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Fault Diagnosis Of Hydraulic Cylinders
Apr 27, 2017

Hydraulic cylinder is the hydraulic system to convert hydraulic energy to mechanical energy of the actuator. The faults can be summed up as the hydraulic cylinder misoperation, unable to push the load and the piston slip or crawl. Because of the malfunction of the hydraulic cylinder causing the equipment downtime, it is important to attach importance to the fault diagnosis and maintenance of the hydraulic cylinder.

Fault Diagnosis and treatment

1, false action or action malfunction

There are several reasons and treatments:

(1) Valve spool stuck or valve holes clogging. When the flow valve or direction valve core is stuck or valve holes plug, the hydraulic cylinder prone to misoperation or action failure. At this time, the contamination of the oil should be inspected; check whether the dirty or colloidal sediment is stuck in the spool or plug the valve hole; Check the body wear condition, wash, replace the system filter, wash the tank, replace the hydraulic media.

(2) The piston rod is jammed with the cylinder barrel or the hydraulic cylinder. At this time anyway, the hydraulic cylinder is not action or very little action. At this time, the piston and piston rod sealing is too tight, whether to enter the dirt and colloidal sediment: the piston rod and cylinder shaft is right, vulnerable parts and seals are invalid, the load is too large.

(3) Hydraulic system control pressure is too low. The throttle resistance in the control pipeline may be too large, the flow valve is improperly regulated, the control pressure is inappropriate, the pressure source is disturbed. At this time, the control pressure source should be inspected to ensure the pressure regulation to the system's prescribed value.

(4) The hydraulic system enters the air. Mainly because there are leaks in the system. At this point should check the hydraulic tank level, hydraulic pump oil suction side seals and fittings, oil suction coarse filter is too dirty. If so, you should supplement the hydraulic oil, handle the sealing and fitting, wash or replace the coarse cartridge.

(5) The initial action of the hydraulic cylinder is slow. In the case of low temperature, the viscosity of hydraulic oil is large, the fluidity is poor, which causes the hydraulic cylinder to move slowly. The improvement method is to replace the viscous temperature performance of the hydraulic oil, at low temperature can be used by heaters or by the machine itself heating to enhance the start-up of oil temperature, the normal operating system of oil temperature should be maintained at about 40 ℃.

2, not driving load at work

The main performance is the piston rod stopping, the thrust is insufficient, the speed drops, the work is unstable and so on, the reason is:

(1) internal leakage of hydraulic cylinder. The internal leakage of the hydraulic cylinder comprises the leakage of hydraulic cylinder seal, piston rod and sealing seal and excessive abrasion of piston seal.

The reason for sealing leakage of piston rod and seal cover is that the new seal should be replaced by crease, extrusion, tear, abrasion, aging, metamorphism, deformation and so on.

The main reason for excessive wear of piston seals is that the speed control valve is improperly regulated, causing excessive back pressure and improper installation of sealing parts or hydraulic oil contamination. Secondly, there are foreign bodies in the Assembly and the quality of sealing materials. The consequence is that the movement is slow and powerless, and it will cause damage to the piston and cylinder, and the phenomenon of "pulling cylinder" appears. The processing method is adjusting the speed control valve, and the necessary operation and improvement should be made against the installation instructions.

(2) Hydraulic circuit leakage. including valves and hydraulic piping leakage. The overhaul method is by manipulating the reversing valve to inspect and eliminate the leakage of the hydraulic connecting pipe.

(3) Hydraulic oil through the overflow valve bypass back to the tank. If the overflow valve enters the dirty material card spool, so that the overflow valve is often opened, hydraulic oil will flow through the overflow valve bypass directly back to the tank, resulting in the hydraulic cylinder oil into. If the load is too large, the relief valve adjustment pressure has reached the maximum rated value, but the hydraulic cylinder still does not get the thrust of continuous action required without action. If the adjustment pressure is low, the pressure is insufficient to achieve the required vertebral force, performance is not thrust enough. The overflow valve should be inspected and adjusted.

3, piston slip or crawl

Hydraulic cylinder piston slip or crawl will make the hydraulic cylinder work unstable. The main reasons are as follows:

(1) The internal Shang of the hydraulic cylinder. The internal parts of the hydraulic cylinder are improperly assembled, deformed, worn or the tolerances of the shape and position are excessive, the movement resistance is too large, so that the piston speed of the hydraulic cylinder varies with the position of the stroke, and the slip or crawl occurs. Most of the reasons are due to poor parts assembly quality, surface scars or sintering produced iron filings, so that resistance increases, the speed drops. For example: piston and piston rod with different heart or piston rod bending, hydraulic cylinder or piston rod to the rail mounting position offset, sealing ring mounted too tight or too loose. The solution is to repair or adjust, replace damaged parts and remove iron filings.

(2) Poor lubrication or machining of hydraulic cylinder bore diameter. Because the piston and cylinder, rail and piston rod and so on have relative motion, if bad lubrication or the hydraulic cylinder aperture ultra poor, will aggravate the abrasion, so that the centerline of the cylinder line decreases. In this way, the piston is working in the hydraulic cylinder when the friction resistance will be small, resulting in slip or crawl. The elimination method is to grind the hydraulic cylinder first, and then according to the requirements of the preparation of piston, grinding piston rod, configuration guide sleeve.

(3) Hydraulic pump or hydraulic cylinder enters the air. Compressed or inflated air can cause the piston to slip or crawl. The exclusion measure is to check the hydraulic pump, set up special exhaust device, fast operation full stroke round-trip exhaust.

(4) The seal quality is directly related to slippage or creep. o SEAL ring in low pressure, and U-shaped seal ring comparison, due to high surface pressure, static and dynamic friction resistance difference, easy to create slip or crawl; the face pressure of U-shaped seal rings increases with the increase of pressure, although the sealing effect is improved correspondingly, however, the difference between static and dynamic friction resistance is also larger, internal pressure increases, the impact of rubber elasticity, due to the increase of contact resistance to lip flange, sealing ring will be tilting and lip elongation, also prone to slip or crawl, to prevent its tipping can be used to maintain its stability.

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