22 Jan 10 12:44
Thanks for the responses guys.
The system will have VFD's, cushioned swing checks, several ARV's and a flow velocity that is reasonable even with both pumps pumping at the same time.
I recieved the following from GA Industries on their method for determining the need for surge protection
"In determining the need for a surge relief valve, we typically consider the following:
1. If the potential surge pressure (in a 'worst case' surge event, i.e. power failure shutdown when pumping at maximum flow) exceeds the rating of the piping, a surge relief valve is definitely called for.
2. If the potential surge pressure approaches the rating of the piping and/or is much higher than the normal pumping pressure, a surge relief valve is typically recommended to protect the piping over long term usage. The sudden development of a surge can be considered a 'shock load'. The long-term effects of repeated 'shock loads' can lead to pipe fatigue and eventually failure, even if the surge pressure is within the pipe rating. This is the situation in "your project" (edited to remove Project name).
Pipe of any material generally does not gain strength over time. Fatigue in PVC piping isn't well defined in the literature. I have attached two different papers that attempt to address the subject from different viewpoints.
3. If the potential surge pressure is well below the rating of the pipe and/or only nominally greater than the pumping pressure, then a surge relief valve may not be required. Many other factors must be considered if foregoing surge protection (e.g. - age of piping, presence of pressure sensitive instruments attached to piping, pipe support & bedding methods utilized, etc.)"
Number 1 was of course obvious. Number 2 was more what I was looking for but maybe with hard numbers/percentages.
Well I think I have formulated a reasonable answer for the client.