Why are graphite bearings used in shielded pumps?

All the shielded pumps I have come across have graphite bearings, and the reason for this is related to the structure of the shielded pumps.

1. It is related to the inherent characteristics of the screen-closing pump; since the motor, the pump shaft, rotor, bearings, etc., are all part of a fully enclosed structure, graphite bearings offer good lubrication properties as well as excellent heat conduction capabilities； . 2. Process medium and structural characteristics: Due to the structural features, it is not possible to use lubricating oil (grease) for lubrication ； To prevent contamination of the process medium, the use of oil or grease for lubrication is also not permitted.

Bearings require a lubricating medium to function, so they are graphite bearings

Because graphite has relatively stable physical and chemical properties, good self-lubricating characteristics, and is easy to obtain, ordinary shielded pumps use graphite bearings.

Shielded pumps also need to be lubricated, but it is not possible to add oil due to structural constraints; therefore, graphite, which has good self-lubricating properties, is used as the bearing material.

1. Shielded pumps are used in special situations involving flammable, explosive, or toxic media. Therefore, leakage must be prevented. 2. Graphite has good self-lubricating properties. Since the medium must not be contaminated by other substances, in order to maintain a compact design, the bearings of shielded pumps are made from graphite, which possesses excellent self-lubricating characteristics. However, any material with good self-lubricating properties can be used to manufacture the bearings of shielded pumps. 3. Meanwhile, the bearings of shielded pumps are also lubricated and cooled by the medium, which is why shielded pumps cannot use rolling bearings or other types of bearings! This post was last edited by zhangya*ong on 2009-3-22 09:57.]

I will briefly add some information on the definition, structure, principle, advantages, and disadvantages of shielded pumps, in the hope that it will be helpful to you. 1. Definition and structure of shielded pumps: A shielded pump is composed of a centrifugal pump and a three-phase asynchronous shielded motor mounted coaxially. Since shielded pumps do not have rotating shaft seals, they can achieve complete leaklessness, and are mainly used in applications where absolute leaklessness is required. In a conventional centrifugal pump, the drive mechanism connects the impeller shaft of the pump to the motor shaft through a coupling, allowing the impeller to rotate together with the motor. In contrast, a canned pump is a type of sealless pump; both the pump and the drive motor are enclosed within a pressure vessel filled with the fluid to be pumped. This pressure vessel has only static seals, and an electrical winding set is used to generate a rotating magnetic field that drives the rotor. This design eliminates the rotating shaft sealing mechanism found in traditional centrifugal pumps, thereby achieving complete leaklessness. 　　A shielded pump combines the pump and the motor together; the rotor of the motor and the impeller of the pump are mounted on the same shaft. A shielding sleeve is used to separate the rotor from the stator of the motor. The rotor rotates within the medium being transported, with power being transmitted to it through the magnetic field of the stator. The manufacturing of shielded pumps is not complicated; their hydraulic end can be designed and manufactured according to the structural types commonly used in centrifugal pumps as well as relevant standard specifications. 2. Features of shielded pumps: ① A unique fully enclosed design without shaft seals (only static seals, no dynamic seals) ensures that the unit will never leak ； ②The closed self-circulating structure can transport any medium while ensuring no pollution to the environment ； ③A brand-new low-speed shielded motor and medium circulation system are employed to ensure low vibration, low noise, and low temperature rise of the unit ； ④The pump body features a tubular design, with identical inlet and outlet diameters that are aligned on the same line; it can be installed at any position in the pipeline just like a valve, offering convenience, speed, and stability ； ⑤No shaft seal, no rolling bearings, maintenance-free, reliable operation ； ⑥The use of vibration isolation devices such as vibration pads, isolators, and metal bellows results in less vibration and lower noise ； ⑦The unique installation structure **reduces the pump’s footprint, enabling savings of over 40% in infrastructure costs.** 3. Advantages and disadvantages of shielded pumps: a) Advantages (1) Fully enclosed. There are no dynamic seals in the structure; only static seals are present at the pump’s casing, which enables complete leak-free operation. It is particularly suitable for transporting flammable, explosive, valuable liquids, as well as toxic, corrosive, and radioactive liquids. (2) High safety. Both the rotor and the stator are equipped with shielding sleeves that prevent them from coming into contact with the material; even if these shielding sleeves are damaged, there is no risk of external leakage. (3) Compact structure with low floor area. The pump and motor are integrated; no centering is required for disassembly or assembly. It has low requirements for the base and foundation, requires little routine maintenance, and results in low maintenance costs. (4) It operates smoothly, produces low noise, and requires no lubricant. Since there are no rolling bearings or motor fans, no lubricant is required, and it produces low noise. (5) Wide range of applications. It can meet the requirements for various operating conditions such as high temperature, high pressure, low temperature, and high melting point. b) Disadvantages: (1) Since shielded pumps use sliding bearings and are lubricated by the medium being transported, media with poor lubricity are not suitable for transportation using shielded pumps. Generally, the viscosity suitable for the medium in shielded pumps is 0.1 to 20 mPa·s. Lubrication of shielded pumps – Due to the constraints of their structure, graphite, which has good self-lubricating properties, is generally used as the bearing material to achieve lubrication. (2) The efficiency of shielded pumps is usually lower than that of centrifugal pumps with single-end mechanical seals, but it is roughly comparable to that of centrifugal pumps with double-end mechanical seals. (3) Operating for long periods at low flow rates results in lower efficiency of the shielded pump, which leads to heating and vaporization of the liquid, causing the pump to run dry and thus damaging the sliding bearings. Based on the above points, the original poster might understand better why now Last edited by Lai Lai on 2009-3-22 01:37]