3. Trouble diagnostics

3.Trouble diagnostics

Hydraulic cylinder trouble, countermeasure and solution

It is not easy to discover trouble locations.The table below shows general symptoms, suggested causes and also solutions.

For repairs, see the suggested causes and solutions in the table.

The cause of machine problems are often not rooted in just a single part. Problems are often due to the relationship of one part with another.In some cases, solutions are required other than those given in the table.In such a case, contact with our company to investigate the problem and its cause further and take appropriate measures.

Item Symptom 1 Piston rod sliding section oil leak (4)Inspection after assembly".) (For the judgment values, see "5. 2 Cylinder head matching section oil leak 3 Pipe and cylinder tube welding section oil leak 4 Operation defect

Item Symptom Related part Symptom

Piston rod A sliding surface has rust and scratches that catch on a fingernail.

1 Piston rod sliding section oil leak Plating is peeling off.

There is foreign matter caught in the inner or outer diameter section. Countermeasure and solution ① Remove the scratches with a whetstone to make the sliding surface smooth (1.5 s or lower).If the oil leak continues, the rod scratches may have damaged the U-ring or other seal, so disassemble and inspect. ② If the scratches or rust cover too large an area to be repaired with a whetstone, replace the piston rod and the U-ring, wiper ring, or other seal and the piston rod bearing part. ① Replate or replace the piston rod. ② At this time, inspect the seals and piston rod bearing part as well and replace any that are damaged.

① Remove the foreign matter. ② If the packing is damaged, replace it.

Rod packing (Buffer ring and U-ring) There are scratches on the inner or outer diameter section.

The lips and groove section are locally carbonized (scorched). Replace the part.

① This may be scorching due to adiabatic compression of air remaining in the cylinder. ② When operating the cylinder for the first time after replacing a packing, run at low pressure and low speed to adequately bleed off the air.

Item Symptom Related part Symptom Countermeasure and solution

1 Piston rod sliding section oil leak Rod packing (Buffer ring and U-ring) The packing has lost its rubber elasticity and is in tatters.

The lip section is defective all the way around.

There is major extrusion of the packing heel section.

Backup ring The part is greatly deformed. ① Replace the part. ② This may be the end of the packing service life, deterioration of the hydraulic oil, or high temperature of the hydraulic oil. a. Replace the hydraulic oil. b. Check the temperature of the hydraulic oil.(The oil temperature should be no higher than 80 ℃ .) c. Check for local high temperature. ① Replace the part. ② Abnormally high pressure may be operating on the packing. a. Check the pressure during operation. b. There may be trouble with the buffer ring section. Inspect the buffer ring section. ① As a rule, replace the rod packing too at the same time. ② Abnormally high pressure is often the cause.The check items for this are the same as those given above for packing heel section extrusion.

Wiper ring

Bearing part (bushing) There is foreign matter caught in the lip. Remove the foreign matter. The lip is damaged.There is other abnormal damage. Replace the part.

There is major wear of the bushing and the gap with the piston rod exceeds the limit on inner diameter wear in "5. (9)Usage limits". Replace the part.

There are large scratches on a sliding surface. ① Replace the part. ② Inspect the piston rod sliding surfaces for scratches and rust.

Cylinder head A seal mounting section has scratches and rust. ① Remove the scratches or rust with a whetstone. ② If the repair does not solve the problem, replace the cylinder head.

Item Symptom Related part Symptom Countermeasure and solution

O-ring There is foreign matter caught in the inner or outer diameter.There is damage to the O-ring.

① Remove the foreign matter. ② If the O-ring is damaged, replace it. ③ Tube interior surface inspection: If there are any scratches or rust, use a whetstone to make the surface smooth. ④ Cylinder head O-ring groove inspection: Same as above ⑤ Backup ring inspection: If the backup ring is deformed or extruded, replace it. Check the above and replace the O-ring. Backup ring The part is deformed or extruded. Replace together with the O-ring.

2 Cylinder head matching section oil leak

Cylinder head A part is loose.

