We operate two separate upgraders, each utilize radial split pumps, one service is single stage the other two stage. The first upgrader is 2 x 100% the second upgrader is growing from 3 x 50% to 5 x 25%. From experience your optimal arrangement is the 3 x 50% arrangement as you do not lose total production in the event of a trip, and you can reduce capacity by shutting down one pump such as in the case of a furnace pigging or partial outage. Reliability takes an exponential decline as additional units are run in parallel, as pump condition is never matched and weaker units are backed out by stronger units. This can be mitigated by a proper control regime consisting of individual recycle loops, but this is rarely ever done due to the added complexity and initial cost. We are also adding a third upgrader and it looks like it will be using a three stage barrel volute design in either 3 x 50% or 4 x 33% operation. I am still hoping for individual recycle lines.