The function of the shaft seal device: Because there is a certain gap between the rotor and the pump casing, a sealing device is installed at the part where the pump shaft protrudes from the pump casing. The seal at the suction end of the water pump is used to prevent air from leaking in, destroying the vacuum and affecting water absorption, and the seal at the water outlet end prevents high-pressure water from leaking out.
Packing seal device (packing)
1. Structure
Mainly composed of: shaft sleeve, packing culvert, packing, water seal, etc.
1. Shaft sleeve: It is used to protect the shaft, prevent liquid from corroding the shaft, and prevent the shaft from directly rubbing against the packing.
2. Packing culvert and packing: (packing box and packing) play the role of separating the outside from the inside of the pump casing to reduce leakage.
3. Water seal: The water seal ring is added to the seasoning culvert and aligned with the external water seal pipe. During operation, the small holes and grooves around the water seal ring form a water ring to prevent air from leaking into the pump. It can also lubricate and cool the packing and bushings, preventing massive wear of the packing and bushings.
2. Treatment of leakage
Working process: In order to reduce the amount of leakage, the packing should first be installed in the correct way.
1) First, thoroughly clean the inside of the packing culvert, and check whether the outer surfaces of the shaft sleeve and the packing culvert are intact and whether there is any obvious wear.
2) The specifications of the packing should be selected according to the regulations, the performance should be suitable for the liquid to be delivered, and the size should meet the requirements. Too fine and it will leak.
3) When cutting the packing, the knife edge should be sharp, the joint should be cut at an angle of 30o to 45o, and the cutting surface should be smooth. The cut packing must be a complete circle after being installed in the filler culvert, and cannot be short or excessively long.
4) After the packing is installed into the packing culvert, the joints of two adjacent circles must be staggered by at least 90o. If it is equipped with a water cooling structure, attention should be paid to staggering the packing culvert's cooling water inlet, and aligning the annular chamber of the water seal ring with the water inlet.
5) After installing the last ring of packing, install the packing gland and tighten evenly until the packing is confirmed to be in place. After loosening the packing gland, re-tighten it to the appropriate tightening force. (Generally, after installing the packing, it is best not to tighten it or to tighten it slightly. After the pump is filled with water, tighten the packing, but let the packing leak slightly. After the pump is started, tighten according to the temperature of the packing and the amount of leakage. Packing. That is, it cannot leak too much or the temperature is too high.)
6) After tightening the packing, check the gap between the packing gland and the shaft. The gaps around the gland should be the same; check whether the pressure around the gland is the same. Prevent friction between the gland and the shaft.
3. Inspection after packing
Check whether the tightening force of the packing gland fastening nut is appropriate. If the tightening force is too large, although the leakage will be reduced, the friction between the packing and the sleeve surface will increase. In severe cases, it will generate heat and smoke until the packing is broken. And the bushing is burned; if the tightening force is too small, the leakage will be large. Therefore, the tightening force must be appropriate. The liquid should gradually reduce the pressure through the gap between the packing and the bushing and form a water film to increase lubrication, reduce friction and cool the bushing. After the pump is started, it is better to keep a small amount of liquid flowing out of the packing culvert. The gland tightening force can be adjusted after the pump is started.
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Machinery Seal
1. Mechanical seal form and working principle
Mechanical seal is a packing-less end face sealing device that limits the leakage of working fluid along the rotating shaft. It is mainly composed of a static ring, a moving ring, elastic (or magnetic) elements, transmission elements and auxiliary sealing rings.
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The mechanical seal works by relying on a moving ring fixed on the shaft and a static ring fixed on the pump casing, and uses the elastic force of the elastic element and the pressure of the sealing fluid to promote the close fit of the end faces of the moving and static rings to achieve the sealing function. of. In the mechanical seal device, the pressure shaft seal water on the one hand prevents high-pressure water from leaking out, and on the other hand squeezes into the moving and stationary rings to maintain a flowing lubricating liquid film so that the end faces of the moving and stationary rings do not contact. Since the flowing membrane is very thin and acted upon by high-pressure water, leakage is minimal. Auxiliary sealing rings are used between the static ring and the sealing gland (B), between the moving ring and the rotating shaft (C), and between the sealing gland and the housing (D) to solve the sealing problems at these leakage points. .
2. Working process of mechanical seal
The static ring and the sealing gland are sealed by the static ring sealing rubber ring, and the elastic tightness of the sealing rubber ring is used to fix the static ring on the sealing gland, and an anti-rotation pin is used to prevent the static ring from rotating; the moving ring uses The elastic force of the elastic element is closely connected with the static ring. The moving ring and the shaft are sealed by the moving ring sealing rubber ring, and are connected to the elastic element through the transmission pin. They rotate together with the elastic element. The elastic element is fixed by fastening screws. Rotates with the axis on the axis. In this way, when the shaft rotates, the rotating shaft drives the elastic element to rotate through the fastening screw, and the elastic element drives the moving ring to rotate together through the transmission pin, thus causing relative rotational motion and good fit between the moving ring and the static ring. contact to achieve the purpose of sealing.
