leversole Posted December 24, 2010 Share Posted December 24, 2010 I believe I understand the tractor protection valve and what it does...I am slightly confused on how it is controlled in a typical B model...There is only one lever in the cab for trailer control, and it is marked normal and emergency, and I thought I read somewhere that it was used to apply trailer brakes in an emergency. So my questions are...How do you charge/dump the trailer parking brake (independent of the tractor parking brake), and how do you start/stop the tractor brake air from leaking out of the trailer hoses when a trailer is not attached...Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/16994-tractor-air-confusion/ Share on other sites More sharing options...
Underdog Posted December 25, 2010 Share Posted December 25, 2010 With the lever in the "normal" position, air is supplied to the trailer, which also releases the trailer parking brakes if so equipped.(spring brakes were not required on trailers until 1977). During "normal" driving, trailer service brakes work as an extension of the tractor's brakes with the foot pedal. The hand control, AKA spike or trolley valve, will apply only trailer brakes, useful for jacknife situations or backing under an older trailer.In the "emergency" position, air to the trailer is shut off, and the spring maxi-brakes will apply. (air pressure in normal driving keeps the springs back). The "emergency" position also allows you to unhook the trailer without losing air thru the trailer supply line.Gregg Quote Link to comment https://www.bigmacktrucks.com/topic/16994-tractor-air-confusion/#findComment-69178 Share on other sites More sharing options...
leversole Posted December 25, 2010 Author Share Posted December 25, 2010 With the lever in the "normal" position, air is supplied to the trailer, which also releases the trailer parking brakes if so equipped.(spring brakes were not required on trailers until 1977). During "normal" driving, trailer service brakes work as an extension of the tractor's brakes with the foot pedal. The hand control, AKA spike or trolley valve, will apply only trailer brakes, useful for jacknife situations or backing under an older trailer.In the "emergency" position, air to the trailer is shut off, and the spring maxi-brakes will apply. (air pressure in normal driving keeps the springs back). The "emergency" position also allows you to unhook the trailer without losing air thru the trailer supply line.GreggThanks! So the Emg/normal switch is like a modern Trailer Air Control? ANd the only addition with the third valve on modern trucks is the trailer parking brake. Modern truck have three valves, tractor park, trailer park,and trailer supply?Thanks again. Quote Link to comment https://www.bigmacktrucks.com/topic/16994-tractor-air-confusion/#findComment-69212 Share on other sites More sharing options...
fifth wheel Posted December 25, 2010 Share Posted December 25, 2010 It is a manually operated valve that charges the t/t protection valve and will not return to a no delivery status upon breakaway or pressure loss.FW Quote Link to comment https://www.bigmacktrucks.com/topic/16994-tractor-air-confusion/#findComment-69214 Share on other sites More sharing options...
greendog32 Posted December 25, 2010 Share Posted December 25, 2010 actually modern trucks are back to just two vales yellow parking and red trailer supply Quote Link to comment https://www.bigmacktrucks.com/topic/16994-tractor-air-confusion/#findComment-69215 Share on other sites More sharing options...
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