1. Push type mechanical seal and non push type mechanical seal

Push type mechanical seal refers to a mechanical seal that compensates for the wear of the sealing surface by mechanically pushing the auxiliary seal along the shaft or shaft sleeve, usually referring to a spring compression type mechanical seal.

Non push type mechanical seals are used to assist in sealing mechanical seals fixed on shafts, usually bellows mechanical seals.

2. Balanced mechanical seals and unbalanced mechanical seals

The pressure in the mechanical seal chamber acts on the moving ring to form a closing force for the slurry pump mechanical seal, and the liquid film between the end faces forms an opening force. Load factor K>1, the seal is a non-equilibrium mechanical seal. Generally, non-equilibrium mechanical seals can only be used for low pressure. When the pressure exceeds a certain limit, the liquid film between the sealing surfaces will be squeezed out. Under the loss of liquid film lubrication and high load, the sealing end face of the mechanical seal will quickly be damaged. Non balanced mechanical seals cannot balance the effect of liquid on the end face, and the end face specific pressure increases with the increase of fluid pressure.

The load factor K is less than 1, and the seal is a balanced mechanical seal. The step on the internal sealing shaft of the balanced mechanical seal causes the sealing end face to move radially inward without reducing the width of the sealing surface of the kettle mechanical seal. The opening force of the seal remains unchanged, but due to the large area of the moving ring exposed to the liquid, a considerable portion of the closing force is balanced. The balancing method of the external sealing of the balanced mechanical seal is the same as that of the internal mechanical seal, except that the direction of the applied force is exactly opposite. In this case, it is necessary to increase the proportion of hydraulic pressure in the closing force to offset the opening force of the liquid film between the non-standard mechanical seal surfaces at the mechanical seal end. Balanced mechanical seals can partially balance the effect of liquid on the end face, and the end face specific pressure slowly increases with the increase of fluid pressure. Generally, non-equilibrium mechanical seals can only be used for low pressure, but for poor lubrication performance, low boiling point, easily vaporized media, and high-speed working conditions, even under low pressure, balanced mechanical seals should be selected. Because for non-equilibrium mechanical seals, when the pressure in the mechanical seal chamber rises, the liquid film between the sealing faces will be squeezed out, causing the sealing face of the mechanical seal to be quickly damaged. Balanced mechanical seals can be used in various pressure applications.

3. Non pressure dual mechanical seal and pressure dual mechanical seal

Single end mechanical seals have only one pair of friction pairs, simple structure, easy manufacturing and disassembly, and generally only require a flushing system without the need for an external sealing fluid system.

Pressure double mechanical seal (formerly known as double end mechanical seal) refers to a complex structure with two pairs of friction pairs that require an external sealing fluid system. The sealing chamber of the pressure double mechanical seal is filled with an isolation fluid that is 0.5-1.5 bar higher than the medium pressure, which plays a role in sealing, lubrication, etc. The isolation fluid lubricates the inner seal. Non pressure double seal (formerly known as series seal) refers to a complex structure with two pairs of friction pairs that require an external sealing fluid system. The buffer fluid in the non pressure double seal chamber is not pressurized, and the process medium lubricates the inner seal.

In general, single end mechanical seals should be preferred because they have a simple structure, are easy to use, and have a low price. But in the following situations, dual mechanical seals are preferred.

(1) Toxic and hazardous media.

(2) High concentration of H2S.

(3) Volatile low-temperature media (such as liquefied petroleum gas, etc.).

With the increasing emphasis on health, safety, and environmental protection in society, the use of non pressure dual mechanical seals has been increasing year by year. This non pressure dual mechanical seal can be widely used in toxic, volatile, and dangerous media such as vinyl chloride, carbon monoxide, and light hydrocarbons. The inner seal (first seal) of the non pressure dual mechanical seal is the main seal, which is equivalent to a single end face internal mechanical seal. The lubrication of the single end face mechanical seal is provided by the sealed medium. The sealed chamber is filled with liquid from the sealing tank without pressurization. Once the inner seal of the non pressure dual mechanical seal fails, causing an increase in pressure in the sealing chamber, it can be displayed, recorded or alarmed by the pressure gauge of the sealing tank. At the same time, the outer seal of the non pressure dual mechanical seal can play a role in sealing and containing leaked liquids before maintenance.

For some toxic and particulate media (or highly corrosive media), the following methods can generally be considered:

(1) Adopt appropriate environmental control measures, such as external flushing+pipeline flushing system with cyclone separator.

(2) Adopting a pressurized dual mechanical seal.

The pressure of the double mechanical seal isolation fluid is higher than the medium pressure, so the pumped medium will not enter the sealing chamber. The inner seal of the pressure double mechanical seal plays a role in preventing the isolation liquid from entering the pump chamber. Therefore, when transporting viscous, abrasive, and high-temperature media, the inner seal of the pressure double mechanical seal does not need to be made of expensive alloys because it is not exposed to the medium. The outer seal of the pressure double mechanical seal only serves to prevent the isolation liquid from leaking into the atmosphere.

4. Internal and external mechanical seals

Internal mechanical seal: refers to the mechanical seal installed inside the sealing chamber.

External mechanical seal: refers to the mechanical seal installed outside the sealing chamber.

Due to the good stress distribution of internal mechanical seals, the specific pressure increases with the increase of medium pressure, and the leakage direction of internal mechanical seals is opposite to the direction of centrifugal force. Therefore, internal mechanical seals are generally selected. Only when the medium is highly corrosive and you do not want to consider using a pressurized dual mechanical seal, should you consider using an external mechanical seal.

5. Rotating mechanical seals and stationary mechanical seals

Rotary mechanical seal refers to a mechanical seal in which the compensating component rotates along with the shaft.

Static mechanical seal refers to a mechanical seal in which the compensating component does not rotate with the shaft.

In general, rotary mechanical seals are used, but when the shaft diameter is large, the speed is high, and the sealing circumferential speed reaches 25m/s, static mechanical seals should be used due to the large centrifugal force generated by springs and other rotating components, high dynamic balance requirements, and high consumption of stirring power. In addition, if the medium is prone to crystallization due to strong agitation, it is also recommended to use a static mechanical seal.

6. Single spring mechanical seal and multi spring mechanical seal

Single spring mechanical seal has a simple structure, and the spring can also serve as a transmission function, but the end face pressure is uneven and not suitable for high-speed operation.

Multi spring mechanical seal has a complex structure, and the spring cannot also serve as a transmission function, but the end face pressure is uniform and suitable for high-speed operation. In general, it is recommended to use multi spring mechanical seals.