Question: Do you ever use PEEK material for the Primary Containment Shell?
Answer: Hayward Tyler has never used PEEK material for the can (Primary Containment Shell) within a Canned motor pump, however it has been considered. The thickness of PEEK material would need to be greater than that of the existing materials used which would adversely affect the motor efficiency. Additionally, using a PEEK can would require additional design considerations for fastening to the mating pieces.
Question: What material options are available for the Sleeve Bearings?
Answer: Sleeve Bearings in canned motor pumps are typically a Carbon Graphite or Silicon Carbide material. Most applications can be serviced by one of these two materials, but if there are other customer requirements accommodations can be made.
Question: What is the clearance between the can and stator?
Answer: Typically, the clearance between the can and stator diameters is 0.8-1.4mm (0.030-0.055″). The clearance changes depending on the motor frame size.
Question: Are these pumps API685 compliant?
Answer: Canned motor pumps are commonly designed and built to API685 standards. Hayward Tyler offers Canned Motor Pumps complaint to API685.
Question: Are solids tolerated?
Answer: Yes, solids are tolerated to an extent before you need to add features to deal with them. In general, pumps with standard SiC bearings can handle 0.02 mm particle size and ~ 1% volume.
Most cases with solids are on a per application basis where the best solution is found during the application engineering process rather than with general parameters. If it is deemed unsuitable for the solids to be inside the motor an internal mechanical seal (that does NOT leak to atmosphere) and a metering pump can be used.
Question: Are there process fluid limitations (high viscosity, for example)?
Answer: In general, the limitations of process fluids are the solid concentration, viscosity, compatibility with fluid film bearings, and temperature. See the below parameters for our typical off-the-shelf canned motor pumps as a reference.
Question: At what temperature is additional cooling required?
Answer: Typically, the maximum fluid temperature in the motor is 120°C before cooling is required. The properties of the fluid are important to determine whether any cooling is required. Additionally, motors above 200kW typically require external cooling.
Question: Is the stator cavity pressurized? How does this pressure value compare with the process fluid pressure?
Answer: This depends on the stator encapsulation method used. If there is a solid encapsulant present in the stator, then this area does not need to be pressurized. If the stator encapsulant is either a liquid or gas, then the stator cavity would be pressurized. In our case, we use either solid encapsulants or Nitrogen gas pressurized to between 0.1-0.2 bar(g).
Question: Are the motor terminals inside of the motor shell behind the stator can?
Answer: The motor terminals are located in an IP55 rated terminal box. The 3-phase windings are jointed to lead cables inside the stator shell. The lead cables connect to the terminal stems either below the terminal plate or pass into the terminal box using a sealed connection.
Question: Do you have an auxiliary impeller to drive process fluid thru the motor?
Answer: Depending on the required circulation path an auxiliary impeller can be used. In simple configurations the natural buoncy of the fluid is enough to circulate around the flow path. The below image shows a typical auxillary impeller on a Canned Motor Pump rotor.
In applications where there is a thrust disc, the disc often acts as an auxiliary impeller too. This can be seen in the below image of a thrust disc, where the slots on the side act like a closed impeller’s slots.
Question: You mentioned 400°C possible operation and saying also that the insulation material organic would allow that. Is that a proprietary material?
Answer: Our HV-X model uses a non-organic insulation material to allow the temperature of the process fluid to be this high without cooling water. The process fluid temperatures for this model and the additional features are as follows:
Operating Temp ≤ 350℃, Super C Insulation, No External Cooling Required
350℃ < Operating Temp ≤ 400℃, Super C Insulation, Additional Air Cooling Necessary
Question: Why, apparently, the aspect ratio for the motor shell is larger than a conventional induction motor?
Answer: Fluid friction drag loss and eddy current can loss are two efficiency losses associated with canned motors; Both are proportional to the diameter of the stator bore (rotor O.D.) Hayward Tyler motor designs take these main loses into consideration along with the bearing span to optimize the overall design of the canned motor.
Question: Shouldn’t we be afraid of debris/crystal etc. passing in the rotor-stator gap? Can you inform the typical size for such type of gap? Is the can material sufficient hard to withstand eventual abrasion?
Answer: The gap between the rotor and stator can is 0.8-1.4mm (0.030-0.055″) depending on the motor size. Understanding the type and size of the debris/solids that are found in the process fluid is critical to whether it would be acceptable to be circulated in the motor. When selecting a Canned Motor Pump, it is important to have the most accurate information possible so the application engineer can determine the proper configuration. This may mean a backflushing system, a barrier fluid to keep the process fluid out of the motor, or that a Canned Motor Pump is not the proper selection. In cases where solids are present, both Inconel and Hastelloy (the most common can materials) have very high resistance to chemical and abrasion corrosion.
Question: How is the can supported in the stator cavity? The pressure differences on either side of the can would seem to either lead to its collapse or its lateral expansion, why does it not do this?
Answer: The stator can is supported by the lamination pack and using back-up sleeves to span the distance between the lamination pack and the end plates. The can is fusion welded to the end plates and then hydroformed. The hydroforming expands the can so that it is sitting flush against the supporting features. During manufacture it is common to perform a nitrogen or helium leak test to ensure the stator is completely sealed. The stator can and supporting features are designed to withstand a typical hydrotest of 1.5x the rated pressure.
Question: Is there a maximum discharge pressure or pressure ratios (Suction/Discharge) for Canned Motor Pumps?
Answer: There is no maximum discharge pressure for Canned Motor Pumps, but our standard maximum rated pressure is 40 MPa. The maximum differential head allowable is 600m when the design pressure is less than 40MPa. It is possible to for us design Canned Motor Pumps with a rated pressure of 55 MPa but it would be a specially designed product.
Question: Are CMPs Suitable for vacuum (Suction) to high pressure conditions? This is for potentially upset conditions that may see vacuum suction situation causing seal failures on a standard centrifugal pump. What would be the NPSHa requirement in that case? Answer: All Canned Motor Pumps are designed as pressure vessels and each Canned Motor Pump can accommodate conditions from vacuum to high pressure. The best way to know if your application would be suitable for a Canned Motor Pump is to give specific conditions for evaluation. Like most centrifugal pumps, having adequate NPSHa (typically greater than o.6m above the pump NPSHr) would typically be required to avoid pump issues such as cavitation.
Question: Does the rotor have windings on them, or magnets?
Answer: Canned Motor Pumps use a squirrel cage rotor encompassing a lamination pack and rotor bars connected to short circuit rings at both ends. There are no windings or magnets on the rotor.
Question: Are the vibration monitors accelerometers on the casing or can you have proximity probes to monitor the shaft?
Answer: The best method for monitoring the condition of the Canned Motor Pump is using a bearing wear monitor, temperature windings and motor current. Canned Motor Pumps are naturally self-dampening due to being filled with fluid, therefore monitoring and diagnosing using vibration can be difficult. When supplied the probes would be accelerometers.
Question: Because the rotor is submerged in the pumped liquid, I’d assume that the efficiency is reduced compared to an external motor because the rotor has to be spun in the pumped liquid. What would be a typical motor efficiency?
Answer: Typically, Canned Motor Pumps are selected due to the increased safety and reduced maintenance they offer. They are typically less efficient than air cooled motors because of the fluid inside the motor creating a larger “air gap” between the rotor and stator along with additional frictional drag on the rotor. It is more common to measure wire-to-water efficiency due to the motor and pump using a common shaft. The pump efficiency can vary so the total efficiency on the Canned Motor Pump can also vary. For the motor alone the typical efficiency is around 10-15% below an air-cooled motor.
Categories: Product Knowledge