By Jim Fitch
Practicing Oil Analysis Magazine
The defoamant (also known as antifoam agents and foam inhibitors) is a common additive in many types of lubricating oils and hydraulic fluids. As the name implies, the purpose of the defoamant is to retard the formation of stable foam on the surface of the oil in the sump, gearbox, or reservoir.
Silicones, or compounds containing silicone, and acrylic copolymers are popularly used in mineral-based lubricant formulations. Lighter grade turbine oils and hydraulic fluids are generally formulated with acrylate anti-foam additives while heavier gear oils, paper machine oils, and crankcase lubricants may use silicone.
When stable foam is allowed to form there is considerable risk that effective lubrication will not be achieved. In many cases foam is merely a cosmetic concern. In other cases it is quite serious and can lead to premature failure of the oil and machine.