So I have a water aspirator [Humboldt H-12020] that I use for pulling a vacuum. It's a venturi system, you use them in chemistry labs. Water flows through it and it sucks air from the side.
It works great. I have to use some plumbing fittings but i put it on my sink and I can pull down to like, -28.5 inHg really quickly. Problem is that I don't like wasting so much water, so I want to build a recirculating system.
water flowrate for similar models requires 6.5L of water per minute, or 103 gallons per hour.
So, I bought a 60$ harbor freight transfer pump, which does 320 GPH.
and it sucks dick it doesn't pull hardly any vacuum at all. With maybe a foot of lift above the water surface, it pulls -10 inHg. I don't know what the frick the deal is.
I'm going to do some experiements with buckets and see just how fast it actually pumps, but it should transfer a 5 gallon bucket's worth of water in a minute, so why is it making such a shit vacuum, especially when I can get a great one out of my sink?
pic is not mine, but it is the same idea.
Mains water pressure is like >100psi, this is probably not putting out enough to match. I'm guessing somewhere in the neighborhood of 40psi. So you gotta boost your pressure somehow. Which makes me wonder what kind of vacuum you could pull if you hooked up a pressure washer at >2000psi. For science?
So the limit on a venturi system is the vapor pressure of the working fluid. Which for water is 23.8 mmHg at 25C. At that pressure it boils the water passing through the nozzle and the pressure goes up again.
But you can cool down the water to get a stronger vacuum. Cold water from the faucet in the aspirator will boil water in a flask on a warm day.
I think it is a pressure thing though, like too much resistance on the output and the pump can't keep up. Like the pump could move 5 GPM across flat ground with no resistance on the output, but putting the aspirator on the end is choking it.
see:
I don't want to have to use a cold trap. Vacuum distilling or vacuum filtering solvents or acids will gradually destroy the seals or oil in something like a rotary vane pump. I can easily change the water in a bucket, it's not cost effective to throw out a bunch of pump oil.
Can you not just run an electric vacuum pump? All of this seems overly complicated.
Electric vacuum pumps cost more and need maintenance/oiling and the use of cold traps to prevent contamination. Despite the goofy appearance this is actually a well-proven way to get a decent soft vacuum with minimal complications
Agreed. The venturi pump is cool because it can be used from an existing pressurized water supply, but if you're going to introduce an electric motor to the system you may as well just use an electric vacuum pump.
I only knew this type of pump working with mercury. Very cool. Try to seal your water pump fittings better, even store bought vacuum pumps and vacuum chambers can be a pain in the ass to get tight.
City water is usable maybe what 4 to 5 floors up? Before it needs pumps and tanks in high rise.
Can your little fountain dribbler push that kind of head?
No? Then it's not much use sadly.
>Can your little fountain dribbler push that kind of head?
this is a blue board, anon
>water flowrate for similar models requires 6.5L of water per minute, or 103 gallons per hour.
That's like $0.30/h in water.
it's also just a mess. i have to remove the screen from the sink, route a hose into the drain (otherwise water sprays all over the place from the force of the nozzle). i don't have any control over the temperature, all the solvents are pushed into the water supply.
i'd just rather have a bucket i can move around and plug in and it's good to go.
that actually could make sense. i did some testing yesterday and it does genuinely move about 5 gallons in a minute. i totally filled a 5 gallon bucket in about that time. but maybe as it crosses zero there's a backflow and water gets sucked into the line. if, for example, i turn off the sink while a vacuum is held, water will be sucked into the line and into the flask.
but, even if that's the case, the seal should still be held. i might try to put a one-way valve in line and see if that makes any difference.
diaphragm pumps pulsate and are likely fricking up the fluid show through the venturi, yielding a shitty vacuum.