An O-ring face seal joint has three flat faces and one elastomer in the middle. The O-ring does the sealing; the two metal faces bottoming out do the limiting. That single design choice is why ORFS behaves differently from a flare or a taper: torque is not what holds the seal, so a joint that is tight is not necessarily sealing, and a joint that feels slightly loose is not necessarily leaking.
How the Seal Works: Three Flat Faces and One O-Ring
The female half carries an O-ring in a groove machined into a flat face. The male half has a flat nose. When the nut is tightened, the flat nose compresses the O-ring into its groove, and then the two metal faces meet. That metal-to-metal contact is the stop: it prevents over-compression of the O-ring, which is what gives the joint its tolerance for torque variation.
Compare that with a 37° flare, where the seal is metal-to-metal on a cone and torque directly controls how well it seals, or with an NPT taper, where the thread itself is the seal. The practical consequence is that ORFS is far more forgiving of a wrench that is not calibrated, and far less likely to weep after a few thermal cycles.
Why an ORFS Elbow Stays Where You Point It
Because the seal is axial, the body can be rotated to any position before the nut is tightened, and tightening does not change that angle. This is the reason ORFS dominates mobile hydraulic ports: in an engine bay or on a valve block, a 90° elbow often has exactly one usable orientation, and a tapered thread would force you to back off and lose the seal.
The nut is what you turn, not the body. Hold the body on its flats and torque the nut; turning the body against a seated O-ring drags the elastomer and can nick it. On reassembly the same rule applies, and the O-ring should be replaced rather than re-seated.
The O-Ring Decides the Temperature Range, Not the Fitting
The steel body is the same in every version. What changes the service envelope is the elastomer. Nitrile (NBR) is the default for mineral hydraulic oil and covers roughly −40 °C to +100 °C, with short excursions higher. Fluorocarbon (FKM) extends that to around +200 °C and adds resistance to many synthetic fluids and aggressive additives, at a higher cost. EPDM is used where the fluid would attack NBR, but it is incompatible with mineral oil — a detail that causes expensive mistakes when a line is refilled with the wrong fluid.
We supply both NBR and FKM as standard, and the O-ring code is listed per size in the table below so a replacement can be ordered without measuring the groove.
Where ORFS Is the Wrong Answer
ORFS is a high-pressure, vibration-tolerant connection, and it is priced accordingly. On a low-pressure return or a drain line, a 60° cone or a bonded washer does the same job for less. Where the mating port is already JIC, forcing an ORFS joint in means two adapters and two extra leak paths — a single conversion adapter is cheaper and more reliable.
It is also the wrong choice where the port face cannot be machined flat, or where the assembly will be repeatedly disconnected in the field by someone without a torque wrench: the O-ring is a wear item, and a scored flat face will leak no matter how tight the nut is. If you are comparing face seal with boss seal, note that ORB seals on a straight thread with a washer at the boss while ORFS seals on a flat face — they are not interchangeable, and our ORB fitting guide covers the difference.
2F ORFS Male O-Ring × ORFS Female — Standard Dimensions
|
Part No. |
Thread E |
Thread F |
O-Ring |
L |
S1 |
S2 |
|
2F-04 |
9/16"×18 |
9/16"×18 |
O011 |
33 |
17 |
19 |
|
2F-06 |
11/16"×16 |
11/16"×16 |
O012 |
38.5 |
19 |
22 |
|
2F-08 |
13/16"×16 |
13/16"×16 |
O014 |
43 |
22 |
27 |
|
2F-10 |
1"×14 |
1"×14 |
O016 |
51.5 |
27 |
30 |
|
2F-12 |
1-3/16"×12 |
1-3/16"×12 |
O018 |
56 |
32 |
36 |
|
2F-16 |
1-7/16"×12 |
1-7/16"×12 |
O021 |
60 |
38 |
41 |
|
2F-20 |
1-11/16"×12 |
1-11/16"×12 |
O025 |
62 |
46 |
50 |
|
2F-24 |
2"×12 |
2"×12 |
O029 |
64 |
55 |
60 |
Dimensions in mm. The O-ring code is what you quote for spares; A and B are end lengths.
O-Ring Material Selection
|
Material |
Typical range |
Best for |
Avoid |
|
NBR (nitrile) |
−40 to +100 °C |
Mineral hydraulic oil, water-glycol |
Ketones, esters, ozone |
|
FKM (fluorocarbon) |
−20 to +200 °C |
Synthetic fluids, high ambient heat |
Ketones, amines, ammonia |
|
EPDM |
−50 to +150 °C |
Brake fluid, steam, phosphate ester |
Mineral oil and grease |
Ranges are typical values for guidance only — confirm against the actual fluid and duty cycle before specifying.
Frequently Asked Questions
Can I reuse an ORFS O-ring?
No. The O-ring has been compressed against a metal stop for the life of the joint and takes a permanent set. Reusing it is the single most common cause of a weep after a repair. Replace the O-ring every time the joint is opened, and check the groove for a chip before fitting the new one.
What torque should I apply to an ORFS nut?
Torque is not the sealing parameter — the metal faces bottoming out is. Tighten the nut until the faces meet, using the specified torque only as a check that the joint has seated. This is why ORFS tolerates an uncalibrated wrench far better than a 37° flare, and why over-tightening does not improve the seal.
ORFS or JIC — which should I choose?
JIC is metal-to-metal on a 37° flare and is simpler and cheaper, with no elastomer to age. ORFS adds an O-ring and a flat face, which gives it better vibration tolerance and lets an elbow be indexed without losing the seal. For high-vibration mobile equipment, ORFS is usually the better choice; for a static, low-cost assembly, JIC often wins.
Do you supply stainless steel ORFS fittings?
Yes, in 316L for corrosive and offshore applications, with NBR or FKM O-rings. Stainless bodies need a lower torque than carbon steel to reach the same face contact, so do not carry a torque figure across from a steel assembly.
Why Choose HGW O-Ring Face Seal Fittings?
When it comes to O-Ring Face Seal (ORFS) fittings, HGW Hydraulic stands out as a leader. With 28 years of experience since 1996, we’ve perfected hydraulic solutions for industries like engineering, mining, and shipbuilding. Our ORFS fittings, crafted from high-grade stainless steel, ensure leak-proof seals and exceptional durability under high pressure. Certified by ISO 14001:2015, HGW delivers precision-engineered fittings that excel in demanding environments. Whether you need standard or custom designs, our O-Ring Face Seal fittings guarantee reliability and performance. Trust HGW Hydraulic for top-quality ORFS solutions backed by decades of expertise—your hydraulic systems deserve nothing less!
How to Choose the Right O-Ring Face Seal Fittings?
Selecting the best O-Ring Face Seal (ORFS) fittings is simple with HGW Hydraulic’s guidance. Consider these key factors:
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Pressure Needs: Our ORFS fittings handle high-pressure systems effortlessly, perfect for mining or engineering tasks.
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Material Match: Opt for stainless steel options from HGW for corrosion resistance and longevity.
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Seal Compatibility: Ensure your O-ring matches the fluid type—our 28 years of expertise ensures a flawless fit.
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Application Fit: From straight to elbow designs, we offer customizable ORFS fittings for any setup. Backed by ISO 14001:2015 certification, HGW Hydraulic provides reliable, leak-proof O-Ring Face Seal fittings tailored to your needs. Reach out today for expert advice and the ideal hydraulic solution!
