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Understanding Performance Fittings
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Understanding Performance Fittings
If you are confused by the nomenclature of hoses and fittings associated with racecar plumbing, you’re not alone. Fittings are often measured in terms that begin with a dash, such as a -6 or a -8. To find out more about how these systems work, we turned to Fuelab, a manufacturer of fuel pumps, filters, pressure regulators and accessories, to help clear up the issue.Get more news about Flange Adapter Rubber Ring,you can vist our website!
This installment of “Tech Matters” will describe the different types of fittings commonly used for high-end racing and street performance applications. The fittings we will discuss are adapter fittings — also called standard, or union — port fittings, and pipe fittings, as well as thread types and size standards associated with each.
Before we get into the types of fittings, let’s first define the thread types used on the fittings, and discuss applicable AN standards.Straight Thread — With straight thread, the threads run parallel cylindrically to each other. Port fittings and adapter fittings using straight thread require use of an O-ring boss seal technique to seal against leakage.
Tapered thread, also known as pipe thread, typically uses a 2-degree angle on the threads, instead of running parallel. This allows the threads to interfere and seal off. Threads must be clean and precise to make up for gaps between threads that allow for leakage. Pipe fittings, which use tapered thread, don’t use O-rings, but rather must use compounds or teflon tape to help seal the threads. National pipe thread taper (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings.
High-end racing and performance fuel delivery systems most frequently implement fuel lines and fittings manufactured to AN standards. During World War II, the U.S. military set specification standards for fasteners and fluid fittings used on military equipment. These standards are headed under “AN” which is the abbreviation for “Army-Navy,” but also is known as “Air Force – Navy Aeronautical Standard.” After the war, many surplus aerospace parts were used for racing, and thus introduced the AN standard into the racing and performance world.
In the case of tubes and hoses used to carry fluid, “AN Size” designates the outer diameter of the hose or tubing in sixteenth-inch increments. For example, an AN size -2 designates a tube OD of eighth-inch (2 x 1/16”), the tube OD of AN size -3 is 3/16” (3 x 1/16”). The AN size number is correctly displayed with a dash before the number.
Each AN size also references a standard male and female thread size that is used on fittings, such as hose-end fittings, adapters, and port fittings. This is known as “AN Thread Size.”
AN fittings have straight thread, and use O-ring seals. The O-ring size is typically defined by the “AS” standard. Dash numbers are typically assigned based on the size. Boss-seal style O-rings are typically in the 900 series. For example -906 is for -6AN ports, and -908 is for -8AN ports.
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