NPSH dry-well submersible installation
NPSH dry-well submersible installation
(OP)
We're in the process of replacing old conventional (dry well) pumps with submersible pumps and I was wondering if NPSHa could be an issue.
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
NPSH dry-well submersible installation
|
NPSH dry-well submersible installationNPSH dry-well submersible installation(OP)
We're in the process of replacing old conventional (dry well) pumps with submersible pumps and I was wondering if NPSHa could be an issue.
Red Flag SubmittedThank you for helping keep Eng-Tips Forums free from inappropriate posts. Reply To This ThreadPosting in the Eng-Tips forums is a member-only feature.Click Here to join Eng-Tips and talk with other members! |
ResourcesThe world has changed considerably since the 1980s, when CAD first started displacing drafting tables. Download Now
Prototyping has always been a critical part of product development. Download Now
As the cloud is increasingly adopted for product development, questions remain as to just how cloud software tools compare to on-premise solutions. Download Now
Engineering-centric businesses face a number of challenges today, but unmanageable design and change processes don’t need to be counted among them. Download Now
|
RE: NPSH dry-well submersible installation
In case you are not familiar with submersibles, it should be noted that the typical submersible pump has a higher maintenance cost for repairs than a centrifugal pump will.
http://books.google.com/books?id=biWHfrpd9gsC&...
RE: NPSH dry-well submersible installation
As bimr says - check your new pump NPSHR and all your parameters - vapour pressure, head of liquid above the pump inlet and air pressure above the liquid (whatever it is)
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: NPSH dry-well submersible installation
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.)
RE: NPSH dry-well submersible installation
RE: NPSH dry-well submersible installation
RE: NPSH dry-well submersible installation
We had good results elsewhere with this kind of replacement.
RE: NPSH dry-well submersible installation
It is probably typical that the average sewage pump is incorrectly sized.
If the existing pumps were installed in 1979, you got your money's worth out of them. I would hope that you are also planning to replace the electrical system as well, because it is probably obsolete.
Are you planning to replace the pumps in the dry well, or install the pumps in the wetwell?
RE: NPSH dry-well submersible installation
The pumps that we need in replacement are relatively small (e.g. Flygt 60 HP, ABS 58 HP). The pumping station constructed in 1979 but pumps were replaced a couple of time since then.
I was first asking about NPSH calculations for such replacement, but reading you: Did you had "bad experiences" with this kind of replacement? (conventional for dry-well submersible?).
RE: NPSH dry-well submersible installation
RE: NPSH dry-well submersible installation
RE: NPSH dry-well submersible installation
The cooling of the motor is done by the flow of pumped medium (water) itself. So it matters that when the pump is selected the diameter of the well is suitable (i.e. not too big relatively to the pump size/discharge flange) to leave an appropriate gap so that velocity of fluid is high enough to cool the motor but not too small neither so that the heat/energy is also dissipated effectively. If the diameter of the well is already known keep that in mind and give the information to the manufacturer.
It matters also to stay within the 80-120 BEP range. There is great deal of pump investment calculation vs. pump efficiency calculations (price of kW.h) to select the optimal pump as normally you get - say from one given manufacturer - many pump sizes that will all do the job more or less. So an option is to have an Lifecycle cost done by the manufacturer to back up the final choice.
A point of importance is the selection of the pump metallurgy. So a water analysis shall be available to select the correct materials and kept in the record in case of failure or claim in the future. Some good performance and resistance can be achieved with a sort of synthetic (polymer) material which is quite cost effective manufacturer may provide normally such solution.
If not bronze would be the next choice for water without ammonia content. Mind the risk of high temperature as material selection for these pumps is very sensitive to combination of corrosive medium (chloride content) and temperature (e.g geothermal conditions). Above 55-60 degC the corrosion problem can be serious and devastating and you may need to switch to a duplex SS material which would make the pump very expensive.
With regard to NPSHrequired that also has to do with the different pumps that you get as many possible selections and the one you finally select. In addition when the pump is pumping the level decreases or fluctuate so that means less NPSHavailable will be affected - anyway double check.
RE: NPSH dry-well submersible installation
Steve