If you operate hydraulic systems at elevated temperatures and pressures, varnish is probably already on your radar, even if you haven’t put a name to it yet. Oxidation and thermal degradation produce polar by-products that adhere to servo and proportional valve spools. It doesn’t take much to affect performance – deposits of just 1-2 microns are enough to cause valve sticking, erratic control and unplanned shutdown.
In one Fluitec case study, a hydraulic press treated with SolvancerⓇ based technology saw clamp speed and cycle time restored almost immediately, recovering production throughput that had gradually been lost to varnish build-up. The operator had not even necessarily identified varnish as the cause until the test results came back, which is fairly typical of how this problem tends to surface. It rarely shows up as a single dramatic failure. Instead, it appears as a gradual drift in performance that gets attributed to something like wear and tear right up until something finally sticks.
Why Standard Oil Analysis Misses The Warning Signs
Standard oil analysis, covering viscosity, acid number and particle count, simply cannot detect the sub-micron polar products that precede varnish formation. By the time those tests flag an issue, the varnish is often already affecting valve performance. This is precisely why teams relying solely on conventional fluid monitoring can be caught off guard – the oil looks fine on paper right up until a valve sticks.
MPC testing, formally ASTM D7843, is the correct diagnostic tool for this. Values above 30 Delta E indicate critical risk and give you a genuine early warning rather than a lagging indicator. This value will differ based on the type of equipment as per OEM. RULERⓇ testing works alongside MPC by monitoring antioxidant depletion, so you get a clearer picture of where your oil sits in its degradation curve, not just where the varnish risk currently stands. Used together, these two tests tell a more complete story than either one on its own, since antioxidant depletion is often the early driver behind the oxidation by-products that eventually become visible varnish.
Treating Varnish Without Taking The System Offline
Once varnish is identified, the good news is that you do not need to shut the system down to deal with it. Products from the SolvancerⓇ family such as DECON AW™ for hydraulic oils (replenishing anti-wear additives as well as dealing with varnish contamination) are usually applied at a 3%-5% treat rate directly into in-service oil, where it dissolves varnish deposits. Combined with ESP™ kidney loop filtration, it removes existing deposits and helps prevent them from reforming, giving you a treatment process that works around your operation rather than against it. For maintenance teams under pressure to keep production running, that distinction between online treatment and a full shutdown is often the deciding factor in whether a varnish problem gets addressed promptly or gets deferred until it becomes urgent.
The Cost Of Doing Nothing
Servo valve failures on a single hydraulic system can run as high as £40,000 a month once you factor in replacement parts and labour. Against that backdrop, the return on proactive varnish mitigation is measured in months, not years, which makes the business case for getting ahead of the problem fairly straightforward. Many maintenance budgets are stretched thin enough that a saving of this size is difficult to ignore once it has been put in front of the right people, particularly when the alternative is an unplanned stoppage that affects production scheduling well beyond the maintenance department itself.
Technical guidance on using oil analysis to control varnish backs up exactly this point, showing that proactive testing consistently outperforms reactive replacement. Case study evidence has also shown that standard analysis methods missed varnish precursors entirely until RULERⓇ and MPC testing were introduced, allowing the problem to be caught and treated before it caused operational disruption.
Building Varnish Control Into Your Maintenance Programme
Varnish is not always immediately obvious. It builds slowly until a valve sticks at the worst possible moment, and by then the cost has already shifted from a manageable maintenance task to an unplanned production stoppage. The teams that manage this well treat varnish control as a continuous process rather than a reaction, testing regularly with MPC and RULERⓇ and keeping treatment tools on hand for when results call for action. This usually means building testing into a regular calendar rather than waiting for a noticeable symptom, since the whole value of MPC and RULERⓇ lies in catching the problem before it becomes visible on the equipment itself.
Peer reviewed research into varnish formation continues to support this approach, confirming that early detection paired with appropriate industrial lubricant treatment is the most reliable way to prevent valve-related failures.
A&S International Supplies The Full Toolkit
A&S International supplies the complete Fluitec varnish control system, including ESP™ filtration, DECON AW™ (part of the SolvancerⓇ family) and MPC and RULERⓇ V™ oil analysis equipment. Having diagnostics and treatment under one roof makes it far easier to move from a worrying test result to a resolved problem without delay, rather than juggling separate suppliers for testing and treatment while a known issue sits unresolved.
Varnish in your hydraulic system does not have to mean unplanned downtime and costly valve replacements. Contact A&S International to discuss MPC oil testing, Solvancer treatment and ESP™ filtration, and find out how quickly Fluitec technology can restore system performance.
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