Can you use PEX tubing to carry vacuum? I’m using vacuum to draw liquids out of a tank in my lab, and I prefer not to use pumps to push the liquid, its sort of volatile. The PEX standards I found online say that it will hold up to what I am pulling through the line, I just haven’t seen the standard PEX connections will seal on vacuum like they do under pressure.
PEX would be my first choice, I’m not really a fan of the silicone tubing that everyone uses, it sort of breaks down over time and I’m trying to “permanent me up a solution.”
Thanks to anyone that can help me out.
You might have to be an early adopter. Obviously the big advantage of PEX is that you need very few joints–in your situation maybe only 2. There are a variety of PEX joint techniques ranging from barbed fittings using the PEX’s “memory” to seal to metal crimp rings and a few others. If you are operating at room temperature I bet you can make it work–the metal crimp rings may be the most robust in your application. I say this from construction experience not lab.
I don’t know about PEX, but I’ve used generic polythylene tubing to carry a vacuum and it works ok. The only problem is that it also seems to break down over time–in particular, although it forms a good seal over a barbed fitting, eventually the tube seems to split. It’s not a huge deal to just cut off the last half-inch and re-fit it, but it’s mildly inconvenient.
I don’t know how well it does down to a hard vacuum, but I pump down to maybe 50 Pa and it’s fine. Obviously that’s more than good enough for moving liquids around.
How hard a vacuum? I’d assume 700 Torr or so would be fine if all you want to do is aspirate liquid using a standard lab diaphragm pump. Perhaps you can heat weld the tubing and a plastic barb adapter together to deal with leaking. My question would be how thick a wall is needed to hold up to the vacuum.
Don’t forget to put a trap inline in front of your pump in case something goes wrong.
Whenever you pull vacuum to drive a liquid, there is a possibility that air will sucked into the system if there is a leak. If the volatile liquid you mention is also highly flammable this is a big concern because now you can have a fire/explosion.
If you have flammability concerns, you can look into pressurizing the head space of the liquid container with an inert gas like nitrogen and then you won’t need a pump. You can use a spray paint drum for a quick solution.
Its not super flammable, so I don’t have to worry about it. Putting it through a pump will cause it to agitate though, so it throws a few vapors that way. Its not very flammable in its best situation, and I keep it at about 30 degrees. I am going to give it a shot here in the next few days, and I will let you guys know how it does. The vacuum isn’t very intense, I am just running a little baby diaphragm pump on it right now. I built a temporary version of what I am thinking of building with PEX, and this lame Home Depot vinyl tubing seems to hold up without caving in or dissolving.
If it’s a volatile liquid, exposing it to reduced pressure (like a partial vacuum) will only exacerbate its volatitly. Pressure reduces vapors, not vacuum.
I used to design pumps for high performance liquid chromatography, a chemical analysis technique that often requires the pumping of acetone. Can you go into more detail about what happens when you pump this stuff at postive pressure?
I don’t think I’ve ever used acetone as an HPLC solvent. Though I’m still somewhat confused why the OP doesn’t want to use a transfer pump or a peristaltic pump. Somewhat volatile liquids get moved by those methods all the time.
When I pump it it gets air in it and gets foamy. I would guess that the bubbles come from the fluid being agitated to the point where it separates. The foam doesn’t generate any heat or loss of heat that I have been able to tell, but it isn’t ideal.
I’ve tried pneumatic pumps, little cheesy pond pumps, hand crank pumps, etc. They all seem to generate this foam one way or the other. The fire marshal would prefer that I use vacuum to move the fluids around since I can bounce them from tank to tank and back and forth. His preference comes from the fact I am using a mixture of chemicals that, while not that flammable or anything, doesn’t have a specific UL list for a pump that is designed and rated to pump the fluid at a specific temperature range, around -10F. I’m sorry to be cagey about what it is, its just something my lab is working on and it is proprietary.
Using vacuum, it just gently flows, and goes where it belongs at good timing. I stumbled upon using vacuum because I needed to flow it in three specific directions and I didn’t have a lot of spare parts and pumps in my lab inventory, but I had a vac pump and a whole mess of valves.
Been using the PEX tubing for about a week, and I can attest that it works very well.
It was kind of a pain to get it to bend and go where I wanted it to go, but it holds up to the vacuum load, the temperature ranges, chemicals, and everything. It doesn’t seem to seep any air.
If it craps out or has any particular issues, I will update this thread.
The cost of it seems to be par to what it would have been to use high wall thickness silicone tubing, but the fittings seem more reliable and I haven’t had to chase down any leaks. The tubing is more rigid, which is nice because it doesn’t get as floppy when it shoots a little air through it.
Excellent. And somewhat surprising. Reason being… most of the time seals work in one direction, i.e. seals & gaskets for pressurized tubing and pressure chambers won’t work when you pull a vacuum, and seals & gaskets for vacuum tubing and vacuum chambers won’t work when you pressurize them.
I’m not sure why the seals would work on the silicone tubing for a while and then just crapped out. The stuff isn’t very reactive the seals just sort of craps out over time when I use the vinyl or silicone tubing. I have moved about 300 gallons of this fluid back-and-forth and we don’t seem to have any problems with the PEX. It looks way more professional than floppy hoses anyway.
The cheesy vacuum pump I use measures vacuum in Mpal. I use a maximum of .03 to move the fluids around. Seems to work okay. I move it about 2 gallons a minute. No foam or fluid separation. Steady pressure. I’m at about 4200 feet above sea level.