Forklifts hydraulic system troubleshooting

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Forklift hydraulic system is an important part of the forklift, devices and steering systems are driven by

hydraulic system. Therefore, forklift hydraulic system quality directly affect the performance of the

forklift. Hydraulic system failures are generally not complicated, most of the fault is reflected in the

implementing agencies, but to specifically identify the fault location and cause of the malfunction, not an

easy task, because the reasons for the phenomenon of the same fault may be a factor in the hydraulic system ,

it could be the combined effects of a variety of factors. In addition, the hidden hydraulic failure, can not

give the inspectors to provide reliable information in the industry, however, a variety of methods can be used

to diagnose system failures as soon as possible, and strive to improve their diagnostic reliability. Common

fork attachment
 hydraulic system fault diagnosis method is as follows.

1, the fault classificationbucket teeth


The hydraulic system failure rate is generally the working process of the forklifts hydraulic system can be

divided into three stages:

Early stages: the normal work of a new forklift at the factory or after overhaul debugging, beginning work at

this stage, the failure rate is relatively high, mainly because of the design may be inadequate, inappropriate

or quality of components used, but Guan, comp onents and piping cleaning is not thorough, and improper

assembly. Failure phenomenon of vibration, leaks, system pressure instability, instability of the actuator

movement, and the temperature is too high. If you take the appropriate measures, the failure rate will

gradually decline.

Run the middle stage: forklift at this stage, the lowest failure rate, triggering 70% -80% of the main reason

of failure is caused by the hydraulic oil contamination or deterioration. Hydraulic oil contaminants in

partial or complete blockage of an orifice or throttle gap of the components to change the system performance

caused by component movement disorders or total failure. Such as multi-way valve, safety valve and relief

valve of the steering system instability, random drift, pressure can also cause the slide valve resistance

increases as well as body movements reflect retardation.

Run an advanced stage: the forklift near the overhaul running late, due to the increase of relative motion

part of the amount of wear of hydraulic components, seals wear or aging and other reasons, the failure rate

increases. Failure phenomenon most of the performance of external leakage to increase the efficiency of the

whole system down and footed.

2, on-site diagnosis

Prior to this, most of the forklift hydraulic system fault diagnosis using the following methods: experience

in France, with years of practical experience of the staff to diagnose the fault system; test method to test

the fault detection, fault system, to determine the cause of the malfunction ; computer law, the use of the

hydraulic system fault diagnosis expert system software failure analysis; replacement method, replacement of
components or analog method to determine the fault location.

The above four methods have their advantages and disadvantages: alone experienced staff has extensive

experience in, otherwise it will lead to blind operation. Fault detection or computer software is the need for

expensive test equipment, high cost and the actual operation is more complex. Replacement method to a certain

blindness. Forklift hydraulic system fault diagnosis is the best way to experience and replacement wears

collectively referred to as the method of logical reasoning. Specific steps are as follows:

Failure to understand the phenomenon. First need to investigate more thoroughly the forklift is a failure in

what circumstances, whether to adjust or repair the component, if the system but also action, must be

personally observed the failure phenomenon.

Analysis of structural works on the forklift hydraulic system diagram for detailed analysis. Familiar with the

structure, working principle and characteristics of each component to determine the cause of the malfunction

by-point analysis of failure phenomena.

Diagnostic measures. The general cause of the malfunction by visual judgment and analysis system. Visual

observation of the action of the each component, the oil level is normal, look oily and systems whether the

vibration amplitude anomalies. Hearing to judge whether the hearing system noise, the relief valve howling

agency action, the impact sound is too large. Touch hand touch pumps, valves and piping and other hydraulic

components, observation equipment if the temperature is too high, abnormal vibration, or whether the drying

phenomenon. Sense of smell smell hydraulic oil odor of deterioration due to overheating of hydraulic oil to

rubber parts to an abnormal odor and hydraulic pump sintering smell.

Exclusion to judge. By the failure to understand the phenomenon, the analysis of causes and check the fault

phenomena steps, you can list the possible cause of the failure itemized reasons and faulty components, and

then use process of elimination, first the components of the easier to check to troubleshoot or determine.

This will focus on some of the more complex components, and then using the substitution method have questions

about the components of the same specifications as the qualified component replacement test. Generally through

the above process, the general failure of the truck hydraulic system can be an effective judgment and

exclusion.

3, fault diagnosis example

Lifting hydraulic cylinder failure: forklift engine speed is increased slowly tilt hyd raulic cylinder action.

Baoji CPC2 forklift engine in the idle state (about 600r/min), forklift no-load, the lifting hydraulic

cylinder, hydraulic cylinder tilt and steering system can work properly. When the throttle, the engine speed

is increased, lift hydraulic cylinders and hydraulic tilt cylinder slow, creeping phenomenon. This phenomenon

is exacerbated as the engine speed increases, but the steering system can still work, you can hear the system

issued a regular noise.

