Technical Requirements For The Design And Manufacture Of Hydraulic Cylinders

General requirements

① The nominal pressure of the hydraulic cylinder complies with the regulations that the pressure should be able to cover the actual working pressure, and there must be a certain safety margin to ensure reliable operation under various working conditions.

② Regulations on the inner diameter of the hydraulic cylinder and the outer diameter of the piston rod:

 

Inner diameter of hydraulic cylinder:

• The inner diameter size should comply with the design requirements and is usually marked in millimeters.
• The tolerance range of the inner diameter should be clearly specified during design, and H and K level tolerances are generally used.
• The tolerance of the inner diameter is mainly affected by factors such as processing technology and materials.

 

The outer diameter of the piston rod of the hydraulic cylinder:

• The outer diameter of the piston rod should also meet the design requirements and is usually marked in millimeters.
• The tolerance range of the piston rod outer diameter should also be clearly specified during design, and h and k level tolerances are generally used.
• The tolerance of the piston rod outer diameter is also affected by factors such as processing technology and materials.

 

③Regulations on the size of the oil port connection thread:

• Thread type: Oil port connections usually use internal threads, and the thread type may be cylindrical thread or tapered thread, such as M series or G series.
• Thread parameters: Specific thread parameters include pitch, thread diameter, etc., usually expressed in millimeters. Thread diameter usually includes the dimensions of the outer diameter and the inner diameter.
• Thread tolerance: The tolerance range of the thread should comply with the standard regulations, usually using the established standard tolerance level, such as 4H/4h, 6H/6H, etc.
• Thread type: Standards may require a specific type of thread, such as a coarse thread or a fine thread.
• Sealing ring specifications: Standards may require the use of O-ring seals of specific specifications and materials to ensure the tightness of the connection.

 

④Regulations on piston rod thread type and size:

• Thread type: Piston rod threads can be internal or external, usually internal, but external threads may be used in certain circumstances.
• Thread parameters: Thread parameters usually include pitch, thread diameter, etc. to ensure connection compatibility with other system components.
• Thread tolerance: The tolerance range of the thread should comply with the standard regulations, and the established standard tolerance level is usually used.
• Thread type: Standards may require a specific type of thread, such as a coarse thread or a fine thread, to meet the connection requirements.
• Surface treatment: Standards may also include surface treatment requirements for piston rod threads to improve their corrosion and wear resistance.

 

⑤Requirements for sealing grooves:

• The size range of the piston and piston rod dynamic seal grooves, including the width, depth, etc. of the grooves.
• The tolerance range of the groove ensures the installation and sealing performance of the seal.
• Dimensional range and tolerance of narrow-section dynamic seal grooves, as well as groove shape and processing requirements.
• Specially designed for narrow section sealing to meet specific sealing needs.
• Types, dimensions and tolerances of sealing grooves with back-up rings, as well as groove processing requirements.
• Backup ring seals are often used to improve sealing performance and pressure resistance.
• The type, size and tolerance of the wiper groove for the piston rod, as well as the processing requirements for the groove.
• The dust ring groove is used to install the dust ring to protect the inside of the hydraulic cylinder from the intrusion of external contaminants.

 

⑥The working environment temperature of the hydraulic cylinder is -20~+50℃, and the working medium temperature is -20~+80℃.

 

Performance requirements

 

①Regulations on minimum starting pressure test measurement values:

• Test method: Specifies the specific method for conducting the minimum starting pressure test, including the setting of the test device, the operating steps during the test, etc.
• Test conditions: stipulates the working conditions of the hydraulic cylinder during the test, such as the type of working medium, temperature, pressure, etc.
• Test result judgment standard: It stipulates the qualification standard for the minimum starting pressure test, that is, the minimum starting pressure value that the hydraulic cylinder must reach during the test.
• Test data record: stipulates the data that need to be recorded during the test, including the pressure value of the hydraulic cylinder before and after the test, test duration and other information.
• Exception handling: Corresponding handling methods and suggestions are provided for abnormal situations that may occur during the test.
• Safety requirements: Specify safety precautions when conducting tests to ensure the safety of test operators and equipment.

