Correct torque specifications for hydraulic fittings by size and type

There's no one torque value that is applicable to every hydraulic fitting. The correct torque is determined by the type of fitting (JIC 37° flare ORFS/SAE O-ring surface seal, NPT/BSPT tapered, and BSPP straight threads with an O-ring) as well as the dash's size, as well as whether the threads are wet-torqued (lubricated) or dry. For a general guideline: JIC 37° fittings range from 6-7 ft-lbs at -02 to 190-258 ft-lbs at -32. ORFS fittings range from 10-12 ft-lbs in -04 to 150-165 ft-lbs when -24. Pipes with tapered threads (NPT/BSPT) are not torqued to a specific ft-lb number—they are tightened manually and have a certain amount of turns. Always verify the datasheet of the manufacturer of the fitting prior to installation, as coatings, materials, and wet vs. dry lubrication change the numbers.

What is the importance of torque accuracy when it comes to hydraulics?

Hydraulic fittings aren't able to last forever. A fitting that is torqued lower than specification leaks oil during tension cycling and vibration. Fittings with torques above the specifications can break a flare or a groove in an O-ring or gall threads to the point that they are damaged to the point that the connection won't seal properly again. Because the majority of hydraulic circuits operate at pressures ranging from 2,000 to 6,000 psi—and mobile equipment applications also add continuous vibration and thermal cycling in addition to that—torque isn't "close enough" to the spec. It's the biggest factor in determining whether the fitting lasts for ten years or leaks in just ten weeks.

The industry splits torque specification into three questions that are practical What kind of seal is the fitting using, and what size? And is it applied dry or wet? Make sure you answer these three questions correctly, and then the right number will follow.

JIC 37° flare fittings

JIC (Joint Industry Council) fittings, designed according to SAE J514, seal metal-to-metal with a flared cone that is 37 degrees instead of relying upon the sealant for threads or an O-ring. This is a crucial distinction to make for torque: The seal's performance is contingent on flare angle and surface condition, not the sealant used or the torque applied. Excessive torque can crush the flare, causing cracks that leak under pressure. Overtightening is the leading reason for a leaky JIC joint, not tightening too much.

Representative wet-torque values by dash size:

Practice in assembly for JIC fittings

Lubricate the cones and threads using hydraulic fluid or a light oil for lubrication and align the mating parts and rotate the flare nut with your hands to ensure that the two surfaces are in contact prior to torquing until the value above. If there's a pad on the body of the fitting, then back it up using an additional wrench so that the flare won't spin when the nut is turned. When a wrench for torque isn't in the shop, then the alternative is to squeeze the nut until it is firm with your hands, then make it a clockwise turn no more than 1/8 or 1/4 turn. Note that the rotation required typically decreases when the size of the fitting increases. This method based on turns is a temporary solution, not a replacement for the assembly of a torque wrench on circuits that are critical.

It's also worth checking whether you are carrying a JIC part in your possession. SAE 45-degree flare fittings appear identical but are not interchangeable with JIC, although dash sizes 2, 3, 4, 5, 8, 10, and 10 share the same thread. Mixing the two angles of your seat won't seal, regardless of the torque you apply.

ORFS (O-ring face seal) fittings

ORFS fittings, manufactured according to SAE J1453, utilize straight threads as well as an O-ring groove machined into the face of male fittings, rather than a flare. The design is designed to provide leak-free service for up to 6,600 pounds This is the reason ORFS is the most popular option for high-pressure mobile and industrial circuits in which flare fittings are more prone to vibration fatigue.

Representative wet-torque values by dash size:

One aspect that could confuse field technicians is that lubricating the O-ring prior to installation decreases the chance of abrasion during the installation. It also could reduce the torque recommended by up to 25 percent. If your chart of reference does not indicate dry or wet, then assume that it's giving a dry (lubricated) number, as this is the most common method of operation However, you should confirm this with the appropriate manufacturer in the event that the connection is critical to the mission.

What is the reason why ORFS allows field rework to be done better than flares?

Since the seal's component is a reusable O-ring rather than a metal cone machined, ORFS fittings can be separated and reassembled without damaging the seal provided that it is replaced with a new O-ring and properly torqued every time. This is an important advantage on equipment that is subject to frequent hose swaps or components on the job.

