Manifold design 1

[spiridij]

I'm working on a design for a device that infuses a slightly viscous material (~7cP) through 4 small nozzles. The nozzles will be embedded into tissue and will likely have different resistance to flow. In order to eliminate the possibility that all of the material will flow through the needle with the least resistance, I thought I could address my concern by building a manifold that somehow controls the back pressure so that any differences in resistance through each needle would be negligible and will result in almost equal flow through each nozzle. Unfortunately, I can't increase the back pressure very much, so that might not be an option. Does anyone else have any ideas on how I can equalize the flow to each of the needles?

 

[RVAmeche]

If you have a very constant flow/pressure you'll be operating at, a flow model should be able to size restriction orifice(s) to be used to ensure flow at the further away needles. How close to equal flow do you need? Throttling valves on each line set during startup may be sufficient. If you have various flows/pressures and still want equal flow, that will be more difficult.

 

[spiridij]

Thanks for the reply, the flow/pressure won't be constant, it will be coming from a syringe that someone will be manually applying pressure to a single outlet that will be split into 4 lines, each line going to a separate needle. I don't need equal flow exactly but if all of the nozzles can be within say 20% of each other that would be great. There would be no way of knowing which of the needles are encountering resistance in advance and it would likely be different each time. Do you still think a throttling valve on each line could work?

 

[ornerynorsk]

Either The Lee Co. or Bird Precision could have a solution. Have used both of these company's products in years gone by in micro-hydraulic pumps and actuators, they are absolutely top notch in their field.

https://www.theleeco.com/

http://birdprecision.com/

Disclaimer - I have no interest, financial or otherwise, in either of these companies.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[GrouchyStressedTensePoor]

Would a spool type flow divider work?

GSTP

Graduate Mechanical Design Engineer
UK

 

[3DDave]

Use 4 separate syringes ganged together. This method is frequently seen in dispensing 2-part epoxies where the resistance to flow is considerably different for each nozzle.

 

[spiridij]

GrouchyStressedTensePoor, can you explain what you mean by a spool type flow divider?

 

[GrouchyStressedTensePoor]

I think 3DDave's solution is a lot more practical and elegant. I am not sure if you will be able to buy a flow divider of the appropriate size, however if you scroll down to Fig. 13-16. at

[URL unfurl="true"]https://www.hydraulicspneumatics.com/other-technologies/chapter-13-flow-controls-and-flow-dividers[/url]

you will see what I mean.

GSTP

Graduate Mechanical Design Engineer
UK

 

[spiridij]

I do like 3DDave's idea, but there would be 8 syringes ganged together. I guess I'll have to give it a try.

 

[GrouchyStressedTensePoor]

Wouldn't there be 4? You could "gang" the syringes together axially/concentrically, which might make it a bit more wieldy. A flow divider could still work, and if you can't find one of suitable size I wouldn't be surprised if you could make one yourself. Maybe even machined from plastic.

GSTP

Graduate Mechanical Design Engineer
UK

 

[hydtools]

In a hydraulic circuit where I want equal flow in four lines I would consider a four section gear splitter. One flow in and four equal flows out through unequal branch pressures. May not apply here. Maybe it would.

Ted

 

[zeusfaber]

Or miniaturise something like the device in this video?

A.

 

[spiridij]

GSTP, there would be 8 syringes since it's a two-part system that needs to mix before injecting into each line. I'll have to look into flow dividers.

 

[D Scullion]

Just came across this article and this thread came to mind. I'm maybe way off field here but thought there might at least be some inspiration or research benefit in this.
Link


Declan Scullion CEng

http://www.leandfm.com

 

[kjoiner]

This may be similar to what Ted mentioned, but would some type of positive displacement pump work for each line?

Kyle

 

[spiridij]

Kjoiner, yes, that would work fine, but unfortunately it's not practical for this application since it's a disposable medical device.

 

[handleman]

For a disposable medical device, I doubt you're going to do better than just using 8 ganged syringes. You might need a squeezer contraption (sorry... technical term ) to mash them all evenly, but that's pretty simple and it would be easy to design as re-usable because it would not be wetted, and you get guaranteed, positive, instantly-verifiable equal flow amounts and rates. I would imagine that (especially as viscosity goes up) the flow dividers have some delayed response, or maybe a minimum flow rate to generate enough pressure differential to operate the innards. You would never have a guarantee or verification of even flow unless you added meters or something. $↑$↑$↑.

If you can get some really high precision molded plastic parts, you might be able to mold a block that holds four gear pump mechanisms on common shafts:

https://www.michael-smith-engineers...lGearPumps/intro-external-gear-pumps-fig2.jpg

You'd have a common "inlet" at the top, but four pairs of gears mounted to a common shaft so they're forced to turn at the same rate, each with its own outlet. Downside of this would be some really tight molding tolerances, and maybe a pretty good amount of flow resistance. Although this same mechanism is used on some fairly high-flow positive-displacement flow meters...

 

[Compositepro]

All kinds of syringe pumps are readily available off-the shelf.

http://www.syringepump.com/

https://www.google.com/search?client=firefox-b-1-d&q=syringe+pump