At the local WTP they are having a surge problem from one of the high service pumps. The pump is a 1600 GPM pump with a swing check and soft start drive. The other two pumps are 2400 GPM pumps with soft starts and electric check valves. The problem seems to be that the pump ramps to full speed before the check even opens, and when it does the pressure spikes from ~110 psi to +160 psi. The drive is an Allen-Bradley SMC flex and according to the tech support folks it doesnt matter what the ramp time is set to, the drive will ramp the motor to full speed as soon it can, which should be easy to do when the pump isnt moving water. We tried to current limit the motor from the drive. When it was set at 200% FLA the motor quickly ramped up to partial speed but when the contacts closed at the end of the set ramp time it jumped to full speed. I changed the current limit to 300% and it ramped up as it always did - with the surge pressure when the check opened. I think ideally what the drive needs to do is quickly ramp to a speed maybe 70%-80% of full speed and slowly ramp up to 100%, but the tech support folks say it wont do that.

Does anyone have any suggustions as to what we can do to fix the surge problem without replacing the drive or installing an electric check valve?

Also, there is a surge relif on the high service line leaving the WTP, if it's working shouldnt this prevent surges from entering the system due to a quick pump start?

I had a similar situation many years ago where the soft start drive would ramp to about 80%, then go to full speed.  The last 20% would send a hammer through the system that rebounded and increased in intensity.  Lots of water heaters blew up.  We tried all kinds of settings to no avail.  The soft start is not a VFD and won't ramp 100%.

We installed a pressure relief valve between the discharge and the suction to solve our problem.  It would open and cut the top out of our spike.

There are a lot of variables involved in your situation as you have 3 pumps of varying flows.  I don't know if your problem occurs with the pump when it is alone, when it is with 1 other pump, or when it is with 2 other pumps.

Either way, you need to make sure your pressure relief valve is operating.  Then the tricky part is to find the correct setting.  If you set it for a pressure with the 1600 gpm pump, your 2400 gpm pump will probably cause it to remain open when that pump is operating or when multiple pumps are operating.

You say the problem is with 1 pump.  What about the other 2?  Does the same thing occur?  If not, what is different about them?

Some other thoughts.  Is the swing check sticking?  Is it spring and lever or weight and lever?  If so, loosen it up, take weight or tension off.

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