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Posted by John Larson, 31 March 2012 · 97 views

A friend who is a veteran engineer in the valve manufacturing industry told me the following over on the power hammer thread:
#2 ptree

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Posted 29 March 2012 - 07:46 PM
John, in industry, air cylinder flow is controlled on the exhaust almost exclusively in every machine I can think of. The probelm with air being compressable is that if you control in, then all the exhaust from the other side runs away, and you build a little pressure in the fed side, the pistion overcomes stiction and moves, the pressure drops as the volume increases and then the cycle starts anew.
I would agree with you to controlling the exhaust

Hydraulic cylinders ARE NEVER controlled exhaust. If you put the rated pressure in the blind side, the rod side being controlled you get a pressure multiplication that can blow seals at the least. Bigger the rod the bigger the issue. In air not a problem as the air is easily copmpressed.


On the basis of this, my anxiety over my way of doing things has been eliminated. That is my test results correspond to his industrial experience. Thanks, ptree.

Today I stayed outta the shop and went to the Fire and Brimstone bladesmithing event just outside the Baltimore beltway in rustic Marriottsville. There were at least five minifurnaces running to convert ingredients into steel. Those blooms were to be transformed as the day wore on into blades. Saw may friends--Sam Salvatti was escorting his new girlfriend :-) --and the rain stayed away. Food was stupendous. Tailgating wasn't too bad. I scored an immaculate manual coal forge blower for a small demo forge that I want to build. Which reminds me, it is my weekend to go down to demo at Jerusalem Mill.

One person who had promised me he was buying one of my 150s when he completed his interstate move told me he had bought another brand. Such is life. Another person said he wants one of my 75s when he scores a big enough job. And yet another couple of guys expressed interest in my old self-contained model built for R&D back in '01 or '02. But nobody has money-- yet. Lotsa favorable comments about the Custom 200 videos. I'm now working with my web site guy to include that footage plus some stills on the site.