The appearance of a characteristic whistle when lowering the boom or jerking of the rod when lifting the vehicle indicates that air has entered the hydraulic system. Such a malfunction hydraulic lift makes the operation of the equipment unstable and dangerous for the vehicle. Eliminating air pollution requires a full cycle of replacing the working fluid and forced pumping of the circuit under load.
First you need to prepare a container for draining the old oil and a clean rag. The process begins by lowering the boom completely to the lowest position to minimize pressure in the system. After this, unscrew the drain plug on hydraulic cylinder or pumping unit, and the waste flows into the prepared container.
Ignoring the procedure for removing air pockets leads to cavitation, which destroys the internal surfaces of the pump and the o-rings. It is critical to use only the oil recommended by the manufacturer for your specific lift model.. In most cases, hydraulic oil with a viscosity of ISO 32 or ISO 46 is used, depending on the climatic operating conditions.
Diagnosis of hydraulic faults
Before proceeding with the active repair phase, it is necessary to accurately determine the nature of the malfunction. Symptoms of inflation are often confused with leaks or mechanical damage to the cuffs. If the lift does not support the load or lowers spontaneously, the problem may lie in the safety valve or wear on the piston cups.
Visual inspection of high-pressure hoses and connecting fittings can help identify obvious leaks. Air enters the system precisely through leaky connections on the suction line, where a vacuum is created. The presence of foaming liquid in the tank inspection window is also a direct sign that the oil is saturated with air bubbles.
For an accurate diagnosis, it is recommended to carry out a lifting-lowering cycle without load and pay attention to the sounds of the pump. Extraneous noise, reminiscent of knocking or hissing, indicates cavitation processes. The table below shows the main symptoms and their probable causes:
| Symptom | Probable Cause | Elimination method |
|---|---|---|
| Jerks when lifting | Air lock in the cylinder | Bleeding the system |
| Spontaneous lowering | Valve leakage | Replacing seals |
| Pump noise | Low oil level | Adding fluid |
| Slow rise | Filter contamination | Cleaning or replacement |
⚠️ Attention: Before starting any work on the hydraulic system, make sure that the lift is completely lowered and secured, and the pressure in the system has been relieved.
Preparing equipment and tools
High-quality pumping is impossible without the right tools and consumables. You will need a set of wrenches for unscrewing the plugs, a funnel for filling in oil and a container with a volume of at least 5 liters for working out. It is also necessary to purchase flushing fluid if the old oil is heavily contaminated with wear products.
Particular attention should be paid to the cleanliness of the work area. Even microscopic dust entering the hydraulic circuit can cause the distributor spools to jam. All tools and containers must be thoroughly washed and dried before starting work.
- 🛠️ A set of wrenches and sockets for removing traffic jams.
- 🛢️ Fresh hydraulic oil of appropriate viscosity.
- 🧹 Clean rags and solvent for degreasing surfaces.
- 🧤 Protective gloves and glasses for the safety of the master.
If your lift design includes fine filter, it also needs to be replaced or washed. A clogged filter creates resistance to fluid flow, which increases the effect of cavitation and promotes the formation of air bubbles.
Complete hydraulic oil change
The fluid replacement process is the foundation for successful pumping of the system. The old oil must be drained completely, for which the lift is installed in the lowest position. Having unscrewed the drain plug, wait until the liquid has completely drained, periodically shaking the columns to remove residues from hard-to-reach places.
After draining, it is recommended to flush the tank and cylinders with a special flushing fluid or a small amount of new oil. This will remove any sludge or metal shavings that may have accumulated at the bottom of the tank. Dirt in the system is the main enemy of tight connections and valves.
Filling of new oil is done through the filler neck using a funnel filter. The liquid level should reach the mark MAX on the sight indicator or be slightly above the minimum level, since part of the volume will go into the cylinders during the first start.
☑️ Checklist for preparing for replacement
Hydraulic cylinder pumping technology
The main stage of the work is to displace air from the working cavities of the cylinders. To do this, you need to raise and lower the lift arms several times without a car. When rising, air will enter the tank through the return line, which is accompanied by a characteristic gurgling sound.
