Schrader valve
Encyclopedia
August Schrader
August Schrader was a German-American immigrant who had a shop dealing in rubber products in Manhattan, New York City, USA. His original shop was located at 115 John Street. In 1845, he began supplying fittings and valves for rubber products made by the Goodyear Brothers, including air pillows...
. The original Schrader valve design was patented in the United States in 1893.
The Schrader valve consists of a valve stem
Valve stem
A valve stem is a self-contained valve which opens to admit gas to a chamber , and is then automatically closed and kept sealed by the pressure in the chamber, or a spring, or both, to prevent the gas from escaping...
into which a valve core is threaded, and is used on virtually all automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
tires and most wider rimmed bicycle
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
tires. The valve core is a poppet valve
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
assisted by a spring
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...
.
Uses
In addition to tube and tubeless tires, Schrader valves of varying diameters are used on many refrigerationRefrigerator
A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...
and air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
systems to allow servicing, including recharging with refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...
; by plumbers conducting leak-down pressure tests on pipe installations; as a bleeding and test port on the fuel rail of some fuel injected engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
s; and in the buoyancy compensator (BC) inflators of SCUBA
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
systems (the inflation button pushes down on the valve, allowing pressurized gas to flow into the BC). Schrader valves are also widely used in high-pressure hydraulic systems on aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
.
Many domestic fire extinguisher
Fire extinguisher
A fire extinguisher or extinguisher, flame entinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations...
s use an internal valve identical to a Schrader valve, but with a lever on top to enable quick release of the pressurised content.
Valve
A Schrader valve consists of an externally threaded hollow cylindrical metal tube, typically of brassBrass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
.
In the center of the exterior end is a metal pin pointing along the axis of the tube; the pin's end is approximately flush with the end of the valve body.
Generally, all Schrader valves used on tires have threads and bodies of a single standard size at the exterior end, so caps and tools generally are universal for the valves on all common applications. The core of the valve can be removed or tightened with a tool.
A new development is Schrader valve stems with integrated transmitters for tire-pressure monitoring systems (TPMS).
Cap
A valve cap is important on a Schrader valve because if one is not fitted, dirt and water can enter the outside of the valve, potentially jamming it or contaminating the sealing surfaces and causing a leak. Rock salt and other chemical deicers used in the winter are especially damaging for the brass components in the Schrader valve.Some valve caps have a rubber-washer
Washer (hardware)
A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring , wear pad, preload indicating device, locking device, and to reduce vibration...
seal
Seal (mechanical)
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage , containing pressure, or excluding contamination...
(or a synthetic-rubber
Synthetic rubber
Synthetic rubber is is any type of artificial elastomer, invariably a polymer. An elastomer is a material with the mechanical property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation...
-washer seal) inside to help make a hermetic seal
Hermetic seal
A hermetic seal is the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.-Etymology :...
(airtight seal). A such rubber-washer-sealing-type cap also helps prevent air from escaping from a slightly leaking valve. In addition, the rubber washer prevents the cap from loosening and falling off due to vibrations and hence being lost, by acting as a cushion between the cap and the valve stem and in this way damping the vibrations. The caps without these rubber-washer seals inside them effectively serve mostly to keep contaminants out of the valve stem, without providing a good hermetic seal. The caps without rubber washers inside them can also loosen and fall off due to vibrations when undertightened, especially if they are made of hard plastic or hard-plastic-lined metal. Valve caps are mostly made of black plastic and also of metal or plastic-lined metal, with rubber washers found inside some caps made of plastic and most metal caps. However, to prevent corrosion due to electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
and malfunction of the electronics in a direct TPMS
Direct TPMS
Direct TPMS, or direct tire pressure monitoring systems refers to the use of a pressure sensor directly mounted on the wheels or tires of a vehicle. The pressure inside the tire is measured using a pressure transducer with the pressure information being subsequently sent to the vehicle to warn the...
(tire-pressure-monitoring system) and avoid costly repairs, metal valve caps without insulating plastic linings should never be used on direct-TMPS-equipped tire valve stems http://www.31inc.com/catalog. Therefore, only plastic caps or metal caps with plastic linings should be used in direct-TMPS-equipped tire valve stems. Moreover, metal valve caps without plastic linings can also cause corrosion and may become stuck to the valve and require breaking of the valve in order to remove it when the cap metal (such as brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
) is different than the valve metal (such as aluminum) http://www.31inc.com/catalog. When the valve caps are installed, care must be made not to leave them loose, as they may not seal properly and may even come loose and fall off. Overtightening the valve caps might damage the rubber washer inside the cap, damage or break the cap itself, or damage the valve. Also, installing the cap at a slight angle can cause stripping of the threads and, therefore, it should be gently finger-tightened while ensuring that it is straight and the threads aren't stripped.
