English 
Spanish 
1.3.9 Technical Requirements for Buffer Devices
The previous articles in this series discussed the Technical requirements for design and manufacturing of hydraulic cylinders-Barrel tube, Technical requirements for hydraulic cylinders-Piston and Piston rod, Cylinder head and cylinder bottom， Guide sleeves, Sealing devices. Today this article will explain Technical requirements for Buffer, Venting, Anti-loosening, and Other Devices.
Buffering is a means of decelerating moving parts (such as pistons) as they approach their end point of motion. There are two main types: fixed (type) and adjustable (type). Hydraulic cylinders employing these two types of buffer devices are uniformly classified as buffered cylinders. The design of cylinders with fixed (hydraulic cylinder) buffer devices is one of the difficulties in hydraulic cylinder design.
1.3.9.1 Technical Requirements for Fixed Buffer Devices
(1) Technical Requirements for Fixed Buffer Devices Specified by Various Standards
The buffering performance of cylinders with fixed buffer devices cannot be adjusted online, and this does not include situations where the buffering performance is changed by altering the viscosity of the working medium (hydraulic oil).
Among the various product standards for hydraulic cylinders, the following two standards specify technical requirements for fixed hydraulic cylinder buffer devices:
① In standard “Hydraulic Cylinders for Marine Hatch Covers,” it is stipulated that: when the input pressure of the tested hydraulic cylinder is 50% of the nominal pressure, the test should be conducted at the designed maximum speed. The buffering effect should be that the piston enters the buffer zone smoothly and slowly.
② In standard “Technical Conditions for Hydraulic Cylinders for Dump Trucks,” stipulates that when the hydraulic cylinder is in its fully extended position, the piston rod should extend and retract at a speed of 50-70 mm/s, and no impact sound should be heard when the hydraulic cylinder automatically stops.
Note: the following description of the buffering effect is more scientific: “There should be no metallic impact sound when the stroke reaches its end.” For details, please refer to international standard “General Technical Conditions for Marine Reciprocating Hydraulic Cylinders.”
(2) General Technical Requirements for Buffer Devices
In addition to the performance requirements for fixed hydraulic cylinder buffer devices specified in the above standards, the following basic performance requirements should be met as much as possible when designing fixed hydraulic cylinder buffer devices:
① The buffer device should be able to absorb the maximum kinetic energy with the shortest possible cylinder buffer length (also known as buffer stroke), that is, to convert all the kinetic energy of the moving parts (including all connecting parts or related parts) into heat energy.
② Pressure pulses and excessively high peak pressure in the buffer chamber should be avoided as much as possible during the buffering process, so that the pressure change is a gradual process.
③ The peak buffer pressure in the buffer chamber (rodless end) should be less than or equal to 1.5 times the nominal pressure of the hydraulic cylinder.
④ If a buffer (device) is installed at the rod end, its buffer pressure should avoid acting on the piston rod dynamic seal (system).
⑤ The conversion of kinetic energy into heat energy causes the hydraulic oil temperature to rise, and the maximum oil temperature should not exceed the maximum allowable operating temperature of the seals.
⑥ In international standard of “Hydraulic Cylinders” stipulates: “For hydraulic cylinders with requirements for buffering performance, the requirements shall be determined through negotiation between the user and the manufacturer.”
⑦ The starting performance of the hydraulic cylinder should also be taken into account. The (minimum) starting pressure of the hydraulic cylinder should not exceed the provisions of the relevant standards; abnormal situations such as delayed or surging movement (abnormal movement), abnormal noise, etc., should be avoided when the piston starts or leaves the buffer zone.
1.3.9.2 Technical Requirements for Buffer Valve and Buffer Device
The buffering performance of a hydraulic cylinder with an adjustable buffer device can be adjusted online; the buffer valve and buffer device is such a device. However, the buffer valve (assembly) here differs from the buffer brake valve commonly used in hydraulic systems.
Among the various product standards for hydraulic cylinders, the following three standards specify technical (test) requirements for buffer valves and buffer devices in hydraulic cylinders:
① In standard “Test Methods for Hydraulic Cylinders” stipulates: “The buffer valve of the working chamber of the test cylinder is fully loosened, the test pressure is adjusted to 50% of the nominal pressure, and the cylinder is moved at the designed maximum speed. The buffering effect is tested when the buffer valve is fully closed.”
② In international standard of “Hydraulic Cylinders” stipulates: “The buffer valve of the working chamber of the test cylinder is fully loosened, the test pressure is adjusted to 50% of the nominal pressure, and the cylinder is moved at the designed maximum speed. When the buffer valve is fully closed, the buffering effect should meet the requirements for buffer cylinders with specific buffering performance requirements, the requirements shall be determined through negotiation between the user and the manufacturer.” It also requires: “The throttling and/or buffering elements installed in the hydraulic cylinder should be free of oil leakage.”
