It’s obvious that a lift table with a load capacity of 500 kg is not designed to handle the same weight as a lift table with a capacity of 1,000 kg. To protect the components of the lift table from damage, a pressure relief valve is installed in the hydraulic system's pressure line. If the pressure in the hydraulic system becomes too high, the valve redirects a portion of the oil directly back to the unit's tank. As a result, the platform no longer lifts.

It is also possible that the motor protection switch of the drive motor has been triggered. If the current draw exceeds the specified value, the motor protection switch interrupts the circuit to the motor to prevent damage.

If the platform is overloaded, the weight should be reduced or removed entirely from the lift table. If overloading can be ruled out, the settings of the lift table should be checked. However, changes to the settings of the pressure relief valve and the motor protection switch should generally only be made by the lift table manufacturer.

It is possible that all or just one phase of the main power connection has failed. Depending on the extent, this issue can result in a complete failure of the lift table control and drive, a failure of the control system alone or a malfunction of the hydraulic unit.

To resolve this issue, a qualified electrician should inspect the entire main power connection, including the main switch, and identify and rectify the cause of the power outage.

If the electric motor of the hydraulic unit rotates in the wrong direction, no oil is pumped from the tank into the cylinders. This means that although the motor can be heard running, the platform does not lift.

A qualified electrician should check the phases at the electrical connection of the motor and swap them if necessary.

In the hydraulic system of the lift table, at least one check valve is installed to hold the lift table in its current position when the hydraulic pump is turned off. If the seat of the check valve is contaminated, it may not close properly. Depending on the valve's position in the hydraulic circuit, the oil can then flow directly back to the tank from the pump.

First, try flushing the check valve by cycling it. If this is not successful, the check valve must be removed and cleaned. If irreparable damage is discovered during this process, the valve will need to be replaced.

If the electric motor is running and its rotation direction is correct, but the platform still does not lift, this could indicate a defect in the hydraulic pump.

However, a coupling defect is more likely than mechanical damage to the pump. To check this, part of the unit often needs to be disassembled. More detailed information can be found in the lift table's operating manual or the technical specifications of the unit. If the coupling is intact, the hydraulic pump may need to be replaced.

Activating the emergency stop button interrupts the power supply to the drive, so the motor is no longer powered and the lift table cannot move. Typically, the control voltage is not affected, meaning that a programmable logic controller (PLC) or a relay, if installed, remains powered, but the electric motor does not receive any energy.

The emergency stop button is often mistakenly used to shut down the machine, even when there is no danger. This should be prevented through proper instruction, as this use is not intended by lift table manufacturers. Especially when multiple people are working with a machine, it can easily be overlooked that the emergency stop button has been activated. To resume operation of the lift table, all emergency stop buttons must be released. Depending on the control system design, it may also be necessary to press a reset button to restore the lift table's functionality.

Hydraulic lift tables require oil to extend the cylinders and raise the platform. A low oil level in the hydraulic unit prevents the cylinders from extending, so the lift table platform does not lift.

Refill hydraulic oil through the tank's filler neck. Be sure that all cylinders are fully retracted before refilling the oil. Otherwise, the hydraulic tank may overflow the next time the cylinders retract. Also, ensure that the maximum fill level is not exceeded.

Even more important than refilling the oil is identifying the cause of the oil loss. If the lift table originally had enough hydraulic oil, the oil must have leaked somewhere. First, check all hydraulic lines for leaks. If these are in good condition, the leak is likely at the hydraulic unit or the cylinders, often due to damaged seals. The leak must be fixed before putting the lift table back into operation.

To prevent an uncontrolled downward movement of the lift table platform, the cylinders are typically equipped with a burst pipe protection. In the event of damage, a spring-loaded disc closes the flow, preventing the cylinders from retracting further. To test the functionality of this safety device, some lift table manufacturers equip their hydraulic systems with a 'bypass' line. This line includes a ball valve, which, when opened, directly connects the pressurized line to the tank, simulating a hose or pipe rupture.

The solution to this problem is relatively simple: The existing ball valve must be closed. To prevent accidental reopening, the ball valve should be secured. Typically, ball valves are equipped with a locking plate to prevent opening without tools.

The electrical control system of the lift table contains several fuses designed to protect the components from excessively high currents. At least one fuse should be present on both the primary and secondary sides of any installed transformer. A blown fuse can result in the failure of the entire control system, making it impossible to raise or lower the lift table.

