Increased Pump Reliability

What type pump, gear, vane or piston- fixed displacement, varible displacement? If a standby condition is "OFF" then regardless of the type pump rotate them in and out of service.
If maintenance reliability is your goal there are other conditions to monitor besides the hours-i.e. analysis of the pumping medium, temp and viscosity and load to name a few. Good luck, maytag

Thank you for your reply. But what i really want to know is if for instance I have a system with four pumps and I need two on load and two on standby, what would be the best way to run these pumps assuming all other factors effecting pump life were removed. Would it be to run two on load untill they begin to deteriate then bring in the standby motors to power the system. Or would it be best to alternate between the two sets of motors for and equal amout of time? I am going to be writing a plc program to control the system, taking it away from relay logic, and knowing the best practice for running I could write this into my program. I will be looking at the other factors you mentioned as part of my project.

Thanks again.