Axial displacement of shielded pump
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I’d like to understand why shielded pumps require axial movement – could some expert explain this?
This post was last edited by 3983596_FPPZ on 2018-11-20 at 16:15. Since the shaft of a canned pump is completely submerged in the medium, normal rolling bearings cannot be used; therefore, sliding bearings have to be employed. Sliding bearings rely on sliding friction both axially and radially to position the shaft (or rotor assembly) and to withstand axial and radial forces. The radial force is borne by the sliding bearings within the pump (which can be called that for now), while the axial force is borne by a pair of thrust plates at each end (with each pair consisting of a moving thrust plate and a stationary thrust plate), thereby preventing the shaft from moving left or right. Due to thermal expansion and the accumulation of manufacturing tolerances, it is not possible for the two pairs of thrust plates to eliminate any clearance in the axial direction at the same time; instead, a small amount of play is allowed. This play is sufficient to accommodate the expansion of the parts as a result of temperature increases as well as the accumulation of manufacturing tolerances ； Nor should it be too large, as this could cause the axial positioning of the rotor assembly to fail, leading to misalignment of the impeller and misalignment between the stator and rotor. Excessive backlash momentum can easily cause damage due to collisions between the thrust discs (moving and stationary thrust discs). Generally, this backlash momentum is set at 0.5–1 mm; a higher value is used when the temperature is high. The same is true for another leak-free pump – the magnetic pump
The main considerations are thermal expansion and contraction as well as manufacturing errors of the parts
The last edit to this post was made by 156026692 on 2018-11-29 at 16:34. Let me explain: I have been working with canned pumps and magnetic pumps for eight years. First of all, the axial movement of a canned pump is an important parameter that determines whether the pump can operate over a long period of time. Since the rotor of a canned motor pump is completely immersed in the medium, a significant forward axial force acts on the rotating parts of the pump once it starts operating. This axial force can only be counteracted by the back pressure exerted by the impeller and the thrust plate; if this counteraction is not sufficient, an additional balance plate structure must be added. Therefore, manufacturers must test the axial movement. Generally, they measure this axial movement in terms of force, but some manufacturers provide it as a specific numerical value. In my opinion, it is better to have a specific range for the axial movement. I hope this can clear up your doubts.
Most of the replies on the forum came from designers and office staff, and the answers were somewhat similar. In practice, due to the Chinese people’s personality traits (which are quite flexible), some maintenance workers of shielded pumps deliberately increase or decrease the clearance during assembly; this doesn’t cause any problems in operation (with very few types of pumps that have strict requirements regarding this clearance). Furthermore, there are also many cases of shielded pumps using rolling bearings.
From the operator’s perspective, a shielded pump is a type of pump that maintains its balance through rotation. At the beginning of operation, due to factors such as speed and flow rate, this balance is not yet achieved; therefore, an axial displacement value needs to be set, with this value generally being provided by the manufacturer.