OT: Any Fluid Handling experts here?, Small scale engineering help requested Options

[lotus_65]

Hi good people, you are the best resource I have at hand, so I'm throwing this out to you all:

At work, I/we utilize 2-2.5 gallon pressure pots that hold 2 similar liquid (gloss & matte) materials (basically glue) that we use to coat our products with an hvlp gun using 10lbs pressure in our spray booth.

Some clients want a combination of the 2 coatings to create a 3rd semi-gloss/satin finish. Best case scenario is that I could mix/blend the 2 in-line somehow, because we could easily customize the coatings per the client's request.

It's logical to me to relate these 2 liquids as something similar to hot and cold water, and I want to be able to coat my products with hot, warm or cold liquid using a manifold to dial the percentages.

As I'm writing this, I feel like it would be ideal to have some type of ball valve at the gun, receiving the two fluid lines, and allowing me to dial the mix right there.

Does anyone know what I'm trying to say, and have a direction to share?

Thanks-
paul

[jd74914]

How accurate would you like it to be and how much do you really want to spend (I know its always as little as possible)?

How viscous is the fluid?

Using needle valves is a good suggestion (ball valves would work too, they just aren't as controllable, think 1/4 or 1/2 turn to open versus 8 turns for some needles), though I would personally attack the problem in a different manor.

I would use orifice plates and two regulators or I-P transducers to change the pressure on the pots. Orifices are easily characterized and by changing the pressure on the inlet (so changing the paint pot pressure) and keeping the outlet pressure constant you can easily change the flow rate through the orifice. The flow rate is simple to calculate as the physics behind them are very well know (and orifice flow calculators abound on the internet).

Using orifices would allow for very precise metering of flow, and would make it very easy to record specific customers' recipes since all you need to record is the orifice size and pressure. As an added benefit they are much easier to clean and less expensive to replace than needle valves.

Incorporating two I-P transducers, which are essentially computer controlled regulators, would allow you to tune the system to always have the perfect pressure on the outlet side by regulating the inlet in accordance to demand. That said, they are somewhat finicky and super expensive so normal regulators would probably work better.

[rwilner]

How accurate would you like it to be and how much do you really want to spend (I know its always as little as possible)?

How viscous is the fluid?

Using needle valves is a good suggestion (ball valves would work too, they just aren't as controllable, think 1/4 or 1/2 turn to open versus 8 turns for some needles), though I would personally attack the problem in a different manor.

I would use orifice plates and two regulators or I-P transducers to change the pressure on the pots. Orifices are easily characterized and by changing the pressure on the inlet (so changing the paint pot pressure) and keeping the outlet pressure constant you can easily change the flow rate through the orifice. The flow rate is simple to calculate as the physics behind them are very well know (and orifice flow calculators abound on the internet).

Using orifices would allow for very precise metering of flow, and would make it very easy to record specific customers' recipes since all you need to record is the orifice size and pressure. As an added benefit they are much easier to clean and less expensive to replace than needle valves.

Incorporating two I-P transducers, which are essentially computer controlled regulators, would allow you to tune the system to always have the perfect pressure on the outlet side by regulating the inlet in accordance to demand. That said, they are somewhat finicky and super expensive so normal regulators would probably work better.

This is a good approach.

You could use panel-mounted PID controllers to control the position of the I to P transducers. I have had good luck with Red Lion controllers -- reliable and cheap. Although between I to P transducers, pressure transmitters, orifices (you'd probably want stainless), etc...things are starting to get expensive.