Notes on Lubrication Systems Flushing
by David Doyle, CLS, OMA I, OMA II
Vice President, Americas

The need to perform flushing of a lubrication circulating system can occur for several reasons.

  • Newly fabricated components or systems
  • Recent maintenance or repairs
  • Excessive contamination buildup
  • Change to a new product formulation

When it is necessary to flush a lubricating circulating system following proper flushing procedures is critical. Details of proper flushing procedures can be involved; the scope of this short eSource article is intended to provide general considerations to flushing a lubrication system. As a recommended reference, guidelines detailed in ASTM Standard D6439 for flushing turbine lubrication systems can be applied to many types of systems.

Proper flushing ensures removal of unwanted contaminants and deposits that can shorten component life and interfere with system efficiency. Unwanted chemical reactions when switching to new product formulations can also be prevented with proper flushing procedures. Some problems resulting from inadequate flushing procedures may be evident right away, other times it can take up to a year or more for problems to manifest.

The product used for system flushing can be a special flushing oil that removes contaminants and previous product residue, while being compatible with the new product to be put in service, or it can be the product intended for service itself. The flushing process should adequately address the specific issue at hand and carried out by experience personnel.

When removing contaminants there are several general factors that can improve the efficiency of the flushing process. Turbulent flow with the use of auxiliary outside pumps can help greatly. A lower viscosity flushing oil at higher circulating speeds will contribute to turbulence flow. A high velocity that is two to three times normal system oil velocity is recommended. Increased flushing temperatures will also aid turbulent flow as well as product solubility. Testing of the product during the flushing process is important to ensure unwanted residues or contaminants are removed. Aggressive flushing is improved by the following parameters:

  • Turbulence
  • High velocity
  • Elevated temperatures
  • Lower viscosity oil

When flushing is needed due to a change in product formulation, ensure the flushing product is compatible with both the old and new product, especially when going from an acidic additive formulation to a basic formulation or vice versa. Compatibility can also be an issue when changing from one base oil type to another. Incompatible additive formulations can create insoluble soaps in the system that plug passageways and reduce additive performance. Many times an additive free neutral oil is a safe and effective flushing medium. This doesn't necessarily mean the new product is always going to be incompatible with the old product. Product compatibility of the old product with the new product can be determined by laboratory testing compliant with ASTM Method D7155, which ALS can perform.

There are situations when special equipment or flushing techniques are required. This is especially relevant to varnish buildup. Standard flushing practices will not adequately address the removal of varnish buildup. Processes such as electrostatic filtration may be required. In severe circumstances, manually removing the varnish buildup may be involved. Testing for varnish potential of the lubricant in service also requires some specialized testing which can be arranged through your ALS fluids testing laboratory.