Bicycle valve
A bicycle valve is a check valve on the tube of the bicycle tire or on the rim of the wheel of a bicycle , the filling the tire with air , gas is used or sealing liquid.
Valve types
There are three basic types of bicycle valves. The names differ depending on the manufacturer and country. Several names are usually given on the packaging (see synonyms in the info boxes).
The distribution of the individual types varies depending on the country, manufacturer, bike type and age.
A bicycle valve sits in a valve stem, the length and diameter of which must match the cross-section and bore of the rim . Dunlop valves for simple steel or aluminum rims usually had shaft lengths of around 25 mm or 32 mm. Today a length of around 40 mm has become established for all three common valve types. For tall aluminum hollow-wall rims with aero profile, Presta valves with shaft lengths of 50 mm, 60 mm and even 80 mm are available. Schrader valves are also offered with an angled and approx. 40 mm long shaft. The valve insert, which points outwards by about 45 °, makes it easier to handle wheelbarrow wheels and other (small) running wheels in which the rim and hub are not connected by spokes but by a continuous disc.
Dunlop valve
Synonyms
Rim bore
Thread DIN 7756
Maximum pressure
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The Dunlop valve is most widespread in Germany, Austria and the Netherlands. It was used on all types of bicycles except racing bicycles until the 1980s and is now predominantly found on everyday and touring bicycles. It was named after the inventor John Boyd Dunlop , the founder of the tire manufacturer of the same name . The Dunlop valve is inserted into slots in the valve stem to prevent it from twisting and secured with a union nut, which also seals the tire. It can be changed quickly and without tools and is accordingly prone to theft and sabotage. The union nut is loosened to release air.
In the original design, a valve insert is used, the lower end of which consists of a closed tube with a lateral air hole. A short rubber hose is pulled over the tube, which is pressed in front of the hole by internal tension and in particular by the air pressure of the tire. If the pump generates a higher pressure than is already present in the tire, the rubber hose lifts off the tube and air can flow into the hose. Manual inflation requires more force with Dunlop hose valves than with the other valve types, as the pump pressure has to overcome the tension in the rubber hose and part of the energy used is converted into heat by the flow resistance of the narrow gap between hose and tube.
Apart from the low-price segment, valve inserts are usually used today instead of hose valves that contain a movable sealing body made of plastic or metal, which can move up and down in the valve tube and is pressed against the round seal seat by the tire pressure in the manner of a check valve . The pressure required to loosen the ball or cylinder from the seal seat and release the path is significantly lower than with hose valves.
The new design of the valve inserts will flash valve , automatic valve , patent valve or the manufacturer about Alligator valve called. The terms Dunlop and Blitz valve are used synonymously today.
Most Dunlop valves are designed for up to 6 bar pressure .
Since Dunlop valves cannot be kept open when pumping like Schrader valves, the tire pressure can only be measured while air can flow through the valve. The pressure gauge of most air pumps only shows the tire pressure when the pump is activated at the same time. Since an increased pressure is initially required with each pump stroke in order to lift the sealing element from the valve seat, an excessively high pressure is displayed during the first pressure build-up, which only adjusts approximately to the actual tire pressure in the course of the pump stroke. But even then, a tire pressure increased by the pressure loss in the valve is displayed.
Presta valve
Synonyms
Rim bore
Thread DIN 7756
Maximum pressure
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The Sclaverand valve was invented by the French Etienne Sclaverand and is therefore usually called the French valve or Presta valve . "Presta" or "presto" in the Romance languages stands for fast , urgent , immediate . The valve head of this check valve is connected to a plunger that protrudes from the opening of the valve and has a fine thread. A knurled nut is screwed onto the tappet and must be loosened to fill the hose. When tightened, the nut secures the valve against gradual loss of pressure and, to a lesser extent, against the ingress of dust. To prevent the nut from being lost, the end of the set screw is compressed.
