HANGZHOU TENGYE MAGNETIC MATERIALS CO., LTD.

Useful Info on magnetic drive pumps from a Magnetic Coupling Supplier

magnetic drive pump

What are magnetic drive pumps?

In a common centrifugal pump, the drive shaft from the electric motor is attached, typically via an adaptable combining, to the impeller with the pump housing. This requires some type of seal where the drive shaft goes into the housing (Figure 1).

In a magnetic drive centrifugal pump, the impeller and the pumped liquid are had within a hermetically secured real estate. The drive shaft from the electric motor turns an assembly of magnets outside of the real estate. Rival this, on the inside of the housing, is a coordinating ring of magnets on a shaft affixed to the impeller (Figure 2). Torque is transferred with the housing as a result of the coupled magnets.

There are likewise magnetic drive positive variation pumps, vane pumps, internal gear pumps, and also exterior equipment pumps and the basic principles and advantages are the same: the pumped liquid is consisted of within a covered housing getting rid of the threat of leakage. For the objectives of this write-up, we shall continue to define magnetic drives in the context of centrifugal pump style.

Why are magnetic drive pumps made use of?

With a common centrifugal pump, some type of seal is necessary to stop the pumped medium from leaking out around the pump shaft, particularly if it is at high pressure. There are three primary alternatives:

  • A soft packaging product compressed around the pump shaft in a ‘padding box’ Packing product is held in area within the opening in the casing (the padding box) and also pressed by a gland nut which can be progressively tightened up as the packaging product puts on or settles (Number 1).
  • Lip seal or O-ring: A rubber or plastic ring fits around the drive shaft as well as is kept in location in a recess in the pump housing.
  • Mechanical seal: A mechanical seal includes 2 components: a fixed element affixed to the pump real estate and a rotating element on the pump shaft. The faces of the two elements are machined to be flat as well as smooth as well as are spring-loaded to keep them compressed. This is the most reliable choice for lowering leakages yet can be costly and also difficult to set up.
Figure 1.Schematic diagram of a standard pump with stuffing box

Leak can not be eliminated completely with any of these solutions and, as a matter of fact, it is important to keep a tiny leakage to oil and cool down the seal and also pump shaft. Sometimes, it is essential to infuse a lubricating substance to prevent overheating and this introduces the possibility of contamination of the pumped liquid.

A pump seal needs tracking and also constant upkeep to stay clear of extreme leak, specifically when the pumped liquid has abrasives. All leaked liquids have to be had and also gotten rid of safely. If the fluid is also poisonous, flammable, contaminated or environmentally damaging, the opportunity of leaks, also minor ones, can be incredibly hazardous. Leakages are among the primary root causes of pump failures or shutdowns and the upkeep of seals and also packing products is pricey as well as taxing.

Environmental issues and also regulations has driven market to carry out cleaner pumping modern technology. A magnetic drive pump consists of the pumped fluid completely within the pump housing. It only has a hermetic seal – a stationary gasket or O-ring – that is exempt to use from moving components and is as a result preferably suited to applications where no leakage can be tolerated either on security grounds or since the costs of recovery as well as therapy are expensive.

Figure 2.Schematic diagram of a magnetic drive pump

How do magnetic drive pumps function?

The coupled magnets are connected to two concentric rings on either side of the containment shell on the pump housing (Figures2 & 3). The external ring is affixed to the electric motor’s drive shaft; the internal ring to the driven shaft of the impeller. Each ring has concerning the same number of the same, matched as well as opposing magnets, set up with alternating poles around each ring. The magnets are usually made of rare earth metals such as samarium or neodymium alloyed with various other metals. One of the most common combinations are Samarium-Cobalt and also Neodymium-Iron-Boron. These complex alloys have 2 primary benefits over typical magnets:

  • Lower mass called for to keep a certain torque– hence smaller sized and also much less intricate pumps.
  • Greater temperature stability – magnetic torque reduces with boosts in temperature levels however much less so with rare earth alloy magnets than with typical iron magnets

Using these products is a major consider the expense of magnetic drive pumps. A lot of rare earth steels are mined in just a couple of places around the World (especially China) as well as costs can be unstable. For example, China manufactures 76% of the World’s Neodymium magnets. In addition to their expense, an additional drawback of these alloys is their bad resistance to rust. It is essential to coat the magnets on the internal ring (which are exposed to the pumped liquid) with some kind of protective material or enclose them in a corrosion immune covering, as an example polypropylene, PVDF (polyvinylidene fluoride), ETFE or stainless steel.

