Question in relation to this: I have a vacuum controller that reads in percent relative to ambient pressure. So you can set it to pull i. e. 98% vacuum and you always have 20 mbar regardless of ambient pressure. Is my thinking correct?
No, if 98% of the ambient pressure your absolute vacuum will change. There is no need to regulate the Vacuum in infusion, you have to make sure that your absolute pressure is below 20mbar.
Use a gauge that measures absolute and not relativ.
For the DIY guys, who hate spending money…
I was into cars before composites, so,I’m using an automotive map sensor (manifold absolue pressure) that I picked up at a junkyard. dirt cheap, (5 bucks complete with wiring pigtail) the voltage output vs pressure is a linear relationship (easy to figure out calibration curve) and the resolution is VERY sensitive as it’s the primary sensor for emissions/fuel control. So if you already own a multimeter and can adjust your brain to read V instead of inHG it works a charm.
As I pay some 9 euro for a simple (relative) vacuum meter, I am not tempted to try something else.
The membrane of a relative meter is positioned between the measuring space (where the pressure is that you want to measure) and ambient pressure.
The membrane of an absolute meter is positioned between the measuring space, and a container “containing” an (almost) absolute vacuum.
Any links to what you use Herman?
See page 14 of this catalogue. But I see I did not even bother to put the really cheap plastic ones in.
http://www.brandscomposiet.nl/products/documentation/n/B52%20Werkplaatsinventaris.pdf
I’m not a professional of infusion. I make my own system with a thomas vacuum pump and whith a piece of PVC tube like a enclousure, for my first experimental projet I’ll use a cheap vacuum gauge. Later I’ll buy better quality products.
The Thomas vacuum pumps only create a vacuum with a absolute pressure of about 150mbar. That is not enough for infusion!
what is the correct vacuum pump for infusion?