Making pressure setting tamper-proof is no easy task.
The Old Timer of Royal Oak, Mich., was a regular contributor to H&P years before we ever even heard of the internet. But most of his advice is just as ueful — and interesting — today.
So rather than leave his wisdom printed on pages archived in our storage room, I pulled out issues from the late 1980s and early 1990s and will reproduce relevant entries in this blog. Here is my seventh entry, which was originally published in the February 1988 issue:
One of our foundries had a complex sand moving system with pneumatically actuated rubber pinch valves to turn flow on and off. The valves operated at 45 psi; with no pressure, the valve was fully open; with 45 psi, the valve fully closed. At higher pressures, rubber bladders could break, mixing air with the sand and fouling the system. That was our problem: the operators always wanted to crank up the pressure.
Our first fix was to set the master regulator and saw off the adjustment handle. The next day, we discovered that the night shift had cut a screwdriver slot into the handle stub so they could change the adjustment. Next, we tried a non-adjustable regulator, only to find it had been replaced by an adjustable model some time during the night shift. A couple of other attempts to lock the air pressure also were thwarted — and, of course, no one ever admitted to tinkering with the equipment.
I finally came up with what was essentially an alarm system. On a high and difficult-to-reach section of the air piping network, I installed a 50-psi relief valve and connected its outlet to an old-fashioned steam whistle. If someone turned up the regulator, the whistle blew immediately and called attention to the culprit.
The night shift guys gave up, but they still had the last laugh. They used the steam whistle as an adjustment guide. When their shift began, they’d turn up the regulator until the whistle sounded, then back down the adjustment until it stopped. That way, they had the maximum pressure that our system would permit.