Correct choice of mechanical seal

The outer seal has the following five major advantages: 1. Easy to install; 2. Relatively low cost; 3. Continuous monitoring and cleaning; 4. Suitable for small stuffing boxes that cannot be installed inside the seal; 5. Because its location is close to the bearing , Less impact on the difficulty of spindle deviation. The main disadvantage is that centrifugal force will throw solid particles from under the seal to the contact surface of the seal. Therefore, this type of seal is mainly suitable for clean liquids that do not contain abrasives. In recent years, separate seals have become another important additional feature in outer seals. The separable seal is a complete assembly, which is installed between the stuffing box and the bearing sleeve. With this design, when the seal needs to be replaced, there is no need to disassemble the pump every time. This type of seal is being developed gradually in conjunction with other design standards. Because this design is easy to replace the seal, it is very important to resist the temptation to only replace the seal without further investigation into the root cause of the failure. Cartridge type seal Cartridge type seal is a sealing device that integrates all functions into one, which includes all sealing elements, glands and shaft sleeves. Since this type of seal does not require any strict installation measures, the installation procedure is greatly simplified, and at the same time the sealing surface and the sealing elastomer are well protected to prevent accidental damage. These advantages also mean that seal repair and replacement time can be reduced.

It has a full-featured cartridge-type sealing device. The use of this seal can simplify the installation procedure and protect the internal components from accidental damage. Almost all kinds of cartridge seals are available on the market, so the risk factors in use can be reduced, and the maintenance time inherent in the use of ordinary seals can also be saved. The dual seal and liquid barrier device adopts the dual sealing surface seal instead of a single seal, which has a higher degree of leakage resistance. Most of these double seals are used in liquids with strong volatility, toxic, carcinogenic, dangerous and poor lubricity.

There are generally three design types for double seals. Each type requires a liquid barrier system between the double sealing surfaces to prevent liquid or gas from leaking. The more commonly used low-cost double seal is a back-to-back seal with rotating sealing surfaces arranged in opposite directions. It often needs a barrier liquid whose pressure should be higher than the stuffing box pressure, about 20 psi, so that the internal seal can always be lubricated by the barrier liquid, and it can also ensure that the sealing surface reaches a certain sealing pressure. In a face-to-face type seal with a more complex structure, the rotating sealing surfaces are arranged in a face-to-face manner, and they often act in opposite directions to the same static sealing surface. This type of seal can use either a high pressure barrier liquid system or a low pressure barrier liquid system. The rotating surfaces of this type of seal are installed in a face-to-face manner, and a high-pressure or low-pressure barrier liquid system is adopted. The third design type of seal adopts a serial arrangement, that is, both rotating sealing surfaces leave the impeller and are arranged in the same direction. . The barrier liquid pressure of this seal is generally lower than the pressure of the liquid pump. In fact, it is equivalent to two sealed, two-stage pressure reduction joint working devices.

All types of double sealing devices require a liquid barrier system. They generally belong to an external closed-loop system, and the liquid used inside is generally different, but must match the liquid in the process. The system includes a reservoir, which should be located as close as possible to the seal. The design of these systems varies widely. Some systems use a pump ring in the seal, while other systems use the principle of thermosiphon effect. The liquid in the liquid storage tank often adopts auxiliary heating or auxiliary cooling methods. In addition, an alarm device can be added to remind the staff to replace the liquid in time. According to the nature of the liquid to be sealed, the barrier liquid system can work at a pressure lower or higher than the stuffing box. In order to achieve the goal of zero leakage during the entire driving operation, the sealing industry has also developed gas barrier seals, which use inert gases such as nitrogen to replace liquid barrier systems. In the double seal with gas barrier, if the inside of the sealing surface fails, only inert gas will be leaked, and the liquid inside will not leak, which will not cause environmental pollution. Regardless of whether liquid or gas is used, the barrier system must be suitable for the specific sealing use, and should be able to identify and alarm immediately once any failure occurs inside the sealing surface, so that appropriate measures can be taken in time.

Environmental control In many application areas, where the seal is installed, the reliable operation and control environment of the seal need to be considered. Therefore, the following points must be paid attention to: 1. The seal should be installed on a high-strength main shaft with minimal deviation. Although the industry standard specifies a maximum deviation of 0.002in for the sealing surface, the requirements for the spindle can be even higher. 2. The seal should be installed in a large-diameter sealed chamber, which can improve the reliability of the seal. Almost all hydraulic pump manufacturers can provide these products. 3. Control the internal pressure of the stuffing box to avoid reaching the flash point. 4. Keep the temperature in the stuffing box within the working parameters of the sealing material. 5. Keep the liquid in the stuffing box clean.