Figure 3.Cross-section of magnet rings and containment shell in a magnetic drive centrifugal pump

The optimum torque that can be accomplished in a magnetic drive pump is identified by the space in between the magnets: the smaller sized the space the larger the torque transfer. However, there is a restriction to how small this can be engineered, since the space must consist of the containment shell and also any type of protective products coating the magnets. For the risk-free operation of the pump, it is essential that there is an affordable gap between the rotating parts and also the control shell, especially if the pumped fluid is extremely thick or includes solids. All parts need to for that reason be machined to high resistances for greatest effectiveness. In addition to these engineering concerns, the product used in the construction of the containment covering is very important in maintaining a high coupling performance in between the two sets of magnets and in lowering power losses because of the generation of eddy currents.

The inner magnet ring, the pump shaft and also its bearing are submersed in the pumped fluid and lubricated by it. It is essential that these components are developed to operate efficiently in the setting. With very thick fluids, rubbing losses can be high; in an abrasive or chemically hostile tool, bearing wear can be a problem. Nevertheless, with the right option of wetted products – including silicon carbide, thermoplastics, stainless-steel as well as high nickel alloys – magnet drive pumps are ideal for taking care of hostile, corrosive as well as dangerous liquids.

Magnetic drive pump or tinned motor pump?

In a canned motor pump, the motor’s rotor winding is encapsulated in a ‘can’ as well as it, and also the whole drive shaft approximately the impeller is immersed in the pumped fluid (Number 4).

Tinned motor pumps often tend to be smaller, have less bearings as well as can be much more effective. They also supply secondary control as criterion: if the ‘can’ is ruptured then the pumped medium is consisted of within the stator real estate. This can be a particular advantage if the pumped tool is so dangerous or costly that additional control is vital. Magnetic pump makers offer second control on some styles yet this is normally an additional expense.

The main drawback of canned electric motor pumps is that a motor failing needs substitute of the entire unit. A magnetic drive pump can be fixed or updated because the electric motor is not an important part of the pump Both tinned and magnetic drive pump designs have versions readily available to handle slurries, liquids at both high and low temperature, and also volatile liquids.

Frequently, the choice of pump depends only on site standards or choices.

Figure 4.Schematic diagram of a canned motor pump


Developments in pump technology have allowed engineers to reduce the size of magnetic drive pumps whilst enhancing their power and performance. Rare earth alloy magnets with high field stamina allow small style. New pump bearing styles as well as a variety of wetted product alternatives have actually boosted pump life time, reduced power losses because of eddy currents and minimized maintenance downtime.

Recap

Different designs of magnetic drive pumps are offered consisting of centrifugal pumps, side channel pumps, turbine pumps, vane pumps and also interior and outside gear pumps. Magnetic drive pumps can be specified for applications where self-priming or dealing with solids or running dry is called for and are often specified for pumping tough liquids such as abrasive fluids, acids, bases, corrosives, flammables, not natural services, fluids with entrained gases, natural liquids, slurries, solvents, toxic liquids, viscous and unpredictable fluids. Magnetic drive pumps are readily available for a vast array of viscosities at low and high temperature levels at capabilities from ml/hr to m ³/ min as well as for high system pressures as well as high differential pressures.

All these various layouts of magnet drive pumps provide the essential benefit of absolutely no leak of the pumped tool.

About Tengye: Tengye is a leading manufacturer of magnetic couplings for magnetic drive pump industry.

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