Hydraulic system leakage refers to the hydraulic components and the system of the cavity flow or temporary fluid, due to pressure, clearance and other problems, a small amount of across the cavity boundary, from the high pressure side to the low pressure side out of a phenomenon. Usually such leaks can be part of two kinds of leakage and the leakage, leakage is refers to the working medium from Gao Qiang leaked to the lower cavity, such as hydraulic transmission oil from high pressure in the cavity within the disclosure, from the directional control valve to the low pressure cavity pressure channel to oil leakage, external leakage is working medium cavity from the work to the external leakage components and systems, Such as gear pump section leakage, hydraulic oil pipe penetration.
Can be divided into the gap by the hydraulic system leak form disclosure, porous leaking, adhesive spills and power leakage, etc., this hydraulic oil as medium for hydraulic transmission of power and energy mechanical equipment, once the problem is not properly handled, it not only affects the performance of system, the damage of hydraulic components, waste of resources at the same time, due to a certain degree of pollution to the environment, Serious cases are more likely to cause accidental injury to the operator. Therefore, it is very important for operators of hydraulic system related equipment to master certain leakage maintenance skills.
Hydraulic system oil leakage of the four hazards
(1) Equipment efficiency decreased significantly and energy loss increased gradually;
(2) The reliability of equipment operation decreases;
(3) Related products (especially light textiles and food) and environmental pollution;
(4) Due to poor sealing, external pollutants are easier to invade, resulting in a vicious cycle, making the host or components appear early wear, serious will lead to the whole machine paralysis.
Causes of system oil leakage and preventive measures
(1) Leakage due to poor processing
① The sealing groove is too deep or too shallow, and the sealing contact surface of the relative moving parts is poor in ellipticity and taper, so that it is difficult to get uniform and accurate compression after the installation of the O-ring. For example, on the cylindrical surface, the annular groove of the shaft and the hole is easy to be deep or shallow, so that the compression of the O-ring can not reach the predetermined value, thus leading to oil leakage. This situation may not be obvious or leakage under low pressure, but it is easy to cause serious consequences under high pressure.
The second case is that when the equipment is sealed in the plane, if the O-type sealing groove is too shallow, it will cause the groove to be stuck in the O-ring during the installation and thus fall off, and the sealing ring may even be squeezed between the joint surface. In this case, there may be no leakage in a short period of time, but after a long time, part of the rubber squeezed between the joint surfaces may be squeezed out by high-pressure oil, resulting in oil leakage.
② The fixed screw hole depth of the plane seal is not suitable, if we adhere to the original design of the screw to be connected or too long problem, even if the surface seems to be tightened, but the actual two planes are not tight, because the seal is not strict and lead to oil leakage, if it is a high pressure state, it may even directly squeeze the sealing ring.
③ The positioning error of the plane seal part leads to oil leakage. Hydraulic pump (or valve) body four screw hole position and flange four through hole position, due to processing errors, or lead to one or two axes can not coincide, thus forming an eccentric E, so that the body hole side falls on the outside of the average diameter of the O-ring, resulting in the final gap caused by oil leakage.
④In the same plane is equipped with a number of O-type sealing rings, the size may not be the same, the installation groove and groove type of two categories. In addition, the causes of leakage include insufficient pressure on the end face, uneven compression, small stop size, O-ring is easy to fall off in the working stage, the joint surface is not parallel, the plane and the screw hole are not vertical, the joint surface is too clean, the groove edge is too thin so that the edge of the force after rolling phenomena may be the cause of oil leakage.
⑤Where the combined sealing pad is used in the equipment, if the chamfering of the hole (including the screw hole) is too large, it will also produce a certain degree of oil leakage.
⑥ Rough sealing surface causes leakage. If sealing surface processing is relatively rough, when pipe tighten, scratches on the surface of the sealing ring, if the circumstances are serious, will make the tip of the hanging plastic softening of the combination sealing ring, then leads to the formation of a seal failure to leak, so you need to processing manufacturers have chosen to use after softening treatment of copper pad (the hardness HB = 32 ~ 45) to replace the composite gasket, This accessory can only be used once, if disassembly after use, will lead to the sealing effect greatly reduced.
(2) Leakage due to improper installation (assembly)
① Installation of pipe joints: oil leakage of pipe joints accounts for a large proportion in the leakage accident.
I. The thread of the pipe joint on the fastening nut and joint should be matched properly. Too loose or too tight may lead to oil leakage;
II. Pay attention to alignment when installing joints;
III. Use of sealing tape and sealant:
The winding direction of the sealing belt must be turned along the thread, generally 1 ~ 2 circles, the more layers of the winding, the more likely it is to loosen in the working stage, and the serious leakage will be caused. If the liquid nylon sealant is used as the filler between the thread and the buckle, the temperature cannot exceed 60℃, otherwise it will melt and cause the hydraulic oil to overflow from the buckle;
IV. With a flamed thin pipe joint, the copper pipe is annealed first and then processed into a round and smooth bell mouth;
V. Connection of welded pipe joint and pipe:
② When installing U-shaped sealing groove, too much compression force will produce lip curling phenomenon, which will cause leakage.
③ Leakage of oil seal.
(3) Leakage due to improper maintenance and material selection
① Seal ring surface damage caused by seal leakage;
② Leakage caused by clearance bite and twisting of sealing ring:
Because the sealing ring material is soft, the sealing gap is large, and often works under high pressure reciprocating movement, it is easy to be squeezed into the gap and bitten. Therefore, when the sealing ring is working under high pressure reciprocating movement, the gap should be reduced as far as possible, and the hard sealing ring should be selected. There are many varieties of this kind of sealing ring. The specific requirements are that when the system pressure is up to 10MPa, the movement radial clearance is 0.2mm. If the sealing material hardness is HS70, there will be extrusion phenomenon.
③ After the oil is polluted, the seal will be damaged, resulting in leakage;
(4) Improve the quality of sealing ring
In order to improve the quality of the sealing ring, it should first be considered from the three aspects of material selection, geometric shape and processing accuracy, and can also be combined with structural design, manufacturing process, mold manufacturing, maintenance and use of many aspects of comprehensive control.
The measures
Different hydraulic systems, the cause of oil leakage may be related to the selected components and their own process, specifications, structure and other factors, here we will illustrate.
(1) segmented multi-way valve plate
The ZFS-L20H2-Y*M-T series oil circuit reversing valve is a piecewise structure (each piece of reversing valve is made of one piece and connected with bolts respectively), which is composed of oil inlet valve piece, oil outlet valve piece and several pieces of intermediate valve piece. There is a certain oil leakage problem when transverse impact occurs. In this case, oil leakage may contain two reasons:
(2) When reversing impact, the double-headed bolt bears periodic tension load, and when boosting pressure, the bolt is stretched; When decompression, return to original state and contract. In this way, the multi-way valve disc will appear a micro state of a close, so the phenomenon of oil leakage. When the pressure reaches 21MPa, the maximum opening is 0.05-0.15mm. The higher the pressure is, the more serious the oil seepage problem is.
The bottom surface of the O-ring is rough, and the pressure oil seepage. When the pressure is reduced, the opening between the valve pieces is closed, and the oil is extruded and permeated outward.
When the above situation occurs, the following measures can be taken to cure the leakage:
(1) The bottom surface of O-ring groove is grinded by extrusion and diamond spraying rod to improve the finish of the bottom surface to △6;
(2) Select high quality O-ring to ensure that it has good sealing performance;
(3) the double bolt is made of high strength diamond material;
(4) A return channel can be added to the gap of the valve plate to introduce the oil into the tank, so as to completely solve the penetration problem.
