Dibnahs update, spring 2025 By the Dibnahs

Robin Nicholson had been pleading for working brakes on the mini-tractor for some while. Hill descent had become far more scary than going up Shelsley in his Mallock.

His prayers have been answered.

We painted the ornate metal debris guard (within the pond) with bitumastic paint,. This job caused a bit of mirth as, in order to paint its innards, Tim Jessop was lowered inside – looking for all the world like some poor, forgotten wretch dropped into an oubliette.

Thanks to many MAC members (notably, Cathy Warner) who donated various hardware and workshop items.

We’d been aware for a while that a large foreign body was stuck in the cast-iron penstock box immediately above the waterwheel. The box’s front houses a vertically sliding metal sluice gate that can be raised or lowered (by a wheel inside the mill) to finely tune water flow going over the waterwheel. The whole front of the box was therefore removed, enabling us to fish out the obstruction - quite a significant lump of tree.

The mechanism for adjusting the sluice gate had not been serviced since about 2010 so, despite the cold, John Townley stripped and refurbished its numerous levers, clevises, pins and threaded adjuster.

Storm Bert’s aftermath delivered us a bit of a shock. A pair of inquisitive Dibnahs went to check the empty pond one Tuesday, to come rushing back hollering “You’ve gotta see this!”. Our 26 tons of distinctively black puddling clay (piled up against the dam wall) was all but invisible, having been coated brown from bottom to top by a tsunami of silt.

In addition, the stream’s usual inlet, via the stepped waterfall to the left of the pond, was bone dry. All the water was now entering the pond on its right hand side. Investigation showed that very heavy rain had caused a major silt-slip into the stream, higher up the hill. This resulted in total blockage of the 30 foot long, 18 inch diameter pipe which takes the stream towards the stepped waterfall. The surrounding sunken valley area was buried to a depth of 2 to 3 feet with fresh silt.

This must have led to the formation of a huge pond of pent up water which presumably let go when pressure finally overcame the blockage in the additional, higher, and equally large, overflow pipe. It must have been an impressive sight when it went as the silt tsunami covering the black clay climbed all the way from the pond’s base right up to the top of the dam wall, some 12 feet higher. Our more active brethren therefore spent most of that Tuesday digging down to the normal pipe, clearing away jammed-in debris as best they could and letting water flow do the rest. This was followed by shifting and carting away all the silt from that general location.

Our large Petter “M” engine (1937, two stroke, 6HP at 720rpm) hadn’t been running right for a while. It was very difficult to start and ran rich when it did, so its spark plug was always sopping wet. It’s a low-compression unit, designed to run on TVO (Tractor Vapourising Oil) which is effectively paraffin to you and me. Hands up all those who remember back to the cartoon adverts featuring “Joe, the Esso Blue Dealer”, with his choir, singing “Smoke gets in your eyes” - as a warning to anyone NOT using Esso Blue paraffin ! The Petter however, can only be started using petrol. This particular money-saving dual-fuel idea finally fell out of favour in the UK around 1974, largely replaced by ever more diesel engines. For many years though it was a staple of powered agricultural machinery, paraffin being a lot cheaper than petrol. The Petter’s fuel atomiser was smashed off before we got it (it sits in the cylinder wall’s inlet port, 1/16th inch away from the reciprocating piston), so it now has a grub screw with a hole drilled through it !

Some years back, David Haggerty engineered an exact replica of the complex, original, brass atomiser-block, using specifications found on the internet. We’ve tried David’s unit in the “M” twice, but it refused to run, possibly requiring more fuel pressure to operate than a mere hole through a grub screw ! There is no reason to doubt David’s excellently crafted atomiser, so we have been looking at the paraffin pump. This wondrously simple affair relies on crankcase pressure changes (at every piston stroke) to actuate a thin, six inch diameter, spring-steel, pump diaphragm. When stripped, it was gummed up, but cleaning it and fitting new gaskets resulted in a gusher of paraffin.

Regarding the mill’s on-line presence, David Siviter kindly agreed to take over running the mill’s Facebook page from Richard Gallé.

We reconvened after Xmas on 7th January and promptly discovered the empty pond had again suffered from exceedingly heavy rain. A fresh layer of debris was in evidence along the stream’s run and throughout the pond basin, such that the old pond drain had partially blocked. The water arriving was thus way more than that escaping, so the pond completely filled (until the rain ceased), resulting in much detritus being washed over the dam overflow into the chamber beyond. This had then backed up into a mini-mountain behind the tunnel-guards in the courtyard mill race, completely demolishing the bars of both guards.

Two further days of digging out ensued.

Our new penstock and sluice arrived on 14th January

Being a very heavy and substantial stainless steel construction, it caused the delivery driver much grief unloading it, despite his truck being equipped with a hydraulic crane. We were the human “lifting tackle” that would be manhandling it into place, so we stripped off its two side cheeks and sluice gate to lighten it, leaving just the one-piece back and base. Following a lot of very chilly, submerged chainsawing, levering and hammering, the old wooden drain-plug box (nicknamed “The Coffin”, as it greatly resembled one) was out of the pond.

At this point Tim spotted something glinting in the mud where the box had been. It turned out to be a small glass vial, complete with ground glass stopper, containing a tablespoonful of gleaming liquid mercury. Amazingly, it had survived for at least 175 years, including our recent digging and crowbarring all around it.

Our earlier foresight in test-fitting a wooden mock-up of the square section outlet-pipe through the dam wall meant we were now OK to go ahead and lower all four of the heaviest stainless steel penstock carcass sections into the pond and commence fitting the thing.

This actually took us two goes due to three bolts shearing, necessitating a drilling/re-tapping job ready for a rematch the following Tuesday. Finally, however, the outlet pipe was successfully bolted to the penstock’s back-plate and the whole heavy, ungainly assembly rotated through 90°, then dug and levered into place. This was much harder than it sounds.

It took five Dibnahs plus millwright Adam and Andy from Costwold Penstocks several hours to pull, push, lever, jiggle, cajole and heave the penstock into place against the dam wall, with the outlet pipe protruding into the dam overflow chamber on the other side. Many more days were spent fitting penstock ancillaries, bolting and grouting-in and rigging the sluice’s drive shaft mechanism. This latter necessitated re-engineering the drive shaft’s UJs from single to double items, as the operating angle was too acute. Finally however, on 25th February, the pond began to re-fill and the waterwheel was run for 30 minutes to help clear built-up silt away from it. To finish the job off, a strong, galvanised, overflow chamber grid was crafted by Headley and fitted in place on 11th March.

Now the pond is full again the remaining three geese are overjoyed.