Preventive maintenance for pumps is done frequently to avoid unpredictable damages and continuous performance. Here are common problem checklist for maintenance;
Cavitation, Abrasive erosion and corrosion:
The pump components may get damaged by different activities, most common are cavitation, abrasive erosion and corrosion.
Cavitation:
Cavitation is the formation of bubbles due to the flow. The bubble crack on the metal parts sounds like rock passing through, which is audible from the pump parts. Cavitation can produce several damages to the pump parts.
- If severe cavitation occurs, the metal part where cavitation occurred should be replaced.
- Welding is done for smaller cavitation effects
Abrasive erosion & corrosion:
Abrasive erosion is the mechanical removal of metal parts by the suspended material in the liquid. The rate wear is proportional to the rate of flow of the liquid.
Corrosion occurs for submerged metal.
- Erosion and corrosion can be reduced by applying appropriate protective films
- For severe problems, damaged parts should be replaced.
Vibration monitoring:
Vibration monitoring helps in knowing the condition of the bearing and other moving parts. There are different types of vibration measuring techniques, proximity type and accelerometric type.
Spectrum plot is made to analysis the vibration data, with X-axis, represent vibration frequency and Y-axis represents the vibration amplitude.
The vibration of particular areas is helpful to understand the bearing condition.
Wearing ring:
Inspect the wearing ring. Wearing ring or seal ring provides perfect sealing for the pump. As the wearing ring clearance increases the efficiency decreases. When the wearing clearance increases above 200 percent the wearing should be replaced. If the wearing to the size is not available the casing and impeller should be replaced.
Packing:
Packing prevents leakage although, some leakage pass through the packing to cool the lubricants.
The packing lubricants have to tighten to prevent leaking, most of the compression packing contains lubricants. As packing is tightened the lubricant is released to lubricate the shaft until leakage past the packing is reestablished.
Bearing:
The purpose of the bearing is to support and locate the shaft of the pump. The bearing can provide radial and axial support.
There are two types of bearing, Fluid film bearing and Antifriction bearing. The bearings should be lubricated properly and sufficiently. The bearing should also be insulated from the frame to prevent circulating current passing through the bearing.
Shaft coupling:
Coupling are used to connect the shaft of the driver. There are coupling such as. rigid coupling and flexible coupling.
Check for the correct alignment of the coupling. Make the coupling rigid if there is any vibration in coupling or misalignment.
Shaft alignment:
Misalignment is a common sometimes serious problem. Poor alignment can cause premature wear or failure of the bearing, overheating of the shaft coupling, and in extreme cases, cracked or broken shafts.
Oil and Lubricants:
The primary purpose of lubricates is to reduce friction between two moving parts, the lubricant can also act as coolant and prevent corrosion. Choosing the lubricant for the purpose is to be done with extreme care. There is oil lubrication and greece lubrication.
For oil-lubricated bearings, use only non-foaming and non-detergent oils. Avoid over-lubrication which can be just as damaging as under-lubrication. For pumps equipped with re-greaseable bearings, avoid mixing greases of differing consistencies or types. When re-greasing, confirm that the bearing fittings are absolutely clean to prevent contamination, which can decrease bearing life.