Dustcap
Encyclopedia
A dustcap is a small cover
used on the valve stem
of a bicycle
or car
tire to prevent dust
or other small particles from entering the valve and damaging it. The dustcap also forms a pressure seal, helping to prevent deflation of the tire
due to slight gas seepage past the tire valve. Dustcaps are usually made from plastic
but may occasionally be made of metal
. The dustcap is internally threaded and is secured by screwing it onto the end of the stem. To prevent corrosion due to electrolysis
and malfunction of the electronics in a direct TPMS
and avoid costly repairs, metal valve caps without insulating plastic linings should not be used on direct-TMPS-equipped tire valve stems.
A dustcap may also refer, on a bicycle, to the crankarm
bolt cover. It is usually a piece of metal or plastic that, on the crankarm, is snapped or screwed into the threaded counterbore
, which houses the bolt that holds the crankarm to its axle, the bottom bracket
spindle. The dustcap serves to protect the threads (on the inside of the counterbore), which are used with a crankarm puller to remove the crankarm from the spindle. It is also possible for the crank arm to squirm on the bottom bracket spindle, causing the crankarm nut/bolt to become loose, leading to the nut/bolt working its way out of the bottom bracket spindle. The dust cap limits the amount of dangerous loosening that can occur.
A dustcap may also refer, on a bicycle, to the metal ring that covers the bearings in a cup-and-cone ball-bearing hubset. These types of dust caps, being press-fit, are difficult to remove with bending or damaging them. It is suggested to press them out from the other side of the hub using a screw driver. In this role the dustcap reduces the dust that enters the bearing races, and extends service intervals.
Cover
- Science and technology :* A covering, usually one that completely closes the object** Lid** Mechanical seal* The outside of an object, not necessarily enclosing the object** Album cover** Book cover, or magazine cover** CD and DVD packaging...
used on the 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...
of a 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....
or car
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...
tire to prevent dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
or other small particles from entering the valve and damaging it. The dustcap also forms a pressure seal, helping to prevent deflation of the tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
due to slight gas seepage past the tire valve. Dustcaps are usually made from plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
but may occasionally be made of metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
. The dustcap is internally threaded and is secured by screwing it onto the end of the stem. 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...
and avoid costly repairs, metal valve caps without insulating plastic linings should not be used on direct-TMPS-equipped tire valve stems.
A dustcap may also refer, on a bicycle, to the crankarm
Crankset
The crankset or chainset , is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain, which in turn drives the rear wheel...
bolt cover. It is usually a piece of metal or plastic that, on the crankarm, is snapped or screwed into the threaded counterbore
Counterbore
A counterbore can refer to a cylindrical flat-bottomed hole, which enlarges another hole, or the tool used to create that feature. A spot face is a very shallow counterbore...
, which houses the bolt that holds the crankarm to its axle, the bottom bracket
Bottom bracket
The bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks...
spindle. The dustcap serves to protect the threads (on the inside of the counterbore), which are used with a crankarm puller to remove the crankarm from the spindle. It is also possible for the crank arm to squirm on the bottom bracket spindle, causing the crankarm nut/bolt to become loose, leading to the nut/bolt working its way out of the bottom bracket spindle. The dust cap limits the amount of dangerous loosening that can occur.
A dustcap may also refer, on a bicycle, to the metal ring that covers the bearings in a cup-and-cone ball-bearing hubset. These types of dust caps, being press-fit, are difficult to remove with bending or damaging them. It is suggested to press them out from the other side of the hub using a screw driver. In this role the dustcap reduces the dust that enters the bearing races, and extends service intervals.