Solutions to Hydraulic System Leaks (Frequently Asked Questions)

I. The Cause of the Hydraulic System Leakage

(1) Defects caused by the design and manufacture;

(2) Pipe joint loosening caused by impact and vibration;

(3) Dynamic seals and fittings wear on each other (especially hydraulic cylinder);

(4) High oil temperature and rubber seal and hydraulic oil incompatibility and deterioration.

2,the Control of the Hydraulic System Leakage Control Scheme

The following is combined with the above several aspects to talk about the leakage control measures.

Scheme 1: Solution to Design and Manufacturing Defects

1. The selection of external hydraulic components often has a decisive impact in the leakage of the hydraulic system. This determines our technical personnel in the new product design, the improvement of the old product, the cylinder, pump, valve, seal, hydraulic accessories, etc., in line with the best of the best, the principle of careful, comparative.

2. Reasonable design of installation surface and sealing surface: when the valve set or pipeline is fixed on the installation surface, in order to get satisfactory initial sealing and prevent seals from being squeezed out groove and worn, the installation surface should be straight, the sealing surface should be refined, the surface roughness should reach 0.8 m, and the flatness should reach 0.01 / 100mm. The surface should not have radial scratches, and the pretension of the connecting screws should be large enough to prevent the surface separation.

3. In the process of manufacturing and transportation, to prevent the key surfaces from bumping and scratching. At the same time, the assembly and debugging process should be strictly monitored to ensure the assembly quality.

4. Do not take some hydraulic systems lightly, but must be eliminated.

Scheme 2: Reduce the Impact and Vibration

To reduce the leakage of the hydraulic system caused by loose pipe joints bearing impact and vibration, the following measures may be taken:

① holds all pipes to absorb shock and vibration;

② The uses low-impact valves or accumulators to reduce impact;

③ appropriately arrange pressure control valves to protect all components of the system;

④ minimize the number of pipe joints, pipe joints as far as possible with welded connection;

⑤ uses straight threaded joint, three-way joint and elbow instead of tapered pipe threaded joint;

⑥ Try to replace each pipe with the return oil block;

⑦ For the maximum pressure used, to specify the use of bolt torque and plug torque for installation, to prevent the binding surface and seals from being eroded;

⑧ Install the pipe fitting correctly.

Scheme 3: Reduce the Wear of the Moving Seal

Most moving seals are accurately designed. If the moving seals are qualified, installed correctly and used reasonably, they can ensure relatively no leakage work for a long time. From a design perspective, the designer can take the following measures to extend the life of the moving seal:

1. Eliminate the side load on the piston rod and the drive shaft seals;

2. Protect the piston rod with dust ring, protective cover and rubber sleeve to prevent abrasive and dust from entering;

3. Design and select appropriate filter device and easy cleaning oil tank to prevent dust from accumulating in the oil;

4. Make the speed of the piston rod and shaft as low as possible.

Scheme 4: Requirements for Static Seals

Static seals prevent fluid leakage between rigid fixed surfaces. Reasonable design of sealing groove size and tolerance, so that the installed seal to a certain extrusion deformation to fill the micro depression of the surface, and increase the stress inside the seal to higher than the pressure of the sealed. 

When the part stiffness or the bolt pretension force is not large enough, the mating surface will be separated under the oil pressure, causing the gap or increasing the gap that may exist from the beginning because the sealing surface is not flat enough. 

As the movement of the mating surface occurs, the static seal becomes a dynamic seal. Rough mating surfaces will wear the seals, and variable gaps will erode the seal edges.

Scheme 5: Control the Oil Temperature to Prevent the Seal from Deterioration

The premature deterioration of seals may be caused by a variety of factors, an important factor is the high oil temperature. 

Every 10℃ temperature increase is halved, so the efficient hydraulic system or forced cooling device should be reasonably designed to keep the optimal oil temperature below 65℃; the construction machinery shall not exceed 80℃; 

Another factor may be the compatibility of the oil used, and the type and material should be selected according to the instruction or relevant manuals to solve the compatibility problem and extend the service life of the seal.