III. Main Types of Cushioning

There are many types of hydraulic cylinder cushioning structures, which we will introduce based on fixed and adjustable cushioning:

1. Fixed Cushioning: The cushioning gap is fixed and cannot be adjusted. The structure is simple, and the cushioning performance is constant.

2. Adjustable Damping: Features an adjustable throttle valve (usually a screw) that allows you to adjust the size of the throttle opening based on the actual load and speed, thereby changing the damping effect.

IV. How to Test Hydraulic Cylinder Cushioning?

The purpose of testing hydraulic cylinder cushioning is to verify whether its cushioning effect meets the design requirements and to check for any malfunctions. Testing can be divided into simple tests and precise tests.

A. Simple Field Test (Qualitative Judgment)

This method does not require complex equipment and mainly relies on the operator’s senses and experience.

1. Auditory Test:

Method: Operate the hydraulic cylinder at low, medium, and high speeds, both under no-load and loaded conditions, until it reaches the end of its stroke.

Good performance: A smooth, muffled “poof” or “hiss” sound of oil throttling is heard, and the sound is continuous and gradually weakens.

Fault Symptoms: A crisp, loud metallic “clanging” sound is heard. This indicates complete buffer failure or insufficient buffering capacity.

2. Visual/Tactile Test:

Method: Observe the smoothness of the hydraulic cylinder’s stopping motion. You can gently place your hand on the cylinder body or nearby connecting parts to feel the movement.

Good Performance: The piston stops smoothly, without any noticeable “jerking” or “nodding” motion, and the overall equipment vibration is minimal.

Fault Symptoms: At the moment of stopping, the entire cylinder body or equipment experiences a noticeable “clunking” impact and vibration.

3. Operating Stability Test:

Method: Allow the hydraulic cylinder to repeatedly perform full-stroke reciprocating motion under load.

Good Performance: The stopping position is consistent each time, and the operation is smooth.

Fault Symptoms: Due to the impact, there may be slight variations in the stopping position, or the system pressure gauge needle may vibrate violently at the moment of stopping.

B. Precise Testing (Quantitative Analysis)

This method requires the use of sensors and testing equipment to obtain objective data.

Required equipment: displacement sensor, pressure sensor, data acquisition system, etc.

Testing steps and analysis:

1. Sensor installation: Correctly install the displacement and pressure sensors and connect them to the data acquisition system.

2. Set test conditions: Determine the test load, oil temperature, and operating pressure.

3. Perform the test: Start the hydraulic cylinder, make it run at the test speed, and record the data of the entire motion-cushioning-stopping process.

4. Data analysis:

4.1. Displacement-time/velocity-time curve: This is the most crucial analysis method.

Good performance: At the end of the displacement-time curve, the curve will smoothly flatten out. Differentiating the displacement yields the velocity-time curve, which shows the velocity smoothly and continuously decreasing to zero in the cushioning section.

Faulty performance: The velocity curve is suddenly truncated at the end, indicating a rigid collision.

4.2, Pressure-Time Curve:

Good Performance: At the beginning of cushioning, the pressure in the cushioning chamber will form a smooth peak, and then decrease as the piston stops.

Faulty Performance: A very sharp pressure pulse (pressure spike) appears, indicating a very violent impact.