If there exist two identical pieces of equipment, in this case two pumps that are the exact same (in theory) pumping the same fluid in the same location at the same rate (everything is the same), how many times does pump A have to fail/breakdown while pump B is fine before I can say that there is a problem with pump A and NOT pump B, rather than saying there is clearly a problem and it exists with both pumps (or saying I can't pass judgment either way).
That is, if pump A failed 50 times in the past 10 years and pump B failed 0 times, that probably means whatever caused pump A is likely unique to pump A. However if pump A failed only 1 time in 10 years, and pump B still never failed.. I'm assuming we'd call that statistically insignificant and I couldn't say either way whether or not the problem is with pump A or pump A AND B.
My thoughts: At first I thought I'd need to know what the nominal failure rate of that type of pump was before being able to figure this out, but then I thought, "if these pumps normally fail 5 times a year, then there's got to be a difference because A is following that trend exactly, but B is 50 failures away from where it should be" and conversely the same logic can be applied at the other extreme, say if the pumps normally fail once every 20 years.. there's still quite clearly a discrepancy.