Insane Hydraulics
Bold and audacious blog about fluid power
Let me start by saying a few words about the motivation behind this little project. As you already know - I enjoy toying with pressure sensors and transducers, which means that I need a reliable pressure source for my tests. The same goes for pressure switches and gauges.
"In the old times," I would use our shop's test bench for my pressure-making purposes. And it works, but it has significant drawbacks.
First - the practice of having a hydraulic pump at a constant pressure which is often very close to its maximum limit for several minutes in a row is a very noisy exercise in wasting large amounts of power. Very tiresome and unnecessarily expensive.
Second - the pressure is always limited by the max pressure of the stand's pump, which, in our case is 400 bar. While being "respectable", it is still absolutely not enough to test a 600 bar transducer or a gauge.
Lastly - a standard system running as a pressure source will have the pressure fluctuating all the time. Not by much, of course, but still - keeping it stable within decimals of a bar for prolonged periods is impossible without active correction. This may be OK for an on/off pressure switch calibration, but it's definitely not enough to map out a sensor's output to evaluate its linearity.
So, my first hack was the "pressure maker one" (used and showcased in this post). The crude contraption was based on a hand pump - a leftover from an old mine project, and it worked a lot better than the test bench, but it was still limited to about 400 bar, and it required a lot of muscle input and "proper" vice to secure it.
What I needed was a small and more elegant solution that didn't require a lot of physical effort from the user - something I could use in my small and cozy home lab. And another very important thing - I came about an interesting phenomenon that happens when you test closed pressurized volumes at reasonably high pressures (400 bar +) - the pressure, even when there's no leakage, can fluctuate in a very interesting manner (something that I will describe in a separate article) and (again - without going into much detail why) so I needed a pressure making device that would not only allow me to pressurize a volume of fluid to high pressure, but also to accurately "tweak" it in order to "correct" the aforementioned fluctuations, and be able to adjust the pressure in very small increments.
Obviously, there are ready-made solutions - from hand pumps to screw-type dead weight pressure testers, but the new ones are quite expensive. And so I could either hunt something down on eBay or build a solution of my own. Since I enjoy making, I decided to go the DIY route, gathered the "supplies" (you can see them in the video below), and built a pressure-making device of my design.
All the machining was done is a standard lathe and a drilling press. And since I also wanted the "gadget" to look nice, I tried bluing the steel parts using the thermal bluing process - something I had never done before, and I must tell you that I'm very pleased with the result. The parts look great, even with all the irregularities in the colors. I personally think they look even better that way! I'll definitely make a post about bluing - what a fun process!
Now - about the function. Having a worm gear driving the pressure-making stage is very helpful because it allows me to tweak the pressure in the tiniest increments - just as I wanted. I understand that my "pressure quality demands" may be extremely nit-picky in comparison with those of "normal pressure consumers", but in any case - the design turned out functional, and I am very satisfied with it.
The video below "shows it all". I crammed in 20+ minutes of assembly footage, so you may want to play it at 2x speed if all you want is to evaluate the design. Do comment.