This eliminates the need for shaft sealing by means of a stuffing box or mechanical seal, which is required for other pump types.The pumped medium serves both to lubricate the motor bearings (plain bearings) and to cool the interior of the rotor. This so-called wet space is sealed off from the atmosphere or the motor winding by a can. This can has an average wall thickness of only 0.1 to 0.3 mm and is made of non-magnetic high-alloy steel. The canister is statically sealed using O-ring seals. Function / feature
The advantage of this construction is clearly that it is completely maintenance-free. No exchange or messages, no exchange of sealing elements, but perfect function during the entire operating time.The smoothness of this design is remarkable. Apart from the damping properties of the water, in which the rotating parts move, the reason for this smoothness is the sliding bearing of the rotor. This eliminates all rolling or rolling noises that occur in rolling bearings z. B. can occur by means of ball bearings.Not only the smooth running, but also the service life and the degree of susceptibility to failure are decisively influenced by this component.The design of the bearing is one of the most important design features of wet rotor pumps. In addition to the structural design of the bearings, the material pairing of the bearing is of decisive importance for the operational safety of the pump. The following combinations have become established in practice:
Ceramic shaft / ceramic bearing
Hardened chrome steel shaft / carbon bearing.
The ceramic bearing, shaft and bearing made of the same material, a pairing that contradicts traditional bearing theory, has very little bearing wear on the basis of the extremely hard and brittle material aluminum oxide ceramic with optimal bearing lubrication. However, if there is no requirement for proper lubrication, e.g. B. Dry running due to air accumulation or steam formation in the event of overheating, there is a risk of blockage after a short time. In addition, the ceramic shaft is relatively susceptible to breakage when subjected to mechanical stress, e.g. due to transport vibrations or when attempting to unblock it due to tilting with a screwdriver.In contrast, the two-material bearing – hardened chrome steel shaft / carbon bearing – shows the very good dry-running or emergency running properties of metal-impregnated carbon bearings. In addition, there is the proverbial break resistance of the hardened steel shaft against impacts and vibrations. Operational behavior
On the basis of decades of practice with millions of pumps, a statistical mean under normal operating conditions and depending on the pump design has resulted in a service life of approx. 40,000 to 70,000 operating hours. This corresponds to an average of 8-12 years with normal heating operation. The optimal functionality of this construction is also underlined by the fact that quite a few wet-running pumps run for more than 15 to 20 years (over 100,000 operating hours) without malfunction and maintenance.Glandless pumps in building technology consistently have the speed control of the drive motors as a special feature. In the meantime, manually switchable controls are no longer permitted for new installations in many countries and have largely been replaced by automatic controls.
The pump suction pipe is then air-evacuated without any special external suction devices.Centrifugal pumps without external or internal suction devices can be operated at a suction lift if the pump body is filled with water before starting the actual fluid displacement. Due to the function of a non-return valve the fluid will be retained within the pump body after switch-off.The construction required for for self-priming capability has a negative effect on the pump efficiency.
They transport the fluid through a star-shaped wheel into a channel next to the impeller. The delivery heads achieved are 5 to 15 times higher than those of radial impellers.The pumps are self-priming. They are used in particular for the conveyance of liquid-gas mixtures (partial gas conveyance) and for special suction requirements.The efficiency is comparatively low. Therefore, the power range is only up to about 4 kW.Due to the narrow gaps, they are generally not suitable for conveying fluids with abrasive components.
They are used especially in the transport of plastic masses and dispersions.Like the eccentric screw pumps, they are suitable for the highest viscosities.
In contrast to the piston pump, however, the plunger does not completely fill the cross-section of the displacement chamber. In principle, the piston rod (plunger) is the displacement body here. It therefore does not move along the cylinder wall in a sealed manner. The cylindrical plunger piston is only sealed via a fixed stuffing box.The inlet and outlet are each controlled by an automatic valve. During the suction stroke, negative pressure is created in the pump chamber. The valve to the suction line opens and liquid is sucked into the pump chamber. During the pressure stroke an overpressure is created in the working chamber, the valve opens to the pressure side and the piston pushes the liquid into the pressure line. In order to compensate for pressure surges, the pressure line in an air vessel contains an air cushion. It is compressed during the pressure stroke and also drives the liquid into the pressure line during the suction stroke due to its stored pressure force. This creates an even flow of liquid.
The standards regulate, for example, the main dimensions of the pump unit. This enables manufacturer-independent interchangeability.The most important standardization organizations for pumps include:
ANSI American National Standard Institute
API American Pertroleum Institute
BPMA British Pump Manufacturers Association
DIN Deutsches Institut für Normung
HI Hydraulic Institute
ISO International Organisation for Standardization
There are two distinctive designs of glandless pumps, one with dry stator windings (Canned Rotor Motor) and one with wet-stator windings (Wet Stator Motor).With this design, there is no shaft seal between the pump and the motor. The pumped medium is used for cooling and lubricating the motor at the same time. Glandless pumps are considered to be particularly low-noise, which makes them ideal for use in living spaces. The omission of the shaft seal makes the system particularly low-maintenance and leakage-free. This also makes canned motor pumps interesting in process technology for applications where leakage-free pumping is important.A disadvantage is the lower efficiency compared to pumps with shaft seals (glanded pumps), especially at higher outputs.Typical applications for canned rotor pumps are as heating circulating pumps, process pumps for the chemical industry and process engineering and as nuclear reactor pumps. Wet stator pumps are mainly used as submersible pumps in wells and for circulating duties in conventional power plants.
As a displacement element, they have an elastic diaphragm whose axial movement is caused either by a direct drive by means of a drive rod or indirectly by transmitting the displacement pressure of a plunger.
The flow is thus directed from the outlet of the preceding impeller into the inlet of the following one. The high-pressure centrifugal pump is often designed as a ring-section pump.With the same design, the delivery pressure (delivery head) increases proportionally to the number of impellers for the same flow rate. If the additional losses due to flow diversion in the inlet and outlet are neglected, the hydraulic efficiency is independent of the number of stages. Thus the characteristic curves of multistage centrifugal pumps can be converted as follows as a good approximation:Hn(Q) = n/m · Hm(Q)
P2,n(Q) = n/m · P2,m(Q)
ηhydr,n(Q) = ηhydr,m(Q)
NPSHn(Q) = NPSHm(Q)n, m – Number of impellers
Q – Flow
H – Head
P2 – Shaft power
η – efficiency
