Look up manometers. They are dead simple to make, no electricity required. I have a configuration in mind myself - it would tolerate lots of evaporation and allows easy reading of multiple vacuum points:
Basically it’s a ~1 gallon reservoir partially filled with water and mostly sealed off from air (leave a small weep hole). The reservoir needs a clear window on one side so the water level can be viewed.
Then connect clear plastic tubes to the bottom of the reservoir (so the water flows into them). Simple 3/16 in aquarium lines will work perfectly fine and the needed water tight connectors are easy to source. Bring the clear tubes back up in front of the reservoir’s viewing window so that the relative water levels can be checked against each other. At this point the water line in each tube will be the same, but connect the free end of the clear tube to a pressure difference and the water level will be pulled up or pushed down relative to the reservoir. For gasifiers you want negative pressure everywhere so the reservoir will be the low base line and vacuum on the sense lines will pull the water in them up (pushed down is bad!).
Be sure the clear tubes rise well above the reservoir before heading off to whatever pressure you are trying to sense. This should be obvious, but if the tube doesn’t have that elevation along it’s path the water will just run out.
You can make some upgrades with styrofoam beads or a layer of mineral oil for evaporation control but not really needed. The reason to have the reservoir big is so evaporation is small relative to volume of water. That keeps the reservoir level relatively constant, but some “topping up” will be needed from time to time.
If you are sensing pressure somewhere “hot” you’ll need to protect the cheap tubing from the heat with something that can handle it. A length of copper tubing would work to handle and shed the heat. Silicone tubing might work as well if the temps are low enough.
Even if you have a fancy electronic system, a simple manometer is a good backup.
Right - you found the manometer’s Achilles’ heel. It wouldn’t work well in a truck that is jostling around.
In a sense “manometer” may still be useful. The classic water tube version measures small pressure differences, which is sometimes hard to find in the wide world of pressure gauges. That same market is served by modern “digital manometers” covering a similar range. They don’t use water so are immune to road bumps. ~40 bucks or so on Amazon with a nice digital display. At that price I’d think twice before heading down the DIY route.
Vlad - those are perfect. $11-12 in small quantities from Digikey or Mouser for the US folks that don’t want to wait for Aliexpress shipping. The output signal is easy for a microcontroller or such to read, but that still leaves you a good distance away from a finished product.
Thanks for info on makeing diy vavuem readers, im not all that great at electronic conversions, though i could build if price gets any higher.So far i found the shelf ones at i think 25 bucks, not too bad, and dont really need them other than too find an inturnal leak if loss of proper vacuem conditions, mostly a unnessisary conveeniance.
Hwew’s my approach to reading a bunch of stuff including pressure/suction for my woodgas experiments:
I do use a simple U-tube manometer to double check gauges and to calibrate electronic sensors from time to time. All you need is a ruler and some clear tubing to make one. i got my scale free from Allpowerlabs several years ago.
Does anybody else have trouble locating the correct range of gauge for our kind of work? I know that I do. I have to refer to my own conversion chart from time to time. You have psi, inchWC, ounce/sq. in, Inches-Hg, mm-Hg, Pa and kPa, Bar, and even Torr and Micron, etc…
Hi pete i have an onon 3500 old school motor with no generator, just woundering what size generator that motor will pull with charco gas ? maybe 1500 watt ? continous.
Hey Rindert; Vacuum gauges is a pretty important subject for gasifier. Could you go into a little more detail about these little gizmos . I read about one that would measure 0-40 kPa which I translate to 0-160 in. H2O. Obviously enough for woodgas work. You show the tubes coming from the various locations on the gasifier. They plug into a “circuit board”. What is that??? Four (?) wires go from this board to, I assume each post of a four position switch. Then a wire or two must go from the 4p switch to a gauge-- volt, amp, ??? Where is the power (+/-) for this. Sorry for having to ask, but electricity is kind of “black magic” to me. I think this system may have a lot of potential for wood gasser’s. TomC
HI Pete,Thanks for all the scale measurment dident know there was so many different vacuem type. THE WC or water coulum, i gess is the one that is sensitive enough for wood gas measure vacuem.
Hi Jan,
I would try to use something very cheap, like this for the final system in your truck. Really there are many of this kind of things you can find in scrap.
A multimeter, like the you showed us will be very useful for setup, calibration, testing… I have one like that. I use it at least once a week.
Tom,
Do not be sorry to ask. If you don’t ask you will not learn.
The little pencil sketch I made is just to show a logical system, it does not show every wire.
A printed circuit board is perhaps better called a ‘printed wiring board’. There is a learning curve involved but after you have gone through it. Making these things is quick, cheap and easy. I think Antony Cartwright really does a good job of explaining.
Rindert
Jan,
Yes you are right. But, I think I can make those sensors measure both pressure and vacuum. You can see the small brass pieces in the picture. I am going to glue them to the backs of the sensor, in place of the square covers I removed.
Here you can see an old style gauge I modified so that it will measure both pressure and vacuum.
Rindert
