Mechanical seals are the most commonly used forms of seals for chemical pumps. However, leakage of pumps due to mechanical seal damage is very common during use. Raw materials, energy is wasted due to pump leakage, and even fires, explosions, poisoning, and environmental pollution are common occurrences. . Therefore, how to properly install and use mechanical seals to reduce leakage, prevent pollution and improve economic efficiency is an important task for chemical companies.
1. Mechanical seal structure
The mechanical seal is mainly composed of a moving ring, a stationary ring, an auxiliary sealing ring, a compensation mechanism (such as a spring) mainly composed of an elastic element (or a magnetic element), and a transmission mechanism that rotates the moving ring and the shaft together.
2. Types of mechanical seals commonly used in chemical pumps
According to the JB1472-75 standard, the pump mechanical seals are available in seven types of 103, 104, 105, 109, 110, 111, and 114 types, which are suitable for different working conditions. In recent years, several corrosion-resistant mechanical seals have been put into use, with good results, such as 151, 152, and 153. Mechanical seal installation Mechanical seals are relatively delicate components. If the installation is not good, the seal failure or the seal life is shortened. The preparation work before installation and the commissioning work after installation must be done. From the practical experience, the following aspects should be noted when installing.
Accuracy requirements for equipment: The parts where the mechanical seal is installed lose their original accuracy due to multiple installations, repairs, corrosion by the medium, etc., or they are old equipment. If no inspection is performed on these equipments, mechanical seals are installed. It often causes seal failure, so there are certain requirements for the equipment to install the mechanical seal.
The tolerance of the perpendicularity of the mechanical seal shaft and the seal cavity: the shaft diameter is 20~40mm, the tolerance value is 0. 05mm; the shaft diameter is 50~80mm, the tolerance value is 0. 06~ 0. 07mm; the shaft diameter is 80 0毫米。 The difference is 0. 08mm. The distance between the shaft and the mechanical seal is not more than 0. 20~ 0. 25mm. Radial runout of the shaft The radial runout of the shaft results in reduced sealing performance, increased leakage, excessive runout, and even cracking of the graphite. In addition, due to the long-term jump of the contact between the moving ring seal and the shaft, grooves will appear on the surface. Therefore, there is a certain tolerance for the shaft runout. When the shaft diameter is 16~50mm, the radial runout deviation [0. 04mm; when the shaft diameter is 55~120mm, the radial runout deviation [0. 05mm. The axial yaw amount is such that the spring force of the mechanical seal does not change too much, and the axial yaw of the shaft is generally required to prevent the balance of the mechanical seal ring and the shaft shoulder from damaging the part [0. 05 mm. The surface roughness of the shaft is not less than 3.2.
Installation inspection of the shaft at the sealing cavity: the transition part of the shaft shoulder and the static ring at the static ring gland should be smoothly connected to ensure that the sealing ring does not scratch and break when passing the shoulder, and at the time of installation It can be guided and easy to install.
Installation check: Check whether the mechanical seal is in conformity with the requirements, whether the parts are complete, the seal size is appropriate, and whether the moving ring and static ring surface are smooth and flat. Cleaning Clean the mechanically sealed parts (except the rubber seal) with a clean wash oil, then wipe dry. When cleaning, pay attention to the protective seal surface, no scratches, scratches, collisions, etc. Determination of the amount of compression When installing the mechanical seal, first check the working length of the spring from the manual, and then use the caliper to measure the free length of the spring to get the compression of the spring. The installation should ensure the deviation of the compression of the spring [1mm. After the inspection is completed, assemble in the correct order.
