Fig. 1 The Revometer as removed from the line shaft. The needle had been stuck at 90 RPM for many years…
As an enthusiastic engineer, I’m always looking for interesting projects from which to learn or otherwise expand my knowledge. Over the years I have been involved with restoring full size railway locomotives, building miniature steam engines and designing multi-material kits for other hobbyists. The associated challenges and frustrations are, I am told, character building but sometimes one picks something a little odd to “have a go at…”
Amberley museum in Sussex is a delightful 36-acre outdoor museum that showcases and preserves rural, transport, industrial and communications history of the south of England. Located on the site of a former quarry where from the 1840s to the 1960s, chalk was extracted and burnt in kilns to make lime for mortar, decorating and agricultural use it has an amazing collection of artifacts and objects.
One significant collection is the large number of stationary engines. These engines, powered by gasoline, paraffin or diesel, were used in a variety of settings including farms, factories and even houses to provide a local power source to drive machinery or to generate electricity. One exhibit was used to power a sewerage pumping system, and another was used as a prime mover on a large swing bridge. Some were even used to provide a source of power for new-fangled electric lighting in large houses.
Aside from the large engines on site there is a huge collection of associated artifacts including a demonstration line shaft that would have originally been used to distribute mechanical power throughout a plant or factory by means of rotating shafts, pulleys and drive belts. These drive systems were often vast, spanning large factories to drive weaving machines, production tools and anything else that needed a source of rotating power. One challenge of these systems is how to monitor the speed of the drive shaft to ensure it is providing the best possible power to the connected machines.
This is where our Revometer tachometer comes into the story…
For a number of years, the Revometer mounted on our line shaft had remained fixed on the wall but out of action. In all the hubbub and excitement of engines chugging away it was an overlooked item that was just left alone as there were always other more important things to do. Deciding enough was enough I declared to the stationary engine group that I will take on the challenge of repairing said device and get it back to its original glory.
With the written approval of the museum curator, I took the Revometer back to my home workshop for what I thought would be a straightforward repair. The Revometer was not a formal accessioned item, but extreme care was still needed.
On examination I was horrified to see that what I assumed would be a simple drive mechanism was anything other than that. Underneath the dial was a complex set of counterweights that would rotate, operating a plunger that in turn would act against a clockwork mechanism to drive the spindle that rotated the indicator hand. It is a delightful, elegant design to translate the rotating line shaft to the indicator without any electronics – purely mechanical.
Fig. 2 The complex internals. Note the 4 sprung counterweights that act on the plunger which in turn drive the clockwork mechanism.
Like any repair on old equipment less is more and I was hoping that a simple repair would suffice. But as I dug deeper, I realised that the plunger mechanism had sheared off and it was impossible to repair without further dismantling. I even designed some 3d printed components hoping they would be a practical but inauthentic fix but access to the internals was impossible without a lot more dismantling.
Removing very tightly fixed screws and bolts in an old piece of machinery is very difficult. This time it was made worse due to the difficulty of accessing screws in such a device short of space. It was also clear that, horror of horrors, someone else had tried to repair the device before me and a number of the screw heads were damaged making removal even more difficult. Thankfully the judicious use of heat and years of experience managed to get them extracted.
The Revometer was finally disassembled and the broken parts identified.
Fig. 3 The broken drive pin that should operate on the clockwork mechanism
At this point I had three choices – 1) put it all back together and pretend that it was always designed to show 90 RPM even when disconnected, 2) manufacture a set of replacement parts at home, 3) try and contact the original manufacturer and see if they could help. I was all set on option 2 but was persuaded by one of the other volunteers to try and contact the manufacturer, so I took options 2 and 3 in parallel!
With a bit of internet searching, I was able to track down the manufacturer Foundrometers, based in Leeds. In 2000, Foundrometers was taken over by RHEINTACHO Messtechnik GmbH of Freiburg, Germany and now offer a range of sophisticated speed measuring devices for modern industry.
I sent an email believing I was on a fool’s errand and got back to making the parts in my workshop.
Well blow me down.
Almost by return I had a delightful email from the managing director of Foundrometers, Darren Cheesbrough. Darren was extremely helpful in guiding me on the repair, even offering to undertake the repair free of charge to help the museum. I decided to carry on with the repair work and Darren very kindly provided, free of charge, the replacement components that were needed.
After a few hours work it was finally reassembled and much to my amazement actually worked.
So, what of the history of our Revometer? Darren offered to do an archive search based on the serial number on the clock face. It turns out, that despite our thoughts that the Revometer was pre-war it was actually just under 60 years old.
Fig. 4 The original Foundrometers order form alongside the Revometer catalogue entry. It seems this Revometer was originally supplied to the Sevenoaks Brick Works. Note the date – 24/5/68
The repaired Revometer was mounted back on the line shaft with a machined drive pully to provide the correct gearing ratio between the drive mechanism and the device.
What did I learn from this experience?
First, you can never stop learning and the great thing about museums such as Amberley is that volunteers get opportunities to expand their knowledge whilst contributing to conserving our industrial heritage. Second, it’s always worthwhile trying to contact original suppliers as they may be interesting in supporting heritage projects.
And in this case, we struck really lucky.
I’d like to acknowledge the support given by the following;
- Darren Cheesbrough, Managing Director of Foundrometers.
- The stationary engine team at Amberley for their wisdom, humour and insights.
- The curator and staff at Amberley Museum.
