The Perfomance Enhancement in Hydraulic Fittings through six sigma dimensions
The Hydraulic Fittings are simply named as fittings used in a Fluid Transmission system, Fittings which are classified in to following standards
1. NPTF/NPT threads.
2. BSP threads.
3. Metric Taper.
The Fittings have Inlet and Outlet port where the fluid transmission takes place, the Fittings connect pipes. It is quite normal to see the gaps between mating threads of the ports and pipes.
There could be very common reasons for malfunction of the fittings
1. Sealing between threads are not Good.
2. Galling between threads.
In both situations, the resultant could be tolerance stacking, A design intent for Good performance of the system is when the dimensions are located at the center of the tolerance.This clearly states that the Orifice diameter and the pipe diameter must be manufactured at the center of the tolerance.
In real world situations, we do find that the Diameter of the orifice (of the fitting) and the Pipe is spread widely away from the center or the mean of the specification. This situation always gets compensated by seals, grease which adds an extra component and may further reduce the reliability of the system (as more working components placed in series reduces the reliability of the system).
There are instances where the Pipe may be at the lowest end of its tolerance, while the orifice at the Highest end of the tolerance which technically is an acceptable part,however this stacked tolerance can result in decreased reliability of the system and sometimes lead of a major Hydraulic application. Such components are manufactured to using a 2 sigma process.
If the orifice and the tubing diameters are manufactured to the center of their respective specification and with a narrow spread of sigma (standard deviation from the Center of the specification), Which will avoid stacking of tolerance and will meet the true design intent. This compliance can be experienced with a Six Sigma process, where 3 out of 1 million fitting orifices or pipes can be an outlier or exist at the extreme end of the tolerance.
A six-sigma process eliminates need for washers, seals and provides a perfect mating between orifice and pipe and further strengthens the reliability of a series systems, which also eliminates the need for parallel redundancies. The Six Sigma process compliant components or systems need very few component replacements and maintenance.
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