Re: Fogging Tachometer / Hour Meter

Posted by dgoddard on October 17, 2015 at 22:17:27 from (104.245.136.182):

In Reply to: Fogging Tachometer / Hour Meter posted by dgoddard on October 13, 2015 at 15:03:03:

Ok so I sort of promised you some pictures.

This is the tachometer/Hour-meter unit. It is 2 inches in diameter.



As mentioned previously I decided to go with putting in a vent hole to prevent the vacuum from damaging the unit. To do that I wanted to be careful not to damage the insides and since it is a permanently sealed unit I decided to be careful so I did it like this:



Ok it looks a bit like overkill but this way I could mill into the housing 0.005 at a time and be pretty sure I was not going to damage something internal.

This way I was able to make a vent hole just where I wanted it. The results look like this.



Next was the water removal in my vacuum chamber that I made.



I put the Tach/Hr-Meter in the chamber and drew a vacuum. As I drew down the vacuum I suddenly could hear the water hitting the Bernouli effect venturi When I pegged the meter at 24 inches of vacuum (It may have been even more than the gage could indicate) I pinched the hose with the vice grip pliers. A half hour later I came back and had not lost any vacuum. I vented the system and hammered the end cap off. The assembly had given up some of its water and was cold. I figured that drawing the vacuum had a refrigerating effect which caused partial water retention. So I set the assembly in front of an electric space heater and in 5 minutes it was getting too hot to handle. I repeated the vacuum process and this time I really heard the water coming out. (a sort of muffled slurping sound after the vacuum was getting down part way). I let it draw down the vacuum until the slurping stopped and then it pegged the meter again. I pinched the hose and left it for an hour this time. Again no vacuum loss. I vented the system and opened it up and the result was completely satisfying. No water at all could be seen any more behind the lens. Both droplets and fogging had cleared. I closed the vent hole with a piece of vinyl electrical tape. I then sealed around the lens edge of the bezel and the case edge of the bezel with clear silicone.

I plan to reinstall it tomorrow and see how it all holds up. If it ever need to be dried again, All I have to do is pull off the tape and repeat the process. Time will tell but I think I have a useful tool here.

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