If a fuse has blown, it should not simply be replaced with a larger fuse. The manufacturer of the lift table carefully selected the fuses to protect the components. Using a larger fuse could damage the components or, in the worst case, even cause a fire.

It is important to determine the cause of the fuse blowing. Possible reasons could include voltage fluctuations on the power supply side or an insulation fault that led to a short circuit.

If the lowering valve is defective, it will not open and the hydraulic oil cannot flow back into the tank. As a result, the lift table platform remains in its position and does not lower. However, it is often not the hydraulic valve itself that is defective, but rather the solenoid coil or the valve’s wiring.

A qualified electrician should first check the control voltage at the valve connector and measure whether the control voltage is present at the contacts when the lowering button is pressed.

If the wiring is intact, the solenoid coil of the valve should be tested. Many hydraulic units have multiple valves, so the defective solenoid coil can be swapped with a functional one.

If both the wiring and the solenoid coil can be ruled out as the cause of the issue, the last option is to replace the lowering valve.

Lift tables are usually equipped with a perimeter toe protection safety strip to prevent limbs or objects from being trapped between the platform and the base frame. If the safety strip is activated, the lift table cannot be lowered any further; only raising the platform remains possible.

First, it should be checked why the safety edge was activated. Often, an object is the cause, blocking the safety edge.

A possible jamming of the safety edge should also be considered and ruled out as a cause.

If neither a blockage nor jamming is present, the electrical connection of the safety strip should be inspected. A broken cable or similar defect can prevent the lift table from lowering.

The electrical control system of the lift table contains several fuses designed to protect the components from excessively high currents. At least one fuse should be present on both the primary and secondary sides of any installed transformer. A blown fuse can result in the failure of the entire control system, making it impossible to raise or lower the lift table.

If a fuse has blown, it should not simply be replaced with a larger fuse. The manufacturer of the lift table carefully selected the fuses to protect the components. Using a larger fuse could damage the components or, in the worst case, even cause a fire.

It is important to determine the cause of the fuse blowing. Possible reasons could include voltage fluctuations on the power supply side or an insulation fault that led to a short circuit.

This issue can occur if one of the following activities was recently performed:

• Replacement of the lowering throttle
• Changing the lowering throttle setting
• Replacement of the burst pipe protection

Burst pipe protections respond to pressure differences between the supply line and the lift cylinders. In the event of a pipe rupture, the pressure in the supply line would suddenly drop to 0 bar, causing the spring in the burst pipe protection to close the flow opening. This prevents further lowering of the lift table.

A malfunction can occur if the characteristics of the burst pipe protection do not match the settings of the lowering throttle. A flow rate that is too high can cause the burst pipe protection to interpret this as a defect in the supply line, causing the valve to close and preventing the platform from lowering.

This issue can only be resolved by a qualified technician. To reopen the burst pipe protection, the lift table must first be raised. The lowering throttle should then be adjusted to achieve a lower flow rate of hydraulic oil. Subsequently, the platform can only be lowered at a reduced speed. It is crucial to ensure that the lines to be opened are depressurized when performing this work.

When the emergency stop button is pressed, the power supply to the lowering valve is interrupted. As a result, the valve cannot be opened via the solenoid, and the lift table remains in its current position.

In this case, releasing all emergency stop buttons is sufficient. Depending on the control system design, it may also be necessary to press a reset button to restore the lift table's movement.

A pressure relief valve protects the lift table from overload, but only during lifting. If loading and unloading the lift table is possible at multiple stops, an electronic pressure switch is often installed. This switch is connected to the control system and locks the lifting and lowering movements of the platform as soon as a programmed pressure is exceeded. In most cases, operation can be resumed immediately after the overload is removed and the error is acknowledged.

How does this fault manifest itself?
Air in the hydraulic system can cause problems because it can lead to uncontrolled movements of the lift table, as the compressibility of air is significantly higher than that of hydraulic oil.

Consider a situation where a load is lifted solely by the hydraulic oil in the cylinders. After the load is applied, the hydraulic oil is compressed, reducing its volume. The cylinders do not extend as much as they would without the load (with a constant amount of oil). However, if there is air in the hydraulic system, it will also be compressed. Due to its higher compressibility, the volume change is much greater at the same pressure, causing the platform to noticeably sink. If air enters the hydraulic system multiple times during the lifting process, this effect repeats and is perceived as jerking.

The solution:
To eliminate the jerking, the hydraulic system must be properly bled by a qualified technician.