The NPT thread and the BSPT thread do not make use of fixed torque values

This is at which a large portion of torque charts are misused. NPT (National Pipe Taper) and BSPT (British Standard Pipe Taper) are tapered threads that seal through thread deformation and typically the use of a sealant or PTFE tape, not by pressing a flare or an O-ring under an unassailable clamp load. Since the seal is based on the distance at which the threads are tapered rather than a certain force of rotation, manufacturers recommend tightening by the direction of hand-tight instead of ft-lbs.

• Klein sizes (1/8" to 1/4" NPT) generally 2-3 turns past the hand-tight
• The mid dimensions (3/8" to 3/4" NPT) generally 2-2.5 turns beyond hand-tight
• Greater sizes (1" and above) generally 1.5-2 turns past the hand-tight

Applying a JICORFS-style ft-lb torque number on a thread fitting that is tapered is a frequent and costly error; either it under-engages with the taper (leak) or breaks the housing of the port (catastrophic failure of cast components). If a supplier's datasheet gives you a torque number for an NPT/BSPT part, treat it as a rough guideline only and always default to the turns-past-hand-tight method with appropriate thread sealant.

Straight thread, sealing o-ring

BSPP (British Standard Pipe Parallel) fittings utilize straight threads, which are bonded to an O-ring or a washer that is bonded to seal at the bottom of the fitting instead of relying on threads to be sealed. Since the seal is a compressed O-ring or washer, rather than thread deformation, BSPP fittings operate more similarly to ORFS fittings in the real world; they use the specific torque value instead of a turn count. However, the figures are less than an equivalent-sized JIC or ORFS fitting, as the O-ring is only required in order to compress enough to form a seal and is not clamped to withstand the force of a flare-loading metal to metal. Always check the torque specifications required for BSPP from the manufacturer of the fitting, as values differ depending on the seal's design and brand in comparison to JIC or ORFS.

General rules that are applicable to all types of clothing

Some practices stand regardless of the type of fit or size:

• Wet-torque, unless specifically stated otherwise. The majority of torque tables published are based on lubricated seals and threads. Dry assembly alters the friction coefficient to release the clamp's load at the specified torque.
• Don't make a guess based just on "it feels tight." It's not reliable for all operators, and it's a primary reason for both joint over- and under-torque in the field.
• Make use of a crowfoot adapter to correct whenever necessary. In the event that you're working with a crowfoot adapter with a torque wrench, then the lever arm shifts in position, and the torque reading is not matched to the actual torque that is delivered to the fitting; the reading has to be adjusted to reflect the increased length.
• Check the condition before reusing. An O-ring groove or flare that has been loosened too much or dropped will not seal properly even when you apply the right torque for subsequent assemblies.
• If in doubt, look first to the OEM datasheet. Generic charts are a good base, but the plating, material, and thread class could change the right number for a particular manufacturer's product.

What happens when I torque too much on the JIC fitment?

A high torque crushes the flare's 37 degrees and may cause cracks, resulting in the possibility of leaks even though the fitting appears tightly secured. JIC seals depend on flare design and finish, not clamping force that is beyond the specifications.

Do NPT fittings come with the torque specifications of ft-lbs?

No. The NPT as well as the BSPT can be described as tapered, spherical threads that seal the thread and sealant; therefore, manufacturers recommend tightening the number of turns over hand-tight, rather than the fixed torque. Any figure in ft-lb used to describe a tapered thread is to be considered an approximate reference only.

Is dry torque or wet torque the right method to use for fittings that use hydraulics?

Wet torque, which is using the O-ring to lubricate the threads or cone with hydraulic fluid prior to installation -- is the method that is most used in the published torque charts because lubrication provides an easier and more reliable clamp load than threads made of dry material.

Can I utilize a JIC fitting with an SAE flare fitting of 45 deg in the same?

No. Although they look similar and share thread sizes across a variety of dimensions, JIC uses a 37° flare seat while SAE utilizes the 45° flare seat. Combining them won't seal properly regardless of the torque used.

Why is it that ORFS do not have the suggested torque when the O-ring is greased?

Lubricating the O ring will reduce friction during installation and increases the chance of damage to seals in assembly. Manufacturers typically permit up to a 25% decrease in maximum torque when lubricated O-rings are compared with dry assembly.