I'm looking for a miniature (has to fit into an enclosure of size 90x35x15mm or 3.54x1.38x0.59in) vacuum pump that should generate a vacuum of 200mBar. The pump will eventually power a set of suction cups that allow a vessel travelling in a municipal water pipe to cling to the pipe wall, and so would need to be capable of handling water. My aim is to have the pump connected to a solenoid valve, which is in turn connected to the suction cup. When I want to latch onto a surface, I would turn on the pump till the desired vacuum inside the cup was reached, then shut off the solenoid to maintain the vacuum, topping it up when needed.

I've done some searching and have managed to find the following pump:

http://www.burkert.com/COM/Products/MicroFluidics/Micro-pumps/7604.html

This pump can generate 200mBar overpressure and is of a suitable size. However, I am guessing that a pump that is capable of overpressurising a container is not necessarily capable of producing a vacuum of the same amount.

What are people's advice on the matter? Can I get vacuum pumps that would fit into my enclosure? Is there a better way of controlling the suction cups?

I'm afraid you are on the start of a major engineering project.  I understand from your writing that you intend to have the required pumping means on board of a vessel / container traveling in a municipal water pipeline.  Looking to the mentioned micro pump, I'm afraid you will not be able to achieve the intended service.

 Let me first answer your question on possible under pressure:  If you download the datasheet of your sample pump, you will see on page 2 a graph showing "flow rate against suction and pressure height". The "suction height" is the vacuum inside the cup as differential pressure to what exists in the municipal water pipeline.  Please note that it is a pump and not a compressor. It is intended to pump liquid and not a gas, but as the pump is self priming, will be capable to transport (limited) amounts of gas. The title above the graph is however "Restart points", which probably means that these values cannot be maintained. This could be queried with the manufacturer.

You will have 3 main issues to solve:
a)    Forces by the water flow on the vessel / container (to be counter acted by cable or suction cups);
b)    Docking to the wall (required pumping rate to move in radial direction and getting to the intended circumferential location); and
c)    Sealing of the suction cups to the municipal water pipe (wall roughness, dirt, required pump cooling and leakage rate).

I will only address the latter point, as your post mentioned that item.  The wall of the municipal pipeline will not be smooth. There will be some leakage through the sealing between pipe wall and suction cups. This will be the required pumping flow, probably this will be a lot more than the 5 ml/min (max) of your sample pump. In case you are able to provide a better sealing, the absence of a water flow could lead to problems as heating up and partial filling of the pump chamber.  

If you have the vessel / container on a cable, why not add a hose to provide the required suction from a larger pump outside the municipal water pipeline?

I have already to correct something in my reply.  If the suction hose for an external pump becomes very long, your post did not mention the intended distance in to the pipeline, the pressure drop over the hose could become too high, as there is maximally 1 bar down to absolute vacuum available.  The use of a venturi in your vessel / container could then be better and water from the discharge of the pump could then be used, but pumping water into a municipal water pipeline is normally due to hygienic reasons a problem.

2011-01-19

Back