Contact US

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!

*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

G1/4 plug leaks on aluminum hydraulic blocks

G1/4 plug leaks on aluminum hydraulic blocks

G1/4 plug leaks on aluminum hydraulic blocks



For some years we have been using high strength 7075T651 aluminum to make drilled blocks. The yield strength of this aluminum is 500Mpa (73,000 psi). Previously they were steel.

After about 2000 pressure cycles 0 to 150bar, we found some plugs G1/4-ED Voss that were not tightened one of which had unscrewed several tenths of a mm until the ED seal extrudes .
On another power plant, it is an electro-distributor cartridge with 2-way valve with 3/4-16 UNF layout that has unscrewed. And the seal in the inlet cone was extruded.

These power-units operate approximately 8 hours a day. There is a 0.75kW-2l / min electro pump unit that runs less than 5% of the time to charge a battery. At night the temperature of the block falls between 0 and 25 ° C. In operation the block heats a bit because the coils of the electro-distributors are powered.

It's been over 30 years that we do the same kind of equipment. Since we changed the material of the blocks we have this phenomenon.

Questions: Does anyone know this phenomenon? And what solution did he bring?

RE: G1/4 plug leaks on aluminum hydraulic blocks

Perhaps plug and valve were not installed tight enough.


RE: G1/4 plug leaks on aluminum hydraulic blocks

Both pressure cycling and thermal cycling need to be evaluated against material parameters other than the yield strength. Aluminum is not a direct replacement for steel, especially in cyclic applications.

You might also consider retention means other than threads, like the cylinders that use two half grooves and a tangential entry, coupled with a malleable ring pressed in as a straight bar through the tangential groove entry. I forget what it's called, but it's been in commercial use for a couple decades in compact cylinders. I've never seen one unscrew.

Or go back to steel, and consider a more machinable grade like 12L14, better drills and fixturing etc, to speed up the cycle time, and perhaps consider reducing the thickness to control weight, if that is an issue.

Mike Halloran
Pembroke Pines, FL, USA

RE: G1/4 plug leaks on aluminum hydraulic blocks

hydtools and MikeHalloran:; thanks for your advices. We will study what changes we need to make.

RE: G1/4 plug leaks on aluminum hydraulic blocks

I have sucessfully used 6061-T6 for many manifolds on mobile applications which experience wide temperature and cyclic pressure variations to 2500psi. All plugs, fittings, and cartridge valves remained tight.


RE: G1/4 plug leaks on aluminum hydraulic blocks


We also do alot of what hydrools mentioned on boats that go to the North Atlantic. 3000 psi Alum 6016 T6 blocks are common. But they would not be cycled as much as your saying. They do often go to 3000psi+

RE: G1/4 plug leaks on aluminum hydraulic blocks

Thank you for your feedback that reassures us.
Decisions taken following other responses in Europe are:
1. Change supplier. Voss plug tests (with the "Voss coat" treatment) proved to be bad compared to the competition.
2. Increase the tightening torque.

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


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. 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