Compare the advantages and disadvantages of using shielded pumps, submersible pumps, or magnetic pumps for liquid chlorine packaging pumps

1.1 Advantages of shielded 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 prevention. This makes it 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 land footprint. 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. 1.2 Disadvantages of shielded pumps (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. (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 evaporation of the liquid; this can cause the pump to run dry and damage the sliding bearings. A intermediate tank must be installed in submersible pumps to maintain a certain liquid level in it, and sealing gas (used during normal operation) as well as emergency sealing gas (used when the pump is not in use for extended periods) are required. Due to some leakage in the seal between liquid chlorine and the sealing gas, a certain amount of liquid chlorine is discharged along with the sealing gas, and the amount of discharge is directly related to the condition of the seal. Mechanical seals are used for sealing the seal gas from the atmosphere; due to dry friction, leaks can occur easily, which results in a pungent chlorine odor being present at the site. Submersible pumps have a complex structure, with many vulnerable components such as bearings, packing seals, O-rings, and mechanical seals, which are not only expensive but also result in high maintenance costs. Since liquid chlorine is a medium that vaporizes easily, it is necessary to take into account the net positive suction head when installing the pump; generally, the shielded pump is installed in a pit 4 or 5 meters deep below the bottom of the tank, and this factor must be carefully considered when selecting the pump. Since shielded pumps have no moving seals, there is no leakage during operation, and the operating environment is better than that of submersible pumps. Shielded pumps have a simple structure with few vulnerable components, and most faults can be repaired on-site. However, if the shielding sleeve leaks or the motor is damaged, it is necessary to send it back to the factory for repair, which is quite troublesome; this is a major drawback of shielded pumps. The investment, maintenance costs, and complexity associated with submersible pumps are higher than those of canned pumps. Due to the different installation methods of these two types of pumps, the site conditions must also be taken into consideration when selecting a pump. As far as I know, the development trend for liquid chlorine transportation is shielded pumps. Since liquid chlorine is a highly hazardous substance, safety must be given top priority regardless of the pump chosen. I. Advantages of magnetic drive pumps Compared with centrifugal pumps that use mechanical seals or packing seals, magnetic drive pumps have the following advantages. 1. The pump shaft has been changed from a dynamic seal to a sealed static seal, completely preventing medium leakage. 2. No separate lubrication or cooling water is required, reducing energy consumption. 3. It changes from coupling-driven to synchronous dragging, with no contact or friction. It features low power consumption and high efficiency, as well as damping vibration effects, which reduce the impact of motor vibrations on the pump and the impact of cavitation vibrations in the pump on the motor. 4. During overload, the inner and outer magnetic rotors slip relative to each other, providing protection for the motor and pump. II. Operating Precautions 1. Preventing particle ingress (1) Ferromagnetic impurities and particles must not enter the magnetic drive and bearing friction pairs. (2) After transporting media that are prone to crystallization or precipitation, it is necessary to flush the pump promptly (fill the pump chamber with clean water after stopping the pump, and drain it completely after running for 1 minute) to ensure the service life of the sliding bearings. (3) When transporting a medium containing solid particles, filtration should be performed at the inlet of the pump flow tube. 2. Prevent demagnetization (1) The magnetic torque should not be designed to be too small. (2) It shall operate under specified temperature conditions; it is strictly prohibited for the medium temperature to exceed the limits. A platinum resistance temperature sensor can be installed on the outer surface of the magnetic pump’s isolation sleeve to monitor the temperature rise in the gap area, so as to trigger an alarm or shut down the pump when the temperature exceeds a set limit. 3. Prevent dry friction (1) Idle operation is strictly prohibited. (2) It is strictly prohibited to evacuate the medium. (3) With the outlet valve closed, the pump shall not operate continuously for more than 2 minutes to prevent the magnetic drive from overheating and failing

Magnetic pump – running idle or operating without liquid. It is recommended to install an anti-idle protection device for the pump, which will shut it down automatically within 2 seconds when the pump is running idle, thereby protecting it from damage. Electronic sample available at: http://www.dnpump.com/PicUp/200910162202501.pdf If you want to minimize maintenance efforts, it’s better to use a built-in anti-idle protection device – it saves time!

Reply to 3# noloo: Could you provide more details about this protector? How does it work to provide protection? Installation status?

I would like to ask: are the double-shell magnetic chlorine pumps produced by Dalian Kehuan Pump Industry good? I would be extremely grateful if any users who have used it could share their experiences!

Reply to 7# yenye66: I’m using it currently; it has been in use for over a year. One unit has developed problems, while the other one is working well. Overall, it’s a good choice – it’s much better than submersible pumps. It takes up less space, is easy to maintain, and produces low operating noise. In my opinion, it’s superior to canned motor pumps and magnetic drive pumps as well, because canned motor pumps require that the medium be free of impurities, otherwise problems can arise, while magnetic drive pumps may experience issues with their magnetic cylinders. Submersible pumps take up a lot of space, are difficult to maintain, and have long pump shafts that can lead to problems.

Thank you so much for the introduction by Lele, the host!

The one we used earlier worked fine, but it broke down recently