AS-LWRA Pump Seal To Suit Lowara Pumps

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Background Knowledge：

The important factors of pump mechanical seal failure——pump vibration & cavitation

Due to reasons such as manufacturing and installation accuracy, all centrifugal pumps have vibrations, and there are perpendicularity errors between all sealing end faces and shaft axis. The perpendicularity error causes an axial swing when the rotary face rotates. The amplitude of the oscillation depends on the size of the error, and its frequency depends on the spring stiffness and quality of components of rotary face, and has nothing to do with the pump speed.

There are many reasons for pump vibration. The main cause of vibration is the imbalance of the rotor, but there are also other reasons. For example: poor pump and motor vibration, bearing failure, loose anchor bolts, etc. The vibration frequencies are different for different reasons. The vibration frequencies of most pumps are equal to the working speeds, but the vibration amplitudes are very different. The maximum amplitude measured from the surface of the bearing box cannot be greater than 0.06mm. If the value exceeds this number, the pump must be stopped for processing. It can be broken down into three directions, namely vertical, horizontal and axial. Among them, axial vibration is the most harmful to the seal. The rotation speed of most process pumps is around 2950r/min. Due to the poor follow-up of the seal, the vibration of pump aggravates separation of rotary face and stationary seat. Instantaneous separation causes sealing surface to open under action of liquid film pressure, and a large amount of leakage occurs. There are solid particles near friction pairs, and their entering between sealing end faces will cause the particular end faces to be damaged, which will cause the mechanical seal to fail. 

Due to rapid gas vaporization or gas overflow in the low-pressure area to the high-pressure area of the same impeller of the pump in operation, rapid condensation occurs. This rapid vaporization and condensation phenomenon is called cavitation , which is characterized by intense hydraulic shock during work.In terms of performance, the outlet pressure has a relatively large and intense fluctuation, and the pump vibration increases, which can cause malignant accidents such as shaft holding and broken shaft, and damage to the seal.The degree depends on the cavitation energy and duration.

The temperature of the medium at the friction pair in the sealed cavity is relatively high, and some of the components vaporize and flow to the low-temperature area to condense. This also has the conditions for cavitation.

The occurrence of cavitation means that there is a fierce hydraulic impact, which drives the seal to make rapid axial movement, which can cause serious damage to the rotary face and stationary seat and auxiliary sealing rings and other parts, and sealing performance of mechanical seal is destroyed.

If cavitation occurs in the pump, mechanical seal damage generally manifests as the following forms:

a. The stationary seat is out of position or the anti-rotation pin is bent.

b. The rotary face is"pulled"into the transmission seat and jammed, and the spring loses its effect.

c. One piece of the friction pair is made of brittle material (such as silicon carbide), and it flakes off due to"being knocked"on the sealing end surface.