 

② Provisions for internal leakage test measurement values:

• Test method: Specifies the specific method for conducting internal leakage test, including the setting of the test device, the operating steps during the test, etc.
• Test conditions: stipulates the working conditions of the hydraulic cylinder during the test, such as the type of working medium, temperature, pressure, etc.
• Test result judgment criteria: It stipulates the qualification standards for the internal leakage test, that is, the maximum allowable internal leakage of the hydraulic cylinder during the test.
• Test data record: stipulates the data that need to be recorded during the test, including the pressure value of the hydraulic cylinder before and after the test, test duration, leakage and other information.
• Test device requirements: Special devices or instruments required to conduct the test may be specified to ensure the accuracy and repeatability of the test.
• Exception handling: Corresponding handling methods and suggestions are provided for abnormal situations that may occur during the test.
• Safety requirements: Specify safety precautions when conducting tests to ensure the safety of test operators and equipment.

 

③Regulations on external leakage test measurement values:

• Test methods and devices: Specifies the specific methods and test device settings for external leakage testing. This may include the use of specialized seal performance testing equipment or testing under actual operating conditions.
• Test conditions: The working conditions during the external leakage test are determined, including the working pressure, temperature and other parameters of the hydraulic cylinder. The setting of test conditions should comply with the design requirements of the hydraulic cylinder.
• Test result judgment standards: It stipulates the qualification standards for external leakage tests, that is, the upper limit of the allowable liquid leakage amount. This is usually measured as the volume of liquid leaked per unit of time.
• Test data recording: It is required to record data during the external leakage test, such as liquid volume before and after the test, test duration and other information.
• Test process control: Control measures during the test may also be specified to ensure the accuracy and repeatability of the test, such as monitoring and adjustments during the test.
• Exception handling: Corresponding handling methods and suggestions are provided for abnormal situations that may occur during the test.
• Safety requirements: Specify safety precautions when conducting tests to ensure the safety of test operators and equipment.

 

④Leakage regulations under low pressure:

• Test device and method: Specifies the specific test device and method for leakage testing under low pressure. This may involve using specialized seal performance testing equipment or conducting tests under specific test conditions.
• Test conditions: The working conditions for the leakage test under low pressure are determined, including the working pressure, temperature and other parameters of the hydraulic cylinder. The setting of test conditions should comply with the design requirements of the hydraulic cylinder.
• Test result judgment standard: It stipulates the qualification standard for leakage test under low pressure, that is, the upper limit of the allowable liquid leakage amount. It is usually measured by the volume of liquid leaked per unit time.
• Test data recording: It is required to record data during the leakage test process under low pressure, such as liquid volume before and after the test, test duration and other information.
• Test process control: Control measures during the test may also be specified to ensure the accuracy and repeatability of the test, such as monitoring and adjustments during the test.
• Exception handling: Corresponding handling methods and suggestions are provided for abnormal situations that may occur during the test.
• Safety requirements: Specify safety precautions when conducting tests to ensure the safety of test operators and equipment.

 

⑤Requirements for pressure resistance:

• Test device and method: Specifies the specific test device and method for pressure resistance test. This may include the use of specialized pressure testing equipment or testing under specific test conditions.
• Test conditions: The working conditions during the pressure resistance test are determined, including the working pressure of the hydraulic cylinder, test duration and other parameters. The test conditions should comply with the design requirements and application scenarios of the hydraulic cylinder.
• Test result judgment criteria: It stipulates the qualification criteria for the pressure resistance test, that is, the maximum pressure value allowed by the hydraulic cylinder during the test. The judgment is usually based on the stability and lack of leakage of the hydraulic cylinder during the test.
• Test data recording: It is required to record data during the pressure resistance test, such as pressure changes before and after the test, test duration and other information.
• Test process control: Control measures during the test may be specified to ensure the accuracy and repeatability of the test, such as monitoring and adjustments during the test.
• Exception handling: Corresponding handling methods and suggestions are provided for abnormal situations that may occur during the test.
• Safety requirements: Specify safety precautions when conducting tests to ensure the safety of test operators and equipment.

