Magnetic Drive Concept.

The sealing method is probably the most critical consideration of any pump selection. The proper sealing method could make the difference between safe pump operation and a potentially hazardous situation.

The ISOCHEM line offers the most desireable design from a sealing standpoint. It employs a gear, centrifugal, or regenerative turbine pump magnetically coupled to the prime mover.

Magnetic drive technology provides a safe and reliable pump for difficult applications.

Magnetic Coupling.

The encapsulated driven magnet assembly is mounted on the end of the pump shaft. It is then contained by a closed-end "can" which seals against the pump housing with a static PTFE o-ring. A drive-magnet assembly, attached to the electric motor shaft, rotates around the containment can. When the drive-magnet assembly rotates, lines of magnetic force cause the driven-magnet to rotate, which in turn causes the pump shaft to rotate.
	The drive-magnet assembly and driven-magnet assembly are actually made up of smaller rare mineral magnets around the perimeter of the assembly. They are alternately oriented in a north pole - south pole configuration. When the coupling is assembled, the assemblies will naturally rotate so that each small magnet inthe drive-magnet assembly is adjacent to a small magnet of the opposite pole in the driven-magnet assembly. The high torque capability of the rare earth neodymium iron and samarium cobalt permanent magnets alleviates the possibility of coupling slippage.

Heat Generation

Lack of internal recirculation presents a problem if the fluid has a low boiling point, is operating near its boiling point, or is heat sensitive. Liquids within the containment can may exceed their boiling point and flash, reducing bearing lubrication and perhaps altering heat sensitive fluids.

Heat Generation and Eddy Currents.   As an alterating magnetic field is introduced into a conductor (in this case, the containment can), eddy currents are induced which cause electromotive forces that resist the motion of the magnetic coupling. The eddy currents represent wasted power that is dissipated as heat. If the containment can temperature is greater than that of the process fluid, the fluid will absorb the additional heat.
Internal Recirculation.
	By circulating process fluid from the pump through the containment can and back to the pump, heat is carried away from the can and there is negligible overallheat rise within the pump. Recirculation is a standard feature in all of our ISOCHEM pumps.

Calculating heat rise in the containment can area is useful for determining if the internal recirculation will allow for adequate heat dissipation without adversely affecting the pumped liquid. The calculated heat rise can also be used to ascertain whether or not the anticipate NPSH problems, as hot fluids recirculate back to the pump suction.

The heat rise in the containment can area for all ISOCHEM pumps is a function of the pump parameters, operating conditions, and fluid properties.

All ISOCHEM pumps are designed to minimize eddy current energy input by using optimum strength neodymium iron and samarium cobalt magets, close magnetic coupling dimensions, and low conductivity containment cans. Internal clearances allow the passage of fluid to remove heat from the containment can area while not significantly reducing the overall pump performance.

The important fluid properties (specific gravity and specific heat) determine the fluid's volumetric ability to absorb, and remove, heat.

Heat Rise = f(Pump Parameters, Operating Conditions, Fluid Properties)

Determining operating conditions include differential pressure and pump speed. Referring to the equations for heat rise below, one can see that decreased differential pressure would lead to a decrease in recirculation and thus, higher temperature rise. Decreased pump speed will reduce recirculation as well, but will also reduce the eddy current input at a greater rate. Thus, heat rise is proportional to the square of the speed reduction.

Constant = 0.006819 °F * USGPM / watts
Energy Input = watts, product specific
Speed Ratio / Pressure Ratio = actual / maximum design, %
Recirculation Flow = USGPM, product specific
SG = Fluid specific gravity
SH = Fluid specific heat, BTU / lb °F