Difference between thermoplastic hoses, polyamide 12, and rubber hydraulic hoses

Selecting the right hose involves balancing technical specifications against the specific conditions of the application. While factors such as operating pressure, fluid, and environment serve as a basis, the interaction between these variables determines which material is most suitable.

Polyamide 12 is often used in lighter-duty systems such as lubrication, while thermoplastic and rubber hoses are preferred in environments with higher pressures or heavy mechanical loads.

Guidelines for material selection

The choice of hose material depends on how the medium, pressure, and environment interact. The following points form the basis for comparing the different materials:

• Application: Polyamide 12 is the standard for lubrication systems and pneumatics. Thermoplastic hoses are often chosen for systems where cleanliness and corrosion resistance are critical. Rubber hoses are the preferred option for power hydraulics with high dynamic loads.
• Pressure build-up: The working pressure and burst pressure depend on the temperature and the type of coupling. Depending on the diameter, wall thickness, and temperature, polyamide 12 is used for pressures ranging from low levels up to approximately 200 bar in specific configurations. For higher pressure classes, thermoplastic and rubber hoses offer solutions, with rubber often being more resistant to sudden pressure spikes.
• Environmental factors: Factors such as UV radiation, salt water, and external heat affect service life. A PU outer jacket (thermoplastic) offers specific advantages in marine environments, while synthetic rubber provides greater resistance to direct contact with hot surfaces.
• System purity: Plastic inner walls reduce the risk of internal contamination of the system. This is an important consideration when choosing thermoplastic hoses over rubber alternatives.

What is Polyamide 12?

Polyamide 12 (PA12) is a plastic tubing widely used in central lubrication systems and pneumatics. The material is characterized by good chemical resistance and flexibility.

In practice, one must take into account the pressure resistance in relation to the temperature, diameter, and wall thickness of the PA tubing. Although a guideline of approximately 200 bar applies to many standard applications, this limit is not absolute; this range may vary depending on different parameters or specific installations. The PA 362 and PA 5224 variants offer different levels of stiffness, in accordance with the DIN 73378 standard.

What is a thermoplastic hose?

A thermoplastic hose consists of a plastic inner core, a polyester reinforcement layer, and a polyurethane (PU) outer jacket. This construction results in a hose that is significantly lighter than rubber variants and resistant to corrosion.

Thanks to microbial stabilization, the hose is resistant to the effects of microorganisms. Although a safety factor of 1:4 is a common standard for the ratio between working pressure and burst pressure, the actual safety margin always depends on the complete system configuration and the type of fluid being transported.

What is a rubber hydraulic hose?

Rubber hydraulic hoses are designed for systems where robustness and the ability to withstand pressure spikes are key. The hose consists of synthetic rubber reinforced with braided or spiral-wound steel wire.

The choice of rubber is often based on the need for mechanical resistance to abrasion or external heat. The steel skeleton ensures that the hose remains stable under high dynamic pressure. High dynamic pressure in a hydraulic system means that the pressure in the hose is not constant but fluctuates rapidly and forcefully.

As with other high-pressure hoses, the 1:4 safety factor is an important technical guideline, but the specific service life is strongly influenced by the intensity of use and the quality of the crimping.

How do you choose the right hose?

Since no single hose is suitable for every machine, the STAMPED method helps you make the right choice. This is an international checklist used to verify all the important characteristics of a system. It prevents hoses from failing prematurely or dangerous situations from arising.

The acronym stands for the following seven points:

S: Size

This involves considering the inner diameter, the outer diameter, and the length of the hose. The inner diameter determines how quickly the fluid or air flows through the hose. A diameter that is too small causes excessive resistance, pressure loss, and heat buildup. The outer diameter is important for the available space inside the machine. The correct length ensures that the hose can move freely and does not become taut.

