×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Pressure compensation piston

Pressure compensation piston

Pressure compensation piston

(OP)
I have a thin walled cylinder that is filled with oil at atmospheric pressure. This cylinder will be subjected to an overburdening external pressure of 22ksi. Under these circumstances the cylinder will crush.
To prevent crush I have added a piston with cross-sectional area of "X." When acted upon by the external 22ksi, the piston moves, decreasing the internal volume of the cylinder, effectively increasing the internal pressure to 22ksi and preventing crush. I need to determine the maximum stroke length of the piston in order to achieve equilibrium at 22ksi external pressure.

Thank you.

RE: Pressure compensation piston

Then you need to know the bulk modulus of your oil (or its inverse, the compressibility), so you can calculate the volumetric change of the oil vs. applied pressure.

Knowing that value would also let you find the increase in pressure of an un-compensated cylinder undergoing elastic deformation (i.e. whether or not the filled cylinder would actually crush).

RE: Pressure compensation piston

(OP)
How would I apply that?

RE: Pressure compensation piston

from wikipedia,

The bulk modulus K can be formally defined by the equation

K = -V dP/dV (note the definition usually includes the term "isothermal", i.e. at a constant temperature)

So, if you wanted to know the volume displaced due to a pressure change, you would calculate

dV = V*Pd/K

from the link below, a typical bulk modulus for mineral oil is 2.5x10^5 psi

http://www.engineeringtoolbox.com/bulk-modulus-ela...

For the 2nd problem, you find the displacement of the cylinder due to external pressure, and calculate the internal volume change, and then use the above equation to compute the pressure change due to that displacement. Link the two equations to find the combined stiffness of the filled cylinder, or just iterate to find the actual displacement and actual internal pressure.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources