Practical Tips for Commissioning Central Lubrication Systems
Air in Central Lubrication Systems – Venting the System
Air in central lubrication systems is one of the most common causes of malfunctions, leading to everything from minor issues to total system failure. Thorough venting of the system after installation or repair is therefore essential.
Air is compressible and causes delayed pressure build-up and release. Air pockets are particularly critical in piston pump systems, where the air cushion is compressed during the pressure stroke and then released during the discharge process, meaning that automatic venting of the system is never guaranteed. The proper functioning of the system can be checked using a pressure gauge.
Procedure:
– Vent the pump without the pipeline connected. Operate the pump until bubble-free lubricant is visible at the pump outlet.
– Connect the main line and operate the pump again until bubble-free lubricant emerges from the end of the main line.
Tip: For grease-filled systems, the process can be significantly shortened by using grease-filled pipes.
Alternatively: The existing low-flow pump in the system can be replaced with an external pump, thus accelerating the filling process.
Caution: Pay attention to the maximum pressure; it should not exceed 20 MPa (for grease-filled systems) to prevent damage to the piping system, fittings, hoses, and manifolds.
– Connect the manifolds and operate the pump until bubble-free lubricant emerges from the outlets. For grease-filled systems, pre-filled manifolds can be used, which speeds up the process.
– Connect the branch lines to the manifolds. Pre-filled manifolds can also be used for grease-filled systems.
– Operate the pump until bubble-free lubricant emerges from all branch lines upstream of the lubrication points. Only then connect the lines to the lubrication points.
– In oil-fired systems, a main line running upwards from the pump to the distributors will improve the venting process and lead to self-venting of the system.
Noise in Assemblies and Systems
Noise in assemblies and systems can have various causes:
– Insufficient oil in the reservoir
The pump draws in air, which can lead to significant noise and vibrations in the pump and on the discharge side. Air in the system can lead to further malfunctions and a lack of lubricant at the lubrication points.
– The suction line is too long or has an insufficient diameter.
An excessively high vacuum develops at the pump inlet, causing cavitation in the pump, which can lead to damage in the pump area. A maximum vacuum of 0.05 MPa is permitted at the pump inlet.
– Vibration transmission from the pump to the motor and the reservoir
An elastic coupling with misalignment compensation must be installed between the pump and the motor. Elastic materials must be installed between the pump support and the drive motor. The pump must be connected to the rest of the system via a hose for vibration damping.
– Pressure relief valve causes noise
Ball valves are unsuitable as pressure relief valves. Ball valves should only be used as safety valves for the maximum pump operating pressure. Pressure relief valves should be hydraulically damped. The flow rate from the pressure relief valve can also be dampened by a section of pipe.
– Oil viscosity
The oil viscosity during start-up can be so high that the permissible vacuum at the pump inlet is exceeded, resulting in cavitation noise during start-up.
– Oil viscosity during start-up can be so high that it also causes cavitation noise. – Flow velocities
The following maximum flow velocities in pipelines should not be exceeded:
up to 10 mm inner diameter: v = 2 m/s
from 10 to 30 mm inner diameter: v = 3 m/s
– Return oil contains air
The oil flowing from the machine or system contains air in small bubbles or is foamy. The solubility of air in oil is exceeded. Cavitation and noise are the consequences if the bubbles are not removed from the oil by specific measures (see Chapter 2.3, Section 2.3.3).