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FIGURE 8 Automatic hydraulic thrust balance rear contact points (normally the thrust bearings). Many canned motor pumps incorporate a principle of hydraulic thrust balance to position the rotation assembly between the forward and rear mechanical contact points. Based on hydraulic principles, automatic thrust balance is accomplished by the pressure of the pumped fluid. Pressure chambers are designed either within the pump chamber using the movement of the impeller or rear of the pump controlling the rate of return of the process fluid.

Figure 8 illustrates hydraulic thrust balance within the pump casing. Balance chambers are located on the front and rear of the impeller. When a change in axial load changes the position of the impeller, either forward or rear, there is an equalizing change of hydraulic pressure in the balance chambers, which immediately returns the rotation assembly into a balance position.

Pressure-Temperature Profile The single most important consideration in the application and successful operation of canned motor pumps is bearing environment control. The process fluid cools and lubricates the bearings and removes the heat generated by the motor. The bearings must remain in a liquid state to provide adequate bearing lubrication.

A number of variables must be considered when considering the state of the recirculation fluid. These variables include vapor pressure, specific heat, specific gravity, viscosity, pump efficiency, motor efficiency, motor load, recirculation flow rate, and the recirculation flow system. A vapor pressure curve versus temperature of the process fluid is also necessary. Figure 9 illustrates heat balance equations necessary to determine the temperature rise of the fluid within the motor section. Figures 10a, b, and c show pressure and temperature profiles for a specific fluid based on the heat balance equations within a canned motor pump modified for pressurized circulation. If the flow rate varies, a new profile should be calculated for each design condition.

A pressure-temperature profile should be calculated for any application where there is doubt concerning the condition of the recirculation fluid.

Installation The installation of a canned motor pump can be much less costly than a conventionally sealed unit because canned motor pumps do not require special baseplates or mounting pads. In fact, many canned motor pumps are stilt-mounted or bolted directly into the system piping. There is only one shaft in a canned motor pump; therefore, alignment of the pump to the driver is not necessary and pump orientation is not critical. The unit can be mounted either horizontally or vertically, with the pump casing

FIGURE 9 Heat balance calculations

up or down. The sleeved bearings are located in the bearing housing. Alignment of the bearings is accomplished by a register fit between the bearing housings and the stator assembly.

Diagnostics Some canned motor pump manufacturers have developed diagnostic systems that monitor the condition of the internal wear surfaces of the pump. Because the

FIGURE 10A Pressurized circulation—points of reference

Pressure

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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