QR-1C leaking

is it used for spring brake hoses or somewhere else

 

I asked the question because you referred to items that are normally unrelated and believe I have seen that valve used on a different application. To my understanding the line connecting where the screw in fitting goes to the park valve, yellow knob on dash, and supplies air through the valve to the spring chambers. The two on the bottom go to park side of brake chambers. The exhaust port is for quick release of air from the park chambers when the yellow knob is pulled. The line on top, balance port, goes to a service relay valve outlet or teed to a service valve control line. It is actually a anti-compounding feature which prevents full service and park brake application at the same time. When air is leaking out the exhaust remove the line from the balance port. Air should never come out the top of the valve and air should only come out of the line if the service (foot) brake is applied. Chase the air and fix the fault.