T: Temperature

Two temperatures must be considered: the temperature of the fluid or air inside the hose, and the temperature of the environment in which the hose is installed. Extreme cold makes materials brittle. High temperatures reduce the strength and pressure resistance of plastic and rubber. The hose material must be able to withstand the extremes of both temperatures.

A: Application

This refers to how and where the hose is used. Relevant factors include mechanical forces such as constant bending, vibrations, or dragging across the ground. The minimum bend radius and the hose’s position—such as whether it is suspended horizontally or vertically—also play a role. Sometimes this requires additional protection, such as a plastic spiral or a fabric sleeve.

M: Material and Medium

This is the substance flowing through the hose, such as oil, water, compressed air, or lubricating grease. The inner wall of the hose and the metal couplings must be fully resistant to this substance. If they are not, the inner wall may swell, soften, or tear. This causes leakage or a hose rupture.

P: Pressure

The hose must withstand the system’s maximum working pressure and sudden pressure spikes. Hoses always require a safety margin. For high-pressure hydraulic systems, a safety factor of 1:4 is the standard. This means that the hose’s burst pressure must be at least four times higher than the system’s working pressure.

E: Ends (Fittings)

This refers to the connections at the ends of the hose. It involves selecting the correct type of thread (such as BSP, NPT, or JIC) or flanges. The fitting must fit the machine components precisely to ensure a reliable and leak-free connection under pressure.

D: Delivery

This includes special requirements and certifications. These include, among others, ISO standards, MSHA fire safety standards, or FDA certifications for the food industry. Requirements such as a pre-conducted pressure test, a specific hose color, or clean packaging for transport also fall under this category.

Important to know when choosing the right hose

Choosing the right hose material cannot be viewed in isolation from the rest of the system. All components in a hydraulic or lubrication system influence one another. For example, if the pump delivers higher pressure or if the fluid becomes hotter, this has a direct impact on the hoses, couplings, and seals. Assessing the entire system prevents a single incorrectly selected component from becoming the weakest link and causing malfunctions.

For complex systems, it is essential to consult the official catalog and product specifications. These documents describe the exact limits of the materials, such as the maximum operating pressure in combination with specific temperatures. Verifying this technical data is necessary to prevent hazardous situations and ensure that the machine continues to operate without unwanted downtime.

Key differences between hose materials

Polyamide 12 vs. thermoplastic and rubber: Polyamide 12 does not have a built-in reinforcement layer (such as polyester or steel wire). This distinguishes PA12 from the other two materials; it is suitable only for lighter applications such as central lubrication and pneumatics, and not for power hydraulics.

Thermoplastic versus rubber: Thermoplastic hoses differ from rubber hoses due to their plastic inner wall and polyester reinforcement. As a result, thermoplastic is lighter, completely resistant to rust, and the inner wall does not release microscopic particles. Rubber hoses, however, can release particles into the medium as they age.

Rubber versus thermoplastic: Rubber hoses differ from thermoplastic hoses due to their steel skeleton and rubber outer jacket. This makes rubber more resistant to extreme external heat and to rapid, powerful changes in pressure (dynamic pressure). In heavy-duty dynamic hydraulic applications, steel-reinforced rubber hoses generally offer greater resistance to such pressure pulses.

The overlap between thermoplastic and rubber

Thermoplastic and rubber hoses overlap in the medium- and high-pressure segments. For both materials, the 1:4 safety factor serves as a technical guideline. The specific operating environment is the deciding factor: a marine environment with UV radiation and salt water calls for thermoplastic, while an environment with high levels of abrasion and heat calls for rubber.

There is no one-size-fits-all solution for every system

Choosing the right material—whether polyamide 12, thermoplastic, or rubber—is critical to the reliability and safety of an installation. Because operating pressure, the medium, and environmental factors constantly influence one another, there is no one-size-fits-all solution for every system. An incorrect choice can lead to premature wear or system failure.

Need tailored advice for a specific application? Feel free to contact Hydynamic for help in choosing the right hose and for more information about material properties.