What are the components of a hydraulic hose assembly?

The hydraulic system definition is that which transmits pressurised hydraulic fluid within a mechanical system. The assembly includes the hose and its fittings. There are different types of hydraulic hoses, but they all have the same components:

Tube: This is the hose’s inner-most part, which carries the fluid from one end of the hose to the other. It needs to be flexible, especially if it’s on a machine with a flexible joint, and compatible with the fluid it transports.

What are hydraulic hoses made of?

Hydraulic tube material typically includes a thermoplastic, synthetic rubber and Polytetrafluoroethylene (PTFE) to resist corrosion and chemical impact. The thermoplastics used are often polyamide, polyester and even fluoropolymers, which has a high resistance to solvents, acids, and bases.

Types of hose material: Tube	Characteristics
Synthetic rubber	– Excellent flexibility
Fluoropolymer	– Outstanding chemical and corrosion resistance – Operates in high temperatures – Long shelf life
Thermoplastics	– Tight minimum bend radii – Superior kink resistance

Reinforcement: This is the strength of hydraulic hose. It’s the reinforcement that determines the working pressure of the hose. Hydraulic hose is defined by its pressure capacity, so pressure determines how the hose is constructed. The more layers in the reinforcement, the higher the pressure rating. It’s typically braided, spiral or helical and is made from single or multiple sheaths of braided wire, textile yarn or spiral-wound wire.

Reinforcement type	Characteristics	Hydraulic hose application
Spiral wound hose	- Two or more sets of helically wrapped high-tensile wire - Makes for a rigid hose with exceptional strength - Limited flexibility	Extremely high-pressure applications: construction equipment and heavy-duty off-road vehicles
Braided hydraulic hose	- More tensile play than spiral hose - This gives hose a tighter radius and good flexibility - Braids overlap, creating wear by rubbing together – can fail when subjected to high-impulse loads	- Low-to-medium pressure applications: construction and agriculture equipment - High-pressure applications: oil and hydraulic lines on construction and agriculture equipment
Helical hose	- Maximum flexibility - Construction prevents collapse under vacuum pressure - Helixes don’t overlap each other, avoiding wear by rubbing against each other; result: better impulse load resistance than plain braided hoses	- Vacuum pressure suction - Return line hose applications that would collapse both braided and spiral hose on itself

Cover: The cover protects the reinforcement and tube from the outside environment. It’s designed as abrasion, ozone and oil-resistant tubing, and to stand up to the elements. It’s typically made of synthetic rubber and/or plastics – usually polyurethane (PUR). The reasons PUR is a popular choice comes down to its excellent abrasion and impact resistance. It’s also the ideal cover hose material due to its vibration resistance.

The synthetic rubber used is usually neoprene, which also offers outstanding abrasion resistance. It can accommodate a range of operating temperatures but has a shorter shelf life than PUR and is not as flexible.

The cover is the component exposed to the outside elements and vulnerable to wear and tear from rubbing against other hoses. Cover your cover. A few of your options include:

Protection	Characteristics
Fire protection sleeves	- Protects against high temperatures, radiation heat, direct flames and liquid metal splashes - The inner sleeve provides good hydraulic hose insulation properties with a 700°C (1,292°F) service temperature - Available in rolls to suit different hose length
Spiral Wrap Hose Protector	- Durable HDPE - Features heavy-duty, double-bevelled edge design to prevent snagging and cutting during installation - Easy and safe to install before or after hose assembly is mounted - Use medium-duty solution for applications where abrasion is not frequent, but protection is still needed
Hose Wear Protectors	- Flexible PVC – durable with high-wear factor - Protects hose and wire abrasion caused by points of contact wear with frames or other abrasive surfaces - Moulded grooves prevent the slipping and wear of cable ties - Easy to assemble and remove

To learn how to protect your hydraulic hoses, see our Quick guide: hydraulics & pneumatics protection in specialist vehicles.

Hydraulic hose fittings

There are different types of hose fittings. Their purpose is to connect hoses securely to your hydraulic system’s components, such as valves, cylinders and pumps. It’s the fittings that help hold and direct the flow of fluid, maintaining the pressure while preventing leaks.

 

Fittings are usually designed to fit a specific hose, and not just regarding size. Fittings have to be compatible with the fluid being used. Hydraulic hose manufacturers advise on the correct fitting to use, so pay attention.

Your hose and assembly will need to seal, and your choice is also part of the fittings. The three major types are:

• O-ring

Excellent for high-pressure applications, preventing leaks. The component’s threads pull the fitting against the port. This traps the O-ring to flatten it, forming a snug seal.

• Mating angle

The seal occurs when two different angles are wedged together. These fittings are sealed with straight or parallel threads.

• Tapered threads

These come in male and female threads. When they’re threaded together, the tapered threads deform. This puts pressure on the couplings, which form a tight seal. These fittings are prone to leaking due to over-torquing. They’re also not precise, but do not use tape to compensate. Tape tends to shred, causing contamination.

Hydraulic hose clamps made of stainless steel are also an excellent way to seal larger diameter hoses where high vibration is a concern. Use plastic hose clamps for an economical way to seal hoses.

You can learn more in Hydraulics hoses and fittings for specialist vehicles.

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