Do AN Fittings Need Sealant?

AN fittings are designed for a reliable metal-to-metal seal, primarily through their flared design, not thread sealants. Therefore, in most standard applications, sealants are unnecessary and can even cause issues. Proper installation, including clean surfaces and correct torque, is crucial for leak-free performance.

However, there can be exceptions. Manufacturers might recommend specific sealants when dealing with certain fluids or extreme conditions. It’s always best to consult the manufacturer‘s guidelines for your particular application to ensure optimal sealing and prevent potential problems.

What Is Hydraulic Fitting Sealant

Hydraulic fitting sealant is a substance applied to the threads or sealing surfaces of hydraulic fittings to prevent leaks. It comes in various forms, including liquids, tapes, and pastes, each designed for specific applications and fitting types. The primary function of these sealants is to fill the microscopic gaps and imperfections present in the threads or mating surfaces, creating a barrier against fluid leakage, especially under high pressure.

The type of hydraulic fitting sealant used depends on the fitting design and the operating conditions of the hydraulic system.

For threaded fittings, like NPT, sealants are essential to compensate for the tapered thread design, which inherently leaves minute gaps. In contrast, fittings that rely on metal-to-metal contact or O-rings for sealing often don’t require thread sealants on the sealing surface, but may use lubricants to aid assembly. Choosing the correct sealant, compatible with the hydraulic fluid and temperature range, is crucial to ensure a reliable and leak-free hydraulic system.

The Role of Sealant in Hydraulic Fittings

Sealant’s role in hydraulic fittings varies significantly based on the fitting type. Threaded fittings, particularly NPT, rely heavily on sealant to compensate for thread imperfections and create a pressure-tight seal. The tapered threads provide a mechanical seal, but sealant, such as Teflon tape or liquid threadlocker, is essential to fill microscopic gaps and prevent leaks under high pressure. This ensures system integrity and prevents fluid loss.

Conversely, fittings designed for metal-to-metal sealing, like AN and JIC flare fittings, or those utilizing O-ring face seals (ORFS), generally do not require sealants on the sealing surfaces. These fittings achieve a reliable seal through precise mechanical contact or O-ring compression. Introducing sealant in these applications can disrupt the designed sealing mechanism, potentially leading to leaks or contamination. However, thread lubricant is sometimes used to aid assembly and prevent galling on threaded portions of these fittings, without compromising the primary sealing surfaces.

Hydraulic Fitting Sealant Types

It’s important to understand that “sealant” in hydraulics can refer to thread sealants or the sealing elements within the fittings themselves (like O-rings). Here are the hydraulic fitting sealant types and their applications:

Thread Sealants:

• Used primarily on tapered threads (NPT/BSPT) to fill gaps.
• Must be compatible with hydraulic fluids.

Sealing Elements:

• O-rings, washers, and the metal-to-metal contact of flared fittings.
• These are integral to the fitting’s design.

Hydraulic Fitting Sealant Types:

Here’s a table summarizing common sealant types and their applications:

Important Notes:

• Always check manufacturer recommendations for specific fittings and hydraulic systems.
• Cleanliness is crucial in hydraulic systems. Contamination from excess sealant can cause serious damage.
• When dealing with O-rings, it is important to lubricate them with a compatible hydraulic fluid before installation.

How Hydraulic Fitting Sealants Work

Hydraulic fitting sealants function through a variety of mechanisms, depending on their type. Thread sealants, designed for tapered thread fittings like NPT, operate by filling the microscopic voids and imperfections between the threads. As the fitting is tightened, the sealant is compressed and forms a barrier that prevents fluid from escaping. This is particularly crucial in high-pressure hydraulic systems, where even minute leaks can result in significant fluid loss and system inefficiency. Teflon tape, for example, acts as a deformable filler, while liquid thread sealants cure to form a resilient, leak-proof seal.

In contrast, sealing elements like O-rings work through mechanical compression. When an O-ring is installed in its groove and the fitting is tightened, it is compressed, creating a tight seal against the mating surfaces. The elastic properties of the O-ring material allow it to conform to surface irregularities and maintain a seal even under varying pressures and temperatures. The selection of the O-ring material is critical, as it must be compatible with the hydraulic fluid and operating conditions to prevent degradation and ensure long-term sealing performance.

Finally, metal-to-metal seals, as seen in flared fittings, rely on the precise deformation of the tubing against the fitting seat. The flared end of the tubing is forced against the fitting’s conical surface, creating a tight, leak-free connection. The accuracy of the flare and the proper tightening torque are essential for this type of seal to function correctly. This eliminates the need for additional sealants, as the metal-to-metal contact itself provides the sealing mechanism.

