1. Push type mechanical seal and non-push type mechanical seal
Push-type mechanical seal refers to a mechanical seal that assists the seal to mechanically press along the shaft or sleeve to compensate for the wear of the seal face, usually referred to as a spring-loaded mechanical seal.
Non-pushing mechanical seals are used to assist in sealing mechanical seals that are fixed to the shaft, typically bellows mechanical seals.
2, balanced mechanical seal and unbalanced mechanical seal
The pressure in the mechanical seal sealing cavity acts on the moving ring to form a closing force, and the liquid film between the end faces forms an opening force. The load factor K>1, the seal is an unbalanced mechanical seal. Generally unbalanced mechanical seals can only be used for low pressure. When the pressure is greater than a certain limit, the liquid film between the sealing faces is squeezed out. Under the action of losing liquid film lubrication and high load, the sealing end face of the mechanical seal will be damaged quickly. An unbalanced mechanical seal does not balance the effect of the liquid on the end face, and the end face specific pressure rises as the fluid pressure rises.
The load factor is K<1 and the seal is a balanced mechanical seal. Balanced Mechanical Seals The steps on the internal seal shaft allow the seal face to extend radially inward without reducing the width of the seal face. The opening force of the seal does not change, but since the moving ring has a large area exposed to the liquid, the closing force is balanced by a considerable portion. Balanced mechanical seals The external balancing method of the external seal is the same as the built-in mechanical seal except that the direction of the force is just the opposite. In this case, the fraction of the hydraulic pressure in the closing force is increased to offset the opening force of the liquid film between the mechanical seal end faces. The balanced mechanical seal partially balances the action of the liquid on the end face, and the end face specific pressure rises slowly as the fluid pressure rises. Generally, unbalanced mechanical seals can only be used for low pressure, but for poor lubrication performance, low boiling point, easy to vaporize medium and high speed working conditions, even at low pressure, balanced mechanical seals should be used. Because for the unbalanced mechanical seal, when the pressure of the mechanical seal chamber rises, the liquid film between the seal end faces is extruded, and the sealing surface of the mechanical seal is quickly damaged. Balanced mechanical seals can be used in a variety of pressure applications.
3, pressureless double mechanical seal and pressure double mechanical seal
The single-end mechanical seal is only a pair of friction pairs. The structure is simple, easy to manufacture and disassemble. Generally, only the flushing system is needed, and no external sealing system is needed.
The pressure double mechanical seal (formerly known as double-face mechanical seal) means that there are two pairs of friction pairs, the structure is complex, and the external sealing liquid system is required. The pressure in the double mechanical seal sealing chamber is 0.5~1.5 bar higher than the medium pressure. The separating liquid acts as a plugging and lubricating, and the separating liquid lubricates the inner seal. The pressureless double seal (formerly known as series seal) means that there are two pairs of friction pairs, the structure is complex, and the external sealing liquid system is required. The buffer in the pressureless double seal sealing chamber is not pressurized, and the process medium lubricates the inner seal. effect.
Under normal circumstances, single-end mechanical seals should be preferred because the single-end mechanical seals are simple in structure, easy to use, and low in price. However, in the following cases, a double mechanical seal is preferred.
(1) Toxic and hazardous media.
(2) High concentration of H2S.
(3) Volatile low-temperature media (such as liquefied petroleum gas).
As society pays more and more attention to health, safety and environmental protection, the use of pressureless double mechanical seals is increasing year by year. The pressureless double mechanical seal can be widely used for toxic and volatile such as vinyl chloride, carbon monoxide and light hydrocarbons. Dangerous medium. The inner seal (first seal) of the pressureless double mechanical seal is the main seal, which is equivalent to a single-end internal mechanical seal, and the single-end mechanical seal lubrication is performed by the sealed medium. The sealed chamber is filled with liquid from the sealing liquid tank, and is not pressurized. Once the inner seal of the pressureless double mechanical seal fails, the pressure in the sealed chamber is increased, that is, it can be displayed, recorded or alarmed by the pressure gauge of the sealing liquid tank. At the same time, the pressureless double mechanical seal outer seal can seal and accommodate the leaking liquid before maintenance.
For some toxic, particulate-containing media (or highly corrosive media), the following methods are generally considered:
(1) Use appropriate environmental controls such as external flushing + pipe flushing system with cyclone separator.
(2) A pressurized double mechanical seal is used.
The pressure of the pressurized double mechanical seal spacer is higher than the medium pressure so that the pumped medium does not enter the sealed chamber. The inner seal of the pressurized double mechanical seal acts to prevent the spacer fluid from entering the pump chamber. Therefore, when transporting such as viscous, abrasive and high temperature media, the pressure double mechanical seal inner seal can be made without expensive alloys because it is not exposed to the medium. The pressure double mechanical seal outer seal only serves to prevent the separator from leaking into the atmosphere.
4. Built-in mechanical seal and external mechanical seal
Built-in mechanical seal: refers to the mechanical seal installed in the sealed cavity.
External mechanical seal: refers to the mechanical seal installed outside the sealed cavity.
Due to the good force of the built-in mechanical seal, the specific pressure increases with the increase of the medium pressure. The leakage direction of the built-in mechanical seal is opposite to the centrifugal force. Therefore, the built-in mechanical seal is generally used. An external mechanical seal is considered only when the medium is extremely corrosive and you do not want to consider a pressurized double mechanical seal.
5, rotary mechanical seal and static mechanical seal
A rotary mechanical seal refers to a mechanical seal that compensates for the rotation of the component with the shaft.
A stationary mechanical seal refers to a mechanical seal that compensates for the component not rotating with the shaft.
Rotary mechanical seals are generally used, but when the shaft diameter is large, the rotation speed is high, and the circumferential speed of the seal reaches 25m/s, the centrifugal force generated by the spring and other rotating elements is large, the dynamic balance is high, and the stirring is consumed. The power is also large, and a static mechanical seal should be used. In addition, static mechanical seals are also recommended if the media is susceptible to crystallization due to strong agitation.
6, single spring mechanical seal and multi-spring mechanical seal
Single spring mechanical seal, simple structure, spring can play the role of transmission, but the end face specific pressure is not uniform, not suitable for high speed operation.
Multi-spring mechanical seal, the structure is complex, the spring can not play the same role, but the end face is evenly pressed, suitable for high-speed operation. In general, a multi-spring mechanical seal is recommended.