minimizing water hammer
minimizing water hammer
(OP)
Hello All,
I am designing a pump station ( 3 pumps, 2d/1s) pumping brackish water with a total flow of 70m3/hr through a DN160 Ductile iron pipe buried 1.5 m from FGL. The total length of the pipe is 2700m discharging into a Box Culvert. To reduce the water hammer effect I have installed a pressure tank at the pump station upstream and a swing Check valve along the line on every 200m. Is 200m a reasonable distance? is there any reference showing the right distance between Check valves?
Thank You
Marc
I am designing a pump station ( 3 pumps, 2d/1s) pumping brackish water with a total flow of 70m3/hr through a DN160 Ductile iron pipe buried 1.5 m from FGL. The total length of the pipe is 2700m discharging into a Box Culvert. To reduce the water hammer effect I have installed a pressure tank at the pump station upstream and a swing Check valve along the line on every 200m. Is 200m a reasonable distance? is there any reference showing the right distance between Check valves?
Thank You
Marc





RE: minimizing water hammer
I am not aware that check valves would help the problem, should it exist.
If you do develop a problem, it will most likely be from pump start/stops, in which case a soft starter would help on startup, but not do much good on a trip.
From "BigInch's Extremely simple theory of everything."
RE: minimizing water hammer
RE: minimizing water hammer
Regards,
Marc
RE: minimizing water hammer
RE: minimizing water hammer
Those checks would keep a pressure wave being reflected back from the end of the pipeline from returning back to the pump, but reflected waves are much less than the original pressure, so any damage has essentially already been done. A closed check would also be a cause of reflection of any subsequent waves emminating from the pump station, which such valves being closer to the pump station would reflect proportionally higher pressures and reflect them sooner.
A very small check valve as a bypass around a fast closing valve that was causing a waterhammer problem could be effective at allowing some of the wave to pass that valve thereby capping the pressure rise ahead of the valve and any wave reflected back to the pump station, but still, the highest pressure at the pump has already occured. Reflected waves are of lesser pressure than the original pressure event causing the wave.
From "BigInch's Extremely simple theory of everything."
RE: minimizing water hammer
RE: minimizing water hammer
BTW a partially closed valve, or a reducer in the pipeline will reflect a spike proportional to the amount of x-sectional flow area reduction it gives, ie a valve 40% open will reflect 60% of the wave back to the pump while allowing 40% to pass through. A 6 x 3 reducer will reflect 75% of the spike allowing 25% of the spike to pass.
Checks in the line would probably stop most of the reflections from traveling from the closed valve back to the pump, but wouldn't do much of anything to mitigate the original pressure spike at the face of the closing valve. IMO.
From "BigInch's Extremely simple theory of everything."
RE: minimizing water hammer
By pressure tank do you mean a vessel with a pressure sustained by compressor or gas charged bladder. If so it is more important that the check valve at the pump station is fast acting of the non slam type.
Putting check valves every 200m appears to be inconsistent with any solution I have known. You may solve the challenge with one intermediate check valve but its location depends upon the pipeline profile and modelling.
Without the pipeline profile it is difficult to estimate the pressure spikes.
Suggest you invest in some engineering and have the system modelled by a competent waterhammer analyst. Using Joukowsky to estimate the maximum presure transient is courageous.
Without know your maximum transient pressure you dont know the design rpessure of the pipeline.
As for software you can choose between AFTs Impulse, Hytran, Kypipe, Flowmaster, Watham and numerous others. Be warned that purchasing the software does not make you a transient analyst.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/