What really happens when you run a hydraulic system without a heat exchanger?

The absence of heat exchangers causes trapped heat to build up within the fluid throughout each cycle, causing temperatures to rise over those of 140-160°F (60-71°C), a safe operating temperature. Once the threshold is crossed when viscosity is reduced seals become hard and leak, varnish develops within internal elements, and the wear of the pump increases dramatically, often decreasing the lifespan of components by 50 percent or more for each 18degF (10degC) increase above the optimal operating range.

Heat exchangers don't get much credit until they're in the wrong. Many operators consider valves, pumps, and cylinders to be the "real" components of a hydraulic system, whereas the cooling circuit is tucked away behind in the background. However, a hydraulic system produces heat each time it is operating via internal leakage as well as friction in fluids and pressure drop through orifices and valves along with mechanical inefficiency. If there isn't a heater in place to eliminate that energy, there is no place for it to go other than into the fluid and then into any component that the fluid interacts with.

Where exactly does the heat originate? Where does the heat actually originate?

All hydraulic systems convert some of their energy input into heat, rather than doing work. This isn't an issue, as it's a fundamental aspect of thermodynamics. Common sources of heat are

• Pressure drop across relief valves as well as flow controls, in which fluid energy is converted directly into thermal energy
• Internal slippage of motors and pumps in which fluids bypass the expected flow paths at pressure
• Fluid friction occurs as oil flows through fittings, hoses, and tight clearances
• Mechanical friction in motors, cylinders, and other components that rotate

If a system is properly designed, the heat exchanger—whether water-cooled, air-cooled, or even an oil cooler that is integrated in the reservoir—eliminates heat in a continuous manner and keeps it within the thermal window. Take it out, or let it fail with no replacement, as the system is left with no means of releasing the heat it produces.

The immediate consequences of the uncontrolled buildup of heat

Breakdown of viscosity

The hydraulic fluid is designed to function within a certain viscosity range. When temperatures increase, it's harder to maintain the film of fluid that's intended to create a barrier between metal surfaces in valves, pumps, and cylinders, which gets too thin to perform its job. This causes contact between metal and metal, increased wear, and a noticeable growth in the amount of internal leakage and creates a vicious cycle that produces even more heat.

Accelerated oxidation

Every 18°F (10°C) increase in the temperature of fluids approximately doubles the rate of the process of oxidation. Oxidized liquid darkens, becomes thicker, and produces acidic byproducts that damage coatings, seals, or metals from within. It is not reversible. Once it has begun, there is no way to stop it. Only replacement of the fluid can fix it. By the time it's apparent the damage to components is often already in progress.

Sludge and varnish formation

When the temperature of the fluid increases, additives break down and insoluble byproducts begin to form and build up on spools of valves or servo components as well as orifices. Varnish is particularly dangerous since it isn't often detected in an oil analysis until it has created sticking valves, irregular actuator movements, or system malfunctions that are difficult to detect.

Seal failure

Elastomeric seals are tested for specific temperatures. The continuous operation that goes beyond those thresholds causes seals to get harder, crack, or even take on the form of a permanent compression set. After that, leaks from the outside and internal bypass leaks grow as well as the system's effectiveness even in normal operations.

Damage from the downstream: what cost you over the course of time?

The short-term effects of overheating are enough to cause concern. However, the cumulative effects over time are where the real price is revealed.

Motor and pump wear

Fluid that is thin and overheated cannot ensure adequate lubrication within close-tolerance components. Pumps can begin to cavitate or exhibit excessive wear on their internals, which is evident first in reduced efficiency before eventually becoming a complete failure. It's typically the most costly single component to replace in a whole system.

Reducing the life span of components

A general rule of thumb utilized widely throughout the power sector Every one degree (10°C) of continuous operation that exceeds the maximum recommended can reduce the lifespan of fluids and consequently the life of any component exposed to the fluid by about half. Systems that are designed to operate continuously for years could have their service intervals dwindle to months.

Unplanned downtime

Overheating doesn't always manifest itself as one major failure. Most often, it manifests up as a succession of seemingly unrelated problems, such as a stuck valve there, a slow-moving actuator there, and a sealing that leaks fluid elsewhere. If left untreated, these tiny problems can lead to unplanned downtime that's much more costly than the expense of the damaged heat exchanger.

