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Home > Tech Guidance > The hydraulic cylinder profile and troubleshooting

Tech Guidance

The hydraulic cylinder profile and troubleshooting
2012-11-01 12:48:13

The hydraulic cylinder profile and troubleshooting

Hydraulic cylinder is a component that can transfer hydraulic energy into mechanical energy. And it is doing rectilinear motion.It has simple structure and can work reliably.When it is used in advance and return motion,there is no reduction gear,neither transimission gear gap.The moving is very stable.And thus hydraulic cylinder is widely applied in many kinds of mechanical hydraulic system.The hydraulic output power is in proportion to piston effective area and the two sides’ pressure difference.The hydraulic cylinder is usually composed of cylinder tube,cylinder head,piston rod,piston,seal,buffer and discharger unit.Hydraulic cylinder is the component in the hydraulic cylinder that transfer hydraulic energy into mechanical energy.And the malfunctions can be classified as hydraulic cylinder no movement,weak power not able to push load,piston slipping or creeping.Many malfuctions of the hydraulic cylinders occur and lead to the failure of machine working.And thus it is important to attach significance to diagnosing and maintenance of hydraulic cylinder.

 Hydraulic cylinder


Diagnosis and handling of malfunction

1.Hydraulic cylinder no movement or faulse movement

Reasons and handling ways

(1)Valve core locked or valve hole blocked.The locking of valve core or blocking of valve hole often lead to hydraulic cylinder no movement or faulse movement.You can check the containmintaion of oil,check whether the dirts or gelatinous sediment lock the valve core or blocked the valve hole,check the abrasion of valve.

(2)The piston rod locked with cylinder tube or the cylinder blocked.The cylinder has no reaction to the control.Please check if the piston and piston rod seal are too tighten,whether there is dirt or gelatinous sediment:the axis of piston rod and cylinder tube are of the same line,the quick wear part and seals are effective or not.

(3)The control pressure of hydraulic system is too low.The throttle resistance in the control pipe is too big,the flow valve is incorrectly controlled,control pressure not proper,pressure source is disturbed.You should check the pressure source,ensure the pressure is adjusted to the standard of system.

(4)Outside air seeps into the hydraulic system.It is because there is leakage in the system.You should check the oil level in the tank,whether the seal of hydraulic pump,pipe connection and oil suction strainerare too dirty.If so,you should add hydraulic oil,clean the seal and pipe connection,clean or replace the oil suction strainer.

(5)The initial movement of hydraulic cylinder is too slow.At very low temperature,the hydraulic oil has big viscosity,bad liquidity.And thus the movement of hydraulic cylinder is very slow.You can change hydraulic oil with better viscosity and liquidity,or you can heat the temperature oil by heater or the machine itself.

Hydraulic cylinder

2.The hydraulic cylinder can not work to push the load.Such phenomenons are like piston rod can not stop at the right place,the pushing power is weak,the velocity decreases,the reliability is bad.They may be caused by below reasons:

(1)Leakage inside the hydraulic cylinder.The leakage may occur when the seal of hydraulic cylinder tube,piston rod and seal of seal cover,piston seal have severe attrition.The leakage of piston rod and seal of seal cover comes from the seal is wrinkled,squeezed,torn,with attrition,aging,going bad,out of shape etc.You should change new seals in such cases.The attrition of piston seal lies in unproper control of velocity control valve,too high minus pressure,wrong installation of seal or oil pollution.There may be other reasons that some extra item comes in during installation or the quality of seal material is bad.All these reasons will lead to slow movement,weak power and even damage of piston and cylinder tube,pulling cylinder.You can adjust the velocity control valve,handle and improve according to the installation manual,clean the filter or replace filter core,hydraulic oil.

(2)Leakage of the hydraulic oil circuit.It includes leakage of valves and hydraulic pipes.You can examine and eliminate the leakage by operating the reversing valve.

(3)Hydraulic oil flows back to the tank by relief valve.When dirty items comes in and stock the valve core,the relief valve will keep open.Hydraulic oil will flows into the tank via the relief valve,which can result in no hydraulic oil coming into the cylinder.If the load is too big,the cylinder can not get enough pushing power to move even the relief valve has reached the biggest adjusting pressure.If the adjusting power is too low,the pressure is not high enough to push,that is weak power.You should check and adjust the relief valve then.

Hydraulic cylinder

3.Piston slips or creeps.The hydraulic cylinder cannot work stably in such case.And the reasons are as below:

(1)The inner hydraulic cylinder is too rough.The incorrect installation,out of shape,attrition of accessories,big friction of movement can lead to the piston having different velocity in different stroke,and thus the piston will slips or creeps.These are mainly because the accessories are of bad quality,there is scar or scrap iron on the surface,the resistance will increase,the velocity will decrease.For example,the axles of piston and piston rod is not in the same line,the piston rod bends.The hydraulic cylinder and piston rod have shifting fixing positon to the guide rail.The seal ring is too tighten or too loose.You should refix or adjust,replace the damaged accessories and clean iron scrap.

(2)The lubrication is bad and the hole of hydraulic cylinder is too big.The piston and tube,guide rail and piston rod have relative movement.If the lubrication is bad or the hydraulic cylinder hole is too big,the attrition will be severe.The linearity of cylinder tube axle will decreases.And thus the piston will slip or creep when working because the friction changes.You should fix and lubricate the cylinder,fix the right piston as standard,fix and lubricate the piston rod,fix the skid ring.

(3)The outside air comes into the hydraulic pump or hydraulic cylinder.The compression or expansion will lead to the piston sliping or creeping.You should check the hydraulic pump,set special discharger unit,exceed the handling of full stroke and discharge the gas for times.

(4) The quality of seal has close relation to slipping or creeping.Compared with “U” shape seal ring,the “O” shape seal ring working in low pressure has higher surface pressure and bigger difference between kineticfrictionforce and staticfrictionforce,which will lead to slipping or creeping.The ”U” shape surface pressure will increase as the pressure increase,though the seal effect will increase accordingly,the difference between kineticfrictionforce and staticfrictionforce will be bigger,too.The inner pressure will increase and effect the flexibility of rubber.Because the contact resistance of ring side increase,the seal will tip-over and the ring side will extend.This will also lead to slipping or creeping.You can use support ring to keep the ring stable.

The hydraulic oil cylinder seals

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