How to Seal AN Fittings

While AN fittings are designed for metal-to-metal sealing and generally don’t require sealant, there are rare instances where a very thin application might be considered, particularly in low-pressure applications or when dealing with minor imperfections. However, excessive sealant is detrimental. Always prioritize proper fitting preparation and assembly.

Step 1: Choose the Right Sealant (If Needed)

Understanding the Risks:

• Using the wrong sealant or applying it excessively can contaminate the hydraulic system, leading to component failure.
• Sealant can interfere with the precise metal-to-metal seal that AN fittings rely on.

Selecting a Compatible Sealant:

• If a sealant is deemed absolutely necessary, choose a low-strength, non-hardening thread sealant specifically designed for hydraulic systems.
• Ensure the sealant is compatible with the hydraulic fluid and operating temperatures.
• Avoid thick, paste-like sealants or those containing particles that could clog filters or valves.
• Anaerobic sealants are sometimes used in very specific applications.

When to Avoid Sealant:

In most high-pressure hydraulic applications, sealant is strongly discouraged.

If the fittings are properly manufactured and installed, they should seal without any additional sealant.

If there are any doubts about the fittings, replace them with new, high quality fittings.

Step 2: Prepare the Fittings

Inspection:

• Thoroughly inspect the fittings and tubing for any damage, such as scratches, dents, or burrs.
• Ensure the flared end of the tubing is perfectly formed and free of imperfections.
• Check the fitting seat for any signs of damage or contamination.

Cleaning:

• Clean the fittings and tubing with a lint-free cloth and a suitable solvent to remove any dirt, grease, or debris.
• Ensure the threads are clean and free of any old sealant or debris.
• Use compressed air to blow out any loose particles.

Deburring:

If necessary, use a deburring tool to remove any sharp edges or burrs from the tubing or fitting threads. This is especially important on freshly cut or flared lines.

Step 3: Applying Liquid Thread Sealant (If Absolutely Necessary)

Minimal Application:

• If a liquid thread sealant is required, apply a very thin, even coat to the male threads only.
• Avoid applying sealant to the first two threads, as this can push sealant into the system.
• Do not apply sealant to the flared surface.

Proper Technique:

Use a small brush or applicator to apply the sealant.

Ensure the sealant is evenly distributed and does not clump or drip.

Follow the hydraulic fitting manufacturer’s instructions for curing time, if applicable.

Step 4: Applying Teflon Tape (Generally Not Recommended)

Why It’s Discouraged:

• Teflon tape is generally not recommended for AN fittings due to the risk of shredding and contaminating the system.
• It can also interfere with the proper seating of the flare.

If Used (Extremely Rare Cases):

• If Teflon tape is used in very low pressure situations, apply only one or two wraps of high-quality tape.
• Wrap the tape in the direction of the threads to prevent it from unraveling during installation.
• Ensure that no tape extends past the end of the threads, so that it cannot break off into the hydraulic fluid.
• Again, this is highly discouraged.

Step 5: Assembling AN Fittings

Alignment:

• Carefully align the fittings and tubing to prevent cross-threading.
• Start threading the fittings by hand to ensure they are properly aligned.

Torque Application:

• Use a torque wrench to tighten the fittings to the manufacturer‘s specified torque.
• Over-tightening can damage the fittings and lead to leaks.
• Under-tightening will also cause leaks.

Inspection:

• After assembly, inspect the fittings for any signs of leaks.
• If a leak is detected, carefully loosen the fitting and inspect the sealing surfaces.
• Retighten to the proper torque, or replace damaged components.

Pressure Testing:

• If possible, pressure test the system to ensure the fittings are properly sealed.
• This is especially important in high-pressure hydraulic systems.

Conclusion

AN fittings are engineered to create a reliable seal through a metal-to-metal connection, specifically their flared design. Therefore, in most standard applications, sealants are unnecessary and can even cause issues. Proper installation, including clean surfaces and correct torque, is crucial for a leak-free connection.

While AN fittings themselves do not require sealant, it is very important to distinguish AN fittings from NPT fittings. NPT fittings are tapered pipe thread fittings, and they do require thread sealant. If you’re in need of high-quality AN fittings for your hydraulic systems, DF Hydraulics offers a wide selection of wholesale options.

Contact DF Hydraulics today to explore their inventory and find the perfect fittings for your needs.