Jonathan, I've just been down the shed and dug the old valve and the new valve out. The old one is 1 and a 1/2 inch and the new one is 1 and 3/4 of an inch. Then I had the light bulb moment. I remember now the 1 and 1/2 inch came with an old set of governors and was not the pattern. I remember now I was loaned the original blue prints for the Pickering steam governors including valve and seats which I was allowed to copy. I must of given Dave a copy and then he cast me two valves. I then gave them to John who machined them up and also made the seats. Dave must then have the pattern he made off my drawings for a 1 and 3/4 inch valve. I have just taken a photo of both valves, side by side if it helps.
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