③ In standard of “Large Hydraulic Cylinders,” stipulates: “With all the buffer valves in the working chamber of the test cylinder fully open, adjust the test pressure to 50% of the nominal pressure, and move it at the designed maximum speed to test the buffering effect when the buffer valves are fully closed.”
Regardless of whether the hydraulic cylinder is equipped with a fixed or adjustable buffer device, it should comply with the provisions of international standard: “The throttling and/or buffering elements installed on the hydraulic cylinder should have no oil (external) leakage.”
1.3.10 Technical Requirements for Venting, Anti-loosening, and Other Devices
1.3.10.1 Technical Requirements for Venting Devices
Venting is the means of removing air from a system or component. A venting device is a component used to remove air or gas contained in the hydraulic fluid of a hydraulic system. Hydraulic systems should be equipped with necessary venting devices (devices) as needed, and these devices should allow for convenient venting.
In standard “General Technical Conditions for Marine Reciprocating Hydraulic Cylinders,” stipulates that hydraulic cylinders should generally be equipped with venting devices.
In standard “Marine Digital Hydraulic Cylinders,” stipulates that digital cylinders may be equipped with venting devices as needed.
In standard “General Technical Requirements for Hydraulic Systems” stipulates: “Single-acting piston hydraulic cylinders shall be equipped with vent ports, located in appropriate positions to avoid the danger to personnel caused by the ejected oil. Hydraulic cylinders shall be installed so that they (vent valves) can automatically release air, or be equipped with easily accessible external vent valves.”
1.3.10.2 Technical Requirements for Anti-Loosening Measures
In standard “General Technical Requirements for Hydraulic Systems” stipulates: Any component installed on or connected to a hydraulic cylinder shall be secure to prevent loosening caused by impact and vibration.
1.3.10.3 Technical Requirements for Other Devices
(1) Technical Requirements for Stroke Adjustment Devices
The positioning accuracy and repeatability of the stroke adjustment devices or mechanisms in adjustable stroke cylinders and other hydraulic cylinders shall meet the requirements of relevant standards, and their operation shall be sensitive and reliable.
In standard “Marine Digital Hydraulic Cylinders” stipulates that the (stroke) repeatability of a digital cylinder should not exceed 3 pulse equivalents, i.e., not exceed 0.03 mm.
In standard “Technical Conditions for Agricultural Double-Acting Hydraulic Cylinders” stipulates that the stroke adjustment mechanism of the hydraulic cylinder should be sensitive and reliable.
(2) Technical Requirements for Setting Up Test Ports
In standard “Technical Conditions for Hydraulic Presses” stipulates that when using hydraulic components with cartridge valves or stacked valves, a pressure test port should generally be installed between the actuator (such as a hydraulic cylinder) and its corresponding flow control component. In outlet throttling systems, a test port should generally be installed at the inlet of the relevant actuator (such as a hydraulic cylinder).
(3) Technical Requirements for Hydraulic Valves
For hydraulic cylinders with hydraulic valves, including hydraulic cylinders with buffer valves, hydraulic cylinders with support valves, and hydraulic cylinders with (proportional) servo valves, plate-mounted valves and/or cartridge valves are recommended as much as possible.
The nominal pressure and other performance indicators of the valves used should not be lower than the technical requirements of the hydraulic cylinder; the mounting surface of the valve or manifold block on the hydraulic cylinder or the cartridge hole of the cartridge valve should comply with the relevant standards.
The protection level, operating voltage, and electrical connections of electrically controlled valves should comply with the relevant standards; generally, electrically controlled valves should also have a manual overriding control device.
(4) Technical Requirements for Sensors
Hydraulic cylinders equipped with sensors, such as pressure sensors, position sensors, displacement sensors, speed sensors, and force sensors, must ensure that the performance indicators of these sensors meet the relevant technical requirements for hydraulic cylinders. Specifically, the protection level, operating voltage, and electrical connections of the sensors must comply with relevant standards; the durability or service life of the sensors must not be lower than the durability index of the hydraulic cylinder in which they are located; the fluid pressure resistance or nominal pressure of built-in sensors must not be lower than the pressure resistance index of the hydraulic cylinder in which they are located; and there must be no external oil leakage at the installation and connection points of built-in sensors.
★★★Review of selected articles in our hydraulic cylinder engineering newsletters:
- Classification and Structure of Hydraulic Cylinders
- Hydraulic Cylinder Parameters and Parameter Calculation
- Hydraulic Cylinder Parameter Calculation Example
- Technical requirements for design and manufacturing of hydraulic cylinders-Barrel tube
- Technical requirements for Piston and Piston rod
- Technical requirements for Cylinder head and cylinder bottom
- Technical requirements for guide sleeves
- Technical requirements for sealing devices
- Several Design Methods for Flow Regeneration Using Differential Circuits
- Design, calculation and processing points of hydraulic cylinders: recommended collection
- Piston rod that is too smooth or too rough will affect the sealing life of the hydraulic cylinder