We operate a pulverised fuel boiler and one of the requirements is for de-mineralized water to be pumped into the boiler continuously. As such, we have two pumps always running. The third pump (a standby pump) is always tripping when brought into service for when conditions are upset and there is a need to deliver extra boiler water to the boilers or when one of the running pumps is being maintained. This standby pump has been changed several times, aligned and still keeps tripping. We are trying to troubleshoot to find out exactly what is causing this one pump alone to keep tripping while the other two are running well without tripping. Previously there were no tripping problems, but this has been happening now for the past few months going back to June 2008. I need to investigate this problem and come up with a solution. What would you advise as the best way forward or as the best way to execute the troubleshoot. I am having meetings with the process engineers and process specialists so that I get more details of the operating conditions and so on. My proposed plan of execution so far can be summarized as follows: • Gather as much data as possible on the pump, motor, valves, NPSH, head, duty etc. • Establish the operating conditions and the worst case scenarios when conditions are upset. • Eliminate an electrical problem by having the electrical people do a thorough check on all the control systems and also by checking the motor and all its supporting accessories. • If all electrical systems are checked and found to be working fine proceed as below. • Do a design from first principles given the operating conditions. • Compare the design and the current status on the pump vis a vis valves, manifold designs, Would it be correct to assume that since these pumps have been operating without any problems for some time now up until this tripping problem started it is some parameter that has changed most recently and cannot be the design and layout?