There are also special pressure monitoring valve caps available that use a spring-loaded piston to raise a green flag when the pressure is at or above the correct setting. Upon losing pressure the green flag is retracted to reveal a red pin, hopefully catching the attention of the owner before fuel is wasted by running the tire under-inflated.
Recently, colored plastic valve caps have appeared. Certain automobile tire dealerships are promoting the use of dry nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
to inflate tires. Dealers claim that eliminating oxygen and water will prolong the life of both tires and wheels. These dealers install green caps to signify that the tires are filled with nearly pure (typically about 95%) nitrogen. In contrast, regular air is approximately 78% nitrogen. The moisture in the air-filled tires condenses in below-freezing temperatures and causes a sudden drop in tire pressure. Dry-nitrogen filling helps prevent this problem. As an alternative to green nitrogen-ID (nitrogen-identification) caps, green nitrogen-ID O-rings to be installed on valve stems under the caps, while still using black- or metallic-colored caps, are also available http://www.31inc.com/catalog.
Other vendors are selling caps in a variety of other colors for purely decorative purposes. The decorative category even includes caps that light up when the wheels move. When used on a bicycle these can also enhance safety by improving the visibility of the rider.
Presta valves vs. Schrader valves
Whereas Schrader valves are almost universal on car tires, bicycle tubes have either Schrader or PrestaPresta valve
The Presta valve is a valve commonly found in high pressure road style and many mountain bicycle inner tubes. It comprises an outer valve stem and an inner valve body...
valves. Both types are good at sealing high pressures. Their chief differences are that Schrader valves are larger and have springs that close the valve except when the pin is depressed. Schrader valves are used in a wide variety of compressed gas and compressed liquid applications.
Compared to Presta valves, Schrader valves used for bicycle tires have a greater diameter, requiring a larger diameter hole in a bicycle rim. While not a concern on wider bike rims, it will weaken a narrow wheel rim, precluding their use on (road) racing bicycle
Racing bicycle
A racing bicycle, also known as a road bike, is a bicycle designed for competitive road cycling, a sport governed by according to the rules of the Union Cycliste Internationale...
s. Another disadvantage of the Schrader is that the air chuck must depress the spring-loaded pin before air can flow during inflation, whereas the Presta valve relies solely on internal air pressure to keep it shut. This means that some air is lost while attaching and detaching pumps to Schrader valves, although this is usually nominal (most of the air which makes the "whooshing" noise when the pump is removed comes from the compressed air in the tube between the pump body and the attachment end, not the tire via the momentarily-open Schrader valve). To fill up a bicycle tire with a Presta-valved tube at a gas station requires an adaptor, while a Schrader-valved tube does not.
Dimensions
Schrader valves are classified by their material, diameter of intended rim hole, length, and shape.- TR-4 - straight metal stem (8 mm dia.)
- TR-6 - straight metal stem (8 mm dia.)
- TR-13 - straight rubber stem (11.5 mm dia.)
- TR-15 - straight rubber stem (16 mm dia.)
- TR-87 - short 90° metal stem (10 mm dia.)
- TR-87C - tall 90° metal stem (10 mm dia.)
and also :
- TR 413- 0.453" rim hole diam.(11,50mm) 1,25" long (=31,8mm)
- TR 415- 0.625" rim hole diam.(15,87mm) 1,25" long (=31,8mm)
- TR 418- 0.453" rim hole diam.(11,50mm) 2" long (=50,8mm)
- TR 425- 0.625" rim hole diam.(15,87mm) 2" long (=50,8mm)
The standard Schrader valve has the following threads:
External thread
- Metric: 7.7 mm OD, thread root diameter is 6.9 mm × 0.794 mm pitch.
- Imperial: 0.305 in OD, thread root diameter 0.271 in × 32 tpi (threads per inch)
Internal thread (to accept the threaded valve core)
- Metric: 5.30 mm OD × 0.706 mm pitch
- Imperial: 0.209 in OD × 36 tpi.
For refrigeration, a 1/4" male flare fitting
Flare fitting
Flare fittings are a type of compression fitting used with metal tubing, usually soft steel and ductile copper, though other materials are also used. Tube flaring is considered to be a type of forging operation, and is usually a cold working procedure. During assembly, a flare nut is...
is used, with the same internal thread as above.
See also
- Presta valvePresta valveThe Presta valve is a valve commonly found in high pressure road style and many mountain bicycle inner tubes. It comprises an outer valve stem and an inner valve body...
- Valve stemValve stemA valve stem is a self-contained valve which opens to admit gas to a chamber , and is then automatically closed and kept sealed by the pressure in the chamber, or a spring, or both, to prevent the gas from escaping...
- Dunlop valveDunlop valveThe Dunlop valve, is a type of pneumatic valve stem in use in some countries, such as Japan, Czech Republic, Poland, Russia, the Netherlands, Germany, Britain, Finland, Sweden, and developing countries...
also called a Woods valve or an English valve