Influence of Circuit Arrangement on Hydraulic Pipe (I)

The service life of the product depends on the conditions under which it is used. And the hose assembly often appear leakage, kink, abrasion, wear or other damage are related to the line layout. Correct hose placement can effectively reduce personal injury or property damage due to hose assembly failure. The commonly used structure of hydraulic oil hose assembly on excavators is generally: A synthetic rubber inner, rubber layer is used to keep the fluid in the pipe. The outer reinforcing layer of the inner rubber layer is braided or wound by steel wire, which can resist the pressure in the pipe. The reinforcing layer has one or several layers according to different specifications.

According to the analysis, the service life of the hydraulic oil hose largely depends on the way of assembling the pipe. The following is about the hose pipe of the hydraulic system of the excavator.

1. Tensile and compress the hose

The length of the hose will become inappropriate due to the different direction of the hose during assembly. Generally, the pilot pipeline is often stretched, and the main oil pipeline will be compressed.

1.1 The tensile

When the pipe is stretched, its inner diameter will become smaller, the flow capacity will become smaller, the wall of the pipe will become thinner, the pressure capacity will be weakened, the maximum working pressure will be reduced, and its actual working pressure will not change.

That is to say, when the hose is stretched, its working pressure may have exceeded the maximum working pressure it can withstand.

At the same time, the hose is pulled between the inner and outer rubber layer and the reinforcing layer. Because of their different toughness, the reinforcing layer and other layers are separated, so that the reinforcing layer steel wire and the outside world contact, easy to be corroded. The length of the hose varies due to the presence of pressure during operation, and it has a certain coefficient of expansion, which increases the pulling force.

The hose is pulled repeatedly under the high frequency pulse of hydraulic pressure. Can cause the hose to be pulled from the hose joint or applied to the joint for a long period of time, resulting in metal damage or seal failure.

When the hose is connected flat, there must be enough slack in the hose so that it can be adjusted when the length of the hose changes under pressure. The minimum bending radius of the hose can also be affected when the hose is stretched. This condition is often overlooked, and piping less than the minimum bending radius will shorten hose life.

Severe bending of the hose to the joint can result in leakage, hose tearing or hose assembly detaching. When the hose assembly explodes, the joint will be thrown at high speed, and the loose hose will be swept out or thrown out with great force, possibly causing personal injury or property damage.

1.2 Compressed

Hose compression is often overlooked, with practical examples illustrating its hazards.

On August 10, 2011, one end of XE260C one-hopper merge pipe (both ends of the hose are elbows at the same time, and an EW joint is connected to the two elbows to form C type, and the joint is internal metric straight thread with 24° external cone with O-type connection) was loosened more than one hour after off-line debugging.

Upon inspection, the joint reached torque during assembly and fastening, but the hose was compressed and the S-type shock buffer of the hose design was replaced by compression straight pipe. When the hose is compressed, the joints at both ends are placed under stress, and the tightening moment = joint moment + the component force generated by the compression of the hose, the tightening moment of the joint is less than the standard moment, and the joint is actually not fastened in place. In addition, the high frequency vibration of the fluid pressure opens the thread. High pressure oil may damage the seal ring.

Like stretching, compression can also change the normal parameters of the hose, affecting its performance and shortening its life.