In hydraulic system piping wiring, many technicians tend to use flexible hoses extensively for convenience and ease of installation. Indeed, hoses offer high flexibility and eliminate the need for complex bending processes. However, if you visit a precision machine tool factory, a large press workshop, or an automated production line, you’ll find that rigid tubing (usually seamless steel or stainless steel) still occupies a central position.
In which operating conditions are rigid tubing irreplaceable? Is it simply because rigid tubing looks “neater”? The answer is far more profound than visual appearance suggests.
1.Harsh environment: Thermal challenges from high temperatures and radiation
The core material of hoses is usually synthetic rubber or thermoplastic elastomer. Although they have an internal steel wire braid layer to enhance pressure, their outer sheath is extremely sensitive to the environment.
(1) Thermal Aging Issues:
In environments near heat sources (such as furnaces, engine exhaust pipes, and large pumping stations), rubber hoses will rapidly harden and crack. This aging is irreversible; once the outer sheath cracks, the internal steel wire layer loses its protection, making the hose highly susceptible to bursting.
(2)Advantages of Rigid Pipes:
Steel or stainless steel pipes exhibit extremely stable physical properties at high temperatures and possess excellent heat dissipation capabilities. At high temperatures, the service life of rigid pipes is typically more than 10 times that of flexible hoses.
2.Frequent pressure fluctuations: Addressing “fatigue failure”
If your system pressure is very high (e.g., above 35 MPa), or if there are severe pressure pulses (such as those from hydraulic breakers or rapidly reciprocating actuators), hoses will face serious challenges.
(1) “Breathing Effect”:
Hose undergoes slight expansion and contraction when pressure increases dramatically. This high-frequency “breathing” not only consumes hydraulic energy and reduces system efficiency, but also accelerates metal fatigue in the internal steel wire layer.
(2)Advantages of Rigid Tubing:
Steel tubing is highly rigid and exhibits almost no expansion or deformation. For high-pressure pulse conditions, rigid tubing provides more reliable structural strength, ensuring the system remains stable even under hundreds of thousands of alternating loads.
3.Long-distance conveying with strict requirements on pressure loss
The efficiency of a hydraulic system largely depends on the pressure loss in the pipeline.
(1) Resistance Coefficient:
Although the inner wall of a hose appears smooth, its frictional resistance is typically higher than that of a seamless steel pipe due to the material’s slight elasticity. Especially at higher flow rates, the temperature rise of a hose is significantly higher than that of a rigid pipe.
(2)Advantages of Rigid Pipes:
The inner wall of precision cold-drawn seamless steel pipes is extremely smooth, resulting in a low resistance coefficient. In long-distance transport, using rigid pipes can effectively reduce pressure loss along the pipeline and lower the heat generation of the oil, which is particularly important for large hydraulic power units.
4.Minimalist Spatial Layout and Precision
While flexible hoses are quick to install, when the number of hoses reaches dozens or even hundreds, their layout becomes a disaster—friction and tangling not only look unsightly but also create hidden dangers for later maintenance.
(1)Rubbing Risk:
Flexible hoses bounce during operation; if two hoses rub against each other for a long time, the outer layer will quickly wear through.
(2)Advantages of Rigid Pipes:
Rigid pipes can be precisely positioned using a pipe bending machine and neatly arranged on the machine body or pipe rack with the help of pipe clamps. This is not only for aesthetics but also for shock absorption and heat dissipation. In limited space, rigid pipe wiring saves more maintenance space.
5.In which locations must the hose be retained?
In the following two situations, a flexible hose is the only option:
(1) Relative motion:
For example, between the boom and stick of an excavator, a flexible hose must be used to handle large-scale folding and rotation.
(2) Vibration damping and isolation:
Installing a short section of flexible hose at the pump outlet and motor connection can effectively cut off the transmission path of mechanical vibration, preventing vibration from being transmitted to the entire rigid piping system and causing the joints to loosen.