How to determine the model of hydraulic cylinder?

Determine the system pressure

Pressure selection depends on load (F), equipment type, available space, and cost. Insufficient pressure increases actuator size, wasting materials and limiting installation flexibility, while excessive pressure raises demands on materials, sealing, and precision, increasing costs.
Fixed equipment (e.g., machine tools) typically uses lower pressure for cost efficiency, whereas mobile machinery (e.g., excavators) opts for higher pressure to save space and enhance power density.

For specific selection, please refer to the following table:

Select the design pressure of the hydraulic cylinder according to the load:

Select the design pressure of the hydraulic actuator according to the host type:

Initial Selection Of Cylinder Diameter D/Rod Diameter

After the design pressure is selected, that is, P is known, and the load size F is also known, the formula is used to obtain S, the force area, and then the cylinder diameter is calculated based on the force area:
Thrust F1 = A1×P1×β Pull F2 = A2×P2×β
A1: Push side piston pressure area cm², A1 = π/4D² = 0.785D²
A2: Pull side piston pressure area cm², A2 = π/4 (D² - d²) = 0.785 (D² - d²)
D: Hydraulic cylinder inner diameter, i.e. piston diameter cm
d: Piston rod diameter cm
P1: Push side action pressure kgf/cm²
P2: Pull side action pressure kgf/cm²
β: Load rate

Note: 1. The actual output of the hydraulic cylinder is lower than the theoretical output. 2. The load rate β value is 80% in the case of small inertia force and 60% in the case of large inertia force.

Example: If the hydraulic cylinder output is 1000 kg and the actuating pressure is 70kgf/cm², what is the inner diameter of the hydraulic cylinder?

Answer: Output F = 1000kg, actuating pressure P = 70kgf/cm², load factor β = 0.8, F1 = A1×P1×β, A1 = F1/(P1×β) = 1000/ (70×0.8)= 17.86cm², A1 = π/4D² = 0.785D², so D² = 17.86/0.785 = 22.75cm², D = √22.75 = 4.8cm = 48mm, so the inner diameter of the cylinder is 50mm.

You can also select from the following table:

According to the selection principle:

1. Refer to the design pressure of the hydraulic actuator according to the host type, generally ≤21Mpa;
2. The cylinder diameter should be small to reduce costs;
3. Select the standard size of the cylinder, remember the formula: P = 4F/π D

Then select the rod diameter 

P ≤10Mpa, d = 0.5D

P = 12.5 ~ 20Mpa, d = 0.56D

P > 20Mpa, d = 0.71D

alt. Hydraulic Cylinder Piston

Select Stroke 

According to the requirements of the overall design of the equipment or device system, determine the installation method and stroke S. The specific determination principles are as follows

1. Stroke S = actual maximum working stroke Smax + stroke margin △S;

Stroke margin △S = stroke margin △S1 + stroke margin △S2 + stroke margin △S3.

2. Principles for determining stroke margin △S

Determine mounting style and stroke S per system design:

S = Smax + △S (△S=△S1+△S2+△S3)

△S components:

△S1: Manufacturing tolerance

△S2: Start position allowance

△S3: End position allowance

(Minimize △S for buffered cylinders)

3.Verify stability for over-length strokes

4.Meet minimum stroke requirements

Select Installation Method

The installation method of the cylinder refers to the form in which the cylinder is connected to the equipment. After the installation method is determined, the installation size is determined.

The principles for determining the installation method:

(1)Flange installation (end flange, middle flange, tail flange)

Fixed hydraulic cylinder mounting suits applications where the force aligns with the support center. Mounting position (head/center/tail) depends on compressive (push) or tensile (pull) stress: compressive prefers tail/center flange, tensile recommends head/center flange. The final selection should consider both structural design and bending stability in long-stroke compression cases.

alt. Hydraulic Cylinder Flange

(2) Hinge installation

Hydraulic cylinder mounting includes tail clevis (single/double) and end/center/tail trunnion types, suitable for curved-path motion in a fixed plane. For angular operations, the torque is proportional to the linkage lever arm and pivot angle.

a) Clevis Mounting (Single/Double Clevis, Welded Single/Double Clevis)

Single clevis mounting is the most common pivoting configuration, suitable for ±3° arc motion. Spherical bearings can be used at either end (note load limits). Double clevis allows full-range angular movement but requires anti-buckling measures for long-stroke thrust applications.