 

⑥Buffering regulations:

• Test device and method: Specifies the specific test device and method for buffer test. This may include the use of specialized buffering devices or testing under specific test conditions.
• Test conditions: The working conditions during the buffer test are determined, including the working pressure, stroke speed and other parameters of the hydraulic cylinder. The test conditions should comply with the design requirements and application scenarios of the hydraulic cylinder.
• Test result judgment criteria: It stipulates the qualification criteria for the buffer test, that is, the maximum deceleration or other performance indicators allowed by the hydraulic cylinder during the test. The judgment is usually based on the deceleration at the end of the stroke during the test.
• Test data recording: It is required to record data during the buffer test process, such as speed, deceleration and other information at the end of the stroke.
• Test process control: Control measures during the test may be specified to ensure the accuracy and repeatability of the test, such as monitoring and adjustments during the test.
• Exception handling: Corresponding handling methods and suggestions are provided for abnormal situations that may occur during the test.
• Safety requirements: Specify safety precautions when conducting tests to ensure the safety of test operators and equipment.

 

Assembly and appearance requirements

① Requirements for assembly quality of hydraulic cylinders:

• Assembly process regulations: Determine the assembly process regulations of the hydraulic cylinder, including the assembly sequence, assembly method, tightening torque, lubrication requirements, etc. of each component. Specifies the specific operating steps and precautions required during assembly.
• Assembly Tools and Equipment: Identify the specialized tools and equipment required to ensure the accuracy and efficiency of the assembly process. Including calibration tools, assembly fixtures, measuring instruments, etc.
• Parts matching requirements: Specify the matching requirements between various parts to ensure that the assembled hydraulic cylinder can work normally. Including clearance, fit clearance, surface roughness and other requirements.
• Assembly quality inspection method: Develop specific methods and standards for assembly quality inspection of hydraulic cylinders. Including inspection requirements in terms of appearance inspection, dimensional measurement, functional testing, etc.
• Assembly quality records: It is required to record key data and quality information during the assembly process of the hydraulic cylinder, including inspection records during the assembly process, assembly employee number, assembly date, etc.
• Assembly exception handling: Specifies specific measures and procedures for handling abnormal situations that occur during the assembly process. Including handling of unqualified products, adjusting assembly processes, reassembly, etc.
• Assembly quality control: Specific control measures to ensure that assembly quality meets standard requirements. Including quality control during the assembly process, establishment and implementation of quality management systems, etc.

 

②Appearance quality requirements of hydraulic cylinders:

• External surface flatness requirements: Specifies the flatness requirements for the external surface of the hydraulic cylinder, including whether the surface is flat and has no obvious depressions or protrusions.
• Oxidation inspection: It is required to check the oxidation condition on the surface of the hydraulic cylinder to ensure that there are no oxidation spots, signs of corrosion or other oxidation problems.
• Coating quality requirements: The quality requirements for the surface coating of the hydraulic cylinder are determined, including the flatness, adhesion, color consistency, etc. of the coating.
• Marking inspection: It is required to check the marking on the hydraulic cylinder, including whether the marking is clear, accurate, complete, and meets standard requirements.
• Inspection tools and methods: Specifies the specific tools and methods required for visual inspection, such as visual inspection, inspection with a magnifying glass, use of scratch detectors, etc.
• Classification and assessment of appearance defects: Appearance defects are divided into different levels, evaluated and classified according to severity, and the impact of various defects on product quality is determined.
• Appearance inspection frequency: Specifies the frequency of appearance inspection, which can be for each production batch, each product or each process, etc.
• Defect handling measures: Specifies the handling measures for discovered appearance defects, such as repair, scrapping or returning to the manufacturer for processing, etc.

 

Other requirements

• The temperature of the working medium is preferably -20~65°C through technical agreement.
• Factory testing is preferably carried out at room temperature as specified by technical agreement.

