I need a pump that can remove water from certain volume (~300ml). Water mixed with washing agent (soap) is pumped into this volume using another pump ~5-20L/minute. This volume is not completely sealed - air can get inside (sometimes easily, sometimes in very limited quantities). I need to guarantee that water will not spill out of this volume. In my understanding I need a water transfer pump, but such that can run dry for a while and work as vacuum pump. I looked what market has to offer, but didn't find anything like that.

So the question is - does such pump exist at all? If so, how it is called, so I can search for it online?

  • $\begingroup$ are those units right, 20 liters a minute into 300ml? basically one second fill time, and you want another pump to keep up with that? $\endgroup$
    – agentp
    Jan 12, 2017 at 1:02
  • $\begingroup$ Well, if one pump can pump that in, don't see why other pump shouldn't be able to pump that out. That said, 20L/minute is a nominal characteristic of the pump, real performance will be lower because water gets into the volume via many small holes (to create many "high-preasure" streams inside the volume). $\endgroup$ Jan 12, 2017 at 2:08
  • $\begingroup$ Given that any shop-vac can do this, can we conclude you don't want a simple vacuum pump? $\endgroup$ Jan 12, 2017 at 17:09
  • $\begingroup$ I don't think that shop-vac can handle 20L/min. Also it doesn't pump water out, it pumps it into container where vacuum is created (AFAIK). $\endgroup$ Jan 12, 2017 at 17:28
  • $\begingroup$ @wonder.mice That is correct, but it wasn't quite clear that you needed continuous pumpin "forever." If there are downtimes, then a valve could empty the vac tank. $\endgroup$ Jan 13, 2017 at 14:38

3 Answers 3


The terms you are looking for are "self priming pump" and/or "run dry pump".

Centrifugal self priming pumps require some water to be in them to start, but can pull a vacuum including air.

Diaphragm pumps pump air or water very well. They can run dry and are self priming. Some are specifically designed to just pump air.

Vane pumps or any other positive displacement pump will be self priming.

Depending on the reliability needs of your application a low cost centrifugal sump pump may work just fine. They are built for some abuse and many have integrated floats that control when they turn on and off.


I would recommend looking at Tesla turbines. If you use a motor to turn it, it acts as a pump and can pump anything from air to crude oil. If you can find one with different distances between the blades, that might help when trying to pump water and/or air. I'm just a student though, so look into it yourself to make sure you're getting what you need.

  • $\begingroup$ I feel like an centrifugal pump would be more common for that. $\endgroup$
    – JMac
    Jan 12, 2017 at 17:20
  • $\begingroup$ This answer could use some additional references to justify why a Tesla turbine solves the problem compared to a more conventional pump $\endgroup$ Jan 12, 2017 at 17:21
  • $\begingroup$ From what I understand, problems with off the shelf pumps is that they are specialized for specific use case. Say, water pumps use water as lubricant and even as cooling medium. Air pumps are not water proof and will short circuit itself when pumping water. From what I read, it's possible to make a centrifugal pump that handles both water and air, but can't find anybody actually manufacturing them. $\endgroup$ Jan 12, 2017 at 17:34

Look at liquid ring vacuum pumps (sizing tips) (really a version of the vane pumps mentioned by ericnutsch). Any fluid they suck will add to the liquid ring, excess fluid will be discharged. Talk to an applications engineer if the pump will have a problem with soap. These pumps exist at flowrates around 10-20 l/min.

In your situation, however, I would look at diaphragm pumps first and at other solutions if the pulsed flow is a problem.


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