THE WORKING PRINCIPLE AND APPLICATION OF MECHANICAL SEALS FOR CHEMICAL CENTRIFUGAL PUMPS

When it comes to pump seals, we may talk about the gland packings and mechanical seals. The mechanical seal is a commonly used component in chemical centrifugal pump, and the generally used seals are spring seals, elastomer bellow seals, etc.

When the mechanical seal is working, it depends on the moving ring fixed on the shaft and the static ring fixed on the pump casing, and uses the elastic force of the elastic component and the pressure of the sealing fluid to promote the fit of the end faces of the moving and static rings, achieving the sealing function. In the mechanical seal device, the pressure shaft seal water, on the one hand, prevents high-pressure discharge water, on the other hand, squeezes into the moving and static rings to maintain a layer of lubricating fluid film, so that the end faces of the moving and static rings are not in contact. Because the flow film is very thin and is affected by high-pressure water, the leakage is small. The auxiliary sealing ring is adopted between the static ring and the sealing gland, between the moving ring and the rotating shaft, and between the sealing gland and the housing, which solves the sealing problem of leakage points.

Types of Mechanical Seals

1. According to the end face, it can be divided into: single end face mechanical seal and double end face mechanical seal.

1) Single end face mechanical seal: a mechanical seal composed of a pair of sealed end faces. The structure is simple, the manufacture and the installation are easy, and it is generally used under the condition that the medium itself has good lubricity and allows little leakage.

2) Double end face mechanical seal: a mechanical seal composed of two pair of sealed end faces. When the medium itself has poor lubricity and is toxic, flammable, explosive, easy to play and has strict requirements on leakage. A sealing cooling liquid with a pressure higher than the medium is introduced between the two end faces to perform sealing and cooling. It is possible to achieve "zero leakage" of the medium. It is divided into axial and radial double end faces.

2. According to the contact mode of the sealing end face, it can be divided into: contact and non-contact mechanical seals.

1) Contact mechanical seal: the end face of the seal 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 the use under high speed and high pressure is subject to certain restrictions.

2) Non-contact mechanical seal: the end face of the seal is in a state of full liquid lubrication. It has low heat generation and low power consumption, and it has no wear during normal operation. It can work under severe working conditions such as high pressure and high speed, but the leakage is large. It is further divided into: hydrostatic non-contact type and hydrodynamic non-contact type mechanical seals.

3. According to the balance method, it can be divided into: balanced and unbalanced mechanical seal.

1) Balanced mechanical seal: it can make the pressure of the medium acting on the end face of the seal unloading. According to the degree of unloading, it is divided into partial balanced type (partial unloading) and over balanced type (full unloading). It can reduce the friction and wear on the end surface, reduce the frictional heat, and have a large loading capacity, but the structure is more complicated, and generally a step needs to be processed on the shaft or the sleeve, and the cost is higher.

2) Unbalanced mechanical seal: it can not unload the pressure of the medium acting on the end face of the seal. It has simple structure, it is widely used when the medium pressure is less than 0.7Mpa.

2. The Working Process of Mechanical Seals

The static ring and the sealing gland are sealed by a static sealing rubber ring, and the elastic tight force of the sealing rubber ring is used to fix the static ring on the sealing gland, and the anti-rotation pin is used to prevent the static ring from rotating. The moving ring uses the elastic force of the elastic component to closely fit with the static ring. The moving ring and the shaft are sealed with a moving sealing rubber ring, and are connected to the elastic component through the transmission pin, and rotate with the elastic component. The fastening screw is fixed on the shaft and rotates with the shaft. In this way, when the shaft rotates, the rotating shaft drives the elastic component to rotate through the fastening screw, and the elastic component drives the moving ring to rotate together through the transmission pin, so that a relative slewing motion and a good fit are generated between the moving ring and the static ring, thus achieving the purpose of sealing.