Bolt There is looseness, stretching or breakage.

Cylinder tube There is abnormal swelling. ① Disassemble the cylinder head and inspect the O-ring and backup ring.If there is damage, replace. ② Check the tube and cylinder head threads for damage and if there is any damage, replace. ③ When the inspection is complete, tighten to the specified torque. See "5. (7)Assembly procedures". ④ Stop rotation.

Replace all the bolts and tighten to the specified torque.

① Replace with a new one. ② Oil leaks at matching sections may be caused by abnormally high pressure (including cushion pressure), so if the tube is swollen or deformed, replace it with a new one.Also inspect the circuit pressure. Replace with a new one.

3 Pipe and cylinder tube welding section oil leak Pipe and cylinder tube

Oil leak from cylinder line connection section Pipe assembly There are cracks on the welding section.

Caution The crack progresses and ultimately the part fractures. A fracture is extremely dangerous, so if a crack is seen, quickly stop work and replace that part. Welding over a crack is ineffective.

Line fastening bolt is loose.

Tighten to the specified torque according to the work procedure. The line is bent. Replace with a new one.

There are scratches on a contact surface. ① Use a whetstone to make the surface smooth. ② If the oil leak does not stop, replace.

Item Symptom Related part Symptom Countermeasure and solution

Operation defect Movement is not smooth. Piston rod Cylinder tube The bending is large and exceeds the stipulated bend warp. (Bend warp: See "5. (3)Maintenance standards".) ① Replace with a new one. ② There may also be damage to seals and sliding parts, so inspect them.If there is any abnormality, replace.

Cylinder tube There are dents. Replace with a new one.Inspect the seal and sliding parts the same as above.

Piston rod Cylinder tube Sliding part Abnormal wear of sliding parts and damaged piston section or foreign matter caught at the cylinder head sliding section ① Replace with a new one.

Inspect the seal and sliding parts the same as above. ② Remove the foreign matter.

Inspect the seal and sliding parts the same as above.

4 Piston seal There are scratches, wear, or other damage. Replace with a new one. Also inspect the cylinder tube interior surfaces.

Internal oil leak The piston rod extends and retracts on its own and drops abnormally during operation. Also, the stipulated speed is not output. Cylinder tube There are scratches and rust on interior surface. ① Use honing or a whetstone to eliminate the scratches and rust and make the surface smooth.If the scratches cover too large an area to be repaired, replace the cylinder tube with a new one. ② Replace with a new piston seal.

Piston nut Tightening is insufficient.

① Tighten to the specified torque. See "5. (7)Assembly procedures". ② The piston rod thread section could be stretched.Measure the diameter where the rod and piston fit together and if this area is tapered, replace the piston rod assembly. Valves Leak from valve. Inspect the amount of valve leakage and service.

Item Symptom Related part Symptom Countermeasure and solution

Operation is unsteady. Air

4

The impact is high when switching over between extension and retraction. Pin bushing Pin There is air remaining in the cylinder. Bleed out the air. a. Cylinder with no air bleeding

Bleed out the air by moving the cylinder back and forth at few times at low pressure and low speed. b. Cylinder with air bleeding (air breather)

After securing the machine so that the cylinder does not move, bleed the air from the air breather. [Tip]

The cylinder extends or retracts somewhat when the cylinder stops suddenly.This phenomenon occurs due to the compressibility of the hydraulic oil.This occurs particularly easily for cylinders with long strokes.

The gap between the installation section and the pin bushing is enlarged. Measure the pin and pin bushing dimensions and replace any part that exceeds its stipulated dimension.

Cylinder sliding operations make sounds. Pin bushing Pin The oil or grease feed is inadequate. Apply oil or grease. There is seizing at matching section. Replace with a new part and apply oil or grease.

Caution

The hydraulic oil expands and contracts with changes in temperature and pressure. This causes the cylinder to extend and retract too, so it can be mistaken for an internal oil leak. For internal oil leaks, always check the temperature and pressure under the same conditions.