My goal in mcgyvering a vacuum pump was to remain under 100,-€ – which I did – and get better results than I have achieved with my shop-vac setup – which I did too. Still, I do not know whether to be disappointed or satisfied.
I wanted to utilize things that I already have, which includes several water pumps that are used to water bonsai trees and vegetable beds in summer and pumping water out of the cellar in the winter and some spare piping from house renovations. So I had to buy only the things for making the vacuum pump itself – in combination with a water pump, the best option seemed to be something based on the venturi principle.
So I went and bought these parts:
© Charly, all rights reserved. Click for full size.
The parts were connected to each other more or less in the order as they are laid out on the picture. The black plastic hose connector was fitted into the brass one to lower its inner diameter. The brass hose connector right next to the right side of the chrome T junction is the inlet nozzle – I have glued an old tip from a silicone sealant tube (not depicted) in it to get the position and size of the nozzle correct. Into the upper brass hose connector was glued the white plastic 6 mm hose connector for the air suction.
So water comes in the T-junction from the right, gets squeezed through a nozzle which sprays into a slightly bigger opening in the outlet left, behind which is again a big pipe. The spray drags with it the air surrounding the nozzle and that way achieves suction through the top of the T-junction.
I am not able to write-up complete how-to, but this is the final product up and running in a vat of water.
© Charly, all rights reserved. Click for full size.
The bubbles show it is working. When I connected the suction tube directly to a new vacuum manometer, I got a suction of whopping 0,6 bar, which did really impress me. Unfortunately, I do not get anywhere near that when I connect everything to the jar. After a few minutes, it stabilizes at this.
© Charly, all rights reserved. Click for full size.
0.22-0.25 bar is still a bit more than what the shop-vac could achieve (which was 0.2). So it is usable and it is a definitive improvement because unlike the shop-vac it can run non-stop with zero risks of overheating anything, and it also makes nearly no noise, so a win there too. But when it achieves this, it still bubbles, so it still draws air. And when I close both ball-valves on the lid (one ball-valve is for pressure release, one for the suction), I start losing pressure in the jar really quickly. That tells me that the jar is not properly sealed and this here is not the maximum this setup can achieve, but an equilibrium between the pump and the improper sealing.
I had to make a new lid from five layers of plywood for this, with two ball-valves and the manometer, so there was a lot of potential for failure. But I did use water/airtight plastic sealant for everything and I went over all connections once more, yet I still cannot identify the leak(s). If it was a pressurized container, I might find the leaks with help of soapy water looking for bubbles, but I do not know how to check vacuum tightness.
So this is where I am now and this is where I leave this be for a few days at least. It has occupied me for three days already, time to go back to making knives.
Perhaps you could blow air INTO the otherwise sealed and not running setup and use the soap trick? Airtightness is bidirectional.
@abbeycadabra, good idea, but I do not have a way to pressurize the system in any meaningful way and I am afraid the jar might explode if I did so. It is constructed to withstand vacuum, but not to be pressurized.
I’m always impressed with your ability to make such things. I wouldn’t even know where to begin. So, yeah, once I get to clean up the cellar a bit more and finish the degu cage, I’ll probably get a vacuum pump for the resin. Though, when watching YouTube videos, I think often their problems are being v impatient and clumsy, because they stir so much v air into the resin, it’s incredible.
Oh, that looks like such a cool idea. I once engineered the manfacturing for a venturi tube used in the gas-pump vapor recovery system hoses to recover condensed fuel vapor. I hadn’t thought of it as a vacuum “source”.
I went browsing for fittings a bit and found this hot-tub part for $25: https://www.spa-daddy.com/Ozonator-Venturi-Injector-AQS715-sd.html. I wonder what it would pull?
@2 Charly
You don’t need a LOT of forward pressure, just barely enough to leack and cause bubbles. Duct-taping a hose to the blower on the shop-vac should be plenty, no? Heck, blow up a balloon and tie that on.
There are venturi vacuum generators, which work by blowing compressed air over a needle. They are dogawful loud tho.
Dunk the jar assembly into a bucket of water with a little colouring agent added,you’ll soon see where it’s getting in.
Also since it does not need to be fast, there are $20 vacuum pumps to be had, called “brake bleeder” -- they pull pretty hard!
@Lofty, I think that could work, I will try that once the lid is fully painted and waterproof.
@Marcus, from what I found about brake bleeders on sale here, they are powered either by hand or by compressed air. Neither of those options is workable for me.
I will probably buy a proper vacuum pump at some point when I had enough fun and need to get serious, but those prices are really prohibitive, with the cheapest 100,-€ -- and god knows how long that piece of crap will last. I will still need to solve the problem with air-tightness in the jar though. The various receptacles on sale for these things cost often over 100,-€ as well.
I have an inexpensive Chinese-made vacuum pukp that cost $100 and has provided excellent service for 10 years. So that comes out to $10/yr for vacuum.
The hand pumps are a pain and are awkward but then so is what you are doing :)
@Marcus, that is encouraging info, I have my eyes on a vacuum for 100,-€, China-made. If I could get at least a few dozen knife-handles out of it it would certainly be worth it.
What I am doing here might be awkward and a pain, but building something out of common items, testing it, and tinkering with it is also challenging and rewarding fun. Plus building your own device has one indisputable advantage -- when something breaks, you can fix it. And since this device has no moving parts, it is unlikely to ever break.
Buying a hand-pump and then spend several hours pumping has neither of those things. It is only awkward and a pain.
But from a purely utilitarian point, building my own belt grinder, which starts at over 1.500,-€, or strong burner, which is not sold here at all, was much better use of my time than building this. On the other hand, at this moment I have a lot of free time, but the money is a finite resource and I need to be careful with it. Times, when I could just go and buy something without examining the price-tag too closely, are a thing of the past.