Using the Extended Eaton-Vickers 35VQ Test, spools were
placed in a bath and Schaeffer's VarniClean® was circulated
across at 140 °F for 7 hours.
Hydraulic systems have evolved to run as efficiently as possible. However, these performance gains have caused equipment to experience higher pressures and hotter temperatures. Both place more stress on the hydraulic fluid and the equipment.
Smaller hydraulic systems use less oil, so flow rates are increased relative to the oil volume. As a result, oil residence times are shorter, which causes the oil to remain at elevated temperatures longer. Higher temperatures can cause oxidative and thermal stress on the hydraulic fluid.
Reduced residence time can prevent contaminants such as foam, water and wear debris from settling out. Foam dissipation is also reduced as the residence time is shortened. The contaminants remain in the thermally stressed oil, causing it to break down and form a tacky substance called varnish.
Varnish is a by-product of increased oxidation and thermal degradation. In its early stages, varnish looks like butterscotch topping on ice cream; it’s soft and pliable. It’s primarily made up of organic residues; the polar bonds present in varnish are attracted to metal surfaces such as servo valves and pump components.
As the used hydraulic oil ages, more varnish is formed. This varnish can come in and out of solution with changes in temperature. Over time, varnish will harden and create thick layers on metal surfaces; it starts to look like peanut brittle. Varnish typically forms on pump housings, reservoirs and filters, as well as on valve spools and bodies.
Varnish weakens equipment performance and shortens the service life of the hydraulic fluid. Poor hydraulic valve response is a detectable sign of varnish. It creates a chain reaction within the hydraulic system, resulting in erratic operation, increased wear on valves and pumps, and shorter fluid life due to increased oxidation and downtime.
In hydraulic fluid, varnish prevents the anti-wear additives in the fluid from doing their job. It increases friction, which negates any efficiency benefits that were gained by the smaller systems. Such friction also generates wear. Because of the sticky, soft nature of varnish, it tends to attract and hold onto wear metals, increasing friction and generating increased wear. This wear can occur in the valves, cylinders, or, more importantly, the pump itself.
Varnish also clogs up pumps, valves, cylinders, solenoids and filters, and it will gloss over temperature sensors. As equipment is pushed to keep up with output, excessive wear occurs on pumps, which can lead to equipment failure.
Varnish must be cleaned out of systems with a product such as Schaeffer’s VarniClean®. This powerful treatment requires supervision as it runs through your system. Its effectiveness is extremely thorough and requires frequent filter changes as it cleans up existing varnish. Trust us!
After cleaning your hydraulic system, refill it with one of our recommended hydraulic oils containing VarniShield®, our proprietary varnish mitigating additive. VarniShield® works by dispersing and suspending varnish precursors and varnish as they materialize; it allows a hydraulic system’s filter to remove the deposits. Schaeffer’s hydraulic fluids with VarniShield® keep systems running cooler, while filters, strainers and valves remain clog-free, enabling efficient full hydraulic oil flow rates.
Hydraulic fluids should be closely monitored for oxidation during service life. Tests such as TAN, Varnish Potential, RULER Method, or the FTIR method will indicate the health of the hydraulic system. These test results need to be trended over time, as a snapshot or a single sample does not give the true picture of the system’s health.
Bottom line: varnish is the enemy to your hydraulic system. Preventative maintenance can eliminate varnish and sludge problems in treated systems while at the same time providing resistance to future oxidation. For more information about Schaeffer’s hydraulic fluids made with VarniShield®, visit www.schaefferoil.com/hydraulic-fluids
