Looking for some components (pneumatics) - Page 1
Forum section: electronics / projects

author: 97hilfel
author_rank: Regular Contributor
timestamp: August 27, 2020, 06:00:00 am
content: Hello everybody,I'm looking into making a more "advanced" version of a weed sprayer (see image in attachments, stolen from random amazon listing, just to give a generic idea) which uses a manual pump to pressurize the tank and push the fluid out through the nozzle.I was wondering if there are very small pumps, that get 12-18-24V power and could pressurize the tank to approx. 1-2 bar over air pressure (its a total of a 15-20L volume partially filled with water/other chemicals).Additionally I was wondering if there are air pressure switches like thermal switches that would basically provide a security to not over pressurize the tank similar to how a standard air compressor works.I was thinking of powering the whole thing with an RC LiFePo battery or just a Makita 18V battery.I hope I'm in the correct forum and thanks for any hints/help!

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2020, 07:13:31 am
content: the switch you need before you do anything is called a pressure relief valve. They come preset to open at some particular pressure specified in PSI

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 28, 2020, 09:29:03 pm
content: Small 12V compressors for inflating car tires can be bought for reasonable prices, but these need 10 to 20A to run "smoothly" (Depending on pressure, of course). With compressed air you store a lot of energy in the tank, and that energy has to come from somewhere.Over pressuring a tank is a pretty dangerous business. Sudden release of the energy in a tank is similar to an explosion. The normal solution is to have at least 2 mechanisms to pevent this, 3 is even better, and also common.The first is some pressure switch, which is a common component. If you want to do it electronic, then those often used car tire pressure meters can be hacked. Add an uC with ADC to measure it's output, maybe some signal conditioning. Again, for extra safety, calibrate the rate of change, and shut the thing off if the uC detects a rate of change outside certain boundaries. This can be a loose wire or a faulty sensor. With a uC a maximum limit on the run time is also simple.The second is a mechanical over pressure vent system. This is likely already implemented in such tanks. If pressure gets too high (for example fill a tank in a cold basement and then leave the filled tank in the sun) then the valve opens and releases excess pressure.Third safety is a compressor that is simply not able to over pressure the tank. So even if for example a relay gets stuck, the compressor keeps running but won't put additional air into the tank above a certain pressure.Over-pressure should be handled with caution. Watch some exploding car tires or airbags on youtube. Rescuers have been killed by airbags going off while attempting to rescue a driver.With a mechanical pump you have feedback of the pressure in the tank. With an air compressor, adding a gauge to see what pressure is in the tank is a good idea.

author: sokoloff
author_rank: Super Contributor
timestamp: August 28, 2020, 10:44:33 pm
content: If you're trying to make something like this, you might just consider buying it ready-made:Chapin International 63985 -I got one about 2 years ago and it's awesome. Uses the same battery packs as my cheap cordless drill and string trimmer, sprays over 20K square feet on a charge, is easily filled and has a variety of tips available. I can spray much more evenly than previously when trying to manage a manual pump sprayer, the pressure of which was constantly shifting.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2020, 10:53:52 pm
content: yea i got one too actually

author: 97hilfel
author_rank: Regular Contributor
timestamp: August 29, 2020, 05:03:58 pm
content: I was hoping to diy one of these on a budget, but I should look around if these exist here in Italy already.

author: 97hilfel
author_rank: Regular Contributor
timestamp: August 29, 2020, 05:12:29 pm
content: I should add:These tanks usually have a mechanical valve that prevents overpressurization.the 1-2 Bar figure was just a basic number that I assumed would not overpressurize the tank, additionally I wanted to add the pressureswitch, ideally without having to add a uC.

author: wizard69
author_rank: Super Contributor
timestamp: August 31, 2020, 12:57:14 am
content: Quote from: 97hilfel on August 29, 2020, 05:03:58 pmYou should be able to find them. Chapin is made in a city (town) several miles from where I live, that are known to ship world wide so I'd imagine there is an importer someplace. They have been going as a business since 1884, I believe, so they must be doing something right.