Radium Engineering deals with fluid connections for automotive applications. Properly connecting fuel, pressurized air, hot oil, etc. is an area in which we have extensive experience. This guide explains the most popular fluid connections currently used in cars for plumbing fuel, oil, coolant, air, and other needs. It will also explain how to properly utilize connections to ensure a leak-free operation. To properly and safely install our products, understanding connections is of the utmost importance. Most of the following information can be found with research, however, we decided to consolidate it in one place and discuss it's relation to automotive applications. Brake line related fittings such as SAE flare, inverted flare, hard lines, etc will not be covered. All listed information is simply a general guide. Please consult with hose and fitting manufacturers before selecting components for safety critical systems. To begin our discussion...
Beaded stem fittings work as a hose-to-fitting connection. This is simply a pipe with a slight flare in it. These are the most common connection types and are found on almost every car. They are inexpensive, effective, and do not require any special end fitting for the hose. Hoses slide on and secure with a hose clamp. An example of a fuel pressure regulator with beaded stem connetions is pictured.
When using beaded stems and rubber hose for fuel injection systems, EFI rated fuel hose should be utilized that can handle the higher pressures found in modern EFI systems. Fuel injection hoses also require special hose clamps as shown below.
Beaded Stem Summary
Common Automotive Uses: fuel lines, coolant lines, radiator hoses, PCV/Emissions hoses.
Benefits: inexpensive, easy servicing, very common, no hose fitting required, no special tools
Drawbacks: not for extremely high pressure, not for high temperature, not as robust as other fluid connections, requires clamp, aesthetics
Push-Lok Hose Ends
Push-Lok hose barbs are a means to attach a hose-end to a rubber hose. Several sharp barbs lock into the inside diameter of the hose and create a seal. Below is an example of a push-lok hose end.
Depending on hose type, these fittings can be difficult to assemble and may require lubricant. Once installed, they cannot be pulled apart and can withstand several hundred PSI. The hose must be cut to remove to preserve the fitting. Most hose manufacturers offer a hose type specifially made for Push-Lok fittings. Push-Lok Hose names may vary (i.e. Aeroquip labels them SOCKETLESS fittings, Russell labels them TWIST-LOK, Summit labels them TWIST-TITE). When fittings are used with the correct hose, hose clamps are not necessary. When using the fitting with a non-Push-Lok rated hose, it is suggested to use a clamp. This combination would only be appropriate for low-pressure applications and one must be careful to ensure the Push-Lok fitting does not damage the hose when a clamp is used. The barbs have the potential to slice through the walls of non-Push Lok hose.
Push-Lok Hose Barb Summary
Common Automotive Uses: aftermarket fuel systems, vacuum/boost hoses
Benefits: reusable, high pressure rating, will not leak, low cost, no hose clamp required
Drawbacks: Requires special hose, can be difficult to assemble, hose must be cut for removal
Tapered pipe threads
In the US, pipe threads are commonly called NPT (National Pipe Thread). NPT are a fitting-to-fitting connection used for attaching a fitting to a hole or another fitting. They work in a simple, crude and effective manner. The male NPT fitting has threads that are tapered. In other words, the fitting has a smaller diameter at the tip and then gets gradually larger in diameter farther up the shank. The hole, or female fitting, also has tapered threads. The difference is that the female fitting has a larger size at the opening of the hole which gets smaller deeper in the hole. As the two are threaded together, the male fitting wedges into the female and the flanks of threads compress into each other forming a seal. See diagram below. Pipe threads are commonly called out by a fractional size such as 1/4NPT or 3/8NPT. More information on sizing can be found here. Teflon (or equivalent) lubricant in the form of paste or tape is used to lubricate the interface and make sure the fittings can be unscrewed in the future.
When using NPT fittings, attention must be paid to materials being used. One of the worst case scenarios is screwing together an aluminum fitting with a stainless steel pipe thread fitting. This combination threaded together can cause the aluminum to "gall" with the stainlesssteel. Most often the aluminum threads are destroyed if the connection is unscrewed. To remove, it is absolutely necessary to apply heavy amounts of anti-seize while paying careful attention not to over-torque. In general, NPT threads in all materials deform when tightened. For this reason, they may not seal as well the second time they are used. This is especially true for soft non-ferrous materials.
Besides NPT, it is important to note there is another family of tapered pipe threads called British Standard Pipe Tapered (BSPT). They work exactly in the same way and look almost identical when similar sizes are compared; however, the threads are slightly different. An NPT fitting will not properly seal in a BSPT fitting. Many Japanese engine engines (Nissan, Toyota, etc) use 1/8 BSPT holes for the oil pressure switches. When using this size for an aftermarket turbocharger kit, it is often mistakenly for 1/8-NPT fitting. Mixing the two sizes will create a slow leak over time.
NPT Fittings Summary
Common Automotive Uses: valve cover PCV fittings, threaded fluid holes in engine blocks (oil, water etc)
Benefits: inexpensive, very common, no special tools required, can be improperly clocked
Drawbacks: permanently deforms threads, not a positive guaranteed seal, sensitive to installation, some fittings cannot be reused, do not swivel, requires teflon lubricant
-AN Conical Seal (aka J.I.C.)
