5-10k psi + hydraulic fluid + flexible = ? material

[ThirdString]

I am looking for a material that would be used as a diapragm that is expanded by pumping hydraulic fluid into it. Working pressure can be as low as 5k psi, but 10k is more desirable. And, being a diapragm, it needs some flexibility to collapse when it is not pressurized. If I have a starting point I should be able to figure out the specifics from there. Thanks!

 

[Demon3]

Well the main point would seem to be to find something that is chemically resistant to the hydraulic fluid. For that I would need to know the polarity of the fluid which I don't.

Wikipedia says "The three most common types of hydraulic fluids are mineral oil, organophosphate ester, and polyalphaolefin. Others are based on glycol esters and ethers, castor oil, or silicone"

So, based on that most hydraulic fluids are non polar and so some polar polymer would be a good choice as the diaphragm as it will not get swollen by the fluid. Some suggestions would therefore be nylon or perhaps a dual layer of nylon for the side exposed to the fluid and some other polymer to give the flexibility you want. Silicones and fluoropolymers may work too as they are no non-polar that they don't mix with hydrocarbons like many of the hydraulic fluids.

So to summarise find out what type of hydraulic fluid you will be using and choose the material based on that. Or, if you can choose the fluid type then do it the other way around, i.e. find the polymer with the mechanics you want at

http://www.matweb.com

and then find the type of hydraulic fluid that is compatible with it (i.e. test to see if the polymer is swollen on exposure to the fluid).

Also a Google search for "hydraulic seal" gave me tons of hits on what materials are used for such applications. E.g.

http://mechanical-components.global...al_Components/Seals/Hydraulic_Pneumatic_Seals

 

[patprimmer]

A polyester block elastomer such as DuPont's Hytrel or DSM's Arnitel would be my first guess as it is quite strong and resists most solvents and oils, but as Demon3 says, more details required.

At 5000 psi, any plastic diaphragm will burst unless travel is limited by a strong housing.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ThirdString]

Thanks for the feedback guys. We're flexible as to which hydraulic fluid, and your input gives me a starting point, since Matweb gives me a lot of options.

And Pat, thanks for the 5000 psi info, as that is significant to my design consideration. I know on most high pressure lines they are reinforced with steel cable or fibers, but are limited in flexibility.

 

[automatic2]

Bladder in an accumulator?

 

[ThirdString]

No, just exploring hydraulic lifting options.

 

[unclesyd]

Not hydraulic, pneumatic. These bags were used by our maintenance people for quite a few jobs. We also used a higher pressure device that resemble a fire hose that used water pressure up to 300 psig.
Your local fire and rescue group might have a set that you can checkout.

http://www.paratech-inc.com/pdfs/reflib_update/ParatechAirLiftingBags.pdf