Progress on the Boulton and Watt Part 2

Progress on the Boulton and Watt Part 1 available here

Well it was predictable that whatever our plans were the virus would probably throw a spanner in the works, and it has taken longer than we hoped to deliver the first step in the Boulton and Watt restoration. But the new steam valve, fresh from the casting pit and gleaming in its blue paint (which will probably be replaced in due course with a more historic dark green) has arrived at the Museum. It is not a cheap item but thanks to the generosity of our donors it is top specification and fully paid for, without any impact on the main Museum finances.

The new valve in its very solid packing case


We were warned the valve was coming. But in the best traditions of doorstep deliveries the packing case appeared in the car park out of the blue. Fortunately it was well disguised in wrapping, and was a little large and heavy for all except the strongest porch thief!

Out of its case and with the traditional “mug” scale. We will be replacing the modern handle with one a little more in keeping with the engine house.


We are now looking at the remaining work needed to the main steam line. Whenever the Museum’s steam engines are run they have to be thoroughly warmed through first, which requires trickling a low volume of steam through them. This has always proved something of an issue; it has usually been achieved by just cracking open the main steam valves, but this is bad practice and may indeed have been responsible for the failure of the previous valve in the Boulton and Watt house through wire drawing (the erosion of the edge of a valve leading to a leak). For this reason we have a long term policy of installing smaller (typically one inch) bypasses and valves to allow warming through to take place while the main steam valve remains closed.

The Museum does not have immediate access to a coded welder and in any case a more satisfactory job can usually be done in an appropriately equipped workshop. So progress on this modification on larger engines has been slow. But the planned works to the Boulton and Watt have now provided an opportunity to make such an installation. This has arisen because of the need to take up some slack in the Boulton and Watt steam line.

The new valve is thinner flange to flange than its predecessor. Normal practice is to take up the gap with a “bobbin piece”; a short length of pipe with a flange at each end resembling, on a much larger scale, the bobbin from a sewing machine. Ideally we would incorporate a takeoff for a bypass line in the bobbin piece but this would be very difficult to do because the bobbin piece is very narrow indeed. However there is already a short section of pipe elsewhere in the Boulton & Watt steam line, installed as part of the original restoration of the engine. So we are now looking at taking this out and replacing it with an extended bobbin piece by the new valve. This will keep the number of flanged joints the same and allow the insertion of a takeoff for the bypass in the new bobbin piece. Better still the new bobbin piece and fittings can be manufactured off site and delivered complete and ready to bolt in. But what about the other end of the bypass? Well we already have a takeoff fitted in the existing pipework so there will be no need to bring a welder on to site at all and the new arrangement should be entirely acceptable to our insurance company. Our onsite contractor Century Millwrights is currently working on the necessary construction drawings and we will then be seeking tenders for the work for which we have provided a full contingency in the project budget.

We all hope that the Museum will be reopening to visitors and volunteers soon, though it will not be business as usual as we are still working out what the new normal will be. This good news about the Boulton and Watt does not mean that everything is rosy in the wider Museum landscape. The staff and Board are working very hard to ensure that the Museum can keep going through 2021 but we still need all the support we can get. After all there is no point in having a fully repaired Boulton and Watt engine if the Museum is no longer in a position to open to visitors. So while this project is fully funded we can put any further donations to the Museum to good use.

Oliver Pearcey

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