×
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

Pumping from a vacuum vessel

Pumping from a vacuum vessel

Pumping from a vacuum vessel

(OP)
For some years we have been manufacturing a system which uses a positive displacement screw pump to remove liquid from a vacuum chamber. To prevent cavitation we keep a metre of liquid above the pump suction port and keep the suction line twice the diameter of the port as close to the pump as possible before reducing to the port size.

I have wondered if a centrifugal pump would have less trouble with cavitation and let us run the vacuum vessel "dry". Or would I still need to keep a head over the pump suction.

Delivery pressure is 2 to 6 bar, vacuum tank pressure above the liquid is 1 to 5 millibar absolute.

Has anybody got experience with this, Don't tell me to ask the pump manufacturer, because we are already successfully using the screw pump outside the manufacturer's specs.

Thanks,

Jeff

RE: Pumping from a vacuum vessel

Power generation facilities use centrifugal pumps to draw down liquid from their steam condensers throughout the world.  What is essential is a vent port to the inlet eye of the impeller so the water or fluid will flow freely into the inlet of the pump.  While in the Navy, this was referred to as submergence control. The pump was set up allow for a standard amount of water to flow freely into the condensat pump and maintain a certain level inside the hotwell.  On the old ships, ones without pumps fitted without mechanical seals. Leaving the vent valve open on the idle condensate pump would allow for a leak path to occur and loss of vacuum as air entered the shaft stuffing box and enter the condenser through the associated piping. You state that you are using a screw pump to perform this at present time.  Is this due to the type of fluid being pumped. Ie. viscosity or just using a pump that will draw an inlet vacuum greater than the vessel to thus draw the fluid into the pump?  You will need to look into how free flowing the fluid is to entering the pump.  More than one stage may be needed to provide enough discharge head to meet your system needs. Look carefully into NPSHR and NPSHA when choosing to go with a centrifugal pump. Most reputible centrifugal pump factory representatives can look at your system parameters and make a recommendation based on your system and fluid parameters.

RE: Pumping from a vacuum vessel

the higher the best, a 10 meter barometric leg would be safe and simple. A side channel pump could be the right choice but a head will always be required (which size of pump are we talking about?).

ET
www.vacuum-guide.com

RE: Pumping from a vacuum vessel

What you are looking for is a "Condensate extration pump" pumps of this nature are designed to operate under the conditions you are describing. I suggest you look round the pump manufacturers and ask a few questions, I'm sure you will come up with the answer.

International College
Naresuan University
Phitsanulok
Thailand

RE: Pumping from a vacuum vessel

(OP)
Thanks all.

The fluid is transformer oil sg about 0.8, and we are degassing and drying in the vacuum chamber, so we can't let any air in before or after the pump. The equipment is often on portable skids or trailer mounted, so we are limited in height. The reason we are using screw pumps is because the customer we build them for is an agent for these pumps and wants to maximise the amount of their product in the plant, but this might change if it becomes more "cost effective" to use a centrifugal pump. I hadn't thought about a side channel pump.

Thanks

Jeff

RE: Pumping from a vacuum vessel

From what I've read in this thread, it appears that the screw pump arrangement works fine, and would be a correct selection for a pumping fixture.

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