To inflate the hose, loosen the knurled nut and briefly push the valve stem to release it from the valve seat. Hoses with a Presta valve are easy to inflate because the sealing body is not pressed against the valve seat by spring force, so that only the momentary counter pressure in the tire has to be overcome. When inflating, make sure that the pump head is pushed far enough over the valve, otherwise the knurled nut can get stuck in the rubber seal of the pump. In this case either the air pushes back into the pump after each pump stroke or the valve does not open properly and the hose can hardly be inflated even with great effort.
The air moving towards the outside, at lower pressure, closes the valve automatically. The higher the internal pressure, the more the truncated cone is pressed into its seat. Presta valves are suitable for high tire pressures, as is common with narrow racing bike tires , in order to keep rolling resistance low.
Presta valves are inserted through a 6.5 mm hole in the rim base. Presta valves can therefore also be used with very narrow rims. With wider rims, their stability is not so much weakened due to the smaller bore. Presta valves can therefore also be found on high-quality mountain bikes . The valve insert can either be connected directly to the threaded sleeve vulcanized to the rubber hose or screwed into the sleeve as a removable element. The removable valve inserts usually have flattened sides so that they can be gripped with pliers or a special tool and screwed out. In the event of a gradual loss of pressure, the tight fit of the insert should be checked.
Special pressure gauges open the valve tappet when it is attached to the valve so that the tire pressure can be measured.
The threaded shaft of the tappet with a knurled nut (both often made of brass) can bend and break when the pump is put on or taken off. Before inserting or removing the hose from the rim, the knurled nut should first be screwed tight so that the head does not break off if it gets stuck on the edge of the hole.
The Sclaverand valve is similar to the Regina valve , which is mainly used in Italy. In the Regina valve, the threaded pin is so short that it does not protrude from the valve tube and therefore cannot be bent. In order to close the valve tightly, a small, loose nut with a threaded sleeve is placed on this threaded rod with a diameter of only around 1.5 mm and screwed on by hand so that the sealing body on the valve head, in the form of a truncated cone, is attached to the valve seat is pressed.
Schrader valve
Synonyms
Rim bore
Thread DIN 7756
Maximum pressure
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The by August Schrader manufactured and designed by his son Georg HF Schrader and patented valve is also used in motor vehicles and therefore also Autoventil called.
When the pump head or a manometer is attached, a plunger is pressed down in the valve, which opens it. Hand pumps for car valves therefore require both a pin to actuate the plunger and a check valve, which is usually located directly in the pump head.
A tire with a car valve can be inflated at any gas station that provides compressed air. Due to the small volume of air in the bicycle tire, the tire pressure should be checked after a short puff of air in order to prevent the tire from bursting. The compressed air systems of the filling stations usually provide a pressure of 4 to 6 bar.
In order to be able to use air pumps for Dunlop and Sclaverand valves with car valves, an adapter with a built-in check valve is usually required.
A Schrader valve always consists of an insert that can be unscrewed and the threaded sleeve connected to the hose. A fork-shaped wrench is required to unscrew the insert, which is often located on the back of the valve cap.
Only the Schrader valve is offered as a version of the roller valve , the lower part of which does not have a thread, but is thinly encased with rubber tubing. This type of valve is not pulled outwards with a valve nut in the rim hole, but only pressed into the rim by the air pressure in the tube.
Also only of the Schrader valve are there variants with a thread-free shaft bent to the side . This version is required for the small pneumatic wheel of wheelbarrows , for the inner wheel of twin wheels (typically on trucks, sometimes with a valve extension (rigid or flexible and attached to the inside of the outer rim) so that it can be reached from the outside) or for off-road vehicles Roller skates or scooters whose tires are only around 150 mm in outer diameter.
handling
All three valve types can be connected to the pump by attaching a head with an embedded rubber seal. The sealing rubber is then often tensioned by turning a lever or turning part of the head. With simple hand pumps, the rubber seal is often simply pressed onto the valve. Some pumps are connected using a flexible connection hose that is screwed onto the valve.