Signs to warn that heat may already be an issue

Operators don't require a thermal camera to detect early signs of cooling issues. Be on the lookout for:

• Reservoir surface temperature is greater than 140°F (60°C) to the point of contact (uncomfortable to keep a hand in place for longer than a couple of seconds)
• A burning or bitter smell in the vicinity of the pump or reservoir, typically an indication of the oxidization of fluid
• The fluid is darkened in comparison to an original sample or has a smell that's distinct
• The cylinder's response to the cylinder is slower, or it exhibits erratic valve response, particularly as the system is warming up during the course of a shift.
• A louder sound from the pump could indicate cavitation resulting from thinned fluid

Any of these alone may not be conclusive; however, two or more happening at once is a clear indication that your cooling system is not able to keep up with the production of heat.

What should you do if your system is getting hot?

Verify that the heat exchanger is functional.

A heat exchanger present but has been damaged, corroded, or has a failing cooling fan will offer less protection than having no fan at all. Examine for blocked air-cooled fins or water-cooled tubes that have been scaled, or a fan not operating.

Check for fluid levels and conditions.

Lower levels of fluid affect the reservoir's ability to release heat in a passive manner, as it has less heat mass and less surface area that is exposed to the surrounding air. An oil analysis that is fresh will confirm that viscosity as well as additive packages are within the specifications.

Examine for elevated system pressure or relief valve activity.

A relief valve that's cracked open faster than it should or running at a higher pressure than the system requires creates excessive heat constantly. Verifying the pressure settings against the specifications of the original design can reveal heat sources that aren't related to having anything to do with the cooler itself.

Take into consideration the duty cycle as well as ambient conditions.

A heat exchanger properly sized to operate intermittently could not be adequate if the system is now in permanent operation. This could happen when ambient temperatures have increased due to seasonal fluctuations or the relocation of equipment. Reviewing the sizing of the unit according to the operating conditions at present is a good idea to conduct regularly, not only during the time of commissioning.

The heat exchanger isn't just an extra component that is bolted to the hydraulic system to make it easier; it's the element that is responsible for keeping each component in the machine within its intended operating limits. If you don't have one, or are operating with one that's not able to fulfill its purpose, it will not result in a catastrophic failure immediately generally. Instead, it initiates an insidious, gradual compounding of thinner fluid, speedier degradation of seals, oxidation, and wear that ultimately results in costly downtime. Identifying warning signs in the early stages and making cooling capacity a priority for maintenance instead of an afterthought is the distinction between a system that lasts for years without issue and one that is unable to function prior to the time it is due.

1. What is the temperature that is considered to be the ideal temperature for hydraulic fluid?

The majority of hydraulic systems are built to function safely between 120 and 140°F (49-60°C). 160°F (71°C) is usually considered to be the maximum temperature before the degradation process accelerates. Continuous operation beyond this temperature range substantially reduces the duration of time for the component and fluid.

2. Can a hydraulic system function without any heat exchanger?

Smaller systems with low periodic duty cycles, as well as the capacity of a reservoir, can operate without a dedicated exchanger if the reservoir on its own is able to dissipate heat effectively. The majority of industrial systems that run continuously or are heavy-duty use require active cooling to remain within safe temperatures.

3. How fast can overheating cause damage to the hydraulic system?

Damage caused by overheating typically occurs more gradually than immediately; it can take days or weeks of high temperatures that are sustained. However, the cumulative effects on seals, fluids, and wear components could reduce the life of the entire system by months or even years when left uncorrected.

4. What's the most cost-effective method of determining the condition of my hydraulic fluid overheating?

A simple infrared thermometer aimed towards the wall of the reservoir gives an instant, low-cost temperature reading. In conjunction with a visual as well as a scent test on the liquid, it will detect early signs of overheating prior to a laboratory oil analysis being required.

5. Do larger reservoirs reduce the need for a heating exchanger?

A larger reservoir boosts the thermal mass of the fluid and the area of its surface, which can help in the dispersal of heat; however, it doesn't completely eliminate the requirement of active cooling for systems that produce substantial heat continuously. However, it can prolong the time until temperatures hit critical levels.