Such an easy thing to have got right at the point of manufacture by making the spindle a little bit longer and with a shallower taper.ġ out of 10 I would have rated it. I already admired some aspects of the design and build, but the lack of a controllable output let it down badly. My conclusions about the Prim Compact? Some work on it has turned it around in my estimation and it’s got the potential to become a good performer. Thanks again to Gieorgi for his contributions to this project and, behind the scenes but we had a chat about it off-forum, to Reese ( hill bill) who also concluded that a shallower taper to the spindle would achieve the elusive simmer. Valve spindle flats now more evident thanks to optimised spindle length. New graphite packing, fuelled up and fired up with the results you’ve seen. Visible is a burnished ring defined by the mating surface in the valve block. I installed it in the valve and rotated it a few times with the control wrench to help it bed in. I popped it back in the drill chuck and shortened it a fraction to arrive at the optimum length. Finishing is done with a fine hand file on the rotating work.Ĭutting a length off the tip of the new profile I drilled a hole in it’s mating surface with the Prim spindle onto which I ‘turned’ (electric drill technique again) a projection to fit the hole - providing a positive joint to prevent movement when silbrazing the two together. I used a technique I’ve used often for small components like this of clamping an electric drill horizontally on a bench, clamping the spindle in the chuck jaws and with the drill set to a low-ish speed, getting a Dremel abrasive wheel to work on it to ‘rough out’ the profile. So, no excess of material on the existing spindle on which to form a new tip profile, given that in doing so, a shallower taper would make the spindle disappear more into the valve.īelow, (bottom in the photo), the tip profile I want, formed on the salvaged Optimus spindle. Telltale is how the spindle’s wrench flats only just emerge in their entirety from the packing nut when the valve’s shut. It also demonstrates the excessive size (around 2mm diameter) of the fuel outlet the valve spindle was asked to regulate. The blackening of the tip of the Prim suggests some blow-back of vapourised fuel-borne carbon from a slightly rich mixture. Profile of the Optimus spindle tip clearly a much shallower taper than the Prim one on the right. I’d kept an Optimus regulator spindle with mangled rack pinion teeth for jobs such as this. Easy to dial in, reliable output with no pulsing or flip into underburn. Pump strokes on 2/3 full tank, so well-pressurised.Ī medium setting, probably the ‘go to’ setting for boiling a kettle of water rather than the crazy max billowing flames up the side of the pot and wasting fuel.Īt last (trumpet fanfare) a decent simmer setting.
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