Lubrication of Compressors - Pressure Oil Lubrication or Splash Lubrication
27 January 2006
Lubricating oil in modern high-pressure compressors must be a true jack of all trades. In addition to its most obvious task of minimising friction and wear, it must also seal cracks, ensure cooling, prevent corrosion and carry away dirt. And as if that wasn't enough, it must also be able to deal with condensation water without losing its favourable properties. Before lubricating oil can tackle these many and varied tasks, however, it must first be transported to the right lubrication points, but how?
In practice, compressor designers make equal use of two conventional systems for this purpose: splash lubrication and pressure lubrication. Just as one has the choice between trains or airplanes in transportation, so both of these systems have their reasons for existence and innate advantages and disadvantages. It is the design engineer's job to weigh up these options and decide which is the most suitable in light of compressor size, final compression pressure and rotational speed, as well as the design of the bearings and motor.
THE COMPACT, ROBUST SOLUTION
In splash lubrication, a pin attached to the connecting rod dips into the oil sump with each turn of the crankshaft. This is no 'gentle stirring of cake mix' but wild agitation with up to 1,800 turns of the crankshaft per minute, filling the crankcase with oil spray and oil mist. As a result, oil reaches all of the places where it is needed. The advantage of this system is its robust, simple and economical construction, which is suitable for smaller compressors up to 80m³/h.
MORE EFFORT, MORE PERFORMANCE
In pressure lubrication, lubricating oil is sucked out of the oil sump with a gear pump. It is brought to the connecting-rod bearings on the crankpin through the hollowed-out crankshaft from where it is projected freely into the crankcase. The resulting splash oil also supplies the other lubrication points. This system is more elaborate and expensive to produce, but the high oil flow volume makes it possible to dissipate more heat from the motor bearings and to supply even more distant lubrication points with sufficient splash oil.
Because of these properties, this type of lubrication is used for mid-sized and large compressors, especially those with high final pressures and capacities. A risk is posed, however, by large amounts of condensation water collecting in the crankcase as a result of improper operating conditions and lack of attention. The oil then floats on a layer of water. In the worst-case scenario, the oil pump becomes a water pump – with devastating results for the compressor.
WELL LUBRICATED WITH THE RIGHT OIL
Design engineers have taken into account the above-mentioned considerations (and many other more detailed ones as well) and confirmed them in tough prototype testing for all Sauer compressors. Whether your Sauer compressor functions with splash or pressure lubrication, everything works better when it is well oiled. This is why you should use only lubricating oils approved by Sauer, check the oil level regularly and never add oil past the maximum fill level indicated.
We will be glad to answer any questions you may have on the operation and monitoring of Sauer compressors.
