Maintenance practice
Let us now discuss some of the general principles related to maintenance and relevant not only to pumps but also to various other hydraulic/mechanical components.
Cleaning of parts
The usual practice is to thoroughly clean all metal parts with mineral spirit or resort to steam cleaning. It is important to bear the following in mind, during the course of the cleaning process:
• Do not use a caustic soda solution for steam cleaning
• All parts (with the exception of bearings) to be dried with compressed air
• Steam-cleaned parts to be coated with oil (preferably with the same type of oil that is used for the system)
• Ensuring that none of the oil passages are blocked. The passages are to be thoroughly cleaned by working a piece of soft wire back and forth, flushed with mineral spirit and later dried with compressed air.
Inspection of gears
• Inspect the gear for scuffed, nicked, burred or broken teeth. If the defect cannot be removed by a soft honing stone, replacement of the gear needs to be carried out. Additionally, inspect the gear teeth for any damage to the original tooth shape that might have been caused due to wear. If this condition is discovered, get the gear replaced.
• Inspect the thrust face of gears for scores, scratches and burrs. If the defect cannot be removed with a soft honing stone, replace the gear.
• If pitting on the gear tooth is found and if the affected area is more than l/3rd of the whole area, replace the gear.
Cleaning, installation of seals
Cleaning of seals
The oil seals must be softly wiped with a cloth made wet with petroleum-based solvents, in order to ensure that the tip is not scratched. Care is to be taken to see that solvents such as trichloroethylene, benzol, acetone and all kinds of aromatics which are harmful to seals especially the ones made of polyacrylate rubber are avoided. Oil seals made of quality material like ester rubber may be cleaned by immersing them in light oil. Care must be taken to wipe off the excess oil on the oil seal.
Oil seals must be stored in a location insulated from direct sunlight and moisture. The storage period of oil seals must as a rule be for a maximum of 2 years only.
Oil seal installation
While fitting an oil seal, it is to be ensured that the spring-loaded main lip side faces the oil pressure side (i.e. towards the fluid to be sealed). Also ensure that the surfaces that contact the lip of the seal are free from any roughness, scoring, pitting or wear as this may result in fluid leakage or damage to the seal. When fitting the seal, ensure that it is pressed horizontally. In case it is inclined, the seal has a tendency to get deformed, resulting in oil leakage. Also during installation, no hammer blows should be given on the seals directly. The following tips are quite important in order to ensure longer seal life.
1. Coating the seal lip with lubricating oil or grease: This prevents dry friction during the initial period of the seal’s movement.
2. Coating the circumference of the seal with adhesive or sealant: While doing this, it is to be ensured that the adhesive/sealant does not make contact with the lip.
The circumference of some seals is precoated with a dry sealant. The sealant is usually colored for easy identification. Such seals do not require any additional sealant during installation.
Inspecting castings and machined surfaces
1. Inspect the bores for scratches, grooves, burrs and dirt. Ensure removal of scratches and burrs with crocus cloth. Also ensure replacement of the part that has scratches or grooves.
2. Inspect mounting surfaces for nicks, scratches and burrs. Get the same removed by using a soft stone or crocus cloth. In the event of the scratches or burrs being difficult to remove, get the part replaced.
3. Inspect castings or housings that are cracked. All machined surfaces are to be
examined on a periodic basis to determine damage if any, that could lead to possible fluid leakage.
Gaskets, seal rings and 0-rings
1. As a general rule, all gaskets, seal rings and o-rings in a component that has been disassembled are to be replaced.
2. Both faces of the gasket are to be examined for sticking foreign matter or scratches and the same removed.
3. Both surfaces of the gasket are to be coated with a liquid gasket. Each brand of liquid gasket has its own drying time and therefore all instructions are to be carefully adhered to.
4. To remove a seal ring, install a thin blade into the seal ring groove, and work one edge of the seal ring out in such a manner that it can be grasped with the fingers and removed.
5. Lightly coat the seal ring contact surface with a lubricant during the installation. If lip type seal rings are used, ensure that the main lip faces the direction of the oil pressure.
0-rings are available in various types and sizes depending on their position, temperature and pressure. They are to be chosen accordingly. 0-rings are also to be replaced carefully, based on application conditions.
Another important point to be noted is that discarded teflon seal rings when burned, have a tendency to emit toxic poisonous gases and therefore this is best avoided.