In Part I of this three-part series, we discussed the most common reasons sludge develops in heat transfer systems. This time, we’ll look at some straightforward steps to help you prevent it from becoming a problem.

When you’ve just invested thousands into new equipment, the last thing you want is for sludge to clog up your system. So how can you keep it from happening?

Start by examining your system carefully. You need to identify the “weak points”—any locations where the fluid comes into contact with air. Once you’ve identified these spots, measure the fluid temperature there during normal operation (commonly in the reservoir or expansion tank). If you find the temperature is over 200°F, here are a few actions you can take:

1. If your system doesn’t currently include an external expansion tank or reservoir, consider adding one. Having a “cold” fluid buffer at the air-contact point can dramatically cut down on oxidation.
2. If your reservoir or expansion tank is running hotter than 200°F, review the fluid flow path. If the fluid is moving directly through the reservoir, reconfigure the plumbing so that the tank is “T’d” into the system instead of being part of the main circulation loop.
3. If the expansion tank isn’t in the circulation loop but is still heating up, you may want to relocate it farther from the main system or use a nitrogen blanket to reduce direct contact with air.

What Else Should I Be Watching?

A few specific pieces of equipment play a big role in keeping sludge at bay—especially heat exchangers and bypass valves. Heat exchangers cool fluid before it enters open reservoirs, slowing down oxidation. Bypass valves, often used on portable temperature control units, allow hot fluid to pass through the expansion tank during startup to vent air and moisture. After startup, however, you’ll want to double-check that these valves haven’t been left open or stuck, which would expose the fluid to heat and air unnecessarily.

In larger systems, you’ll often find a secondary line leading to the expansion tank. This should normally remain closed but can be opened temporarily for venting. Including this in your maintenance checklist will prevent unnecessary oxidation and fluid breakdown. Remember: hot reservoirs and expansion tanks are one of the fastest ways to accelerate oxidation.

My Equipment Seems Fine—What Else Can I Do?

If your thermal fluid supplier provides a fluid analysis program, it’s smart to use it. Regular analysis helps you determine the right time for oil changes and allows you to make system adjustments that extend the life of your fluid investment. Duratherm offers one of the most comprehensive analysis programs in the industry—and it’s free to customers.

Of course, oxidation and sludge prevention doesn’t rely on maintenance alone. The right fluid chemistry also plays a role. All Duratherm fluids, for example, include a robust additive package designed to combat oxidation. Whatever supplier you use, confirm that their fluids are formulated with oxidation protection—especially important if your system is open to the atmosphere.

We hope this gives you a clearer picture of how to prevent sludge from forming. But what if your system is already fouled? Stay tuned for Part III, where we’ll explain how to clean it up and get things running smoothly again.