 

Technical requirements for hydraulic cylinders specified in other standards
(1) Applicability
① Resist instability. In order to avoid bending or instability of the piston rod of the hydraulic cylinder at any position, attention should be paid to the stroke length, load and installation type of the cylinder.
② Structural design. Hydraulic cylinders should be designed taking into account predetermined maximum loads and pressure peaks.
③Installation rating. When determining all load ratings of a hydraulic cylinder, its mounting type should be taken into consideration.
PS: The rated pressure of a hydraulic cylinder only reflects the pressure-bearing capacity of the cylinder, but not the force transmission capacity of the installation structure.
④The load generated by the limiter. When the hydraulic cylinder is used as a limiter, it should be based on the maximum
The load determines the size of the hydraulic cylinder and the selection of its mounting type.
⑤Resistant to shock and vibration. Any components and accessories installed on or connected to a hydraulic cylinder, their installation or connection
It should be able to prevent loosening caused by impact and vibration during use.
⑥Accidental supercharging. Measures should be taken in the hydraulic system to prevent the pressure from being unexpectedly high above the rated pressure due to differences in effective piston area.

 

(2)Installation and adjustment
The best way to install a hydraulic cylinder is so that the reaction produced by the load acts along the center line of the hydraulic cylinder. Hydraulic cylinder installation should minimize (less than) the following situations:
Excessive deformation of the hydraulic cylinder structure due to load thrust or tension; lateral or bending loads; rotational speeds of articulated mounting types (which may necessitate the use of continuous external lubrication).

①Installation location. The mounting surface should not deform the hydraulic cylinder and allow allowance for thermal expansion. The hydraulic cylinder is mounted in an easily accessible location for maintenance, buffer adjustment and complete component replacement.
②) Fasteners for installation. The selection and installation of fasteners for the installation of hydraulic cylinders and accessories should be able to withstand all foreseeable forces. A tripod-mounted hydraulic cylinder may exert shear forces on its mounting bolts. If shear loads are involved, it is advisable to consider using a hydraulic cylinder with a mechanism to withstand shear loads. Fasteners used for installation should be sufficient to withstand the overturning moment.

(3)Buffer and reduction device
When internal buffering is used, the design of the hydraulic cylinder should take into account the effect of the pressure increase caused by load deceleration.

(4) Adjustable stroke end stop
Provision should be made to prevent external or internal adjustable end-of-travel stops from loosening.

(5)Piston stroke
Stroke length (including tolerances), if not specified in the relevant standard, shall be specified according to the application of the hydraulic system.
PS: Tolerance of stroke length:
Maximum stroke: refers to the maximum stroke length that the hydraulic cylinder can achieve. This parameter is very important for design and installation limitations, as it determines the maximum range of movement of the hydraulic cylinder.
Limit range: Also called stroke limit or stroke end point, it refers to the farthest position that the hydraulic cylinder is allowed to reach during operation. This parameter is typically used to adjust the stroke range of a hydraulic cylinder to suit the needs of a specific application.

(6)Piston rod
①Material, surface treatment and protection. Appropriate piston rod material and surface treatment should be selected to minimize damage, corrosion and foreseeable collision damage, and to protect the piston rod from foreseeable damage such as indentations, scratches and corrosion, a protective cover can be used .

②Assembly. For assembly, the piston rod with a threaded end should have a structure that can be used to apply a reverse force by the hand, and the piston should be reliably fixed on the piston rod.

(7) Maintenance of sealing devices and wearing parts
Sealing devices and other wearing parts scheduled for maintenance should be easily replaceable.

(8)Single-acting hydraulic cylinder
Single-acting piston hydraulic cylinders should be designed with a vent port and set at an appropriate location to avoid danger to personnel from discharged oil spray.

(9)Replacement
Integral hydraulic cylinders are undesirable, but when used, parts that may wear should be replaceable.

(10) Gas emissions
① Deflate position. Hydraulic cylinders installed on stationary industrial machinery should be capable of automatic venting or provide an easily accessible external vent. When installing, the vent port of the hydraulic cylinder should be at the highest position. When these requirements cannot be met, relevant maintenance and use information should be provided.
②Exhaust port. Hydraulic cylinders with a gas chamber should be designed or equipped with an exhaust port to avoid danger. Hydraulic cylinder utilizes exhaust port
The air should be able to be removed without danger.

(11)Tightness
The seal should meet the technical requirements of the working medium and working conditions. When the hydraulic cylinder is under 1.5 times or 1.25 times the nominal pressure, all joint surfaces including the sliding mating surface (at rest)
There should be no external leakage. Under the nominal (or rated) pressure of the hydraulic cylinder, the internal leakage amount and the external leakage amount at the piston rod comply with the standard requirements. The seals of the hydraulic cylinder should be resistant to high temperature, corrosion, aging, hydrolysis, and have good sealing performance. They can not only meet the sealing requirements of oil, but also meet the requirements of the environment (such as marine air).