The Baoji CPC2 forklift hydraulic system including the Hydraulic systems and hydraulic steering system in two

parts. Learned using the site, the forklift is already running the mid-stage, first of all should be excluded

from the design unreasonable factors listed in logical analysis of failure phenomena in Figure I (see Figure

1) analysis of the system principle. From the figure and the above sympto ms, the first can rule out the

possibility of multi-valve fluid flow through the fault. In Figure 1, right side of the valve oil flow through

the four possible fault is: the oil pressure is not enough, a decrease of the rate-limiting valve failure, the

pipeline blockages and insufficient flow. Down the speed limit valve and piping blockage fault factors can be

excluded based on practical experience, check and focus on enough oil pressure and flow rate less than two

cause of the malfunction.

Lifting hydraulic cylinder leakage (the grounds of the judgment-by-inspection measures can be seen, if within

the drain lift hydraulic cylinder deflated plug will have hydraulic oil outflow), the pipeline without

leakage; a metal rod close to the at the safety valve on the multi-way valve, listen with the ear, not hear

the overflow s ound, which indicates that not enough oil pressure will not be the main reason for failure.

Touch the pump, I feel the vibration. Correspond to changes in engine speed, low noise can hear the pump

issued preliminary judgment pump faulty. Inadequate flow of fault analysis, the lack of pump oil is the main

reason. According to the circumstances of observation and the use of time that the pump speed factor is not

the cause of the malfunction. Therefore, the only fault factor in the lack of pump suction. Judgment and so,

when removing the pump suction line to check and found that the accumulation filter piece, clear the filter

films and other debris in the vicinity of the pump suction port, re-installed on a new oil filter, by running

test The system is working properly.

Failure: Forklift repair debugging found that the tempe rature of hydraulic oil tank. A of Baoji CPC3A forklift

ongoing repair, commissioning, its no-load or full load hoisting speed can meet the design requirements,

steering systems work properly, but forklift launch 1Omin about the hydraulic oil tank temperature $ 80 ° C

and rising trend.

According to the characteristics of the failure phenomenon and forklifts initial run, you can list the fault

logic diagram shown in Figure 2. In accordance with the fault diagnosis method of examination did not hear the

relief valve overflow sound; hand-touch multi-way valve did not feel the vibration phenomenon. Unloaded or

fully loaded lifting speed can achieve the design requirements of the phenomenon, can be excluded multiple

valve failure factors. So that the problem is concentrated in the shunt valve for the overflow and the pump is

faulty for two reasons. Excluded absorbing poo r, the oil viscosity inappropriate attentively listened to,

touch and observe the pump working conditions and found that the mechanical failure of the pump is unlikely,

the problem would be concentrated in the shunt valve. Open the shunt valve and found no anomalies, but found

that the oil return port of the shunt valve in the steering does not work when there is no hydraulic oil

outflow. Steering does not work, there are hydraulic oil outflow. Determine the fault occurred in the steering

on this phenomenon. Replacement of the new steering, failure to exclude. By check steering gear with the

original design should be as happy without reaction, install the steering happy to have a reaction, it created

a steering relief valve often overflow diversion in the median, causing the system heat.

Failure: hydraulic transmission Forklift maintenance advance II block speed. A hydraulic transm ission Forklift

two conservation the following faults: hanging I block normal, not only did not hang II block II block should

be the speed, but I block speed. Dismantling the gearbox to see I gear clutch drum surface due to friction

heat generated into the purple and blue, forward I blocked the two under the clutch gear driving gear and

input shaft I gear are not free to rotate to prove that the clutch internal The friction plate has been burnt.

Disintegration I gear clutch and found that the clutch shaft (gearbox input shaft) lubricants Road has been

aluminum plug the piston on the back of a large agglomeration of aluminum powder, clutch master, driven

friction disc sintered at high temperature as a whole, can not be separated. In addition, the gearbox at the

bottom of the outer layer of the cylindrical filter wire has been completely stripped broken, to be crushed

in to a block granular. Only the torque converter in the forklift hydraulic drive system have aluminum, so the

torque converter to the disintegration of the overhaul, you can see the turbine on the back of severe grinding

marks, aluminum powder is resulting.

The cylindrical metal filter of the forklift with the adhesive sticking to the filter holder, thus judged,

after a long soak and vibration in the 80 ~ 90 ℃ oil and metal filter gradually loosened, and ultimately out

of the filter net fixation, transmission gear broken and crushed into blocks of granular into the torque

converter in the fluid circulation line, continue to hit the turbo back in the high-speed operation, produce

large amounts of aluminum powder. Aluminum transmission flow back through the circulation line into the I gear

clutch lubricant Road and congestion, the clutch in the case of lack of lubrication high-speed rotation to

produce high temperature, resulting in the sintering of the friction plate. In this way, hanging forward II

block, in fact, drive two pairs of gear pair: the input shaft gear and output shaft gear gear and driving gear

and output shaft II gear pair. Since I block the transmission of the gear pair Vice transmission gear ratio is

greater than II, so the ultimate role of the I gear Vice II gear clutch in a slipping state, the frictional

resistance of the friction plate under the hanging II block when forward speed is slower than I block. After

the last replacement of damaged parts, according to specifications to repair the fault and eventually

disappear.