If the lift table manufacturer has provided a bleed screw on the cylinder, bleeding is usually straightforward: The limit switches must be bypassed or disconnected, the bleed screw slightly opened and the lift table driven with pressure against its upper end position. The escaping hydraulic oil should be collected with a cloth until only oil without air bubbles comes out. Please observe the maximum duty cycle and the manufacturer's instructions.

For cylinders without bleed screws, the hydraulic connection must be slightly loosened. When the cylinder is then pressurized slightly, some hydraulic oil will escape. Once no air bubbles are visible in the hydraulic oil, the hydraulic fitting can be tightened again. When loosening the hydraulic line, it is crucial to ensure that the line does not tear away from the cylinder. Always use maintenance supports and wear appropriate protective gear (safety glasses, gloves etc.).

Contaminated bearing tracks can prevent the free rolling of the movable bearing roller. The contamination may either be rolled over or pushed back and forth by the movable bearing roller, which can cause jerking. Additionally, there is a risk that foreign particles could penetrate the bearing track or the movable bearing roller, leading to long-term impairment of the lift table's operation.

To avoid such problems, manufacturers recommend regular cleaning of the lift table, particularly the bearing tracks. The frequency of cleaning depends on the local operating conditions and therefore cannot be universally prescribed.

With increasing usage time, it may become necessary to re-lubricate the bearings of the lift table or, in the case of non-lubricatable bearings, to replace them entirely.

Lift tables with a high cycle rate typically have lubricatable bearings. These bearings can be re-lubricated either through a central lubrication system or directly at the grease fittings.

Standard lift tables, on the other hand, are usually equipped with maintenance-free sliding bearings that are designed to match the planned service life of the lift table. However, if a bearing failure occurs, the manufacturer can replace the bearings. Depending on the extent of the damage, it may also be necessary to replace bearing pins and other adjacent components.

Just as with jerky lifting, jerky lowering of the lift table can also be caused by air in the hydraulic circuit. The solution is to have the hydraulic system bled by a qualified technician.

If the hydraulic cylinders are equipped with a bleed screw, you can easily loosen it and drive the lift table against its upper end stop (disconnect the limit switch). The escaping hydraulic oil should be collected with a cloth. Continue driving the lift table against the stop until only hydraulic oil without air bubbles comes out of the bleed screw. Be sure not to exceed the maximum duty cycle specified by the manufacturer.

For cylinders without a bleed screw, the hydraulic fitting on the cylinder must be slightly loosened. Then, perform the bleeding procedure as described above. Ensure that adequate safety precautions are taken, especially to avoid the risk of hose rupture.

Contaminations on the roller bearing track can impair the smooth operation of the moveable bearing roller. In most cases, this problem can be resolved with a simple cleaning. Use a hand brush and a cleaning cloth to thoroughly clean the tracks.

Ensure that the maintenance supports are properly in place during all maintenance work beneath the platform.

If the hydraulic cylinders remain extended for an extended period, the piston rods may dry out. The lubrication film necessary for smooth retraction is missing, which can cause the platform to lower jerkily.

To resolve this issue, soak a clean cloth in hydraulic oil and gently rub it on the piston rods of the hydraulic cylinders. This will restore the lubrication film.

Before lift tables are shipped, manufacturers usually subject them to extensive testing. Therefore, the issue described here is rare. However, it can happen that in some new lift tables, the cylinder seals are still very tight, leading to increased resistance when retracting.

To resolve this issue, it is recommended to use the lift table continuously. With regular use, the seals will settle and the resistance will gradually decrease.

A broken cable in the wiring of the safety strips can, similar to a jamming of the safety strips, cause the lift table platform to lower in jerks. An intermittent contact due to the broken cable can be interpreted by the control system as a brief activation of the safety strips. This results in the sudden stopping of the lowering movement of the lift table.

A low oil level or loss of hydraulic oil can prevent the lift table from reaching its upper position. In this case, the hydraulic pumps lack the necessary oil to fully extend the cylinders.

First, check for any hydraulic oil leaks and repair them. Then, refill the tank of the hydraulic unit. Ensure that all cylinders are fully retracted and do not exceed the maximum fill level.

Most lift tables use electromechanical switches to detect the upper and lower lift positions. These switches are necessary to turn off the hydraulic unit at the upper position and to close the lowering valve at the lower position.

Typically, the limit switches are mounted so that the end positions can be adjusted flexibly. During transport of the lift table, the switches may shift, causing the lift table to stop at the wrong position.

