Common causes of oil leakage in NMRV series gearbox oil level plug/drain plug

Seal failure

This is the most direct reason. The sealing between the plug and the box is usually achieved through O-ring seals, gaskets, or thread sealants.

Aging or damage: Rubber parts such as O-rings and gaskets will gradually age, harden, crack, lose elasticity, and cause sealing failure when exposed to high temperatures and oil immersion for a long time.

Material mismatch: If the material of the seal is incompatible with the lubricating oil (such as ordinary rubber encountering certain synthetic oils), it may corrode, swell, and fail.

Installation damage: Improper operation during the replacement of plugs or seals may cause the O-ring to twist and be scratched by threads, making it unable to form an effective seal.

2. Improper installation of screw plugs

The tightening state of the plug directly affects the sealing effect.

Insufficient pre tightening force: The screw plug is not tightened or becomes loose under long-term vibration of the equipment, resulting in gaps at the threaded connection and lubricating oil leaking out under pressure.

Excessive pre tightening force: Overtightening may cause thread slippage, screw plug deformation, or excessive compression of the sealing gasket/O-ring, which can actually damage the sealing structure.

Thread issues: Damage or impurities (such as iron filings or old sealant) in the threaded holes on the plug or box, or confusion between metric/imperial threads, can cause a tight fit.

3. Problem with threaded holes in the box body

The casing of NMRV reducers is mostly made of aluminum alloy die-casting, and the condition of the threaded holes is crucial.

Threaded hole damage: During disassembly and assembly, rough handling or use of inappropriate tools may damage the threads inside the box, resulting in ineffective locking of the plug.

Casting defects: In rare cases, there may be casting defects such as sand holes and air holes around the threaded holes of the box, forming leakage channels.

4. The pressure inside the box is too high

Although this is more of the main cause of shaft seal oil leakage, excessive internal pressure can also exacerbate leakage at the plug.

Ventilation hole blockage: When the gearbox is running, the temperature rises and the air inside the box expands. If the ventilation cap (respirator) is blocked by dust and oil, and the internal pressure cannot be released, it will search for the weakest link (such as the gap between the screw plug) to "push" the oil outward.

Excessive refueling: If the oil level is too high and the gears stir violently, not only will the oil temperature rise, but it will also cause an increase in pressure fluctuations inside the tank, increasing the risk of oil leakage.