Chemical valve selection

[Kizniche]

Hello all,

If I've come to the wrong place with my issue, I apologize. However, I can't think of a more knowledgeable group on this subject. I've been developing a chemical dispersal system at my university and have come to a wall in the design process, with the necessity for a valve.

Essentially, I have a 30 psi pneumatic compressor that forces compressed air through a jet nebulizer (Pari trek S). A thin layer of fluid is aspired from the reservoir and aerosolized by the force. There are a number of solvents and alcohols that are aersolized, and leave the nebulizer reservoir as a vapor of 0.5 - 5.0 micron diameter droplets (to facilitate evaporation- essential to the design). I've found that even as little as a 0.1 psi restriction in the outflow severely reduces the ability for the jet to operate (by testing low cracking pressure check valves). As an open system will permit evaporation of the solution in the reservoir, I have been looking for a suitable valve for the outflow port that's normally closed until the system is to disperse.

There are a couple constraints for the design, and they include the use of low battery power that does not permit the use of a higher-pressure compressor, low cracking pressure check valves provide too large of a pressure drop and restricts the amount of aerosol produced, and the micrometer opening of the diaphragm (of the low-cracking pressure check valves I've tested thus far) is restrictive enough to cause the vapor to condense back to a liquid and cause sputtering.

I have looked at numerous valves and have not been able to find one suitable except for biochem-fluidics rotary valve with a 12-volt stepper motor. This is rather expensive and I would rather use this as a last resort.

I've also been looking at air-operated valves but cannot find a suitable valve with a low enough pilot pressure (all I've seen are 40+ psi) to be used with this system.

If anyone can provide their insight or suggestions as to a particular valve that would be suitable, I would me most appreciative.

Kindest regards,
Kyle

 

[LittleInch]

I've read this a few times and whilst there is a lot of information there, there is also a lot missing (size, flow rate, air velocity etc).

A diagram would also help.

From what is written I think you're looking for an isolation valve which stops your reservoir evaporating, but which doesn't have any flow or pressure effect when operating.

Given you have low voltage supply, why don't you look up solenoid operated valves? These are very common on air supply systems and if you look hard enough should be able to find one which is as big or bigger than your piping / tubing so as to create pressure drop similar to that of the tubing.

~air operated valves in industrial systems usually operate on a nominal 80-100 psi system so lower pressure would probably be difficult to find.

Have I got this right?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[moltenmetal]

What does this "low battery power" mean: are you operating industrial equipment including a compressor to evaporate solvents in an area without access to any AC power?

You either need a motor-operated or air-operated full port valve such as a full-port ball valve- or a manual valve of the same kind if someone is around to operate it. You need to be able to power that device. If it operates intermittently it won't draw much power.

 

[gerhardl]

To avoid pressure loss through valves at lower air-pressure it is essential that all air tubing (not only the valve) is large, with as few as possible restrictions, bends and reductions. The correct selection of a valve is of course important. Note:A valve with a given nominal diameter might have a real opening far less in diameter or with other inner restrictions and bends. Ask for details!

The pneumatic operation of such a valve, with a solenoid valve giving air to the actuator is only a question of a large enough actuator, may be a size or two above the 'normal' actuator for the valve. Power=pressure times area. Note: Any restrictions on time for closing and opening? Long opening/closing will give smaller/cheaper tubing and solenoid valves for operating the main valve.

Guessing your diameter is something between 1/4" and less than 2"Ii would presume you could find a reasonable prized solution using a standard ball-valve with a double acting oversized actuator. Material: either stainless/teflon or pure plastic construction. Other solution might be suggested if you can present more detailed info.