Fault Diagnosis of Hydraulic Cylinder

Hydraulic cylinder is a hydraulic system to convert hydraulic energy into mechanical energy executive components, belong to hydraulic parts. The fault can be summarized as hydraulic cylinder misaction, inability to push the load and piston slip or crawl. Due to the failure of hydraulic cylinder and resulting in equipment shutdown phenomenon is not uncommon, therefore, we should pay attention to the hydraulic cylinder fault diagnosis and maintenance work.

Failure of Action

The reasons and treatment methods are as follows:

1. The spool is stuck or the valve hole is blocked. When the flow valve or direction valve spool is stuck or the valve hole is blocked, the hydraulic cylinder is prone to misoperation or operation failure. At this time should check the oil pollution situation; Check whether dirt or glial sediment is stuck in the spool or blocked valve hole; Check wear condition of valve body, clean and replace system filter, clean tank, replace hydraulic medium.
2. The piston rod and cylinder are stuck or the hydraulic cylinder is blocked. No matter how to operate at this time, the hydraulic cylinder does not move or little action. At this time should check whether the piston and piston rod seal is too tight, whether into the dirt and glial precipitate: piston rod and cylinder shaft line is in the middle, wearing parts and seals are failure, the load is too large.
3. The hydraulic system control pressure is too low. The throttle resistance in the control line may be too large, the flow valve is not adjusted properly, the control pressure is not appropriate, and the pressure source is disturbed. At this time, check the control pressure source to ensure that the pressure is adjusted to the specified value of the system.
4. Air is entered into the hydraulic system. Mainly because there are leaks in the system. At this time, the liquid level of the hydraulic tank should be checked, the seals and pipe joints on the suction side of the hydraulic pump, and whether the crude oil filter is too dirty. If so, the hydraulic oil should be replenished, seals and fittings should be treated, and the coarse filter element should be cleaned or replaced.
5. The initial action of the hydraulic cylinder is slow. In the case of low temperature, hydraulic oil viscosity is large, poor liquidity, resulting in slow hydraulic cylinder action. The improvement method is to replace the hydraulic oil with better viscosity and temperature performance. At low temperature, the oil temperature can be improved by heating the heater or heating the machine itself, and the oil temperature of the system should be kept at about 40℃ for normal operation.

Load Cannot be Driven While Working

The main performance is inaccurate piston rod stop position, insufficient thrust, speed decrease, unstable work, etc. The reasons are as follows:

1. Internal leakage of hydraulic cylinder. The internal leakage of hydraulic cylinder includes the leakage caused by excessive wear of hydraulic cylinder block seal, piston rod and seal cover seal and piston seal.

The cause of sealing leakage of the piston rod and the sealing cover is that the sealing parts are wrinkled, squeezed, torn, worn, aging, deterioration, deformation, etc., at this time, the new sealing parts should be replaced.

Excessive piston seal wear is mainly caused by improper speed control valve regulation, resulting in excessive back pressure and improper seal installation or hydraulic fluid contamination. Secondly, when assembling, foreign bodies enter and the quality of sealing materials is not good. The result is slow action, weak, serious will also cause damage to the piston and cylinder, the phenomenon of "pulling cylinder". The treatment method is to adjust the speed control valve, according to the installation instructions should do the necessary operation and improvement.

2. Leakage of hydraulic circuit. Including valve and hydraulic line leakage. The inspection method is to check and eliminate the leakage of the hydraulic connection line by manipulating the reversing valve.
3. The hydraulic oil is bypassed back to the tank through the relief valve. If the relief valve enters the dirt and jams the spool, so that the relief valve is normally open, the hydraulic oil will flow directly back to the tank through the relief valve bypass, resulting in no oil in the hydraulic cylinder. If the load is too large, although the regulating pressure of the relief valve has reached the maximum rating, the hydraulic cylinder still cannot get the thrust required for continuous action without action. If the adjustment pressure is low, the insufficient pressure can not reach the required vertebral force, which is manifested as insufficient thrust. Check and adjust the relief valve at this time.

The Piston Slips or Crawls

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

1. Internal astringency of hydraulic cylinder. The hydraulic cylinder internal parts are assembled improperly, parts deformation, wear or shape and position tolerance exceeds the limit, the action resistance is too large, so that the hydraulic cylinder piston speed changes with the different stroke position, slip or crawl. Most of the reasons are due to poor assembly quality of parts, surface scars or sintered iron filings, so that the resistance increases, the speed decreases. For example: piston and piston rod different heart or piston rod bending, hydraulic cylinder or piston rod on the guide rail installation position offset, sealing ring installed too tight or too loose. The solution is to repair or adjust, replace damaged parts and remove iron filings.
2. Poor lubrication or poor processing of hydraulic cylinder aperture. Because the piston and cylinder, guide rail and piston rod are relative motion, if poor lubrication or hydraulic cylinder aperture is out of whack, it will aggravate wear, so that the cylinder center line straightness is reduced. In this way, when the piston is working in the hydraulic cylinder, the friction resistance will be large and small, resulting in slip or crawling. The elimination method is to first repair grinding hydraulic cylinder, and then according to the requirements of the preparation of piston, grinding piston rod, guide sleeve configuration.

3 hydraulic pump or hydraulic cylinder into the air. Air compression or expansion can cause the piston to slip or crawl. Elimination measures are to check the hydraulic pump, set up a special exhaust device, quick operation of the full stroke several times exhaust.

4. Seal quality has a direct relationship with slip or creep. When the O-ring is used at low pressure, compared with the U-ring, it is easy to slip or crawl because of the higher surface pressure and the larger difference between static and static friction resistance. The surface pressure of U-shaped sealing ring increases with the increase of pressure, and although the sealing effect is correspondingly improved, the difference between static and static friction resistance also increases, and the internal pressure increases, which affects the elasticity of rubber. Due to the increase of the contact resistance of the lip edge, the sealing ring will tip over and the lip edge will extend, which is also easy to cause slippage or crawling. In order to prevent it from tipping over, supporting ring can be used to maintain its stability.