Comparison of mechanical seals and packing seals


Comparison of mechanical seals and packing seals

1. Packing seal:

The structure is simple, the price is cheap, and the maintenance is convenient, but the leakage amount is large and the power loss is large. Therefore, packing seals are used to transport general media such as water; not suitable for petroleum and chemical media, especially in expensive, explosive and toxic media.

.

2 mechanical seal:

The sealing is better, the leakage is small, the service life is long, but the price is expensive, and the processing, installation and maintenance are higher than the general sealing requirements. The mechanical seal is suitable for transporting petroleum and chemical media and can be used in a variety of different viscosity, highly corrosive and particle-containing media.

Packing seals are a traditional contact seal that is widely used. The utility model has the advantages of simple structure, convenient replacement, low cost, wide application range (can be used for rotation, reciprocating and spiral motion sealing), and axial movement is allowed for the shaft of the rotary motion. It does not

The foot is slightly poor in sealing performance, the shaft is not allowed to have large radial runout, the power consumption is large, the wear shaft is short, and the service life is short.

The packing seal is adhered to the filler portion through the surface of the shaft to form a labyrinth effect to achieve sealing. Since it is a sliding seal, there should be enough liquid for lubrication to ensure a certain life of the seal, the so-called bearing effect.

Fillers also require materials:
1. Certain elastoplasticity
2, chemical stability
3, impermeability
4, good self-lubricating, small friction coefficient and wear resistance
5, temperature resistance
6, easy to install and disassemble.

The mechanical seal has good sealing performance, stable performance, less leakage, low frictional power consumption, long service life, little wear on the shaft, can meet various working conditions, and is widely used in petrochemical departments, but its mechanism is complex and manufacturing precision. High, expensive

Maintenance is not convenient.

The mechanical seal, also known as the end seal, has at least one pair of end faces perpendicular to the axis of rotation, which is under the action of fluid pressure and compensating mechanical external elastic force (or magnetic force), and the auxiliary seal is matched with the other end face. Relative

East, thus posing to prevent leakage. Since the two sealing end faces are closely fitted, a small gap is formed at the boundary between the sealing end faces. When the pressurized medium passes through the gap, a very thin liquid film is formed, which causes resistance, prevents the medium from leaking, and causes the end face to be obtained.

Lubrication, thereby obtaining a long-term sealing effect.

The packing seal is a conventional gland seal. It relies on the gland to create a compressive force that compresses the packing, forcing the packing against the sealing surface (the outer surface of the shaft and the sealing cavity), creating a radial force that seals and thus acts as a seal. Radial

The force is distributed exponentially along the length of the packing. In order to maintain the "on" state of the packing, the radial pressure on the inner ring is at least equal to the internal pressure of the system, which means that the radial pressure of the outer ring is much higher.
It features a packing seal for large stuffing boxes and heavy duty applications. It is mainly used for low-viscosity liquid pumps such as clean water pumps. It is not suitable for flammable, explosive, valuable or toxic liquids. Packing seals can be used in addition to being pumped

Rotating occasions. The packing sealing structure is simple, convenient in operation and maintenance, and low in cost. Insufficient power consumption, poor sealing reliability, and easy wear on the shaft during use.

The mechanical seal is a shaft seal device that resists leakage by a pair of or pairs of end faces that are relatively slid relative to the shaft under the action of the fluid pressure and the elastic force (or magnetic force) of the compensating mechanism to assist in sealing. Common mechanical seal structure by static

Ring (static ring)

1, rotating ring (moving ring)
2, elastic components
3, spring seat
4, set screws
5, rotating ring auxiliary seal
6, and the stationary ring auxiliary seal
7. The components are assembled, and the anti-rotation pin 7 is fixed on the gland 9 to prevent the stationary ring from rotating. Rotating rings and stationary rings can often also be referred to as compensating rings or non-compensating rings depending on whether they have axial compensation capabilities.

There are four channels of fluid leakage in the mechanical seal: A, B, C, and D. The leakage passages of C and D are respectively the seal between the stationary ring and the gland, the gland and the casing, and both of them are static seals. The B channel is the seal between the rotating ring and the shaft.

After the surface friction and wear, it can only follow the compensation ring in the axial direction for a small amount of movement, in fact still a relatively static seal. Therefore, these leak paths are relatively easy to block. The most commonly used static sealing elements are rubber O-rings or polytetrafluoroethylene.

A vinyl V-ring, and a rotating ring or a stationary ring auxiliary seal as a compensating ring, sometimes a rubber, Teflon or metal bellows structure having a function of an elastic member. The A channel is the opposite end of the rotating ring and the end face of the stationary ring.

Dynamic seal, which is the primary seal in mechanical seals and the key to determining mechanical seal performance and longevity. Therefore, the processing of the sealing end face is very demanding, and in order to maintain the necessary lubricating liquid film between the sealing end faces, the cavity must be strictly

The pressure per unit area on the end face is too large, and it is difficult to form a stable lubricating liquid film, which will accelerate the wear of the end face; if the pressure is too small, the leakage amount will increase. Therefore, in order to obtain good sealing performance and have sufficient life, design and install mechanical seals.

When making sure that the pressure per unit area of ​​the end face is in the most appropriate range.

Compared with soft packing seals, mechanical seals have the following advantages:
1 Sealed reliably In long-term operation, the sealing state is very stable, and the leakage is small. According to rough statistics, the leakage is generally only 1/100 of the soft packing seal;
2 The service life is generally 1 to 2 years or longer in oil and water media, and usually more than half a year in chemical media;
3 friction power consumption, the friction power of the small mechanical seal is only 10% to 50% of the soft packing seal;
The 4-axis or sleeve is substantially free of wear;
5 The maintenance period can be automatically compensated after the long end face wears. Under normal circumstances, frequent maintenance is required.
6 good vibration resistance is not sensitive to the vibration, yaw of the rotating shaft and the deflection of the shaft to the sealing cavity;
7 Wide range of applications Mechanical seals can be used for low temperature, high temperature, vacuum, high pressure, different speeds, as well as a variety of corrosive media and abrasive media.

But its shortcomings are:
1The structure is more complicated, and the manufacturing and processing requirements are high;
2 installation and replacement is more troublesome, and requires workers to have a certain level of installation technology;
3 When an accident occurs, the handling is more difficult;
4 One-time investment is high. (Source: Hebei Innovation Sealing Material Co., Ltd.)
The main products of our factory have the following major categories: one: packing series: carbon packing, PTFE packing, graphite packing, high water based packing, aramid packing, PTFE cutting wire packing, gathering Tetrafluoroethylene packing, expanded PTFE packing, asbestos packing, carbon fiber packing, butter cotton packing, oil-impregnated cotton packing, linseed packing, canvas coil packing, ceramic fiber packing, nylon disc Root, composite fiber packing, ceramic packing, and other products.
Two: various gasket series: PTFE gasket, toothed gasket, asbestos gasket, ladle gasket, metal wound gasket, graphite gasket, high strength graphite composite gasket, PTFE gasket gasket, rubber flange Pad, asbestos manhole pad, asbestos hand hole pad, special seal ring for autoclave, asbestos flange pad, etc.
Three: rubber products: silica gel, fluorine rubber, nitrile rubber, neoprene and other special-shaped products.
Four: PTFE products series: PTFE rods, belts, membranes, mats, etc.


'Comparison of mechanical seals and packing seals

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