Modern petrochemical and gas industries typically use horizontal centrifugal canned pump units with magnetic couplings similar to Villina-GNGC type pumps. They are designed for transiting neutral, corrosive, toxic, as well as explosive and flammable liquids in stationary conditions, the vapors of which can form explosive mixtures with air. Magnetic coupling pumps combine complete tightness, smooth operation, long service life and high maintainability.
A sub-type of horizontal pumping units are high-temperature pumps
Temperature of the pumped fluid: -50°C to +420°C; viscosity up to 26 cSt; density 2,000 kg/m3 maximum; mass concentration of solid non-abrasive inclusions up to 0.2%; size 0.2 mm maximum
Permanent magnets (SmCo) with an operating temperature of up to 450°C are used for operation in these temperature conditions.
The pump, a part of the pumping unit, is a single-stage or multi-stage horizontal centrifugal section-type canned pump powered by an asynchronous explosion-proof AC electric motor
It consists of a suction housing and a pressure housing with nozzles. The pressure housing contains cascades which include impellers and thrust rings with guide vanes.
Racks containing driving and driven high-temperature half couplings.
The torque from the electric motor to the pump is transferred using a magnetic coupling. The driving half coupling is mounted directly on the electric motor shaft. The driven magnetic half coupling is mounted on the pump shaft.
The tightness of the pumping unit along the shaft is provided by a non-magnetic isolation shell installed between the magnetic half couplings. No leaks of the pumped fluid have been observed. The cooling of the isolation shell which is heated during operation due to the influence of eddy currents, is carried out by the pumped fluid.
The magnetic coupling of the half couplings provides non-contact torque transfer from the electric motor to the pump shaft.
The impellers are mounted in sequence on the pump shaft and secured by keys from turning. Axial movement of the impellers is limited by the installation of interstage sleeves.
Radial and axial loads on the shaft are taken up by sleeve type bearings which are lubricated and cooled by the fluid pumped by the pump.
The unit is mounted on the foundation using a bed plate to which the unit is bolted.
The Villina GNGC type horizontal centrifugal canned pumps are made to API 685 and meet all modern standards and requirements for equipment in contact with explosive and flammable pressurized fluids.
Before commissioning, it is necessary to make sure that the pump shaft rotates freely and smoothly, by turning the blades of the electric motor fan by hand after having removed its cover.
The installation location must meet the following requirements:
- free access to the pump must be provided for its maintenance during operation, and its disassembly and assembly must be made possible;
- the pipelines must be fixed in such a way so as to prevent the transmission of mechanical loads from them to the pump;
- the pump discharge nozzle must be below the level of the liquid in the pumped volume
Note - Operation is allowed without observing the above rule provided that the unit is equipped with devices that prevent a "dry" start of the pump.
- for vibration damping, the understructure must have sufficient bearing capacity. An understructure 1.5 times heavier than the pump must be provided for as a minimum measure (an understructure 5 times heavier than the unit is recommended).
During a trial run you must:
- include flushing of pipelines in the start-up routine of the system with the unit;
- provide for the installation of filters with mesh cross section 0.25 mm maximum and cleaning of filters for the start-up period;;
- make sure that the pump shaft rotates freely and smoothly, by turning the blades of the electric motor fan by hand after having removed its cover.
Before commissioning, fill the pump with liquid up to the discharge nozzle. To do that you should:
- open the shut-off device on the suction line;
- open the release devices on the suction line, discharge line and on the pump body;
- fill the pump until small jets of clean liquid without air bubbles gush out of the release devices in sequence;
- briefly (for 30-60 seconds) open the shut-off device on the discharge line or (in case of overpressure in the discharge line) the shut-off device on the deaeration line;
- before starting the unit, check the closing of the valve on the discharge line. If the pump is started with the discharge valve open, this can cause an overload of the electric motor and separation of the magnetic coupling;
- make sure the electric motor shaft rotates un the right direction which must correspond to the direction of the arrow on the pump body;
- make sure that there is no overheating of the electric motor, excessive noise and vibration of the pump body.
When the nominal power of the unit is more than 5.5 kW, it is recommended to start the unit using a soft starter. This is due to the fact that powerful electric motors experience significant loads at the starting moment, which can cause the magnetic coupling to separate and can even cause its mechanical damage.
Rotating parts of the pumping unit such as impellers and bearings are subject to wear during operation of the pumping unit.
The design life is provided by replacement (if necessary) of high-wearing parts of the pump and its components.
To prevent failures and accidents, it is recommended to equip the units at the place of operation with automatic monitoring and protection system which provides:
- suction and discharge pressure control;
- blocking of an empty pump start;
- motor overload protection;
- temperature control of the isolation shell;
- temperature control of electric motor bearings;
- temperature control of the electric motor winding.
The Villina brand guarantees reliable and trouble-free operation of Villina-GNGC type high-temperature horizontal centrifugal canned units with magnetic couplings during the warranty period provided that non-corrosive fluids are used, the units are properly maintained and stored in proper conditions.