Air Bubbles (Void) in Dispensing Needles?

Question

I have an array of 21GA dispensing needles with a polyethylene top and a stainless steel needle shaft. I am trying to drip water through it at a constant rate but air bubbles get in the way of the shaft an slow the drip rate and soon enough it happens to many of the needles, reducing overall drip rate. Are there any quick n cheap (or otherwise) solutions to ridding the needles of air bubbles. I thought of utrasonic transducers providing tiny vibrations to break it up, but there are none small enough for my application and it is an expensive alternative. Any suggestions?

Answer 1

I would probably try switching to a pressurized system with a valve instead of a drip system. The easiest and cheapest way to do this to get a large cylinder of compressed gas (so the pressure remains virtually constant), and get some tubing and valves from a hardware store. Remove the plunger from the syringe, and attach a hose to the syringe with rubber tubing. Adjust the valve until you get the rate you want. You can get large cylinders of nitrogen or helium from an industrial supply store for a fairly low price Sometimes they charge a deposit for the canister, and you pay only for the gas you actually use, which should be pretty small for your application.

Answer 2

A high pressure purging of the system at start should
clear any bubbles initially present.
Deaerate the feed water.
I suspect the water warms in your process causing air to come out of solution. If the feed water is heated first and the bubbles allowed to rise and then the water is kept in a closed container to prevent reaeration it might solve your problem.