A pressure releasing device contains a tubular body member with a slidable slider member inside. The pressure releasing device is connected to the output of the high-pressure pump and high-pressure water will flows through the pressure releasing device when the pump is turned on and, when the pump is turned off, the high-pressure backflow will force the slider member to quickly block the inlet of the pressure releasing device. A pressure releasing opening controlled by a low-pressure valve is provided along the tubular body member. When the pump is turned off, the high-pressure backflow will be quickly released through the pressure releasing opening and the low-pressure valve helps to keep the water pressure inside the hose below a low pressure level to prevent dripping.

A valve assembly for use in conjunction with spring applied, air release parking brakes of the character found in heavy-duty truck-trailers which, in a single valve housing provides system pressure protection, prevents compounding application of the brakes and performs the parking brake release function in an expedicious and highly reliable manner.

An air brake control system for use in truck trailers having at each axle compressed-air brakes including spring brakes and service brakes, and each trailer being coupled to receive compressed air through an emergency (supply) gladhand and to receive service brake signals through a service (control) gladhand, the invention comprising an integrated brake valve system for each axle of each trailer, including a common valve housing; a spring brake valve cluster having a non-return check valve connected to receive and pass air pressure from the emergency gladhand and to deliver it directly to the spring brakes and an air pressure responsive shuttle operative to open the check valve whenever the emergency line pressure falls below a predetermined spring brake isolation pressure above which the spring brake holding pressure is not affected by fluctuations of the emergency gladhand pressure; and including an air tank supply valve cluster connected between the emergency gladhand and the tank and operative to sense pressure in the emergency gladhand and to open at a tank-filling threshold pressure above the predetermined spring brake isolation pressure to pass air to the tank and having a tank protecting check valve to prevent backflow of air from the tank; and including a pressure amplifying service brake relay valve cluster connected between the tank and the service brakes to supply and modulate air to the latter responsive to variations in the service gladhand pressure.