To correct this error, the limit switches need to be readjusted. Move the lift table to the desired end position and adjust the limit switch until you hear it engage.

A leak in the hydraulic line or improperly tightened connections can cause hydraulic oil to escape from the pressure line. This missing oil prevents the cylinders from staying extended, causing the platform to lower.

If you notice oil loss around the connections, carefully tighten the relevant fitting. Be cautious not to overtighten hose fittings, as this could cause the hose to burst. Hoses should only be tightened to a snug fit by hand.

The seals of the hydraulic cylinder can also be a potential source of a leak in the hydraulic circuit. A defect in the cylinder seal requires a replacement, which typically can only be performed by the manufacturer of the hydraulic cylinders.

Check valves are used to block the flow of oil in one direction. A common example is the check valve located just after the pump, which prevents pressurized hydraulic oil from flowing back from the cylinders to the tank through the pump.

These valves work through a combination of a ball, spring and ball seat that seals the flow opening. If the ball seat is contaminated, the ball may no longer seal properly. This allows hydraulic oil to flow back into the tank, causing the platform to lower.

Minor contamination can often be resolved by simply flushing the valve, meaning repeated raising and lowering of the lift table platform may help. For more severe contamination, the check valve must be removed and thoroughly cleaned, for example, using compressed air. In the worst case, the valve may need to be replaced.

Some lift tables are equipped with an emergency lowering valve. This valve allows the platform to be lowered even if the control system or power supply fails. If the emergency lowering valve is open, the platform will lower.

However, there should generally be no issues with a permanently open emergency lowering valve, as most of these valves are self-resetting and automatically close again.

The lowering valve connects the pressure line directly to the hydraulic tank. If the lowering valve is contaminated, it has similar effects to a contaminated check valve: Hydraulic oil flows from the cylinders back into the tank, causing the lift table platform to lower.

First, try flushing the valve by repeatedly raising and lowering the platform. If the problem persists, the valve should be removed and thoroughly cleaned with compressed air. If cleaning is unsuccessful, the last resort is to replace the valve.

Most lift tables are equipped with maintenance-free plain bearings. However, these are not completely immune to wear or defects. If you hear a noise coming from the direction of the scissor bolt, the movable bearing or the fixed bearing of the lift table, this could indicate a bearing defect.

A slight 'gurgling' sound often indicates air in the hydraulic system. First, check the oil level of the lift table, ensuring that all hydraulic cylinders are fully retracted. If hydraulic oil is missing from the tank, identify and fix the cause if necessary. Then, refill the hydraulic oil.

Since the procedure for bleeding the hydraulic system has already been described several times in this article, we refer you to the section 'Lift table raises in jerks -> Air in the hydraulic system.'

If the noise is coming from the area of the hydraulic unit, this could indicate a defect in the pump or electric motor, often caused by bearing damage. Fixing this issue is usually not straightforward. Often, a complete replacement of the hydraulic unit is the quicker and more cost-effective solution.

If the lift table is brand new or electrical work was recently performed, the unit might be running on only two phases instead of three. This should be checked and corrected by a qualified electrician.

If the lift table is operated near or above its load limit, it may happen that hydraulic oil is directed back to the tank through the pressure relief valve (PRV). The PRV acts as an overload protection in the hydraulic circuit and protects the components from excessive pressure. If the operating pressure exceeds the set PRV value, oil flows back into the tank.

In a tightly constrained load range, this can cause the lift table to still raise, but very slowly. The resulting acceleration forces cause the PRV set pressure to be exceeded, resulting in some of the hydraulic oil flowing back to the tank. This means that the full flow rate of the pump is not available for the lifting movement and the lifting speed is greatly reduced.

This operating condition should be avoided. A slower lifting speed leads to a longer runtime of the unit, which results in increased heat generation in the hydraulic oil. This overheating can damage the hydraulic components. The load should be reduced immediately.

If an overload can be ruled out, the issue likely points to a defect in the hydraulic pump. In this case, a replacement is unavoidable. It is recommended that this work be carried out by the lift table manufacturer.

In some cases, the problem could also be caused by a continuously activated lowering valve, especially if recent work has been done on the lift table’s electrical system or control unit. If the lowering valve remains open and the installed throttle allows less oil to pass through than the pump can deliver, this will result in a reduced lifting speed. By unplugging the lowering valve connector, you can quickly confirm or rule out this as the source of the problem. The same applies to any installed bypass.