One thing I found out by reading the Barton manual is that on the UA-50 (I imagine all the UA pumps are the same) is that engaging the clutch is a 2 step process. Step one is bring the lever "up" about 1/2 way to get the pump spinning, then back down for a second, then back all the way up. This will engage the pump eaiser, and I imagine is easier on the pump internals, being somewhat "gently" brought up to speed.
Another thing the booster line is good for on the older trucks is when recirculating water to keep the pump cool. Open the booster nozzle, put it in the tank fill opening on the top of the truck (engine technically, but whos checking), then open the gate to the booster line. This will allow the pump to actually move some water, and not heat up the water inside the pump when the pump is engaged but not flowing water. if you ever hear what sounds like popcorn coming from your pump, your seconds away from the pump blowing up. The popcorn sound is caused by the water turning to steam inside the pump.. It's not good at all.
Bottom line, either move water thru discharges or use the booster line method. A pump thats pumping but not actually moving water (due to closed discharges) will only heat the water and cause very bad things to happen inside the pump.
