The PRM-pumps are end suction, top discharge, single stage, radial split volute casing pumps of back-pull-out design with closed impellers. The mechanical design meets the API 685 requirements.
The bearing bracket design allows the removal of the complete unit including outer magnets and ball bearings without depressuring the pump or exposing the pumpage to the atmosphere.
The volute casing of standard design is cast en bloc and centerline supported.
The casing forms - together with the containment shell - the pressure retaining pump unit. Maximum allowable pressure at PT is determined by the shell design and the material. The pump casing has metal-to-metal fits with confined compression controlled gaskets.
Pump flanges are full or spot faced on the back and designed for through-bolting.
The single elements of the multipolar magnetic coupling are permanent-magnets made of "Cobalt Samarium - Rare Earth". Power is transmitted by a magnetic field, built up by the outer and inner magnets, through the containment shell. This kind of magnetic coupling works synchronously without slip and transmits the required torque to the impeller.
The magnetic couplings are designed to transmit rated motor power up to 160 kW (217 HP) at 2900 rpm, respectively 195 kW (265 HP) at 3500 rpm. The couplings are sized to fit the maximum power consumption of the rated impeller and allow also at least 5% increase of the installed impeller diameter. If nothing else is foreseen, the transmissible coupling power, the rated motor power and the available moments of inertia are sized for direct-on-line starting of the electric motor.
Internal cooling flow from discharge to discharge
In the magnetic coupling, eddy currents are generated which lead to heat and cause temperature rise of the containment shell. To dissipate this heat and to cool the sleeve bearings, the PRM-pumps use internal cooling flow with pumped liquid as standard.
The cooling flow is led from the discharge side behind the impeller into the chamber between the slide bearings and through the pump shaft via the rotor back vanes again to the discharge side. This design pressurizes the slide bearings and the containment shell with nearly the full discharge pressure and the product remains stable in this area.
The internal cooling flow works without auxiliary piping, no additional thread or flange connections are available. External circulation from discharge flange through magnet end or external flushing will be available as an option.
Balancing thrust loads
Thrust loads of the closed impellers are balanced by wear rings, impeller balance holes and the rotor back vanes. The pump shaft, connected to the impeller is floating. During operation no thrust loads are available, no thrust bearings are required. Start-up rings keep the shaft unit in position at start-up and at shut-down.
Renewable wear rings are furnished on both the casing and the impeller. Front and back wear rings are part of the axial balancing system.
Mating wear surface materials have a difference in Brinell hardness of at least 50 HB.
Thread connection for containment shell surface temperature probe is standard. Bearing brackets have threaded M8 connections for permanently mounting vibration transducers.
Drain connection, venting
The complete pump can be drained by the drain connection at the bottom of the volute casing. There is no separate drain connection in the magnet end. The PRM-pumps are self-venting. No air or gas will remain in the magnet end when filling suction and discharge pipe. Exception is taken for PRMW HTM-pumps.