The replacement of mechanical seals in centrifugal pumps is crucial to ensure optimal performance and longest service life of the pump. Some danger signals suggest that it may be time to replace the malfunctioning mechanical seal. Fortunately, the process of replacing mechanical seals is relatively simple.
When to replace the mechanical seal
Mechanical seal is one of the most important components in centrifugal pumps. They can prevent leakage of pumped liquids or air. In standard centrifugal pump components, a mechanical seal is located between the pump housing and impeller, allowing the impeller to rotate without causing leakage of the pumped liquid. Like any mechanical component, the seal will wear out and eventually need to be replaced.
When centrifugal pumps find it difficult to maintain the correct pressure, seal leakage is often a part of the problem. These faults may not immediately manifest as sealing related issues. For example, a pump may consume more liquid than normal, which is an early sign of liquid leakage in a certain location (such as a seal).
The process of replacing mechanical seals usually follows a typical structure, although each pump may have slightly different requirements. The following are the standard steps to follow.
1. Pump preparation
Turn off the pump power and cut off the power (to prevent accidental pump start-up), and start preparing to disassemble the pump. In addition, it is necessary to cut off the connection between the pump and the liquid, ensure that the inlet and outlet valves of the pump are firmly closed, and then discharge the liquid from the pump casing.
2. Pump disassembly
This stage varies depending on the pump. Many centrifugal pumps today adopt a pullback design, in which the mechanical seal can be found by simply removing the bearing components without removing the pump housing from the inlet and outlet pipelines. The mechanical seal can be removed from the pump by removing the sealing gland and the fasteners (gaskets and bolts) connecting the sealing chamber.
However, some centrifugal pumps do not use this easily accessible design. For these pumps, it is necessary to completely disconnect the pump and its casing from the inlet and outlet pipelines or remove the core package, and then remove the bearing components to reach the seal. In some pumps (such as certain vertical pumps), the motor may also need to be removed.
Regardless of whether the pump casing needs to be disconnected or not, for some pumps, the impeller needs to be disassembled in order to replace the mechanical seal.
3. Replacement of mechanical seals
At this stage, it can be seen from the pump shaft and housing that there is a set of seals (such as cantilever and vertical suspension pumps), as well as two sets of seals (such as two end support pumps). Nowadays, many centrifugal pumps use containerized mechanical seals, which are very easy to replace.
Remove the fasteners connecting the sealing gland, first gently push the sealing gland away from the sealing chamber with a top screw, and then carefully remove the old seal.
Once the old seal is removed, a new seal can be installed. Please remember to use a new O-ring or washer first. During the installation process, close attention should be paid to the specific conditions of the new seal, such as cleanliness, surface quality, etc.
Attention:
Touching the sealing surface with your hands may bring grease or debris to sensitive sealing surfaces, which may damage new sealing parts.
In addition, please be sure to carefully check the instructions for the specific pump used for rotary sealing. These pumps typically have different installation requirements.
4. Pump reassembly
For pumps that require removal of the impeller to replace the mechanical seal, first reinstall the impeller onto the pump shaft. Like a new seal, a new O-ring or gasket should also be used when reinstalling the impeller.
Once the impeller is in place, the pump core can be reinstalled into the pump casing. For pumps removed from the pipeline, the pump inlet and outlet flanges can be reconnected to the inlet and outlet pipelines, and then couplings can be installed. During the pump reinstallation process, please patiently align the pump and motor, as this step may take some time to complete. Once everything is properly in place, tighten the pump housing with bolts and reconnect other bolts or screws as needed.
5. Restart the pump
The final step in the mechanical seal replacement process is to restart the pump to ensure that everything is working properly. Before reintroducing the fluid into the pump, it is best to ensure that the fluid entering the pump is clean and free of debris at this stage. Using new or recently filtered fluids that meet cleanliness standards can help keep the pump system in good condition and prevent situations such as seal or pipe degradation.
In addition to checking the fluid quality, it is also necessary to confirm whether the pump needs to be vented before starting. After exhaust (if necessary), reopen the inlet and outlet valves and restart the pump - closely monitor to confirm everything is normal.
