the main shaft by relatively thin spokes, rather like a bicycle wheel. This makes the wheel lighter than a conventional heavy-spoked wheel, and therefore more efficient. The secret of the suspension wheel is to take the power not from the main shaft (which would necessitate strong, heavy spokes to transfer the power from the rim to the shaft) but directly from the rim. The gear wheel which engages with the rim to effect this can be seen on the far side of the wheel.

Another advantage of taking the power at the rim rather than from the main shaft is that the speed of rotation of the drive from the wheel is much higher, much closer to that required to drive the mill machinery; conventional water wheels require more gearing to raise the slow speed of the main shaft to the speed required for machinery operation, and this reduces efficiency.  

The new left hand blind, made of buffalo hide with steel strengthening, is readied for positioning. Temporary straps hold it in a rolled-up state, and when these are removed it will unroll and hang like a curtain, ready to be fixed to the metal frame which will raise and lower it. The shaft above the blind and the toothed metal racks in the centre of the picture are part of the raising and lowering mechanism for the blind. 

Entrance to the side of the wheel chamber, closed to the public for the duration of the work 

A view down into the wheel pit showing the as-yet rolled up blind. The large stone weight in the foreground is used to counter-balance the blind, to minimise the physical effort and strain on the rack and frame mechanism to raise the blind. There is a similar counter-weight for the right hand blind. 

Here the blind has been allowed to unroll, and is ready for fixing to its frame 

Here is the old blind, cut into sections to make it easier to remove 

There was plenty of other activity around the mill this morning, mostly concerned with decorating the premises for Christmas. Here a Christmas tree opposite the head gardener's house is dressed.

Next week is the volunteers' Christmas lunch at Quarry bank. Before tucking into that, I'll nip across to the wheel chamber to see how the millwrights are progressing with replacement of the blind. By then, they might even have finished and gone!


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