TROUBLESHOOTING /SYSTEM PERFORMANCE

Ｄ-1. Lift arm fails to rise or is slow to rise.

（４）Drop in shovel main relief valve pressure or faulty main pump main oil pressure value：２０．６MPａ（２１０ kgf／ｃｍ2）

Measure the shovel control valve main pressure.

Measure the main relief pressure in accordance with the descript ion in the section of measurement of system performance.

Drop in main pressure

Adjust the relief valve set pressure or replace the valve.

Oil pressure does not rise even after the abovementioned Adjust the overload relief valve, or repair or replace the main pump.

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

Ｄ-1. Lift arm fails to rise or is slow to rise.

（５）Faulty operation of priority valve

Disassemble and inspect the priority valve incorporated in t he orbitroll.

Check the spool ① for sticking and the orifice ② for clogging.

Spool is sticking and/or orifice is clogging.

Clean or replace faulty parts.

Normal

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

Ｄ-1. Lift arm fails to rise or is slow to rise.

（６）Damaged to piston seals in lift cylinder

Check the lift cylinder for internal leakage.

1. Tilt back the bucket and lower the lift arm to the lowest pos ition.

2. Disconnect the hose ① from the cylinder bottom. Close the dis connected end of the hose ① with the plug ② to prevent fluid from spouting from th e hose.

3. Start the engine and move the control lever to the "Lower" po sition to apply pressure to the piston rod (cylinder head) end.

Caution: Be careful not to let the control lever move into th e "Float" position from the "Lower" position.

4. If fluid flows out of the cylinder port ③, the cause can be d etermined to be damaged to piston seals in the cylinder. Repair the lift cylinder.

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

Ｄ-1. Lift arm fails to rise or is slow to rise.

（７）Broken couplings and worn splines in HST pump and main pump

If the lift arm does not operate at all when the shovel control lever or steering wheel is operated, start the engine to check whether the travel system (H ST system) is normal.

Faulty travel operation

Worn spline of the coupling ① in the main pump or broken coupling ② or worn spline in the HST pump

Repair or replace faulty parts.

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

Ｄ-2. Lift arm exclusively lowers (drifts) when control valve is in "Hold (Neutral)" position

The Amount Of The Lift Arm Drift

When a user complains that the lift arm lowers with the control valve in the "Hold Neutral)" position, first check that the amount of the drift is within the standard value (normal).

1. Measure the “natural depression distance of hydraulic cylinde r” in accordance with the description in the section of measurement of system perfo rmance.

2. Refer Performance standard list for standard value.

Much larger than standard value Within the standard value

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

Ｄ-2. Lift arm exclusively lowers (drifts) when control valve is in "Hold (Neutral)" position

To Piston Seals In Lift Cylinder

the lift cylinder for internal leakage.

1. Tilt back the bucket, then lower the lift arm to the lowest p osition.

2. Remove the hose ① from the cylinder bottom end and close the disconnected end of the hose ① with the plug ② to prevent oil from spouting from the hose.

3. Start the engine and move the control lever to the "Lower" po sition to apply pressure to the piston rod (cylinder head) end.

Caution: Be careful not to let the control lever move into th e "Float" position from the "Lower" position.

4. If oil flows out of the cylinder port ③, the cause can be determined to be damaged piston seals in the cylinder. Repair the lift cylinder.

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

Ｄ-2. Lift arm exclusively lowers (drifts) when control valve is in "Hold (Neutral)" position

oil-tightness of control valve lift spool

and inspect the control valve.

1. If there are dents, scratches, rust and corrosion on the surf aces of the spool ① and housing ②, rectify them with a #2000 emery paper or oil stone .

2. If they are beyond repair, replace the section assembly. Repair the control cylinder or replace the section assembly.

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

D-3.Lift cylinder does not generate enough force to raise frontwheels off ground

（１）Faulty operation of antipode valve

If drift of the lift cylinder is normal but the cylinder cannot generate a force enough to raise and hold the front wheels off the ground, remove the antipode valve and inspect it.

1. If the poppet seal surface ② of the antipode valve ① is in po or contact with its seat, pressure oil in the piston rod side flows directly to the drain circuit through the antipode valve, so that the lift cylinder cannot generate power to raise and hold the front wheels off the ground.

Clean or replace antipode valve.

Troubleshooting

TROUBLESHOOTING /SYSTEM PERFORMANCE

D-4. Lift arm drifts quickly at specific position

（１）Bulged or scratched cylinder tube

Measure the inside diameter of the cylinder tube at several loca tions to check for a bulge. Also check the rubbing surface for dents and scratches.

Standard inside diameter：７０ｍｍ

Repair or replace the cylinder tube.

（１）Faulty operation of load check valve

If drift of the lift arm is normal but the lift arm momentarily lowers and then starts to rise when the lift lever is moved to the "Raise" position with the bu cket loaded, remove and check the load check valve for the lift position.

１．When the load check valve is normal, fluid can flow in the directions indicated by arrows →, but not in the directions indicated by

２．Therefore, even if the pressure P1 acting on the lift cylinder piston becomes greater due to the load on the bucket than the pump pressure P2, the lift arm does not lower.

３．However, if the poppet seat ① surface is damaged, foreign matter is jammed, the poppet is sticking or the springs ② is damaged, the fluid on the P1 side flows to the P2 side, causing the lift arm to lower momentary.

Clean or replace the load check valve.

Troubleshooting