If a hose with a Schrader valve cannot be inflated, this is usually due to the fact that the central spike in the pump head does not press the plunger in the valve far enough.
With the Sclaverand valve, the rubber insert of the pump head must be pushed far enough onto the valve so that the air can enter unhindered. Occasionally the valve cone jams in the valve seat and has to be loosened by pushing the plunger (after the lock nut has been loosened).
In the case of the quick release valve, too, the blocking element of the valve insert occasionally sticks to the valve seat and has to be blown free due to the build-up of particularly high pressure.
With Schrader and Sclaverand valves, it can happen that they do not protrude far enough out of the rim base to push the pump head open far enough. If there is an external thread, the nut supplied can be used to pull the valve out further. Alternatively, the jacket can be pressed in from the outside in order to push the valve a little way out of the hole. If some pressure has built up in the tire, the valve should stay in the correct position by itself. If the valve is still too close to the rim, a tube with a longer valve stem can be used. With the Sclaverand valve in particular, the stem length varies greatly.
Compatibility and adapters
Simple air pumps and pressure gauges usually fit both Dunlop and Sclaverand valves. In order to inflate Schrader valves, pumps with a wider receptacle and a centrally fixed pin are required.
Air pumps suitable for all three types of valves,
- are provided with two separate recordings or
- can be converted for the other valve type by exchanging or turning the rubber and insert around
- have an enlarged rubber sealing ring, which is pressed together by a clamping mechanism on the pump head and can thus be adjusted to the different valve diameters.
Pumps for Schrader valves are often supplied with adapter pieces that also enable use with Dunlop and Sclaverand valves (adapter 2 in the illustration). These can also be used to inflate the tires at the gas station. It should be noted here that many pump devices either do not display the tire pressure at all or only display it very briefly during inflation.
The Alligator company has developed a universal valve based on the quick valve that should fit almost all valve blocks. With this valve, the pressure can only be measured during the pumping process.
Powerful compressors, which are suitable for inflating thin racing bike tires, often burst conventional hoses if care is not taken to adhere to the pressure indicated on the casing. If the air pressure is too high, old jackets with a porous rubber compound or exposed fabric can suddenly develop a crack several hours after the tire has been inflated, from which the tube escapes and bursts, or it can slip out of the rim, even if nothing is noticeable at first.
Valves and inserts
Dunlop valve with hose attachment
Dunlop valve with ball (quick valve)
Loosen the knurled nut that fixes the valve stem to the rim
Presta valve
The Sclaverand valve insert differs from the Schrader valve insert by the knurled nut and the tappet with external thread
Schrader valve insert, long
Schrader valve insert, short
Left: Schrader valve insert - middle and right: valve stubs for insertion in tubeless vehicle rims (shown smaller than the valve insert)
Universal valve insert from Alligator, can be screwed into the Sclaverand valve stem, it is attached to Auto and Dunlop valve stems using a union nut
Italian regina valve
Italian regina valve with cap
literature
- Fritz Winkler, Siegfried Rauch: Bicycle technology repair, construction, production. 10th edition. Bielefelder Verlagsanstalt, Bielefeld 1999, ISBN 3-87073-131-1 .
Web links
- Half-sections of a Blitz and a Sclaverand valve including a representation of the latter's functionality
- Different lengths of different valve types at Continental
- Different lengths of different valve types at Schwalbe
Individual evidence
- ↑ Improvements in Pumps for Inflating Pneumatic Tires and the like. European Patent Office, accessed February 13, 2011 .
- ↑ Valves schwalbe.com
- ↑ Our History. In: schraderduncan.com. Archived from the original on July 27, 2014 ; accessed on August 7, 2019 .
- ↑ GHF SCHRADER Valve (US Patent No. 495,064, April 11, 1893; PDF 661 kB)