Even after replacing the seals, the oil cylinder is still leaking oil.

1. Improper seal selection

There are many types of seals, made of various materials, each designed for different operating conditions.

(1) Operating Condition Matching: If your hydraulic cylinder operates under high temperature, high pressure, or high speed conditions for extended periods, and you choose ordinary seals that are not heat-resistant, even if they are imported, they will quickly age, deform, and lose elasticity.

(2) Incorrect Structure Selection: For example, for piston seals, should you use a Glyd ring or a U-ring? The applicable pressure and starting torque are completely different. If the wrong structure is chosen, the seal cannot effectively “open” under high pressure, and the oil will naturally leak out through the gaps.

Recommendation: Provide complete operating condition information, including the medium, temperature range, and pressure.

2.Damage during installation

While seemingly simple, seal installation is actually fraught with hidden dangers.

(1) Sharp Edge Scratches: If the cylinder threads or oil hole chamfers are not smooth, or if a guide tool is not used and the seal is forcibly pushed past a sharp edge, a “wound” will instantly appear on the seal surface. This wound becomes the channel for oil leakage.

(2) Twisting and Twisting: Uneven force applied during piston rod or piston installation can cause the seal ring to twist. Once twisted, the sealing lip cannot evenly adhere to the metal surface, making oil leakage inevitable.

(3)Tool Damage: Using a regular screwdriver or a sharp tool to pry open the seal directly can puncture it.

3.Inner wall of the hydraulic cylinder

Seals are attached to the inner wall of the cylinder or the piston rod. If the contact surface is damaged, there’s little that can be done.

(1) Inadequate surface roughness: Imported seals require extremely high surface roughness (typically Ra 0.1-0.4μm). If the inner wall of the cylinder is roughened, rusted, or has excessively deep machining lines, the seal will feel like it’s being rubbed on sandpaper, quickly wearing down and leaking oil.

(2) Geometric accuracy deviation: The cylinder exhibits “tapering” or “ellipticity.” Imported seals typically have very small clearances. If the cylinder deforms, causing the clearance to fluctuate, the seal will be “squeezed” into the clearance and sheared, resulting in damage.

Key points for inspection: Always check the condition of the relevant mating surfaces each time you replace a seal.

4.The overlooked “extrusion gap”

When the seal is in operation, on the high-pressure side, it is pushed towards the gap. If the seal support ring is worn or not installed at all, the high pressure will force the root of the seal into the gap between the piston and cylinder, causing the root to be “eaten off.”

Although imported seals have high pressure resistance, if your hydraulic cylinder is old and the wear has exceeded the allowable clearance, even the best seals will be forced out.

Solution: Measure the clearance between the piston and cylinder, and between the piston rod and guide sleeve. If the clearance is outside the tolerance range, the support ring needs to be thickened or the mechanical parts replaced.