If the lifter is equipped with cylinder bleed screws, they should be opened slightly when the rod is raised. As soon as clear liquid without bubbles comes out of the hole, tighten the screw tightly. This operation is repeated for each cylinder separately.
It is important not to allow the pump to run dry or with a critically low oil level. Periodically stop the engine and check the fluid level in the tank, adding it if necessary. The air leaving the system is replaced with new oil.
⚠️ Attention: Do not keep the lift button turned on for a long time after the rod reaches the extreme position - this will lead to overheating of the oil and damage to the seals.
To speed up the process, you can use the method of creating an artificial load. On some models, it is recommended to open the pressure relief valve slightly during ascent to create turbulence and flush air pockets out of dead spots.
The nuances of pumping two-post lifts
On two-post models, it is important to synchronize the bleeding of chains and cylinders. If one cylinder is pumped better than the other, the carriages may become out of sync. Pump the circuits one by one, controlling the lifting height of each side.
Checking operation under load
The final stage is testing the equipment under real load. A vehicle whose weight is at least 50% of the lift’s lifting capacity is driven onto the platform. A series of ascents and lowerings are performed with holding in the upper position.
At this moment, you need to carefully monitor the pressure gauge (if installed) and listen to the operation of the hydraulic pump. A smooth hum without jerks or pressure dips indicates successful air removal. The movement of the carriages must be smooth and synchronous.
If there is a “soft” movement or a drop in pressure, the pumping procedure must be repeated. Sometimes it takes several cycles to completely remove the smallest bubbles dissolved in the oil. Stability of work is the main criterion for the quality of work performed.
- 🚗 Place the car on the lift in the center of the platform.
- 🆙 Raise the car to a height of 10-15 cm and stop.
- ⏱️ Pause for 1-2 minutes, controlling the lowering.
- 🔄 Lower the car and repeat the cycle 3-5 times.
Key takeaway: Successful bleeding can only be achieved through an integrated approach: changing the oil, bleeding the cylinders and testing under load.
Common mistakes and safety precautions
A common mistake made by mechanics is to use the wrong types of oils, for example, transmission or motor oils. They have a different viscosity and additive package, which leads to rapid wear plunger pairs and destruction of rubber seals.
Another problem is insufficient cleaning of the system before filling. Remains of old oxidized oil mix with new oil, sharply reducing its lubricity and causing foaming. Hydraulics does not tolerate neglect of cleanliness.
When operating a lift, always be aware of the risk of falling heavy loads. All maintenance work is carried out only with the booms lowered and the electric motor de-energized. The use of faulty equipment is prohibited.
⚠️ Attention: It is prohibited to carry out welding work on elements of the hydraulic system or near high-pressure hoses to avoid damage from sparks.
Regular maintenance, including checking the oil level and hose condition, will extend the life of the equipment. Make sure connections are tight and change consumables promptly.
Helpful Hint: To prevent condensation from forming in the tank, try to keep the filler cap tightly closed, especially in high humidity conditions.
How often should the lift hydraulic oil be changed?
The recommended oil change interval is once a year or every 2000 operating hours. However, for intensive use in dirty conditions, the interval should be reduced to 6 months.
Is it possible to mix different brands of hydraulic oils?
It is strictly not recommended to mix oils of different manufacturers and types. Chemical reactions between additives can lead to sedimentation and loss of fluid properties.
Why does the lift get hot after pumping?
Heating can be caused by residual air in the system, too high system pressure, or the use of oil with the wrong viscosity. Also check that the bypass valve is working properly.
What type of oil is best for winter?
For work in the cold season, it is better to use oils with a viscosity index of HV (High Viscosity) or special all-season hydraulic fluids that maintain fluidity at low temperatures.
What should I do if there are still jerks after pumping?
If jerking persists, check the condition of the cylinder rods for scoring, the serviceability of the throttle valves and the absence of mechanical damage to the chain drive.