1. Analysis of mechanical seal failure of centrifugal pump Centrifugal pump shutdown is mainly caused by the failure of mechanical seal. The performance of failure is mostly leakage, and the reasons for leakage are as follows:
1 Leakage of the static sealing surface of the static ring, the main reasons are: the flatness of the end face, the roughness does not meet the requirements, or the surface is scratched; there are particulate matter between the end faces, causing the two end faces not to operate in the same way; the installation is not in place, the way is not correct.
2 compensation ring seal leakage, the main reasons are: gland deformation, pre-tightening force is uneven; installation is not correct; the quality of the seal ring does not meet the standard; the seal ring selection is wrong.
The actual use effect shows that the part of the sealing element that is ineffective is the moving, the end face of the static ring, the centrifugal pump is sealed, and the crack on the end face of the static ring is a common failure phenomenon. The main reasons are:
1 When the sealing surface is too large, the flushing fluid can't take away the heat generated by the friction pair; the flushing liquid leaks away from the gap of the sealing surface, causing the end surface to overheat and be damaged.
2 The liquid medium vaporizes and expands, so that the two end faces are separated by the vaporization expansion force. When the two sealing faces are pressed together, the lubricating film is broken and the surface of the end face is overheated.
3 The liquid medium has poor lubricity, and the operating pressure is overloaded, and the tracking surfaces of the two sealing surfaces are not synchronized. For example, the high speed pump speed is 20445r/min, the sealing surface center diameter is 7cm, and the line speed is up to 75m/s after the pump is running. When there is a sealing surface lag, the rotation cannot be tracked, and the sealing surface is damaged by the instantaneous high temperature.
4 The seal flushing liquid orifice plate or filter is clogged, resulting in insufficient water and invalidation of the machine seal.
In addition, the sealing surface surface of the sliding groove, the gap when the end surface is attached, the sealing element fails, the main reasons are:
1 The liquid medium is not clean, and there are tiny hard particles, which slide the sealing surface at a high speed and scratch the surface of the end surface and fail.
The pumping parts of the 2 pump are poor in coaxiality. After the pump is turned on, the end face is shaken once every revolution, and the running track of the moving ring is not concentric, causing the end face to vaporize and overheat and wear.
3 The frequent occurrence of hydraulic characteristics of the liquid medium causes the pump unit to vibrate, causing the sealing surface to be misaligned and fail.
The liquid medium corrodes the sealing element, stress concentration, soft and hard material coordination, erosion, auxiliary sealing 0-ring, V-ring, concave ring is incompatible with liquid medium, deformation, etc. will cause mechanical seal surface damage failure, so The damage form should be comprehensively analyzed to find out the root cause and ensure that the mechanical seal runs for a long time.
2. Requirements after the centrifugal pump stops running. 1 After the centrifugal pump stops running, the pump's population valve should be closed. After the pump is cooled, the valve of the auxiliary system is closed.
2 High-temperature pump parking should be carried out according to the provisions of the equipment technical documents. After parking, it should be half-turned every 20 to 30 minutes until the pump temperature drops to 50 °C.
3 When the cryopump is parked, when there is no special requirement, the pump should always be filled with liquid; the suction valve and the discharge valve should be kept normally open; the cryopump with double mechanical seal, the liquid level controller and the sealing liquid in the pump seal chamber The pumping pressure of the pump should be maintained.
4 Pumps that are easy to crystallize, easy to solidify, and easy to precipitate, should be blocked after stopping the pump, and flush the pump and pipeline with water or other medium in time. 5 Discharge the liquid accumulated in the pump to prevent rust and cracking.
3. Storage of centrifugal pump 1 The pump that has not been installed should be coated with a suitable rust inhibitor on the unpainted surface. The oil-lubricated bearing should be filled with the appropriate oil. The grease-lubricated bearing should only be filled. A grease, do not use mixed grease.
2 pumping clean liquid, flushing, suction line, discharge line, pump casing and impeller for a short time, and draining the pump casing, the suction line and the flushing liquid in the discharge line.
3 rows of net bearing housing oil, add clean oil, thoroughly clean the grease and refill with new grease.
4 Seal the suction and discharge ports, store the pump in a clean, dry place, protect the motor windings from moisture, and spray the inside of the pump casing with anti-rust liquid and anti-corrosion liquid.
5 The pump shaft rotates once a month to avoid freezing and lubricate the bearings.
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