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John Larson


I haven't posted a blog since mid-December. The 75 mentioned then has been completed some time ago and is awaiting somewhat better weather for delivery 40 miles up the road. I did receive the order for a 125 and I will be starting on that about Feb 16. I have also been building a special 125 for myself to use in R&D. It uses a custom 4" bore cylinder with internal modifications to improve air flows. It uses a 13" hammer head stroke instead of standard 11" to help me determine later in the year whether or not the steam hammer-like valving is more beneficial with more air space. It ought to be. In any case its early operation with standard back pressure throttling shows that its new-to-me ceramic five-port valve (with 40% better flow potential) in conjunction with the cylinder flow potential provides beastly top end power with traditional Iron Kiss control at light treadle.

The hammer design is a thought extension of the work done in August-September-October where a second throttle valve on the inlet air was tried. Now I am using tie rods from the treadle to external throttle shaft levers on each side--one for exhaust throttling and one for intake throttling. This surmounts the complexity of running two valves with one throttle shaft and allows readily converted linkage to intake-only, exhaust-only, or both intake and exhaust throttling. Intake-only throttling uses less air to run any utility hammer, but then exhaust dumps to ambient. This provides a rather clunky behaviour at die contact such that planishing blows are sub-par compared to exhaust-only throttling where the treadle tends to determine the degree of pressure drop across the cylinder ports upon reciprocation.

Some people decry back-pressure controlled utility hammers for their air compressor requirements in contrast to in-flow controlled versions. Point taken. Part of my tedious R&D program is learning how to merge the two approaches.


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