① For non-lifting hydraulic cylinders, it is recommended that the sealing structure be a support ring plus dynamic seal. The support material is recommended to be tetrafluoroethylene filled with bronze powder or reinforced polyformaldehyde with long molecular chains.
② For hydraulic cylinders used for weight lifting, for oil chambers where oil leakage will cause heavy objects to fall, the dynamic seal should be a rubber-covered fabric V-shaped sealing ring.
③Some hydraulic cylinders can use settlement to calibrate (calculate) internal leakage.
PS: Although Article 2 comes from standard regulations, there is a problem with its applicability.

(12)Assembly requirements
① Components should use inspected and qualified parts and purchased parts, and be assembled in accordance with the regulations and requirements of relevant product standards or technical documents. Any deformed, damaged and rusted parts and purchased parts cannot be used for assembly.
② After the cylinder body has undergone 100% non-destructive testing, the weld strength should not be lower than the strength index of the base material and the weld quality; for hydraulic cylinders using hinge shafts, the hinge shaft should be integrally forged and should undergo 100% non-destructive testing. meet the requirements.
③ Sharp edges on machined parts, except for sealing grooves and edges, which are not shown on the working drawing, should be removed. Parts should be deburred and carefully cleaned before assembly. They should not contain any contaminants such as iron filings, burrs, fibrous impurities, etc.
④ During assembly, cotton yarn, paper and other easily shed fibers should not be used to wipe the cylinder cavity, parts mating surfaces and entrances and exits.
flow channel.
⑤Defective seals that have exceeded their effective service life should not be used during assembly. The dust rings and seals are not allowed to be scratched, twisted, curled or detached and other abnormal phenomena.
⑥After passing the factory test, the exposed oil port of the hydraulic cylinder should be covered with a dust cover, the exposed threads of the piston rod and other connecting parts should be covered with protective sleeves, and the moving parts should be coated with anti-rust grease.
⑦ A clear and permanent mark or sign should be made on the hydraulic cylinder at an appropriate and obvious location, or at the location specified in the drawing. Fixed prefabricated signs, which should be clear, correct and flat.
PS: For more detailed assembly technical requirements, the edges of each sealing groove cannot be chamfered or rounded by fitters, including the use of various power tools for chamfering or rounding.

(13) Appearance requirements
① The outer surface of the hydraulic cylinder should not have defects such as folding, obvious waves, cracks, burrs, bumps, scratches, rust, etc.
② The exposed surface should be treated with coating, passivation layer, paint, etc. for anti-corrosion (rust) treatment. The coating should be free of defects such as cracks, peeling, peeling, or vacuoles; the surface should be rust-free or scale-free before painting, and there should be no rust pits.
③When painting, anti-rust paint should be applied first, and then the topcoat. The coating should be uniform, consistent in color and smooth. Putty should not be applied before spraying.

(14)Safety technical requirements
The design and manufacturing of hydraulic cylinders must provide users with basic safety guarantees for use within the specified service life. Any kind of hydraulic machinery may be dangerous during adjustment, use and maintenance. Therefore, users can only reduce or eliminate the danger by adjusting, using and maintaining it according to the safety technical conditions or requirements of the hydraulic machinery.

① If necessary, such as hydraulic cylinders used in special occasions, risk assessment should be carried out during design.
② Risk reduction measures should be taken during design and manufacturing, such as reliable anti-loosening measures for various fasteners.
③ For dangers that cannot be avoided in the design and manufacture of hydraulic cylinders, such as the unexpected stroke of the slider (driven by the hydraulic cylinder) and the accidental drop of its own weight, the OEM should take safety protection measures, including risk (hazard) warnings.
④For more specific safety technical requirements (conditions), please refer to relevant standards and comply with them.

 

EASTAI Company adheres to strict process standards and innovative design concepts in the design and manufacturing of hydraulic cylinders, and continuously improves product quality and technical level. We will continue to be committed to research and development, provide customers with better quality hydraulic cylinder products and services, and develop together with our partners to create a better future.