Observations on the system with conic bush – figure 1

Locking happens when pressure exercised on the conic bush placed between the shaft and impeller.Through the conic bushes it's possible to obtain both the power transmission and location of the impeller on the shaft.When pump is assembled in a workshop with specialist equipment and by expert and prepared staff, trained to exercise the right pressure level on the conic bush it's possible to obtain the correct assembly.The situation is different when the pump is mantained by the user.Indeed, not having access to the necessary equipment, lacking the reference positions for assembly and in absence of the necessary training to exercise the exercise the right pressure on conic bush, the assembly will be less than perfect.As we said, it's easily deducible the reason for which, often, pump will have to be extracted again from well to intervene and take again the locking of an impeller which is remained slow in the previous intervention.In addition, with this impeller locking system, the guide bearings will be in direct contact with the pump shaft surface. During normal pump use, and more so when the liquid contains sand and silt, there is abrasion between the shaft area and the guide bearing.The abrasions' substance and the progression with which they happen, are favourite by the shaft's modest superficial hardness.When the abrasion exceeds acceptable limits, we have to intervene to re-establish the initial conditions, which, in this case, we is only possible with a new shaft.

Considerations on system with key and shaft casing – figure 2

In this system the power transmission is entrusted to the unified keys, which are in their respective shaft and impeller's seats, while the casings put between impellers, protect the shaft entirely and guarantee with precision the hydraulic pitch distance.In addition the shaft casings are in a dynamic contact with the fixed bearing in the diffuser, carrying out the impeller's guide task.Generally shaft casings are manufactured in stainless material and are superficially hardened or relined with a high hardness material.These characteristics make the bushes highly resistant to the wear and always easily replaceable in case of eventual abrasion.Moreover, the keys and shaft casing system, simplifies the disassembly and/or the reassembly by the user, who can carry out the repair effectively, without specialized equipment or training.

CONCLUSION http://www.imkv.cn/?p=166

The considerable technological difference between the two systems comes out with obvious clearness from the above observations.The conic bush system has a price benefit resulting from a lower production cost.The higher cost of the key and shaft casing system, are more than compensated for by the numerous advantages, which include: the ease of disassembly and reassembly, the possibility to substitute the shaft protection casings when they are worn and to rely with certainly on the impeller's locking on the shaft in the correct position.