API 685 PROCESS PUMP
TYPE PRM and PRMW
20 Year Service Life Design
Flows to 4000 GPM - head to 690 feet
-
Working pressure to 711 PSI
Operating temperature to 390F -
850F using PRMW design with out cooling water.
Centerline supported - Class 300 ANSI flanges - 600 optional
Labyrnth oil seals - Casing and Impeller wear rings
Sealed drive magnets - Confined compression controlled gaskets
Optional secondary containment, heating jackets, containment shell probes
• Technical Illustration
General
Magnetic coupled DICKOW-Pumps of the series PRM are heavy-duty sealless pumps. The containment shell forms a hermetically sealed system to separate the pumped liquid from the atmosphere. Meets the new API 685 specifications for canned and magnetic sealed horizontal pumps. Very similar to the time proven NMR with options that are required for the API685 specification.
Applications
Magnetic coupled PRM-pumps are designed to improve plant reliability and
personnel safety and to reduce maintenance costs, in the Oil & Gas, Petro-chemical
and Chemical industries. PRM Pumps are particularly suited for handling toxic,
explosive or other dangerous liquids, which react when they contact the
atmosphere and where leakage is not acceptable. For all of these services, the
containment shell replaces expensive, complicated single or double mechanical seal
systems and related control equipment.
PRM capacity is approximately 4000 GPM and differential head 690 feet at 3500 rpm.
Construction
PRM-pumps are end-suction, top-discharge, (DIN or ANSI Flanges), single stage, and radial split volute casing pumps in back-pull-out design with closed impellers. Flange to flange dimensions are according to ENL 2858 (ISO 2858). The mechanical design meets or exceeds requirements of API 685 (API 610 for magnetic sealed pumps) requirements.
DESIGN FEATURES
Containment shell
The containment shell is designed as a pressure vessel to separate pumped
liquid from the atmosphere. The containment shell is bolted to the bearing
housing in a manner that allows removal of the bearing bracket including drive
magnets and ball bearings without draining the pump or exposing the pumped
liquid. The pressurized PRM-containment shell is hydroformed Hastelloy
C. The working pressure of the pump is dependent upon the containment
shell thickness.
For motor horsepower over 200, The energy saving containment shell offers exceptional
benefits. Consisting of two shells.
A) The inner shell, which accepts the radial loads, consists of centered rings.
These rings are insulated from each other by confined Gore-Tex-PTFE gaskets and
preloaded by a wave spring to avoid leakage.
B) The outer shell consists of a slotted tube with welded dome and an adapter
flange. This shell accepts the axial loads, This unique design, together with a
special magnet assembly, reduces the magnetic losses by approximately 50%,
compared to a normal Hastelloy C containment shell. The maximum allowable
working pressure is 500 PSI at 390 degrees F(35 bar at 200 degrees C) .
Magnetic coupling
The single elements of the multipolar magnetic coupling are manufactured as
Cobalt-Samarium (Rare Earth), a permanent magnet material with unlimited life.
The internal magnets are completely encapsulated and no contact with the liquid
occurs.
Energy is transmitted to the hermetically sealed liquid end by a bank of
external magnets passing torque through the sealing shroud to a bank of internal
magnets. Inner and outer magnet rings are locked together by magnetic forces and
work as a synchronous coupling. The inner magnet ring transmits the required
torque direct to the impeller. No slippage occurs between inner and outer
magnets. The magnetic drives are designed for electric motors with direct on
line starting. Should a subsequent increase of motor power be required, the
nominal power of the coupling can be increased by adding further rows of
magnets. Per the API 685 specifications, the drive magnets are in a sealed
container to protect against damage
Internal circulation from discharge to discharge
To over come, eddy currents generated heat and prevent excessive temperature rise in the containment shell, forced fluid circulation is used to dissipated heat by an internal cooling flow. 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 helps to avoid flashing of the liquid in this area. This pressurization enables the PRM-pumps to maintain low NPSH requirements and handle boiling liquids such as propane, butane, butadiene etc.
Balancing thrust loads
Wear rings, impeller balance holes and the rotor back vanes balance thrust
loads of the closed impellers. The pump shaft connected to the impeller is
floating. If thrust loads push the impeller to the suction side, the rotor
thrust bearing closes the gap, S (shown on the figure of Internal Circulation)
and the pressure at the rotor front side will increase and counteract the
impeller movement until the system is stable again.
Double sleeve bearings
The pump shaft is held in place by two sleeve bearings. These bearings are located in the pumped liquid. Bearing material is a diamond coated pure alpha-grade Silicon Carbide. SiC is corrosion proof in most acids and hydroxides and its extreme hardness makes it suitable for handling many pumped liquids including those with abrasive solids. The SiC-bearing parts are installed with a shrink-fit in holders or mounted resiliently. This protects the bearings against impact or thermal stress. Design temperature is 360 degrees C. Both stationary sleeve bearings are located in the same bearing housing, which guarantees concentricity.
Anti-friction bearings
The outer magnet shaft is fitted with generously dimensioned anti-friction bearings. The bearings are L10 rated for life in excess of 3 years. The oil bath is protected against atmosphere by a replaceable labyrinth seal. Oil level is controlled by a constant level oiler and additionally by a bullseye sight glass. Oil mist lubrication is available as an option.
Internal clearances
The radial clearance between driven rotor and stationary containment shell is 1.4 mm (0.055"). Together with the wear resistant SiC-bearings, handling of solids is possible.
Containment shell protection
The clearance between the rotating drive magnets and the stationary containment shell is larger than the clearance between the rotating magnet holder and the bearing bracket lantern. This prevents containment shell rupture in the event of ball bearing failure.
Monitoring
Threaded connection for installing a fluid temperature probe in the internal cooling flow is standard. Additional temperature probes for containment shell protection and leak detection devices are available as options.