The importance of defoamants

One of the most common issues experienced by lubricants is the formation of foam. This is a particular problem in machinery that has a lot of system turbulence. Foam can have a detrimental effect on a machine’s ability to operate when it gets out of control, which is why lubricants are manufactured to contain defoamants, or anti-foam agents, as they are also known.

Defoamants and their role

Defoamants are additives that tend to be made up of either polymethacrylate of methyl silicone. Various concentrations of these chemicals are blended with oil, depending on its viscosity, and other properties of the oil. Occasionally, the type and amount of defoamant blended into an oil will depend on the application for which the oil is designed to be used in. For example, oils that are used in gear oils, where bubbles will stay in the oil longer, are more likely to foam, which means more defoamant needs to be used.

Most lubricants are formulated with anti-foam agents in order to reduce the risk of a stable foam forming on the surface of the oil level. In order for a lubricant to perform well, there needs to be a precise balance between anti-foam agents and the other additives in the fluid. If the amount of defoamant is too low, thee machinery it is present in will have issues, and if the level is too high, an excess of foam could be produced.

How defoamants work


When machinery is in operation, air becomes entrained in lubricant and the resulting air bubbles try to reach the surface. As a bubble is rising through the fluid, it travels through and picks up any amount of anti-foaming agents, which have been blended into the oil.

Defoamants work a bit differently to the majority of other additives in that they are suspended in the lubricant, rather than being dissolved. This is vital because it stops defoamants from otherwise losing their ability to reduce foam.

When an air bubble entraps some defoamants and reaches the surface, the additive sets to work in impairing the bubble wall’s film strength, weakening the chain and letting air spill into the bubble, stopping foam from forming in excess. This keeps the oil and the machinery it is operating in, in good condition, so that you do not need to worry about excess foam, most of the time. However, sometimes, defoamants can stop being effective, so you should monitor the situation on a regular basis, as best practice.