BASIC KNOWLEDGE OF PUMP SEALS (3)

The oil seal of chemical pumps is a self-tightening pump seal. It has the characteristics of simple structure, small size, low cost, easy maintenance, and low torque resistance. It can not only prevent media leakage, but also prevent external dust and other harmful substances from entering. It has a certain compensation ability for wear, but it is not resistant to high pressure, so it is generally used in chemical pumps which are used in low pressure occasions.

Chemical pumps rely on the principle of centrifugation to pump liquid materials. Chemical pumps made of special materials are suitable for pumping corrosive liquids in bottles, barrels, cylinders, tanks or other containers. Due to the dangers of corrosion, volatilization, explosion, etc. of the medium pumped by chemical pumps, the sealing performance requirements of the pump body are much higher than other types of pumps.

The oil seal of chemical pumps should be installed on a shaft with a manufacturing accuracy of h8 to h9, a surface roughness of 1.6 to 0.8μm and a surface hardening treatment. The sealed medium should not contain solid particles and impurities, otherwise it will cause rapid wear of the oil seal and shaft, making the seal invalid.

When choosing this kind of sealing method, we must fully consider the performance and requirements of the materials delivered by the chemical pump to avoid unnecessary leakage and prevent accidents.

1. The main factors causing oil leakage of the oil seal

Poor sealing is the main cause of oil leakage. When the shaft is worn and forms a groove, even if the new oil seal is replaced, it will not be sealed. The sealing pressure between the oil seal lip and the shaft is reduced, resulting in an excessive amount of interference between the oil seal lip diameter and the shaft diameter after installation.

Taking the crankshaft oil seal of S195 diesel engine as an example, the main reasons for poor sealing are:

1) Poor quality of oil seal manufacturing

2) Poor quality of shaft or bearing

3) Improper use and maintenance

4) Improper installation

5) Improper storage, adversely affected by environmental pollution

2. Measures for oil leakage

1) Master and recognize the basic knowledge of fake and inferior products, and purchase high-quality, standard oil seals.

2) During installation, if the roughness of the outer surface of the shaft diameter is low or there are defects such as rust, burrs, etc., smooth it with a fine emery cloth or whetstone, apply clean engine oil or grease to the lip of the oil seal or the corresponding position of the shaft diameter.

Apply sealant to the outer ring of the oil seal, wrap the key groove on the shaft with hard paper to avoid scratching the lip of the oil seal, use a special tool to rotate and press the oil seal inward, and don't pound it hard to prevent deformation of the oil seal. When there is lip cuffing, the spring falls off and the oil seal is skewed, the oil seal must be removed and reinstalled. It should be noted that when the shaft diameter is not worn and the spring force of the oil seal spring is sufficient, do not tighten the inner spring without authorization.

3) When the general working conditions of the oil seal applied to the machinery are bad, the environment temperature difference is large, the dust is many, and the vibration of the machine tool frequently changes the stress condition of the machine parts, it should be checked and maintained.

4) If the shaft diameter and bearing wear seriously, the rubber is aging or the spring is invalid, it should be repaired and replaced in time.

5) For abnormally heated parts or assemblies, the fault should be eliminated in time. Avoid mechanical over-speed and overload operation to prevent the temperature of the oil seal lip from rising, rubber aging, and early lip wear.

6) Always check the oil level of the engine oil. If there are too many impurities in the engine oil, and if there are alloy powders and metal iron filings, replace the engine oil completely. The quality of the oil to be replaced must meet the requirements of the season.

Commonly used pump seals are various, in addition to oil seals, there are spring seals, elastomer bellow seals, etc.