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Common Failure of Hydraulic Hoses

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Failure of Outer Rubber Layer

Cracks in the surface of the hose: Cracks on the surface of the hose can cause the hose to be bent in cold conditions. If cracks are found on the outer surface of the hose, watch for cracks in the inner rubber of the hose and decide whether to replace the hose immediately. Therefore, do not move the hoses or disassemble the hydraulic system in cold environment, and do it indoors if necessary. If you need to work in a colder environment for a long time, you should replace the cold-resistant hoses.

Blistering on the surface of the hose: The appearance of bulging hose is due to unqualified hose quality or improper use. If the bulge appears in the middle part of the hose, it is mostly due to the quality of the hose production, and should be replaced by qualified hose in time; if the bulge appears at the joint of the hose, it is probably due to improper installation of the joint. Steel wire braid / winding hose joint and hose connection end has detachable, buckle two forms, detachable joint jacket and joint core on the hexagonal shape, the outer wall of the joint core is conical, easy to disassemble the hose. After the core is connected to the nut, the steel wire is inserted to prevent loosening. When assembling, the outer rubber layer should be peeled off, the core head should be set, the jacket should be tightened, and then the hose should be pressed with a mold on the special equipment to make the hose get a certain amount of compression to achieve a tight connection.

The hose is not broken but a lot of oil seepage:If a hose is not found to be ruptured but there is significant oil seepage, the cause is as bellow:

  • When passing through high pressure liquid flow inside the hose, the inner rubber is eroded and abraded until a large area leaks out of the steel wire layer leading to a large amount of oil seepage. This failure generally occurs at the bend of the pipe, the hose should be checked and replaced, and ensure that the bending radius of the hose in use meets the technical requirements.
  • The hose is in a high temperature environment, causing the inner rubber layer to deteriorate, and oil leakage occurs at high pressure flushing.

Severe deterioration of the outer rubber layer of the hose, with micro-cracks on the surface: This is the performance of the natural aging or high temperature baking of the hose over a long period of time. Due to aging and deterioration, the outer layer of oxidation constantly makes its surface layer brittle, with the extension of time brittle layer deepened, the hose in use as long as a slight bending, will produce tiny cracks. Encounter this situation, the hose should be replaced.

Failure of Inner Rubber Layer

The inner layer is hard and cracked: Due to the addition of plasticizers in rubber products, the hose is flexible and plasticizable. The hose works under high temperature and pressure, and the hose overheats, which can cause the plasticizer to overflow. In addition, overheated oil through the system cylinder, valve or other components, if a large pressure drop will make the oil decomposition, resulting in the hose inside the rubber layer oxidation and hardening. In this case, you should first check whether the hydraulic system working temperature is normal, the valve throttle, pump suction channel is smooth, etc., after excluding all factors that may lead to high oil temperature and fluid decomposition to replace the hose. If only the inner rubber below the hose rupture is hard and the above remains good, it means that the hose rupture is overly squeezed, bent too sharply or twisted and other phenomena lead to oil heating and accelerated oxidation, which will cause the inner rubber to be hard.

The inner layer is seriously deteriorate and obviously swollen: The inner layer The reason for the serious deterioration and obvious swelling of the inner rubber layer of the hose is that the hydraulic oil is used for an extended period of time or the presence of oxidized and deteriorated dirt in the hydraulic system, and the hose is chemically deteriorated, and broken rubber pieces are found at the oil return port. If this phenomenon occurs, the physical and chemical indicators of hydraulic oil should be checked, and the compatibility of the system fluid and the rubber material inside the hose and the working temperature should be checked to see if they meet the standards.

Failure of Reinforcement Layer

Rupture of hose, rusting of braided steel wire near the rupture: If the hose ruptures, peel off the outer rubber layer to check and find the rusting of the woven/wound steel wire near the rupture, which is mainly due to the role of moisture or corrosive substances in the outer rubber layer, weakening the strength of the hose, resulting in rupture at high pressure. In this case, the outer layer is generally accompanied by fracture, abrasion or serious deterioration, so that the outer layer loses its protective effect on the reinforcement layer. In this case, we must first check and exclude the outer layer of mechanical damage, chemical corrosion and high temperature baking and other undesirable factors, and then replace the hose. However, there are cases where the outer rubber layer is well maintained but the reinforcement layer is ruptured by embroidery, and the rupture is usually within 200mm from the hose joint, most of which are due to unqualified joints, as moisture enters the inner edge of the jacket and makes the reinforcement layer absorb moisture, resulting in rust causing the hose to rupture due to reduced pressure strength.

The hose reinforcement layer is not rusted, but irregularly broken wire appears: If the hose broken, peel off the outer rubber layer check did not find the reinforcement layer rust, but the reinforcement layer length direction appeared irregular broken wire, the reason is mainly the hose by the high frequency impact force. There are many intersections between the steel wire and the steel wire of the braided reinforcement layer, and when the pressure inside the tube changes significantly, these intersections also move wrongly with the change of the tube diameter, so that the steel wires rub against each other. If the hose is subject to high-frequency impact pressure, the intersection will occur frequently friction, resulting in steel wire breakage. For the hose often subjected to high-frequency impact, the steel wire winding skeleton should be used as a reinforcement layer.

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