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Saturday, November 20, 2021

Vacuum Pump Testing Started

 I started testing the vacuum pump to see if it could draw down lower than previous tests.

I was only able to draw about 25 inHg in previous tests.  So today, I started tracking down issues with the vacuum system.  

What I found was encouraging.  See, to be used in a freeze dryer, the pump has to draw down to 600 Pa or lower.  A rough calculation tells us the pump will need to draw down to less than 29.2 inHg.  

Sealing hoses and fittings for vacuum use can be a challenge.  A leak does not manifest itself as a drip, for instance.  It cannot be observed from outside.  Basically, everything is backwards.  

I found the vacuum canister had a design flaw in its fitting port.  I fixed that flaw.  It took some doing, but the seal is now reliable and vacuum tight.

I fixed a few hose leaks and a leaky valve packing.

Sealing most vacuum leaks can be performed like any other leak.  The difficult part is finding the leak.

I used Vacuum Grease to seal threads and hose fittings.  It is designed to do just that.  

I was eventually able to draw down to the limit of the gauge on the vacuum canister.  But it is way better than it was in previous test.  I will have to hook the vacuum sensor up to the canister to get a more accurate reading.

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