A 90 degree elbow compression fitting turns a lubrication line through a right angle without bending the tube. Built to the DIN 2353 and ISO 8434-1 bite-type system, it seals with a cutting ring and 24 degree cone for grease and oil lines.
What an Elbow Compression Fitting Does
Bending small-bore tube risks kinks, and every kink restricts flow and weakens the line. An elbow makes a clean right-angle turn, keeps the bore open and allows disconnection at pumps, valves or distribution blocks.
Technical Specifications
Four body materials cover centralized lubrication duty. Working pressures assume matched tube and correct assembly; all share a burst-to-working ratio of 4:1.
| Body material | Working pressure | Burst pressure |
|---|---|---|
| Brass CW617N | 500 PSI (35 bar) | 2,000 PSI (140 bar) |
| Carbon steel St37.4 | 5,000 PSI (345 bar) | 20,000 PSI (1,380 bar) |
| Carbon steel 16MnCr5 | 7,250 PSI (500 bar) | 29,000 PSI (2,000 bar) |
| Stainless steel 316L | 6,000 PSI (415 bar) | 24,000 PSI (1,655 bar) |
Temperature windows are -20°C to +120°C for brass, -40°C to +200°C for carbon steel and -60°C to +400°C for 316L. Carbon steel carries zinc plating at 8 to 15 um or zinc-nickel at 10 to 15 um; use 316L for washdown, food processing and marine environments.
Tube Sizes and Threads
Metric tube runs from 4 to 18 mm outside diameter; imperial options cover 1/4, 5/16, 3/8 and 1/2 inch for legacy equipment.
| Tube OD (mm) | 4 | 6 | 8 | 10 | 12 | 15 | 18 |
|---|---|---|---|---|---|---|---|
| Wall thickness (mm) | 0.5 | 1.0 | 1.0 | 1.0 | 1.0 | 1.5 | 1.5 |
Port threads cover NPT 1/8 (10-27 TPI), 1/4 (18 TPI), 3/8 (18 TPI) and 1/2 (14 TPI), BSPP G series, BSPT R series and metric M6 x 1.0 to M16 x 1.5.
LL, L, and S Series
Three duty series divide the range: LL (very light) for low-pressure small-bore oil lines, L (light) for general lubrication and S (heavy) for the highest pressures. Bore follows tube OD in each series, so flow stays unrestricted. For layout help, see the grease line tubing and fittings selection guide.
How the Seal Works
Tightening the nut drives the cutting ring into the 24 degree cone. The ring’s edge bites a shallow groove into the tube wall while its back face presses the cone, giving two sealing lines: ring-to-tube and ring-to-body. With the ring at 320-450 HV against a 150-250 HV body, the ring cuts the tube rather than deforming the body, and the bite holds against vibration.
Installation
Steel or copper tube:
- Cut the tube square and deburr both edges.
- Slide on the nut, then the cutting ring.
- Push the tube fully against the body stop.
- Tighten finger-tight, then 1.25 turns further.
- Undo, confirm an even bite, and re-tighten.
For nylon tube, fit a support sleeve insert into the bore first, then tighten 0.75 to 1 turn past finger-tight, never over 1 turn; the insert stops the bore collapsing. Use an appropriate thread sealant on tapered threads. Matched polyamide lubrication tube keeps dimensions consistent.
| Steel/copper tube OD | 4 mm | 6 mm | 8 mm | 10 mm | 12 mm |
|---|---|---|---|---|---|
| Torque (Nm) | 12-15 | 18-22 | 25-30 | 35-42 | 50-60 |
| Nylon tube OD | 6 mm | 8 mm | 10 mm |
|---|---|---|---|
| Torque (Nm) | 10-12 | 15-18 | 22-26 |
| Nylon tube OD (mm) | 6 | 8 | 10 | 12 |
|---|---|---|---|---|
| Support sleeve insert required | Yes | Yes | Yes | Yes |
Troubleshooting
| Symptom | Likely cause | Action |
|---|---|---|
| Weep at the cone after assembly | Nut under-tightened | Add about a quarter turn and recheck |
| Ring slides on the tube | Tube too soft or under-tightened | Re-make the joint at the correct torque |
| Tube cracked behind the ring | Over-tightened nut | Cut back the tube and fit a new ring |
| Leak after reassembly | Worn cutting ring | Replace the ring, keep the body |
| Threads will not seat | NPT and BSPT mixed | Match thread form on both sides |
What Is Supplied
Each elbow is supplied as the body with nut and cutting ring, ready for prepared tube; nylon support sleeve inserts are ordered by tube OD. Send tube OD, thread and working pressure via our quote form.
Frequently Asked Questions
What is a bite-type elbow compression fitting and when should I use one?
It seals by driving a hardened cutting ring into the tube wall against a 24 degree cone. Use one where a line must turn a corner under pressure.
How do I choose between LL, L and S series?
Match series to pressure: LL for low-pressure oil, L for general lubrication, S for high-pressure grease with thick-wall tube. Tube OD must match the series bore range.
Can an elbow compression fitting be reused?
The body and nut can be reused; the cutting ring is single-use. When re-making a joint, fit a fresh ring from our sleeves and ferrules range.
Why does nylon tube need a support sleeve?
Nylon walls are soft, so the cutting ring’s bite would collapse the bore. The support sleeve stiffens the tube end from inside and keeps the bore open.
What happens if I under-torque or over-torque the nut?
Under-torquing leaves the ring without a full bite, so the joint weeps and the tube can pull out. Over-torquing cracks the tube behind the bite. Stay within the torque values above.
Can I mix NPT and BSPT threads?
No. Both are tapered pipe threads, but angle and pitch differ, so a mixed joint seals on a few threads and leaks or strips. Match thread forms on both sides.
How should I cut and prepare the tube?
Cut square with a tube cutter, deburr both edges and confirm the tube end sits against the body stop. A skewed or short end prevents an even bite.
How do I pair elbows with straight fittings?
Same-series elbows and straights share the 24 degree cone and ring system, so one tube spec covers the run. Use straight compression fittings in-line and elbows at turns.
How do I remember the temperature limits for each material?
Think in steps: brass -20°C to +120°C for indoor oil lines, carbon steel -40°C to +200°C for machinery, 316L -60°C to +400°C for cold or hot, corrosive plant.
How do I get a quote for elbow compression fittings?
IsoHiTech Lubrication Systems was founded in 2023, engineering since 2006, and supplies the full DIN 2353 elbow range in all four materials. Send tube OD, thread, series and quantity via the quote form or email inquiry@isohitech.com.
