German KNF seals KNF models KNF prices

KNF seals are sealing devices installed to prevent leakage between the pump shaft and the casing. Common types of shaft seals include packing seals, mechanical seals, and dynamic seals. The shaft seal of a reciprocating pump is usually a packing seal. When transporting media where leakage is not permitted, a diaphragm reciprocating pump can be used. The shaft seals of rotary pumps (including vane pumps, rotor pumps, etc.) mainly consist of packing seals, mechanical seals, and dynamic seals. The shaft seal of a reciprocating pump is usually a packing seal. When transporting media where leakage is not permitted, a diaphragm reciprocating pump can be used. The shaft seals of rotary pumps (including vane pumps, rotor pumps, etc.) mainly consist of packing seals, mechanical seals, and dynamic seals.

KNF seal classification

1) Packing seal: The packing seal features a simple structure, low cost, and easy maintenance. However, it has high leakage and significant power loss. Therefore, packing seals are used for transporting general media, such as water; they are generally not suitable for petroleum and chemical media, especially for valuable, flammable, explosive, or toxic media. 2) Mechanical seal: Mechanical seals (also known as face seals) provide good sealing performance with minimal leakage and long service life, but they are expensive and have higher requirements for machining, installation, maintenance, and repair compared to general seals. Mechanical seals are suitable for transporting petroleum and chemical media and can be used for media with various viscosities, strong corrosiveness, and solid particles. The American Petroleum Institute standard API610 (8rd edition) stipulates that cartridge mechanical seals shall be equipped unless otherwise specified by the user. 3) Dynamic seal: Dynamic seals can be divided into back-vane seals and auxiliary impeller seals. During pump operation, the centrifugal force of the back vanes (or auxiliary impeller) reduces the pressure of the medium at the shaft seal to atmospheric or negative pressure, preventing leakage during use. When the pump stops, the centrifugal force disappears, and the sealing effect of the back vanes (or auxiliary impeller) fails; at this time, the shutdown sealing device provides the sealing function. Shutdown sealing devices paired with back-vane (or auxiliary impeller) seals often use packing seals. There are two types of packing seals: standard type and mechanically adjustable type. Standard packing seals are similar to those in general packing-sealed pumps, requiring a slight positive pressure at the shaft seal to avoid dry friction of the packing. Mechanically adjustable packing seals use counterweights to loosen the packing during pump operation and tighten it when stopped. Dynamic seals offer reliable performance, low cost, and easy maintenance, making them suitable for transporting media with a high content of solid particles, such as slurry pumps and ore pulp pumps in the phosphate industry. The disadvantages are greater power loss compared to mechanical seals and shorter service life of the shutdown sealing device. The seal between the rotating pump shaft and the stationary pump casing is called the shaft seal. Its function is to prevent high-pressure liquid from leaking out along the shaft or outside air from entering along the shaft. For centrifugal pumps, the shaft seal is a dynamic seal. Depending on whether the sealing surfaces are in contact, dynamic seals can be classified as contact dynamic seals and non-contact dynamic seals. In contact dynamic seals, the sealing device contacts the shaft, resulting in relative friction between the two. Contact dynamic seals include packing seals and mechanical seals.

KNF seal operation

1) If slight leakage occurs after the pump starts, observe it for a period. If the leakage does not decrease after continuous operation for 4 hours, stop the pump for inspection. 2) The operating pressure of the pump should be stable, with pressure fluctuations not exceeding 1 kg/cm². 3) During pump operation, avoid cavitation to prevent dry friction and damage to the sealing surfaces. 3) Check the sealing condition regularly. During operation, if leakage exceeds the standard, it should not exceed 5 drops/min for heavy oil and 10 drops/min for light oil. If there is no improvement within 2-3 days, stop the pump to inspect the sealing device.

KNF seal specifications and applications

1) Standard single-lip: Generally used for sealing mineral oil, water, and other media in high- and low-speed rotating shafts and reciprocating motion. Standard oil seals are used in environments with less dust and impurities, resistant to medium pressure<0.05MPa, maximum linear speed 15m/s, reciprocating speed<0.1m/s. 2) Standard double-lip: In addition to the usage characteristics of the above S type oil seals, they also provide dust protection. Standard oil seals with a dust lip can prevent dust ingress, resistant to medium pressure<0.05MPa, linear speed ≤ 15m/s. 3) Springless type: Springless single-lip inner-cage rubber oil seal. Generally suitable for low-speed conditions, sealing lubricating grease. Linear speed ≤ 6m/s. 4) Outer-cage single-lip: Single-lip outer-cage rubber oil seal with spring, featuring a thin waist, good followability, and good rigidity. Standard oil seals are used in environments with less dust and impurities, resistant to medium pressure<0.05MPa. Rotational axis linear speed ≤ 15m/s. 5) Outer-cage double-lip: Double-lip outer-cage rubber oil seal with auxiliary lip, featuring a thin waist, good followability, high rigidity, and good concentricity. Standard oil seals with a dust lip can prevent dust ingress, resistant to medium pressure<0.05MPa. Rotational speed ≤ 15m/s. 6) Assembled single-lip: Outer-cage oil seal assembled from inner and outer cages with rolled edges, featuring high installation precision, fast heat dissipation, and heavy-load characteristics. Suitable for heavy-load conditions under high temperature and high speed, medium pressure ≤ 0.05MPa, maximum linear speed ≤ 15m/s. 7) Unidirectional return type (right-hand, left-hand): Angled ribs are manufactured on the air side of the lip, utilizing fluid dynamics principles to generate a unidirectional pumping action with a return effect. Related to the shaft's rotation direction, the radial force is smaller than that of standard oil seals due to the return effect, reducing wear and heat generation, and extending service life. Suitable for medium pressure<0.05MPa, rotational speed ≤ 20m/s. 8) Pressure-resistant type: Short lip and short, thick waist, providing pressure resistance, working pressure ≤ 3MPa. Suitable for medium pressure ≤ 3MPa, applicable as shaft end oil seals for high-pressure pumps. Generally, the PV value ≤ 8. Rotational axis linear speed ≤ 15m/s.

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