Micheal ,there was dicussion regarding some of this on the Goat a week or so back .To reiterate , if one is running a train downgrade , the engineer oes not use the engine brakes at all ,unless the train is extremely difficult to operate . Tender brakes are routinely bailed off ,unless that extra braking power is needed . Rule of thumb : the longer the train , the better the braking power, because of more wheels to brake with . You also use far less air than with a short train .Many passenger cars ,because they were usually in short trains had the special quick-acting H triple valve ,but I would guess the "San Juan" was a very difficult train to take down Cumbres(the RPO's weighed 30 tons!) Running the helper light is another deal .The engineer switches back and forth between the drifting throttle and locomotive brakes .Yes ,if the driver brakes aere used excessively ,the tires could heat up to the point where they work loose .That you don't want.If you run the drifting throttle against the cylinders (the cutoff is pulled back to the "reverse" position), the backpressure prevents the cylinders from oiling properly ,so the engineer runs the danger of spalling the cylinders by excessive running "in the breeches" . The third valve on the tenders of older engines was the "dump valve" or emergency brake valve .After the installation of 6-et on the larger K-class engines ,the dump valve was moved to the back cab wall ,over the engineer . That is why it appears in a lot of old photos painted red .If you are doubleheading or in a mid-train helper ,this valve comes in very handy .I saw Earl Knoob use it once when we were mid-train and the piston came loose and broke the cylinder head ! He had the presence of mind to jump up and pull the air ,as the brake stand was cut out .
