Enlever autant de vieux fluide hydraulique du moteur que possible est toujours le but d'une vidange d'huile ! De nombreuses stratégies améliorent la quantité de fluide qui quitte le système.
When changing hydraulic fluid, the goal is to remove as much of the old fluid as possible so that the new fluid is not contaminated. Below is a step-by-step guide plus tips, safety precautions, and extra techniques to help you do a thorough job.
Why Is It Important to Drain Hydraulic Fluid Thoroughly?
Hydraulic fluid degrades over time and absorbs contaminants from many sources:
- Manufacturing contamination (in the system or fluid)
- Wear and abrasion of internal parts
- Corrosion and oxidation
- Cavitation effects
- Ingress of water or air
- Seal leaks allowing abrasive particles in
These impurities reduce the fluid’s performance, can damage valves, pumps, seals, and other components, and shorten equipment life. Therefore, hydraulic fluid must be replaced on a regular maintenance schedule—and draining thoroughly helps prevent the leftover “bad” fluid from contaminating the new fluid.
On a Side Note: If your goal is to maximize your fluid’s performance, your equipment’s performance and overall health, and possibly extending drain intervals it is important to consider adding an oil analysis program if you do not have one in place. Additionally, the proper use of various filtration and breather options can be extremely helpful to reaching these goals.
Safety First: Precautions Before Draining
Before you begin, always keep safety your top priority:
- Relieve system pressure
Many hydraulic systems remain pressurized even when off. Before disconnecting any lines or opening ports, release all pressure (often by operating actuators in neutral, or using a pressure-relief valve). Fluid under pressure can penetrate your skin — a serious injury. - Allow system to cool
Hydraulic fluid can become very hot during operation. Wait until the system has cooled to avoid burns. - Wear protective gear
Use gloves, safety glasses, and other appropriate PPE. Never use your bare hands to check for leaks. - Avoid contamination
Don’t open the reservoir or cover more than needed. Dust, dirt, or moisture entering while you work can spoil new fluid.
Step-by-Step Process to Drain Hydraulic Fluid Thoroughly
Below is a more fleshed-out procedure:
1. Prepare your tools and work area
- A clean catch container large enough to hold all the fluid
- Wrenches, sockets, screwdrivers
- Replacement filters
- Clean rags, absorbent mats
- A desiccant breather (if not already installed)
- (Optional) portable filter cart or pump for assist draining
2. Position all cylinders and expansion elements to “closed” or minimal extension
With cylinders fully retracted (or in closed positions), there is less fluid trapped inside them and expansion components. This allows more fluid to be drained.
3. Allow air ingress
To let fluid flow out freely, air must be allowed into the circuit (for example via breather ports). In practice, all breather ports should be open (or replaced with desiccating breathers) to prevent moisture or dust from entering.
4. Remove return-line filters (if applicable)
These filters often trap a significant amount of fluid. Removing them opens more flow paths and allows additional fluid to drain.
5. Locate and open drain ports
- The main reservoir will typically have the largest drain plug or valve — this is where most fluid will exit.
- Some systems include secondary or low-point drains on lines, valve blocks, or low areas in the circuit. You should open those too, if accessible.
6. Gravity drain
Let gravity do most of the work. The fluid should flow out into your container. Be patient — allow sufficient time for fluid to stop draining noticeably.
7. Assist with purging (optional but helpful)
To push out fluid remaining in lines and components, you can:
- Cycle the controls slowly (move valves, actuators) while drained, so residual fluid is forced out.
- Use compressed air (applied carefully and safely) to blow lines (only if equipment design allows and after pressure is relieved).
- Use a portable filter cart or vacuum pump to suck remaining fluid from hard-to-reach areas.
Many operators of heavy equipment use a “purge” approach: drain the reservoir, disconnect a return line, run actuators in certain patterns, then reattach lines. This helps move contaminated fluid into the waste container rather than leaving it behind.
8. Flush the system (if needed)
If the system is particularly dirty or contaminated, a flush is recommended:
- Use a compatible, low-viscosity “flush” fluid or solvent.
- Fill the system, run it to circulate, then drain while hot.
- Replace filters again and clean the reservoir before final refill.
This helps dislodge sludge, varnish, or residual contaminants.
9. Close drains and reinstall filters
Once draining (and flushing, if done) is complete, close all drain plugs, reinstall filters and seals (with new crush washers if required), and ensure everything is tightened properly.
10. Refill with new hydraulic fluid
Refill to the correct level using the manufacturer’s recommended fluid type. As you refill, you may need to bleed air from the system (open relief or vent ports, cycle actuators).
11. Run and check the hydraulic system
- Run the hydraulic system for a short time, move actuators to help remove air bubbles.
- Let the system rest, recheck fluid level, top off if needed.
- Inspect all connections, seals, and joints for leaks.
- Monitor for unusual behavior.
- If the system behaves inconsistently or power feels weak, you may be experiencing early low hydraulic fluid symptoms.
12. Dispose of old hydraulic fluid properly
Used hydraulic fluid is hazardous. Follow local regulations or recycling centers for oily waste. Never dump it into drains, soil, or water systems.
Tips and Common Pitfalls
- Work with fluid warmed: Heating fluid (by running the system lightly before draining) helps it flow more easily and carry more contaminants out.
- Install a desiccant breather: This helps filter moisture and particulates out of incoming air, preventing future contamination.
- Cycle hydraulic functions while draining: This forces trapped fluid out of lines, cylinders, and valve bodies.
- Avoid over-loosening: Too loose drain plugs or open ports can introduce debris or make it hard to control the flow.
Follow manufacturer’s specific steps: Each machine may have unique valves or purge paths. Always consult your equipment manual.
Properly draining hydraulic fluid is essential for maintaining the efficiency and longevity of your equipment. At BioBlend, we offer a range of high-performance, lubrifiants respectueux de l'environnement designed to keep your hydraulic systems running smoothly. From preventing contamination to selecting the right fluid for your needs, our solutions help you maintain your equipment’s peak performance. Explore our full product lineup, see how we support various industries on our industries page, or visit our homepage to learn more. Need expert guidance? Contact us today for tailored recommendations.
FR 
EN