Need miniature gas pump

What about a small diaphragm pump?

You don't say what size constraints you have, except that it must fit inside a pipe - how big is the pipe?

Have you looked at the portable air sampling pumps? I don't know what they are made from though...

What about a peristaltic pump?

John.

Diaphragms are usually made out of elastomers that react with water vapor and affect my sample gas. An exception might be a metal bellows pump, but they also have drawbacks. Ideally the pump would have a volume of less than 10 cc and would fit into a piece of metal tubing less than 1.0 inch diameter. The best pump I have found to date is a MEDO free piston pump. It has organics inside it and is not totally sealed, but performs reasonably well.

Ohh that is small... how about using these ultra miniature hydraulics cylinders operated by an air supply?

Then the cylinder would be of metal and tiny, a couple of check valves and a pulsing air supply to power it?

I'm sure I've seen something like this used in medical applications, for some reason the manufacturer of Lee Dickens in the UK comes to mind - they make really tiny medical and aerospace valves and pumps etc...

http://www.sensortechnics.com/index.php?fid=300&fpar=YToxOntzOjQ6InBjaWQiO3M6MzoiMjg0Ijt9&isSSL=0&aps=0&blub=5d87c225ba198c7d1dd66fe59752a12c

These people do miniature pumps, not sure what the materieal is though...

John.

Thanks for the tip. The Sensor Technics pumps are not suitable because all the wetted parts are plastics that have water vapor permeability and/or water weight gain issues. I looked at Lee Dickens and could not find any miniature pumps.

Maby a peristaltic pump could do the job with silicone tubing or an other speciality tubing.

Manny brand aveliable.

http://www.autocludepumps.com/?gclid=CLqjqYXB85ECFQ-SHgod4nIkrA

Can you draw the sample through by suction? If so, an eductor pump using instrument air as the prime mover might work for you. The pump can be found in stainless steel and you probably won't need any sort of critical orifice in the eductor suction port because you are not trying to establish a diluting sampler, just pull some gaseous sample through your test column, right?

I mean basically, you have two choices: Push the gas through or pull it through. An eductor can be throttled by constructing a bypass dump so you could tune the sample delivery.

Good Luck!

Joe

Unless there's some magic to having the pump inside the tubing, I'm jumping on the peristaltic pump bandwagon. Tygon or other inert tubing shouldn't have any water reactivity issues, and the pump itself is isolated outside the system, so its component materials won't matter.

An interesting test one can perform is to deliver dry gas to an analyzer through different types of tubing. When one uses tygon, pvc, teflon, silicone, urethane, or any of the common plastics, one finds that water molecules are picked up by the gas flowing through the tube as measured by an increase in water vapor on the downstream end. When one uses clean metal tubing, the increse in water vapor is minimal. This is why I can't use a peristaltic pump or any pump with plastic wetted components.

From pores in the wall of the plastic(s), I presume. If the tubing is dessicated first, I wonder if this would still happen? Hard to visualize a whole lot of water in the pore spaces, but if it is measurable, then it must be real!

You could minimize this effect by using mostly clean metal tubing with only enough tygon, teflon, etc. for the pump to work its peristalsis on, could you not? That would require maybe on the order of inches of tubing rather than yards or whatever distance you're working at.

Enviroman, you are forgetting that almost all plastics absorb water vapour to some extent, and of course they can give up that water vapour as well...

I learnt this a long time ago (late 70s) when we needed a small quantity of plastic components injection moulded, the moulders told me how much it would cost and I asked "How much!!" He then told me that the plastic comes in 50 kg sealed sacks and to open a sack means it has to be used or thrown away due to moisture absorbtion...

John