Double Mechanical Seal

About Double Mechanical Seal

Double mechanical seal include axial double face seals and radial double face seals. It is suitable for media with poor lubrication, toxic, flammable, explosive, volatile, containing abrasive particles and gases, etc. Usually, a sealing auxiliary system is required, that is, isolation fluid is introduced into the sealing cavity between the two end faces to improve the lubrication and cooling conditions of the mechanical seal.

소개

Generally, Double mechanical seal requires an external sealing fluid system, which introduces sealing fluid into the sealing cavity for sealing, lubrication and cooling, and is mostly used for circulating cooling. The sealing fluid can not only flush the friction pair and improve the working environment of the mechanical seal, but can also be used to determine whether the primary sealing surface has failed.

Performance Characteristics

Double mechanical seal has many excellent properties, mainly in the following points:

1. Low end temperature
Although the temperature is higher, the maximum temperature is about 100°C, which is a big change from the situation where the friction pair is at 350°C in field applications. If back cooling is used, the temperature will be even lower.

2. Less cooling water consumption
Cooling water is only used when the back is cold, which greatly reduces the amount of cooling water used on site compared with the original.

3. Good sealing effect
The spiral groove can be used to pump sealing oil to the medium to prevent hot oil from leaking outward. The contact seal on the outside of the seal prevents seal oil leakage. The double-end mechanical seal has two end-face seals. If the primary seal fails, the secondary seal can still seal to prevent leakage.

4. Small end face wear and long service life
Through analysis and research on the sealing dynamic and static rings after continuous operation, the end faces of the non-contact dynamic and static rings are almost not worn, and the contact end face wear is greatly reduced compared with the original sealing end faces, and no thermal cracking occurs. The service life is extend.

봉인 원리

The principles of single mechanical seal and double mechanical seal is the same. They are both coordinated compensation mechanisms to prevent fluid leakage by using the fluid pressure and elastic force of the rotating (friction) device near the end vertical axis to maintain height and relative sliding.

When working, due to the fluid pressure joint force and the elastic force of the elastic element, the end face sealing ring is at an appropriate pressure ratio (pressure), so that the two contact surfaces (ring, static ring end surface) are closely attached to each other, maintaining a layer of thin oil film gap and minimum value between the end face, thereby achieving the purpose of sealing. There is double mechanical seal with two end face seals. If the seal fails, the two-stage seal can still be sealed to prevent leakage. General double-end seal sealing fluid system needs, introduction of blocking seal liquid seal, lubrication, cooling, seal cavity, mostly used for cooling cycle. Sealing fluid can not only clean the friction pair of mechanical seals, improve the working environment, and be an important means of detection, but can also serve as a major sealing surface failure.

Failure Analysis

Rotating equipment failures, due to double mechanical seal leakage and closure, account for about 50% of the total repair equipment. The failure mechanism of the double mechanical seal is basically the same as the failure mechanism of the single-end mechanical seal, and is the main cause of sealing surface failure. During the operation of the pump, the heat generated due to friction and mixing will increase the temperature of the sealing surface. Coupled with the effect of the medium, vaporization will occur, the sealing surface of the sealing ring will wear, the medium will thermally deform, and even thermal cracks will occur. . Some media will intensify curing, polymerization, crystallization, coking and corrosion when temperatures change. Various abnormal conditions will aggravate or directly lead to seal failure in the short term.

Solutions

1. Check whether the auxiliary device is started normally to ensure the sealing fluid level and pressure within the operating range and the sealing of the fluid system.

2. Avoid seal dry friction causing pump losses.

3. Frequently check that the auxiliary devices are working properly.

4. Reduce the impact of vibration on the machine itself and heat seal.

Conclusion: There are many reasons for the failure of double mechanical seal, which are also very complicated. Corresponding solutions can be adopted. Double mechanical seal leakage is directly related to process operation, installation and maintenance. Standardizing operations and strengthening daily production management are safeguards and necessary measures to improve sealing efficiency and lifespan.