In various rotating equipment, mechanical seals are the core components to prevent fluid leakage. The rationality of the it selection directly determines whether the equipment can operate stably for a long time. A successful sealing scheme is by no means a simple model matching, but the crystallization of an in-depth understanding of working conditions and targeted design.

-Bonve Pump Industry Cam-type Double Rotor Pump-

I. Basic Analysis of Seal Selection

Before determining the seal type, a "physical examination" of the main engine working conditions must be carried out. This includes four basic parameters: pressure, temperature, rotating speed and shaft diameter. At the same time, the "characteristics" of the medium are crucial: is it high-viscosity or volatile? Are there any solid particles? Is it corrosive? Whether the main engine operates continuously or intermittently also affects the heat dissipation and lubrication state of the seal. The requirements put forward by the main engine for seal leakage rate, service life, installation space and reliability are the boundary conditions for selection. On this basis, the type and material of the seal can be scientifically selected, and corresponding auxiliary systems such as flushing and cooling can be planned.

II. Selection of Structural Forms under Conventional Working Conditions

Under conventional working conditions, the determination of structural forms mainly depends on pressure and speed.

1.Working Pressure: The seal chamber pressure is the primary indicator. When the pressure exceeds 0.5\0.7MPa, a simple balanced seal is no longer competent, and a partially balanced design must be selected to reduce the specific pressure generated by the medium and prevent excessive end-face wear. For media with poor lubricity, even if the pressure is as low as 0.3\0.5MPa, this structure should be considered in advance. For high-pressure or ultra-high-pressure conditions, double-end or multi-end seals shall be adopted to realize step-by-step pressure reduction.

2.Circumferential Speed: When the linear speed exceeds 30m/s, the influence of centrifugal force on rotating parts intensifies. At this time, a stationary mechanical seal shall be selected, with the elastic element placed at the non-rotating part to avoid fatigue failure caused by high-frequency vibration.

3.Medium Characteristics: For weakly corrosive media, internally mounted seals with compact structure and reasonable stress are the first choice. When the medium is highly corrosive or easy to crystallize, the externally mounted and outward-flowing structure becomes a safer choice because it is easy to observe and the medium does not contact the spring. However, it should be noted that its applicable pressure is usually low (below 0.2~0.3MPa).

III. Countermeasures for Special Working Conditions

High-Temperature Conditions (>120°C)

High temperature is the "number one killer" of mechanical seals. Its hazards are as follows: first, the medium cannot effectively take away frictional heat, but instead reversely heats the seal ring, causing vaporization of the end-face liquid film and resulting in dry friction. Second, high temperature will carbonize the resin in resin-impregnated graphite, and the precipitated hard particles will scratch the seal end face like sandpaper. Third, rubber sealing rings will accelerate aging and lose elasticity.

To cope with high temperatures, the key lies in cooling and heat resistance. On the one hand, forced flushing or circulating cooling systems must be adopted to forcibly cool the seal end faces. On the other hand, high-temperature-resistant alloys or silicon carbide shall be selected for materials. When the operating temperature exceeds 250°C, conventional rubber rings can no longer be used. At this time, adopting a single-spring metal bellows structure is an ideal choice. It can not only maintain elastic compensation at high temperatures but also eliminate the need for auxiliary sealing rings.

-Bellows Mechanical Seal-

Low-Temperature Conditions (<-50°C)

When the medium temperature drops to the "cryogenic zone" of minus 50 degrees Celsius, the challenges are completely different. Most media are liquefied gases with low boiling points and low viscosity, which are extremely easy to vaporize. Ordinary metals will undergo cold brittleness, and rubber will lose elasticity like plastic. What is more troublesome is that if the low-temperature sealing device is in contact with the atmosphere, water vapor in the air will freeze on the cold sealing surfaces, aggravating the wear of friction pairs.

For cryogenic working conditions, the design idea needs to be comprehensively innovated. First, metal bellows are used to replace rubber auxiliary sealing rings, and stainless steel or copper alloys are often selected to ensure their elasticity at low temperatures. Second, to reduce fatigue damage of bellows caused by increased low-temperature brittleness, a stationary structure shall be adopted with the bellows placed on the stationary side. In addition, cold insulation measures must be taken to isolate the seal chamber from the atmosphere, prevent icing and reduce cold loss. Finally, friction pair materials shall be selected from bronze or graphite with excellent thermal conductivity, matched with uniform low-temperature flushing fluid to prevent vaporization of the end-face liquid film due to temperature rise.

Whether at high or low temperatures, the core logic is to establish a stable and subtle "barrier" between friction pairs through precise materials science and fluid control. In many special equipment conveying high-viscosity media, such as some rotor pumps designed for high-temperature hot oil, the selection of mechanical seals needs to take into account the viscosity-temperature characteristics of the media, and its selection complexity is often higher than that of ordinary centrifugal pumps.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

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We look forward to working with you to drive efficiency and innovation in industrial fluid transmission with precision technology.