×
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

Maximum Piston speed

Maximum Piston speed

Maximum Piston speed

(OP)
I realize this is a question with numerous constraints, but here goes.

Is there a maximum piston speed above which I need to be concerned?  If there is, will looking at the PV characteristics of the piston seal and guide bushings be an adequate design check?

At present, I am designing around a Bimba 500 psi oil cylinder.  I called Bimba tech support, and the gentleman stated that 8(!) in/sec would be a maximum *fluid* speed in my lines to avoid cavitation; he would say no more.  When pressed, he stated that they recommend a maximum *piston* speed of ~20 in/sec for their pneumatics.  I would guess that being lubricated with oil, hydraulics could sustain much higher speeds.  true?

I am hoping to move the piston at up to 30in/sec.  Fluid temperatures are anticipated to be low.  loads will be relatively low, with the exception of ~.1 sec accelerations, where the ram will see full system pressure along with translation of the piston.

The piston will be in sea water, so the seals simply need to last longer than the external packaging, which has unknown aluminum alloy end-caps coupled to SS304 body.  galvanic corrosion is active.   

 

RE: Maximum Piston speed

The speed is limited by the seal capability.  The paramters include pressure and velocity as well as temperature and seal material.
See here http://www.marcorubber.com/ucups.htm for examples.
I have run pistons 35 ft/sec through Disogrin polyurethane seals.

Ted

RE: Maximum Piston speed

The person at Bimba tech support is talking rubbish.

8"/sec fluid velocity will not cause cavitation. 8000"/sec might, but then that will depend on the fluid vapour pressure and the line pressure. Most modern hydraulic systems are run with fluid velocity at around 50 ft/sec, and the risk is turbulent flow which pushes up the pressure losses.

It is linear velocity of the rod and piston seals that will ultimately dictate the speed of the cylinder. Making the ports big enough to fill the cylinder will push the cylinder size up. Pushing the cylinder size up will increase the contact area of the seals and thus reduce the allowable speed.

If the cylinder is not load holding, ask about low friction seals.

Adrian  

RE: Maximum Piston speed

Quote:


8"/sec fluid velocity will not cause cavitation. 8000"/sec might, but then that will depend on the fluid vapour pressure and the line pressure.
It isn't the speed that causes cavitation it is the the sudden decelerations when a over haul load is stopped by quickly reducing flow.

This shouldn't be a problem in this example since the hammer is stopped when it impacts the anvil, not by cutting flow flow to the cap or driving end of the cylinder.

Quote:


I am hoping to move the piston at up to 30in/sec.  Fluid temperatures are anticipated to be low.  loads will be relatively low, with the exception of ~.1 sec accelerations, where the ram will see full system pressure along with translation of the piston.
Accelerating to 30 inches per in 0.1 second is an acceleration rate of 300 inches per second^2 which is about 0.77g which is less than the acceleration due to gravity.
The acceleration and speed should be easy to achieve with gravity alone.

  

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

 

RE: Maximum Piston speed

Oops, got threads mixed up, but moving at 30 inches per second is done all the time.  Accelerating at 300 inches per second^2 will depend on the net force and mass being accelerated.

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

 

RE: Maximum Piston speed

The cylinder problem you have is not in the acceleration or the maximum speed it is the stopping at the end of the cylinder movement. The inertia of the piston and seal will cause part failure, the piston will come loose on the rod or the piston seal will shear into the piston to barrel gap.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: Maximum Piston speed

(OP)
Yes, as soon as the Bimba tech said (and repeated) the 8"/sec fluid speed statement, I thought, "I need a more knowledgeable opinion.  Eng-Tips, here I come- again!"

Ed,
I am designing the travel limits to be the cylinder endcaps. (I am using the full stroke of the piston for each cycle).  Will this help with the piston-rod separation issue?  should I consider cushioned endstops?

thanks once again, you guys are a great resource.  I realy appreciate the time you put into considering my questions.

    

RE: Maximum Piston speed

Consider cushion stops.

Ted

RE: Maximum Piston speed

Do not use any hydraulic cylinder as a stop if there is much inertia in the system unless you want to spend a lot on development and repair. We are currently working on a 5 ½" bore x 3 ½" rod cylinder that has seen over 250,000 lbs of extension force and enough side loads to compress the 2" wide wear ring length over .005" causing metal to metal contact.

It is ok to cushion the non anvil end of the cylinder as the hammer contacts an end stop. The anvil end of stroke should have extra travel. One of the anchor ends should be shock isolated.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

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! Already a Member? Login


Resources

Research Report - How Engineers are Using Remote Access
Remote access enables engineers to work from anywhere provided they have an internet connection. We surveyed our audience of engineers, designers and product managers to learn how they use remote access within their organizations. We wanted to know which industries have adopted remote access, which software they are using, and what features matter most. Download Now
eBook - Managing the Context of Product Complexity Using the Digital Twin
Keeping track of changes to complex products is difficult—think Aerospace & Defense equipment, new generations of commercial aircraft, and software-based automobiles. A new way to managing the digital context of the physical product is required and the answer is the Digital Twin. This ebook explores the opportunity available for Operations and Maintenance for the Digital Twin. Download Now
White Paper - Trends in Industrial Filtration
Substantial progress has been made in filtration technologies in recent years. New filter media materials, designs and processes have led to filters that are more efficient, reliable, compact and longer lasting. This white paper will discuss the various trends that are impacting operational responsibilities of MROs today and the resources that are available for staying up-to-date on the latest filtration solutions. 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