When selecting the right oil for Positive Displacement (PD) blowers or vacuum boosters, it’s important to consider the three primary components the oil is formulated to protect: bearings, seals and gears. Oftentimes, the best option for one of these is not the same as the best option for the others, so a choice needs to be made for the most critical component, while also accounting for the secondary ones.
Failure to use the correctly specified oil for bearings, seals and gears often results in reduced performance, higher operating temperatures, unexpected maintenance, and catastrophic failure. All of these affect the bottom dollar and production. Also important to remember is that while ambient air temperature has some effect on the overall temperature of the blower, the unit’s gears, seals, and bearings are first and foremost concerned with what is occurring inside of the oil sumps, not outside.
The oil temperature, speed, shaft diameter, gear size, and bearing type are of primary importance, and overlooking these parameters in specifying the proper oil is an oversimplification that may result in machine damage and a foreshortened operating life. Here’s a review of these critical components and what to know to help specify oil for these components to help ensure peak performance and machine longevity.
Seals without proper lubrication can blister as shown.
The Vital Role of Bearings, Seals and Gears
Let’s first discuss bearings. The differential pressure, rotor weight, belt tension, and helical gear loads are all fully supported by the bearings. They have a big job to perform and must perform at full speed for months or years without failing. Additionally, roller and ball type bearings are often a considerable source of wear due to the metals and heat. Correct oil specification is critical for protecting these key components from metal-to-metal contact, high temperatures, sludge build-up, corrosion, and chemical outbreak. When specifying the oil formulation for bearings it’s important to balancing various factors such as bearing type, speed, size, and loading characteristics.
Seals, meanwhile, ;perform a crucial function in providing a barrier between the oil in the sumps and the process gas and ambient air. Unlike bearings, which experience mostly rolling friction, lip and mechanical face seals endure perpetual sliding and the resistance and heat generation that accompany it. It is critical that the specified oil is properly suited to provide the adequate film strength and cooling capacity under load and at the necessary operating temperature and speed. Improperly lubricated seals blister, crack, and can even leak.
Perhaps the most critical components considered when determining the proper oil for a positive displacement rotary lobe blower are the gears. Some manufacturers use hardened, matched helical gearsets for higher load capacity, longer life, ease of timing adjustment, and quieter operation. This style of gear requires special consideration because of the relative sliding that occurs between meshing teeth. The oil must be equipped to handle the accelerated thermal breakdown occurring in localized hot spots which are created by the immense pressure at the points of contact. Viscosity must remain sufficient at the operating temperature in order to maintain a proper film thickness between sliding faces. Improper gear lubrication leads to abrasive and fatigue wear, loss of timing, increased wear metals, and catastrophic failure.
Subscription users only!
Subscribers are able to view the whole article. Please register/subscribe (it's free and easy) to read all articles.