-AN (Army/Navy) style fittings are commonly spotted in engine bays in red and blue anodized colors. They are very popular to use for all fluid types from oil to fuel to brake lines. History of this style of fitting can be found online. They are also known as J.I.C. fittings (mostly in the hydraulic industrial world) and use a 37 degree conical seal. JIC and -AN fittings can be interchanged with each other. This style of fitting originated in military applications and over the years have made their way into the automotive aftermarket realm. Authentic MIL-spec -AN fittings are constructed to exacting tolerances and are very expensive. Luckily, many automotive aftermarket companies exist today that manufacture -AN "style" fittings that may not be MIL-spec but still work great for our needs. These would include Russell, Earl's, Aeromotive, Radium, Red Horse Performance, and many more.
Here is an example of some -AN hose and fittings being use on a Nissan SR20DET.
These fittings work by mating a tapered conical surface on the male fitting into a reverse tapered surface in the female ftting, shown below. When the B-nut (female side, blue) is tightened it draws the two gold and gray parts together and a metal-on-metal mechanical seal is formed between the two conical surfaces. THE THREADS DO NOT DO ANY SEALING.
Over-tightening the B-nut can cause leaking. It takes suprisingly litle torque to fully tighten an -AN fitting. Many auto parts retailers sell -AN wrenches that are aluminum so they do not marr the surface of fittings. These wrenches are also very short, helping in tight spaces while preventing over tightening. DO NOT USE ANY TYPE OF TEFLON, LOCTITE, SILICONE SEALANT, ETC ON -AN FITTINGS! They are designed to screw together dry. A small amount of light oil may be used to assist screwing the B-nut down in some applications. The male and female tapered conical surfaces need to be clean and free of scratches or dings, otherwise they may leak. More information can be found here. The 37degree -AN/JIC flare should not be confused with a different fitting type, 45 degree SAE flare.These two are not compatible with each other and will leak!
Photo courtesy of Car Craft Magazine
Shown above, special tools can be used to form a 37 degree flare in hard tubing which allows a leak free way to transition from hard tubing to hose using all 37degree flare fittings. This is useful for plumbing fuel lines on a car.
The chart below explains how these fittings are referenced. So when you hear "I need a dash six ninety hose end" you know the person is working with 3/8" ID hose.
These fittings are available in a variety of different colors and materials. For most automotive/engine related plumbing, aluminum is suitable. Visit your local high performance parts retailer to see all the options. -AN hose ends are installed on a hose by different means. The Push-Lok fitting shown above would be used to convert a rubber push-lok compatible hose to be used with an -AN fitting. However, the traditional -AN hose end is assembled to the hose using a screw down collar.
Another way to attach a hose end to a hose is by crimp. Here is a photo of a -AN hose ends that are crimped by a special machine on to the hose.The hose type in this picture is PTFE teflon with a black sheath covering the stainless steel braid material.
Photo courtesy of Edelbrock
The photo above shows several different hose types from Russell Performance, but all have a -AN hose end installed. Why so many different types of hose? Many factors influence what hose to select for your application. Pressure rating, operating environment, aesthetics, cost, ease of assembly, etc. Contact the manufacturer if you are unsure what hose is best for your application.
The photo below shows a small sample of the different hose types and hose-end fittings available from Aeroquip.
Photo courtesy of Eaton/Aeroquip. Link to Aeroquip Product Catalog
-AN Conical Seal (J.I.C.) Fittings Summary
Common Automotive Uses: aftermarket plumbing of fuel, air, coolant, and oil, used on racing vehicles of all types
Benefits: positive seal, uninterrupted flow, wide variety of fitting and hose configurations available, easily serviced, suitible for high pressures and temperatures, very robust connection, easy to disassemble, most can swivel after assembly
Drawbacks: high cost, assembling hose-end to hose can be labor intensive
O-Ring port fittings (commonly called ORB for short) are an excellent way to attach a -AN hose to a threaded hole. They work by compressing an O-ring into a chamfered groove around the opening of the threaded hole. This creates a reliable seal and is easily serviceable. The female hole MUST have the the chamfer at the opening in order for the O-ring to work properly. If there is no chamfer, the O-ring will be damaged from extreme compression and the fitting will never fully tighten up. The male and female threads are both straight threads, no tapers on this one. The standard is to use -AN threads for these port fittings. This means that the threads are the same as the threads on the 37 degree tapered -AN fittings shown above. This is handy because you can slip an O-ring onto a tapered -AN fitting and thread it into an O-ring port hole and it will work perfectly. There are a wide variety of O-ring port to -AN adapters available from all major fitting manufacturers.
Here is an example of a fuel pump with O-ring ports:
Photo Courtesy of Car Craft Magazine
O-Ring Port Fittings summary
Common Automotive Uses: aftermarket oil pumps, catch cans, fuel rails, fuel pump ports
Benefits: Positive seal, wide variety of adapters available, easily serviced, suitible for high pressures, replaceable sealing element, very robust connection, easy to disassemble.
There are more connections used in the automotive industry, but these are the ones that are dealt with the most by autmotive builders and enthusiests. Understanding what products to use and how to properly use them will result in a leak-free reliable connection. If you are unsure, contact us for assistance or consult with your builder.