The brake pedal has foot valves attached to it. When you step on the brake pedal, this is the valve that starts the brake application. The foot valve can be mounted under the floor of the cab or inside the firewall.
What does a foot valve do on air brakes?
The foot brake valve is used to actuate and control the brakes on all wheels when the vehicle is in motion.
What is a hand valve on a truck?
The hand valve, or “spike” (Fig. 39) is added so that you can apply the trailer’s brakes independent of the tractor. The hand valve is typically supplied from primary and secondary circuits and plumbed to a double-check valve (which is also fed from the foot valve).
What is a spring brake control valve?
A spring brake control valve is normally a push/pull type valve fitted with a yellow, four-sided knob located near the driver (See diagram 4-3). Most spring brake control valves are pushed to supply air and release the spring brakes, then pulled to exhaust air and apply the spring brakes.
What is the purpose of foot valve?
The basic function of a foot valve is to prevent water from flowing back down the pipe. It can also be described as a foot valve that would only allow the pump to pull water up but does not allow the water to flow back down.
What is a double foot valve?
The Dual brake foot valve is a floor mounted, treadle operated valve with two separate supply and delivery circuits. Used in a dual circuit system.
What are the five basic components of an air brake system?
The basic components are compressor, governor, airlines, air tanks, brake pedal, and foundation brakes. In this day and age, these are not the only components.
How can you manually check the slack adjusters?
With service brakes in the released position, mark the push rod even with the brake chamber. Make a full brake application and mark the push rod again. Measure between the two marks to determine the length of push-rod travel (stroke).
How do hand valves work?
The tractor-protection valve and relay emergency valve are operated by application air, as explained in the foot-valve application. Closing the hand valve releases the brakes by closing off application air. Air pressure in the chambers and lines will exhaust, also as explained in the previous foot-valve application.
What is a semi hand valve?
Explanation The trailer hand valve, also called the trolley valve or Johnson bar, is used to work the trailer brakes. It should be used only to test the brakes. Using it while a vehicle is in motion could cause a skid.
What does the Red air line do?
Air and Electrical Lines
The red line is the air line for the trailer’s emergency brake. The green line is the electrical line. The blue line is the air line for the trailer’s service brake. Connect these lines to the corresponding couplers and socket on the trailer before moving the trailer.
How do you test a spring brake valve?
You can check the operation of the trailer spring-brake valve by closing the supply valve on the tractor or by disconnecting the supply line between the tractor and trailer with the supply valve in the open position.
At what low air pressure do spring brakes apply?
5.4.7 – Low Air Pressure
The spring brakes will come on when the air pressure drops into the range of 20 to 45 psi. A heavily loaded vehicle will take a long distance to stop because the spring brakes do not work on all axles.
What are spring brakes held back by?
Spring brakes are usually used to meet these needs. When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes. A parking brake control in the cab allows the driver to let the air out of the spring brakes.
Why it is called foot valve?
Overview: A foot valve is a type of check valve that is typically installed at a pump or at the bottom of a pipe line (hence the name). Foot valves act like ball check valves, but have an open end with a shield or screen over it to block debris from entering the line.
What is the best foot valve?
PVC foot valves are a good choice for most applications; they are cost-effective and lightweight. However, in applications that require temperatures or pressure that don’t allow for PVC, or that require specific chemical resistant materials, there are metal valve options like brass and stainless steel.
What is the difference between check valve and foot valve?
Check valves and foot valves are designed to stop water from going backwards when the pump shuts off. Check valves are normally on the discharge side of pumps, and foot valves are on the intake of pumps.
