Prototyping & Model Testing

The pumps necessary for this massive undertaking – with the level of efficiency necessary -- are simply not made anywhere. They are much too large to physically test them other than in the field when they’re installed, so the process involved extensive model testing. Fairbanks Morse has invested heavily in testing and R&D over the course of the last ten years. This allowed us to put a model test together very quickly. Having taken those steps, Fairbanks had most of the equipment needed so we were able to (approximately three months after contract award) run model tests. There were eighteen people that showed up for a week long model test. Witnesses included the corps, their engineers and all other stakeholders, including the pump station contractor.

Initial Propeller Design

The birth of the final propeller design came from an 18 inch model test that we performed in the Fairbanks test labs. Our design software allowed us to actually take our 18 inch pump and increase the size to 140 inches across. This scaling of pumps from prototypes is something we are extremely expert in doing. After sending the design to the foundry, we empowered the foundry company to employ their special expertise for pouring -- so that it could be manufactured cost-effectively while meeting our performance specifications. Fairbanks required an exact model with vane intersecting the body as designed. The foundry took our model and determined how to do the pour, apply machining, etc., according to our exact specification.

Nailing the Hydraulics

A lot has to do with the surface finish and making sure the models are accurate. At the rapid prototyping stage, we knew that we didn’t have the variables of casting – that the pitch on each blade would be identical. When we were done we took our model propeller and put it across a Coordinate measuring machine. The scan showed the largest discrepancy on the model (an 18 inch diameter propeller) was about 12 thousandths off our model – which is about as accurate as it can be measured. Our success has been due, in large part to the precision engineering conducted to get the model truly accurate so we would make sure that the hydraulics are peaked.

Engine Challenges

A normally aspirated engine has a high torque at start up. But if you’re relying on a smaller engine with a turbocharger to it, the turbochargers have to get up to speed before they can really get the power draw. From an engineering standpoint, we felt we had several choke points on start up to make sure we had adequate torque to start these large pumps. Fairbanks worked with its engine vendor to go back and retest those points in order to generate additional power at those points for the torque we needed. This is a high specific speed pump –13,000 specific speed. This means a huge power draw at no flow -- about three times what it is at the rated point. You have to get past that in order to generate the flow. Our start up analysis was very detailed in order to confirm that we’d have enough engine torque to start – because the pump isn’t really producing flow until you exceed the priming head of the pump.