×
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

Can I cause damage to cylinders by pulling a vacuum?

Can I cause damage to cylinders by pulling a vacuum?

Can I cause damage to cylinders by pulling a vacuum?

(OP)
I'm making a hydraulic suspension system for a heavy truck (mining equipment hauler). Essentially, it's a trailing arm design with a hydraulic cylinder in the place of a usual spring/shock. As a safety feature, the cylinders have an on-off valve attached on the "extend" side of the cylinders to make sure hoses depressurize for servicing.

One of our techs shut this on-off valve and jacked up the frame of the truck. Magically, the cylinder extended without a way for fluid to fill the "extend" port! There's only one explanation- when you jack up the frame of the truck, the axle is hanging off the cylinder. The axle is so heavy we're pulling a vacuum in the cylinder (see attached picture). With the orientation I know for a fact the piston seal is wetted on both sides, but the O-rings and cartridge on the valve are dry and see a vacuum on one port.

Will this cavitation cause damage in a cylinder or a cartridge valve? If so, what failure modes can I expect from this?

RE: Can I cause damage to cylinders by pulling a vacuum?

While cavitation is linked to damage, it isn't cavitation that causes it - it's the energetic collapse of the fluid into the cavity that does the damage. It's unlikely that any damage will be done unless the vehicle is allowed to fall from a great height, like off a cliff, to push the cylinder back

The usual concern with this case in hydraulics is that people who service them may have a mental model that doesn't include that a vacuum won't hold the cylinder up and they get crushed or mangled when they open the pressure-side thinking it won't move because the non-pressure side is closed off. Even in this case the hydraulics will usually be fine and just people or external machinery will take the damage.

Since your tech was surprised by this, I'd suggest finding them a hydraulics safety course to take before they are seriously injured by some other misunderstanding.

RE: Can I cause damage to cylinders by pulling a vacuum?

I would expect no failure due to low pressure.

Ted

RE: Can I cause damage to cylinders by pulling a vacuum?

I can't workout how what looks like a hydraulic cyclinder is acting like suspension unless you've got some gas in the system somewhere, but that's not the issue here I suppose.

Issues for a pure vacuum are low, but the hydraulic oil will probably be vapourising a little and hence when the load goes back on you will have some gas in the system, or the valve or cylinder valves leak because they are not expecting negative pressure. Or air bypasses it and hence you end up with air in the system you don't expect.

If you have a small leak you could get some damage from high flowrate air passing small point on the valve or cylinder seal, but seems unlikely to be an issue unless you do it lots of times.

Oh and it's not magic - it's physics. ;0)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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

eBook - Efficient and Effective Production Support with 3D Printed Jigs and Fixtures
Jigs and fixtures offer manufacturers a reliable process for delivering accurate, high-quality outcomes, whether for a specific part or feature, or for consistency across multiples of parts. Although the methodologies and materials for producing jigs and fixtures have evolved beyond the conventional metal tooling of years past, their position as a manufacturing staple remains constant due to the benefits they offer. Download Now
Overcoming Cutting Tool Challenges in Aerospace Machining
Aerospace manufacturing has always been on the cutting edge, from materials to production techniques. However, these two aspects of aerospace machining can conflict, as manufacturers strive to maintain machining efficiency with new materials by using new methods and cutting tools. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close