×
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!

*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

Mechanical Seal

Mechanical Seal

Mechanical Seal

(OP)
Hi,

We have a situation where we operate three horizontally split case centrifugal pumps that are connected to the same suction line and discharge line. When operating under suction mode, the gland packing are known to leak air into the system. Usually it's one pump duty and two of the pumps on standby.

I have been told that to prevent air leak into the system, a flushing line that bleeds water from the pump volute and provides pressure on the packing gland can be installed. This should solve the air leak through the duty pump. However air would still leak into the pumps through the packing gland of the standby pumps.

Hence, i am thinking of mechanical seals on all three of the pumps. My question is how good are mechanical seals under very low or vacuum condition? Would low pressure in the pump push the two faces apart to leak air into the system?

Thanks for any information

RE: Mechanical Seal

Can't you just isolate the inlet lines of the standby pumps?

Or actuate the valves which are there.

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

RE: Mechanical Seal

You can add the discharge flush as you indicate. If you take the flush stream off of the main header, downstream of the check valve, it will flush the packing on all pumps, even the ones that are not running. If you choose to go with mechanical seals, that will work as well. Most seals are designed to take slight reverse pressure with no impact. However, even with mechanical seals, the reliability would likely be better if you provide a flush line to cool and lubricate the seal. We use this flush arrangement on pumps in vacuum service on most of our surface condenser systems.

Johnny Pellin

RE: Mechanical Seal

Does your system have sufficient NPSH if it's drawing other pump casings into vacuum?

RE: Mechanical Seal

Yes. The stream is water at perhaps 90 F. There is sufficient elevation head for the pumps to run under partial vacuum with no cavitation problems.

Johnny Pellin

RE: Mechanical Seal

(OP)
Hi All,

Thank you for the response.

#littleinch - That is definitely one option. I will look further into that.

#JJpellin are you saying if we go with mechanical seals, flushing would need to be provided for all the pumps simultaneously? is that the case for pumps on your surface condenser system? There needs to be some sort of flow control to prevent high velocity water from damaging the mechanical seals?

RE: Mechanical Seal

Yes. You know the discharge pressure. You know the suction pressure. Size an orifice to provide 1 gpm per inch of seal diameter.

Johnny Pellin

RE: Mechanical Seal

Of course, the best solution from this point is to get a mechanical company involved.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

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

eBook - Functional Prototyping Using Metal 3D Printing
Functional prototypes are a key step in product development – they give engineers a chance to test new ideas and designs while also revealing how the product will stand up to real-world use. And when it comes to functional prototypes, 3D printing is rewriting the rules of what’s possible. 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