3. Types of mechanical seals
1. According to the end face, it is divided into: single end face and double end face mechanical seal.
1) Single end mechanical seal: a mechanical seal composed of a pair of sealing end faces. It has a simple structure, is easy to manufacture and install, and is generally used when the medium itself has good lubricity and allows trace leakage.
2) Double-end mechanical seal: A mechanical seal composed of two pairs of sealing end faces. When the medium itself has poor lubrication, is toxic, flammable, explosive, easy to explode and has strict requirements on leakage. A sealing cooling liquid higher than the medium pressure is introduced between the two end faces for sealing and cooling. It is possible to achieve "zero leakage" of media. It is divided into axial and radial double end faces.
2. According to the balancing method: balanced and unbalanced mechanical seals.
1) Balanced mechanical seal: It can unload the pressure of the medium acting on the sealing end face. Different degrees of unloading are divided into partial balance type (partial unloading) and over-balanced type (complete unloading). It can reduce friction and wear on the end face, reduce friction heat, and has a large load-bearing capacity. However, the structure is complex and generally requires a step to be machined on the shaft or sleeve, which is costly.
2) Unbalanced mechanical seal: It cannot unload the pressure of the medium acting on the sealing end face. It has a simple structure and is widely used when the medium pressure is less than 0.7Mpa.
3. According to the arrangement of springs: spring built-in mechanical seal and spring external mechanical seal.
1) Spring built-in mechanical seal: the spring is in contact with the medium. It is susceptible to corrosion and is easily blocked by debris in the medium. If the spring rotates with the axis, it is not suitable for use in high-viscosity media.
2) Spring external mechanical seal: the spring is not in the medium and does not come into contact with the medium. Used on equipment with highly corrosive, high viscosity and easily crystallized media.
4. According to the number of springs: single spring mechanical seal and multi-spring mechanical seal.
1) There is only one spring in the elastic element (sealing compensator). The spring wire is thicker, corrosion-resistant, and solid particles are not easy to accumulate at the spring, but the force on the end face is uneven.
2) There is a set of springs in the elastic element (sealing compensator). The force on the end face is relatively uniform, and it is easy to increase or decrease the number of springs to adjust the spring force. The axial length is short, but the spring wire is thin, the corrosion resistance life is short, and the installation size requirements are strict.
5. According to the form of elastic element (seal compensator): rotating mechanical seal and static mechanical seal.
1) Rotary mechanical seal: the elastic element (seal compensator) is rotated with the shaft. It is widely used because it is easily affected by the centrifugal force on the spring when rotating, which will affect the pressure of the sealing end face. Not suitable for high speed situations.
2) Static mechanical seal: the elastic element (seal compensator) does not rotate with the shaft. Suitable for high speed situations. Suitable for high speed situations.
6. According to the leakage direction of the sealing fluid (medium): internal flow mechanical seal and external flow mechanical seal.
1) The direction of sealing fluid (medium) leakage between end faces is opposite to the direction of centrifugal force. The leakage is small and the sealing is reliable.
2) The direction of leakage of sealing fluid (medium) between end faces is the same as the direction of centrifugal force. When the rotational speed is extremely high, it is more suitable to strengthen end face lubrication, but the medium pressure is not easy to be too high, generally 1-2MPa.
7. According to the contact mode of the sealing end face: contact type and non-contact mechanical seal.
1) Contact mechanical seal: The sealing end face is in a boundary or semi-liquid lubrication state. The structure is simple and the leakage is small, but the wear, power consumption, and heat generation are large, and its use under high speed and high pressure is subject to certain restrictions.
2) Non-contact mechanical seal: the sealing end face is in a fully liquid lubricated state. It has low heat generation and power consumption, no wear and tear during normal operation, and can work under harsh working conditions such as high pressure and high speed, but the leakage amount is large. It is further divided into: hydrostatic non-contact and hydrodynamic non-contact mechanical seals.
a. Hydrostatic non-contact mechanical seal: It uses externally introduced pressure fluid or the sealed medium itself to generate a hydrostatic effect through the pressure drop on the sealing end face.
b. Hydrodynamic non-contact mechanical seal: a seal that uses the relative rotation of the end face to generate a hydrodynamic pressure effect on its own, such as a spiral groove end face seal.
Others include bellows mechanical seals and single-pole, bipolar (multi-pole) mechanical seals.
