4 Problem to Ask Before Switching Hydraulic Fluid

How do you know when it’s time to change the hydraulic fluid in your machines? Do you treat it like your car engine and swap the oil every 3,000 miles—or hours in this instance? Or do you simply go from a time standpoint (e.g., annual)? Based on the importance of hydraulic equipment to your operation, the best way to get the most out of your oil and make sure it’s ready to dump and recharge, is by taking a sample and sending it to a lab for a thorough analysis.

Changing your oil based on time alone, without a reference to the condition of the oil, is like taking a shot in the dark. The only way to truly know when your oil is ready is by evaluating it first. Doing so also helps you diagnose any performance issues and prevent future machine failure.

To help you avoid the problems of switching too late, or the wasted cost of switching too early, make sure you ask yourself these 4 questions before swapping the hydraulic fluids in your machines:

How critical is the machine and what is the sump size?

The first two factors to consider when determining whether to switch out hydraulic fluid in your unit are the criticality of the machine, along with its sump size. The answer to this will help determine if you should first take an oil sample and send out for lab analysis, or simply switch out the fluid because the PM is due. For example, it doesn’t necessarily pay to take a fluid sample of a non-critical machine with a small sump, because it doesn’t cost nearly as much to fill, and if the machine goes down, it can be repaired without backing up production. On the other hand, in a highly critical system, the wear data becomes important, because even if the system has a small sump, you can’t afford any downtime. Likewise, if your machinery has a large sump, any mistakes you make in fluids usage will be costly, so you’ll want to make sure you get everything right. 

A third factor to take into account is the amount of physical component repairs associated with the system. Even if your set of machines aren’t necessarily critical or have relatively small sumps, if you’re replacing a lot of components—such as pump motors and valves—the hydraulic unit may be a prime candidate for fluid analysis and/or adjustment of the service frequency.

Based on oil sample data, do you need to change out your hydraulic fluid?

Once you get the sample data back from analysis, look at the data for things like viscosity, oxidation levels, wear rate, and additive content, as well as contaminants in the system. Based on what the data shows, does it indicate that your oil is ready for a switch? For example, is the viscosity too thin? Are oxidation levels too high? Have your additives deteriorated? If so, we’ll cover that in our next point.

It’s worth noting, however, that hydraulic systems theoretically have very little make-up fluid in their systems (if there are no leaks and no blown line occurrences). This means the fluid you put in the system when you charge up is likely what will be in there when doing PM, testing, or other maintenance activity. Some machines do leak, so make-up fluid will need to be added along the way, which can potentially impact the fluid data/condition. Be aware that it may skew your oil sampling data.

If it’s time to change out fluids, is the product you’re using the one you want to use going forward?

Now that you’ve had time to view the results of your sampling, the next thing you need to consider is whether or not you’re satisfied with the performance of your current oil. Is it deteriorating faster than you need it in order to meet your budget for fluid maintenance? Is it threatening your equipment life? If oxidation, wear, or cleanliness issues are identified, you need to make the proper adjustments in order to prevent any long-term problems with your machines.

What adjustments must be made to ensure you don’t have the same problems in the future?

If you aren’t satisfied with your hydraulic fluid’s performance, it’s crucial that you identify the problems and make the necessary changes that will extend the life of both the fluid and your machine. Whether it’s a matter of switching from a monograde oil to a multigrade oil, increasing the antiwear additives, including more detergent, or anything else.

Given the cost of fluids these days, you’ll want to make sure you aren’t wasting usable fluid by swapping it out too soon, and you also want to avoid damaging your system or losing valuable production time by leaving it in past its effective life.