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My excuses in advance for the probably-bad wording of the question, I'm just an hobbyist without much knowledge in engineering. To the point I can't google for information on my problem since I don't even know the applicable terms... So please bear with me :-)

I want to automatize my DIY ultrasonic LP cleaning machine by adding automatic fill/drain of the ultrasonic cleaner (see drawing).

Pump setup

After the cleaning is done, the ultrasonic cleaner is emptied to the solution tank below; dirt will settle at the bottom of the tank. The cleaning solution has a bit of alcohol in it and is heated during the cleaning process so I want the solution tank to be sealed to reduce evaporation that would change the solution's alcohol/water ratio.

Of course, air has to flow in and out of the tank during pumping or draining, and during cooling of the solution in the tank so I need a form of relief valve? Or is it another type of component, perhaps a kind of pressure regulator? I thought about simply using a valve but that wouldn't be practical as I don't want to have to periodically open the valve during the cooling of the solution to let air in.

I know of two requirements, 1) it has to allow bi-directional flow and 2) it has to work at very low pressure, as the solution tank will likely be a plastic water dispenser which is not able to withstand much pressure.

I hope I explained the problem clearly enough. If not feel free to ask for mode details. If you could recommend products that would be nice. Thanks for your help and please don't make fun of me :-)

-J

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  • $\begingroup$ Answering my own question after further reading, it seems I need two types of relief valves. One is a vacuum relief valve which lets air enter in the tank while it is emptied or during the solution cool down. The other device needed is a "regular" over-pressure relief valve that will let air out when the tank is filled back. Both should be low pressure and adjustable. Is that correct? $\endgroup$
    – Joe
    Commented Feb 28, 2022 at 2:01
  • $\begingroup$ Yes, you would need both types of relief valves. A conservation vent can accomplish both functions in one device if you can find one for your size tank. Keep in mind how much pressure or vacuum your solution container can withstand. $\endgroup$
    – J. Ari
    Commented Feb 28, 2022 at 19:00
  • $\begingroup$ @J. Ari Thank you so much for your help. The tank is plastic and can flex, but it will be placed in a compartment so I don't think it could withstand more than a few psi. I couldn't find a conservation vent for these low pressures but have found two devices adjustable from 0 psi to about 20 psi. Can I ask if you can confirm the two devices in link would work? Pressure valve: link VACUUM pressure valve: link Many thanks! $\endgroup$
    – Joe
    Commented Mar 1, 2022 at 0:34
  • $\begingroup$ I can't really comment on whether they will work or not because I don't know the details of your setup. As a minimum, you want to make sure the relief devices allow for an equal volume of air to come in as liquid leaves and vice-versa. The tricky part is knowing what your set pressure should be since plastic tanks aren't usually pressure rated/tested. $\endgroup$
    – J. Ari
    Commented Mar 1, 2022 at 1:59

2 Answers 2

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I think using valves for this is overkill. I would recommend hooking up a tube a few feet long to a port in the top of the tank, and leave it open to the air. The diffusion length will limit evaporation, and it doesn't require any significant pressure differential to operate. The diameter of the tube will depend on your pump flow rate, but just a guess an ID of 3/16in should be fine.

If you really want it to have zero leakage. You could use some PVC pipes and ping pong balls to create a pressure equalization valve using the following arrangement:

DIT Pressure equalization valve with low static pressure

(I just sketched this quickly so I don't know if all the ID's/OD's would work out, but you get the idea). The light weight of the ping pong balls allows very low static pressures to open the valves.

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  • $\begingroup$ Thank you @Drew for taking the time to write this very thorough answer. I did imagine such a setup using lightweight plastic balls, but once I factored in the time to go buy the balls and PVC pipes (I have neither of these around), I figured I might as well just buy the 15$ vacuum relief valve. It's adjustable from 0 to 20 psi so I think it could be adjuted for the very small vacuum involved. $\endgroup$
    – Joe
    Commented Mar 4, 2022 at 18:46
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I also think valves are overkill for this, but suggest instead that you tackle the concept that "air has to flow in and out of the tank during pumping or draining"

If you think of a bellows or syringe system as the tank, you can remove such a need. The tank volume just has to be flexible. You can also combine this concept with your pump to gain some control over pressure (and hence vaporization). If you have sealed hydraulic or pneumatic cylinders of appropriate volume available, you could just replace the relief valve with them while reworking the pump and tank system to be a bit more appropriate (there's a reason one does not suck water out of a well, but instead pushes it out!).

With a bit more work, you can also circulate your solution through a filter rather than just depending on settling.

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  • $\begingroup$ Thank you for your reply. Are you suggesting using a pressure tank? $\endgroup$
    – Joe
    Commented Apr 4, 2022 at 0:57
  • $\begingroup$ i suspect your pressure range would not be suitable for an off the shelf well tank. a custom compressible tank and using it as a piston instead of your pump is what i suggest. more info regarding ultrasonic cleaner volume might help figure out just how custom you would need to go vs using available pistons. $\endgroup$
    – Abel
    Commented Apr 4, 2022 at 3:07

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