Go
New
Find
Notify
Tools
Reply
  
-star Rating Rate It!  Login/Join 
Posted
I have this system that uses pump 'x' to deliver fluid 'y' throught my plant. The duty point of the pump is 800gpm @ 179ft.

There is a second, smaller pump in the system, and its design duty point is 100gpm @ 85ft.

The purpose of the second pump is to serve as the main delivery when end user demand decreases. I have been considering using a VFD [on the larger pump] to basically replace this pump. My concern however, is the effect this extreme deviation from the design duty point will have on the pumps.

Can anyone give some advice?

Driver Details:

Pump 1: 460V/100hp/1800rpm
Pump 2: 460V/10hp/1800rpm
 
Posts: 13 | Location: Jamaica | Registered: 14 August 2006Reply With QuoteEdit or Delete MessageReport This Post
Posted Hide Post
In general, a VFD allows you to keep the pump closer to its BEP during demand changes than if there were no VFD. Specifically , when you slow down the pump to match lower demand, you are also lowing the pump BEP. So from this perspective, adding a vfd should improve pump reliability. I think it is particularly true in this case where demand apparently varies as low as 10gpm... so if you are in the 10 -20 - 30 gpm range your 100gpm is way to the left of bep under the existing non-vfd setup

Just to mention some miscellaneous reliability considerations for VFD's"
1 - More likely to hit a resonance during some operating conditions. That may of course reduce your life. There may be strategies for blocking the speed in question if you know about it.
2 - There is more complex equipment driving the machine which is more likely to fail. (a vfd is more complex than a simple breaker or starter).
 
Posts: 3071 | Location: Texas Gulf Coast | Registered: 20 February 2005Reply With QuoteEdit or Delete MessageReport This Post
Posted Hide Post
Need also to check that the allowable operating speed range for the mechanical seal. We have seen seal failures on a VFD pump due to it being run below the minimum operating speed of its N2 gas lubricated mechanical seal.
 
Posts: 124 | Location: Melbourne, Australia | Registered: 05 May 2004Reply With QuoteEdit or Delete MessageReport This Post
 Previous Topic | Next Topic powered by eve community  
 


Copyright © 2004-2008 NetexpressUSA Inc. All rights reserved.