Friday, September 27, 2013

Greiner Vibrograf Poseidon LT-100 Service

In our classroom on the casing table we have a dry watch case waterproofing tester.  It uses very cool technology.  Basically, you stick the cased watch inside the machine on a table then bring down an arm with a micrometer attached to it and rest it on the crystal.  The machine then subjects the watch to (in our case) -0.7bar pressure then a +7.00 bar pressure.  If the micrometer senses the watch case deforming, and remaining deformed you know there is a pressure differential between the inside and outside of the case and it is water tight.  If it does not deform, or does slightly then returns to normal, then you know there is a leak somewhere.

We were having an issue with the vacuum -0.7 bar test on our machine.  It would only work sometimes and we were wondering why.  So I emailed the manufacturer and got a call from the service center in California.  They were very helpful and explained some things I could try to remedy the problem.

After tearing the whole machine apart, servicing it, then putting it back together and ending up with the same result I started fiddling around with the diagnostic mode.  This mode which is built into the service program allows you to activate all of the separate valves in the system manually.  I finally noticed that we only achieved enough pressure in the venturi (which draws the vacuum out of the test chamber, using high pressure airflow) when the compressor was running. 

It turns out the air compressor we are using to feed the testing machine is not charging the tanks at as high a PSI as it used to.  Because of this we were only getting one full negative pressure vacuum test before the machine would mysteriously fail the test.  With this information now I can attempt to service the compressors regulator or just make sure to drain the tanks enough to bring the motor back on to provide me with a high enough pressure to run the test.

Regardless of the extra work, I learned a lot about the workings of the machine.  It is well designed, built and very elegantly put together.

The machine in question

The venturi which creates the vacuum for the system using 'Bernoulli's principle' is the plastic T fitting on the left labelled "S". To remove the top plate and test chamber, you must disconnect the input and bleed lines from the back plate,

And the manifold pressure line,

And the ribbon cable and grounding wire

Here you see the valve stack.  They control vacuum pressure, air in and air out

A solenoid case without its electromagnet

Some small metal shaving on the sealing face of the solenoid, this was removed

The solenoid post, core and spring

These were all removed, wiped clean, blasted with air then reinstalled

The final valve assembly

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