Selection issues for benzene medium transfer pumps

Both shielded pumps and magnetic pumps work fine; personally, I think shielded pumps are better as they are also a bit cheaper. Centrifugal pumps are prone to leakage. Is the diaphragm pump delivering a lower flow rate?

Any of them will work; the choice can be made based on specific needs. Relatively speaking, benzene is a highly toxic, flammable, and explosive substance. The use of leak-free pumps such as shielded pumps or magnetic drive pumps is safer. For centrifugal pumps, it is important to ensure that the mechanical seal is in good condition to minimize leaks. Diaphragm pumps are suitable for applications requiring low flow rates but high head pressures; however, the flow rate is pulsatory, and due to benzene’s strong solvency, the diaphragms tend to get damaged easily.

It is recommended to use a shielded pump: this type of pump has high requirements regarding the cleanliness of the medium. With the development of the chemical industry and increasing awareness of environmental and safety issues, the demands on pumps used in the chemical sector are also rising. In some applications, there is a strict requirement for zero leakage from certain pumps, and this demand has contributed to the advancement of shielded pump technology. Due to the lack of a shaft seal, shielded pumps can achieve complete leaklessness, which has led to their increasing use in chemical processing plants. 1 Principles and structural features of shielded pumps: Ordinary centrifugal pumps are driven by connecting the impeller shaft of the pump to the motor shaft through a coupling, thereby causing the impeller to rotate together with the motor. In contrast, shielded pumps are sealless pumps; both the pump and the drive motor are enclosed within a pressure vessel filled with the medium to be pumped. This pressure vessel has only static seals, and an electric winding set is used to generate a rotating magnetic field that drives the rotor. This design eliminates the rotating shaft sealing mechanism found in conventional 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. Furthermore, the manufacturing of shielded pumps is not complex; their hydraulic sections can be designed and manufactured according to the structural formats commonly used in centrifugal pumps as well as relevant standard specifications. 2 Advantages and disadvantages of canned pumps 2.1 Advantages of canned pumps (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 to 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 land occupation. 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. Due to the absence of rolling bearings and 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. 2.2 Disadvantages of canned pumps (1) Since canned pumps use sliding bearings and are lubricated by the medium being transported, media with poor lubricity are not suitable for transportation using canned pumps. Generally, the viscosity suitable for the medium in shielded pumps is 0.1 to 20 mPa·s. (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.

For shielded pumps, our factory chooses shielded pumps; other types of pumps are prone to leakage, while shielded pumps have better sealing performance

Of course, shielded pumps or magnetically driven pumps should be used. However, the choice between the two depends on the specific conditions! In China, shielded pumps are generally preferred, while in Europe, magnetically driven pumps are more commonly chosen!

Diaphragm pumps are the safest; magnetic pump issues aren’t that serious either. We use magnetic pumps. As for shielded pumps, we’ve never used them and don’t know much about them – we don’t think they’re necessary, haha; they also don’t really suit the needs of factories. Additionally, centrifugal pumps are not very safe due to the direct contact between benzene and the impeller. It easily accumulates heat, which is dangerous. Since it is a conveying medium, what is the flow rate? Diaphragm pumps are expensive, and their flow rate is not high either; one of the pumps in our factory can only handle a little over two cubic feet per minute.

The diaphragm rupture issue is also something that needs to be taken into consideration!

Benzene is a highly toxic, flammable, and explosive substance; it is essential to use pumps that do not leak. Shielded pumps or magnetic drive pumps are the best choices for this purpose. Shielded pumps are relatively more expensive, while magnetic drive pumps are cheaper. The choice can be made based on individual circumstances

This post was last edited by zccchunchen on 2011-5-30 23:33. Screen pumps or magnetic pumps are both acceptable; make sure to keep spare parts for the components that are prone to damage

It is recommended to use shielded pumps; a triphenyl processing project I designed used magnetic pumps, which are operating well currently.