Tube to tube connectors

[Josef_G]

Hello all,
I'd like to connect two tubes as follows:
Tube 1 -
ID = 3.5mm
OD = 6.8mm

Tube 2 -
ID = 18.0mm
OD = 21.1mm

IS there a standard connector that can be used to connect these tubes?
I'm building a prototype and have considered 3D printing a connector and fastening the tubes to it with zip locks.
Obviously not the greatest idea, but I'm still mostly unfamiliar with tubing systems, components and practices.

Any help will be greatly appreciated.

 

[danschwind]

I've never seen tubing with those dimensions.

Maybe look if the manufacturer has any assortment of fittings in his catalogue? You will probably need to connect a bunch of reductions on one another. Why the diameter change in the first place?

 

[Josef_G]

Thanks for the reply!

I've got a pressure relief valve mounted onto the piece with the bigger dimensions, which I would like to use as a fail-safe in my system.
The flow through these tubes is very slow, so my assumption is that the change in dimensions will only negligibly change the pressure.

I've been searching the catalogues and haven't found anything yet.

I think at this point I might need to prepare another piece to mount the relief valve onto.

 

[danschwind]

You should not assume this - you should calculate.

What is the manufacturer of those tubes? Their dimensions are very odd IMO.

 

[Josef_G]

Once again, thank you very much for your reply.

I'm not certain who the manufacturer is. These are pretty old tubes that served their purpose well enough in the meantime. I could consider changing them if it helps me solve this problem, and
hey will definitely be replaced sooner or later.
Based on your line of questioning it seems that my best option is to search for a complete set of tubing from a single manufacturer, which sounds like a good idea.

Regarding the pressure calculation -
How do you suggest I calculate the pressure? The flow is comprised of a foam, which is made from a liquid with a viscosity of approximately 3 [MPa*s].
As foam is highly compressible and made of a fairly viscous liquid, I'm uncertain how to approach the issue quantitatively. Do you suppose Bernoulli's could at least get me in the right ballpark?

 

[danschwind]

I suggest you take a look at Swagelok's catalogue.

This 'foam' is basically a liquid with a lot of entrained air? Or something different? I've never dealt with something like this before, but you would need to find a model to calculate the pressure drop of this fluid.

 

[hacksaw]

evidently you're dealing with plastic tubing, there are tons of choices,

 

[jari001]

What are the pressures ranges in consideration here? If I read the thread right, you want to connect the outlet of a relief valve to a smaller sized tube with a 3D printed connector and zip-ties, which may just be asking for a bad time even if it's a temporary measure.

Also, if hacksaw is right and it's plastic tubing please tell us what they are made of, even if it's to distinguish between a hard or soft material. If it's plastic tubing, generally there are fittings to join between a variety of standard sizes.

If you know the manufacturer of the foam/foam system, they may have the flow/pressure drop data that you can use to size these tubes. I vaguely recall foams being modeled as Bingham plastic or power-law fluids, so Bernoulli's equation alone may not be accurate. There's also 2 phase behavior that may or may not be negligible.

 

[Josef_G]

jari001 -
Regarding the tubing:
You are correct, except that I don't necessarily WANT to use a printed part, but might consider it.
I think I will go with danschwind's suggestion and order a complete set from a single supplier. I will likely opt for plastic tubing.

Regarding the calculation:
Unfortunately the foam is not supplied, but generated by us, and we still haven't entirely determined it's characteristics.
Thanks for the suggestions, I will look into those.

 

[jari001]

Generally speaking, you wouldn't want to reduce the relief valve outlet line to something smaller than the inlet connection. Could you use a burst disc instead of a relief valve so you don't have concerns of the outlet path of the relief valve not being the right size?

 

[Mconlon]

What type of material is this tubing made out of?