A bleed screw is a device used to create a temporary opening in an otherwise closed hydraulic system, which facilitates the removal of air or another substance from the system by way of pressure and density differences. [1]
On a home radiator unit, the bleed screw can be opened, usually by means of a key, to allow unwanted air to escape from the unit. Bleed screws are also found on some pump types fulfilling a similar purpose.
They are most often located at the top of the radiator on the side of the inflow pipe. The screw itself, usually a hexagonal or square knob, is inside a small round protrusion.
The key looks similar to that used to wind a clock. It is inserted into the protrusion, mates with the bleed screw and turns it. Opening the bleed screw then allows air which has risen to the top of the radiator system (the top of the radiator itself) to escape and new water to take its place. Removing the air and allowing water to displace it makes the radiator work more efficiently since water conducts heat better than air.
A domestic radiator may need bleeding in this way either during a heating upgrade, power flushing or simply when the radiator feels colder at the top can indicate there is air in the radiator that needs to be released. [2]
Engine cooling systems can also have bleed screws. They can take the form of a bolt with a hole through the middle that is threaded into a hole on the engine's cylinder head. This hole goes into the water jacket of the cylinder head. In other designs, the bleed screw is placed in the uppermost hose which leads to the heater core, i.e. at the highest point of the cooling system.
When the bleed screw is loosened, antifreeze is added to the engine's cooling system and the increase in fluid pressure displaces air through the opened bleed screw. When liquid begins to flow out, all air has been removed from the system and the bleed screw is closed.
Bleed screws are not common on cars today and are only necessary when design of an engine's cooling system results in areas where air can be trapped in the system.[ citation needed ] Air in the system can lead to overheating of the engine and in modern cars also to poor vehicle operation (e.g. problems with the AC system or incorrect engine idle).
On a hydraulic vehicle braking systems, the bleed screws (sometimes known as bleed nipples or bleeder valves) are located at the top of each brake caliper to allow bleeding of the braking system. Whenever service work has been performed on the braking system which might have introduced air into the system (i.e. the hydraulic system has been opened), the air must be bled out. This is necessary for correct operation of the system, because air compresses (as opposed to brake fluid which is not compressible). Air in the system reduces the maximum pressure applied to the brake pistons and can lead to loss of braking ability.
Cars with manual gearshift use a clutch. Clutches are controlled from pedal by bowden cable or hydraulic systems, some use the fluid in common with the brake system. As a dead end of the hydraulic system, the slave cylinder is equipped with a bleed screw.
A pump is a device that moves fluids, or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy.
A valve is a device or natural object that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.
A drum brake is a brake that uses friction caused by a set of shoes or pads that press outward against a rotating cylinder-shaped part called a brake drum.
An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is conventionally subdivided into hydraulics and pneumatics. Although steam is also a fluid, steam power is usually classified separately from fluid power. Compressed-air and water-pressure systems were once used to transmit power from a central source to industrial users over extended geographic areas; fluid power systems today are usually within a single building or mobile machine.
Bleed air is compressed air taken from the compressor stage of a gas turbine upstream of its fuel-burning sections. Automatic air supply and cabin pressure controller (ASCPCs) valves bleed air from high or low stage engine compressor sections. Low stage air is used during high power setting operation, and high during descent and other low power setting operations. Bleed air from that system can be utilized for internal cooling of the engine, cross-starting another engine, engine and airframe anti-icing, cabin pressurization, pneumatic actuators, air-driven motors, pressurizing the hydraulic reservoir, and waste and water storage tanks. Some engine maintenance manuals refer to such systems as "customer bleed air". Bleed air is valuable in an aircraft for two properties: high temperature and high pressure.
Hydraulic machines use liquid fluid power to perform work. Heavy construction vehicles are a common example. In this type of machine, hydraulic fluid is pumped to various hydraulic motors and hydraulic cylinders throughout the machine and becomes pressurized according to the resistance present. The fluid is controlled directly or automatically by control valves and distributed through hoses, tubes, or pipes.
Hydronics is the use of liquid water or gaseous water (steam) or a water solution as heat-transfer medium in heating and cooling systems. The name differentiates such systems from oil and refrigerant systems.
Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines are purged of any air bubbles. This is necessary because, while the brake fluid is an incompressible liquid, air bubbles are compressible gas and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. The same methods used for bleeding are also used for brake flushing or purging, where the old fluid is replaced with new fluid, which is necessary maintenance.
A hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism.
An axial piston pump is a positive displacement pump that has a number of pistons in a circular array within a cylinder block. It can be used as a stand-alone pump, a hydraulic motor or an automotive air conditioning compressor.
An air brake or, more formally, a compressed-air-brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad or brake shoe needed to stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers, in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of trucks and heavy road vehicles.
The following outline is provided as an overview of and topical guide to automobiles:
The wax thermostatic element was invented in 1934 by Sergius Vernet (1899–1968). Its principal application is in automotive thermostats used in the engine cooling system. The first applications in the plumbing and heating industries were in Sweden (1970) and in Switzerland (1971).
Aircraft systems are those required to operate an aircraft efficiently and safely. Their complexity varies with the type of aircraft.
Radiators are heat exchangers used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine.
Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating.
A rotary union is a union that allows for rotation of the united parts. It is thus a device that provides a seal between a stationary supply passage and a rotating part to permit the flow of a fluid into and/or out of the rotating part. Fluids typically used with rotary joints and rotating unions include various heat transfer media and fluid power media such as steam, water, thermal oil, hydraulic fluid, and coolants. A rotary union is sometimes referred to as a rotating union, rotary valve, swivel union,rotorseal, rotary couplings, rotary joint, rotating joints, hydraulic coupling, pneumatic rotary union, through bore rotary union, air rotary union, electrical rotary union, or vacuum rotary union
An automatic bleeding valve or air release valve (ARV) is a plumbing valve used to automatically release trapped air from a heating system.