When designing or maintaining a centralized lubrication system, 90% of the attention goes to the pump. However, the pump is useless if the lubricant cannot reach the bearing. The tubing and fittings-the veins and arteries of your machine-are just as critical. A single kinked hose, a crushed compression sleeve, or a leaking connector can cause a pressure drop that starves the entire system, leading to machine failure.
At Ishan Precision, we supply not just pumps, but the entire ecosystem of lubrication hardware. In this guide, we will dive into the often-overlooked world of high-pressure tubing, compression fittings, and installation best practices. Whether you are repairing a leak or piping a new machine from scratch, this is what you need to know.
Choosing the Right Tubing Material: Nylon, Copper, or Steel?
Not all tubes are created equal. The environment of your machine dictates the material you must use. Using the wrong tubing is the #1 cause of recurring leaks.
1. High-Pressure Nylon Tubing (The Industry Standard)
For 80% of CNC applications, Nylon 12 (PA12) tubing is the material of choice.
Pros: Flexible, easy to route through drag chains, resistant to vibration fatigue, and translucent (allowing you to visually inspect oil flow).
Cons: Can melt if exposed to hot metal chips; lower pressure rating than metal.
Best For: Connecting moving parts (like the saddle or cross-slide) and general piping inside the cabinet.
Specs: Standard sizes are 4mm (O.D.) and 6mm (O.D.). Always ensure the tubing is rated for at least 25 kgf/cm² for oil systems.
2. Copper or Aluminum Tubing
Pros: Heat resistant, holds its shape rigidly (does not sag), extremely durable.
Cons: Harder to install (requires bending tools); prone to work-hardening and cracking under heavy vibration.
Best For: Static lines that run along the casting base, or areas exposed to hot chips and coolant splash.
3. High-Pressure Grease Hoses
For heavy-duty grease systems (injection molding, excavators), standard nylon will burst. You need reinforced hose with a synthetic rubber core and fiber braiding.
Specs: typically rated for 200+ kgf/cm² (3000 PSI).
Best For: Connecting the pump to the main distributor, or for flexible lines on heavy presses.
Understanding Compression Fittings: The "Olive" Principle
Almost all lubrication systems use Compression Fittings. Unlike plumbing at home which might use Teflon tape or glue, these fittings rely on mechanical deformation to create a seal.
The three main components are:
The Nut: Screws onto the port.
The Sleeve (Olive/Ferrule/Bushing): A small brass or aluminum ring that slides over the tube.
The Insert (Stiffener): A small metal tube that goes inside the nylon tubing to prevent it from collapsing.
How it works: As you tighten the nut, it compresses the "Olive" against the tubing. The Olive deforms, biting into the tube and creating a permanent, high-pressure seal.
Critical Rule: Never omit the Insert when using nylon tubing. Without the insert, the compression force will crush the hollow plastic tube, causing the connection to loosen and leak within days.
Step-by-Step Installation Guide: How to Prevent Leaks
A leak-free system starts with proper installation technique. Here is the process our technicians use:
Step 1: The Cut
Use a dedicated Tube Cutter (guillotine style). Never use side cutters, pliers, or scissors.
Why? Pliers crush the tube into an oval shape. An oval tube will not seal against the round Olive. You need a perfect 90-degree, circular cut.
Step 2: Assembly
Slide the Nut onto the tube. Then slide the Olive on. Finally, push the Insert fully into the end of the tube.
Tip: If the tube is stiff, dip the end in warm oil to make inserting the stiffener easier.
Step 3: Bottoming Out
Push the tube into the fitting port until it hits the bottom (the "shoulder"). Hold it there firmly. If the tube pulls back even 1mm during tightening, the seal may form at the wrong spot, creating a weak joint (a "dead volume" area).
Step 4: Tightening
Tighten the nut by hand until it is snug. Then, use a wrench to tighten it further.
For Nylon: Usually 1.5 to 2 full turns.
For Copper: Usually 3/4 to 1 turn.
Warning: Do not over-tighten. If you crank it too hard, you can crack the brass Olive or shear the threads. Once an Olive is cracked, it cannot be reused.
Thread Types: M8, M10, PT, or NPT?
When ordering replacement fittings, you must identify the thread type on your machine or distributor block. This is often the most confusing part for buyers.
Metric (M8x1, M10x1): The standard for Ishan, Showa, and most Asian/European machines. Note that M8x1 is a fine thread, different from the standard coarse M8 bolt you buy at a hardware store.
PT (BSPT / R): British Standard Pipe Taper. Common in older Japanese and Taiwanese machinery. It has a tapered thread that seals as you tighten it. (e.g., 1/8 PT).
NPT: National Pipe Taper. The American standard. Note: PT and NPT are not compatible. The thread angles are different (55° vs 60°). Forcing an NPT fitting into a PT hole will ruin the manifold.
If you are unsure, Ishan Precision offers thread gauge kits and adapter fittings (e.g., M10 male to 1/8 PT female) to solve any compatibility issue.
Troubleshooting: Why Is My Fitting Leaking?
If you spot oil dripping from a connection, check these three culprits:
The "Missing Insert" Error: Take the fitting apart. If the nylon tube looks crushed or flattened, the installer likely forgot the support insert. Cut the damaged section off and reinstall with a new insert and olive.
The "Reuse" Error: Compression olives are single-use items. Once deformed, they cannot be compressed again. If you remove a tube, you should ideally cut off the old ring and install a fresh one.
Vibration Loosening: On high-speed punch presses, vibration can back the nut off. Use a dab of medium-strength thread locker (Loctite Blue) on the nut threads (never inside the fluid path) or use a paint marker to "torque mark" the nut so you can visually check if it has moved.
Conclusion: Don't Skimp on the Hardware
It is tempting to buy cheap, generic fittings to save a few dollars. But consider this: a $2 fitting that fails can drain your $500 pump reservoir overnight, creating a massive oil spill on your shop floor and running your $100,000 CNC machine dry.
Your lubrication system is a high-pressure hydraulic circuit. It demands respect. By using genuine Ishan high-pressure tubing and fittings, and following the proper installation procedures, you ensure that every drop of oil paid for by the pump actually reaches the bearing that needs it.
Need spare parts? Browse our catalog for a full range of 4mm/6mm nylon tubing, compression bushings, adapters, and tube cutters ready for immediate shipment.
