O-ring boss seal
Encyclopedia
An O-Ring boss seal is a technique for joining two fluid-carrying pipes
, hose
s or tubing. In an o-ring boss (abbreviated ORB) system, a male
threaded
part is inserted into a female threaded part, providing a mechanical seal. This system differs from others in that an additional nut is tightened over an o-ring into a beveled area, creating a fluid-tight seal.
This system is used most frequently in hydraulics
, although it has been applied to other systems including compressed air systems and vacuum pump
s, such as many Robinair pumps, in which the intake tee has an o-ring boss seal on the bottom. Since the ORB system is relatively rare, it can be confused with other connection systems, such as NPT
. While threads of different connectors sometimes fit (although often very inexactly), o-ring boss seal system connectors should never be used with any other type of connectors, as leaks are likely. Under the high fluid pressures commonly seen in hydraulic systems, a leak or failure of the connection is quite dangerous and could lead to loss of life.
Because ORB adapters are relatively rare, one can be fashioned using a 37 degree AN (Army/Navy) flare fitting
because the threads are compatible in diameter, pitch and spacing. To do this, a suitable o-ring, washer and nut are obtained separately. The flared end of the male AN flare is machined off. Optionally, a chamfer
tool (or, if one cannot be obtained, a drill bit) can then be used to knock the inside shoulder off and make a reverse or inward angle that will smooth the flow of the fluid into the fitting bore. The last step is often unnecessary because most applications don't require a smooth flow of fluid unless operating at an extremely high flow rate.
This system has the advantage of being able to be tightened mechanically before being sealed. Most threaded systems, such as NPT, have a seal provided by a taper in the thread, so it is difficult to orient both ends of the hose, pipe or tube so that it is not twisted. In the o-ring boss system, this problem is eliminated because the threads do not seal the connection and therefore can be rotated at least a full revolution before they are sealed while maintaining a proper mechanical connection. The orientation problem could also be solved with a suitable union.
Plumbing
Plumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
, hose
Hose (tubing)
A hose is a hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called pipes , or more generally tubing...
s or tubing. In an o-ring boss (abbreviated ORB) system, a male
Gender of connectors and fasteners
In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally assigned the designation male or female...
threaded
Threaded pipe
A threaded pipe is a pipe with screw-threaded ends for assembly.- Tapered threads :The threaded pipes used in some plumbing installations for the delivery of gases or fluids under pressure have a threaded section that is slightly conical . This is called a "tapered thread"...
part is inserted into a female threaded part, providing a mechanical seal. This system differs from others in that an additional nut is tightened over an o-ring into a beveled area, creating a fluid-tight seal.
This system is used most frequently in hydraulics
Hydraulics
Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...
, although it has been applied to other systems including compressed air systems and vacuum pump
Vacuum pump
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...
s, such as many Robinair pumps, in which the intake tee has an o-ring boss seal on the bottom. Since the ORB system is relatively rare, it can be confused with other connection systems, such as NPT
National pipe thread
National Pipe Thread Tapered Thread is a U.S. standard for tapered threads used on threaded pipes and fittings. The taper rate for all NPT threads is measured by the change of diameter over distance. The angle between the taper and the center axis of the pipe is 1° 47′ 24″...
. While threads of different connectors sometimes fit (although often very inexactly), o-ring boss seal system connectors should never be used with any other type of connectors, as leaks are likely. Under the high fluid pressures commonly seen in hydraulic systems, a leak or failure of the connection is quite dangerous and could lead to loss of life.
Because ORB adapters are relatively rare, one can be fashioned using a 37 degree AN (Army/Navy) flare fitting
AN thread
The AN thread is a particular type of fitting used to connect flexible hoses and rigid metal tubing that carry fluid. It is a US military-derived specification that dates back to World War II and stems from a joint standard agreed upon by the Army and Navy, hence AN.AN sizes range from -2 to -32...
because the threads are compatible in diameter, pitch and spacing. To do this, a suitable o-ring, washer and nut are obtained separately. The flared end of the male AN flare is machined off. Optionally, a chamfer
Chamfer
A chamfer is a beveled edge connecting two surfaces. If the surfaces are at right angles, the chamfer will typically be symmetrical at 45 degrees. A fillet is the rounding off of an interior corner. A rounding of an exterior corner is called a "round" or a "radius"."Chamfer" is a term commonly...
tool (or, if one cannot be obtained, a drill bit) can then be used to knock the inside shoulder off and make a reverse or inward angle that will smooth the flow of the fluid into the fitting bore. The last step is often unnecessary because most applications don't require a smooth flow of fluid unless operating at an extremely high flow rate.
This system has the advantage of being able to be tightened mechanically before being sealed. Most threaded systems, such as NPT, have a seal provided by a taper in the thread, so it is difficult to orient both ends of the hose, pipe or tube so that it is not twisted. In the o-ring boss system, this problem is eliminated because the threads do not seal the connection and therefore can be rotated at least a full revolution before they are sealed while maintaining a proper mechanical connection. The orientation problem could also be solved with a suitable union.