b) Trunnion Mounting (Head/Center/Tail)

Center trunnion is standard, enabling weight-balanced positioning. Trunnion pins withstand shear loads only – use full-length bearing blocks near shoulder faces to minimize bending stress. Tail trunnion applications mirror double clevis. Head trunnion suits smaller rods; limit stroke to ≤5×bore diameter to manage overhung loads.

alt. Hydraulic Cylinder Base

(3) Tripod installation (front and rear tripods, left and right tripods, welding tripods)
Foot-mounted cylinders are suitable for fixed installations where the mounting plane is offset from the cylinder centerline. This configuration generates a tipping moment during operation. Proper structural anchoring and load guidance are critical to prevent excessive side loads on the piston rod. Available in end-foot and side-foot mounting variants.

End Buffer Selection

The following working conditions should consider choosing two-end buffer or one-end buffer:

1. When the hydraulic cylinder piston runs throughout the entire stroke and its reciprocating speed is greater than 100mm/s, two-end buffer should be selected.
2. When the hydraulic cylinder piston has a one-way reciprocating speed greater than 100mm/s and runs to the end of the stroke, one-end or two-end buffer should be selected.
3. Other specific working conditions.

Selection Of Port type and Diameter

1. Oil port type: internal thread type, flange type and other special types. The selection is determined by the connection method of the connecting pipeline in the system.
2. Principle of oil port diameter selection: Under the condition that the medium flow rate in the connecting pipeline between the system and the hydraulic cylinder is known, the medium flow rate through the oil port is generally not more than 5m/s. At the same time, pay attention to the flow rate ratio factor to determine the oil port diameter.

Hydraulic Cylinder With Valve

1. Maintaining pressure: Sliding valve type reversing valves have gap leakage and can only maintain pressure for a short time. When there is a requirement to maintain pressure, a hydraulically controlled one-way valve can be added to the oil circuit, and the tightness of the cone valve closing can be used to maintain the pressure of the oil circuit for a long time.
2. "Support" of the hydraulic cylinder: In a vertical hydraulic cylinder, due to leakage of the sliding valve and the pipe, the piston and the piston rod may slide down under the gravity of the piston and the piston rod. Connecting the hydraulically controlled one-way valve to the oil circuit of the lower chamber of the hydraulic cylinder can prevent the movable parts such as the hydraulic cylinder piston and the slider from sliding down.
3. Locking the hydraulic cylinder: When the reversing valve is in the middle position, the two hydraulically controlled one-way valves are closed, which can tightly seal the oil in the two chambers of the hydraulic cylinder. At this time, the piston cannot move due to external force.

alt. Hydraulic Cylinder Valve Block

Specific Working Conditions For Condition Selection

(1) Working Medium

Standard medium is mineral oil. For other media, consider their impact on seals and material compatibility. Recommended: ISO VG 32/46 anti-wear hydraulic oil. Optimal operating temperature: 20-55°C (operation prohibited below 15°C or above 70°C; use heaters/coolers as needed). Replace oil every 1-6 months with tank cleaning. Maintain oil cleanliness to prevent filter clogging, noise, and pump wear.

(2) Ambient Or Medium Temperature

The normal working medium temperature is -20°C to +80°C. If the working temperature exceeds this, attention must be paid to the effects on the sealing system, material properties of various components and cooling system settings and other conditions.

(3) High Operating Accuracy

For servo or other hydraulic cylinders with low starting pressure requirements such as medium and high pressure, attention must be paid to its impact on the sealing system, material properties of each component and detailed design.

(4) Zero Leakage

For hydraulic cylinders with specific pressure maintenance requirements, attention must be paid to its impact on the sealing system, material properties of each component and other conditions.

(5) Working Pressure And Speed, Working Conditions such as:

a) Medium and low pressure system, piston reciprocating speed ≥70-80mm/s

b) Medium and high pressure, high pressure system, piston reciprocating speed ≥100-120mm/s, attention must be paid to the impact on the sealing system, material properties of each component, connection structure and matching accuracy.

(6) High-frequency vibration working environment: attention must be paid to its impact on factors such as material properties of each component, connection structure and detailed design.

(7) Low temperature icing or contaminated working environment, working conditions such as:

a) High dust environment;

b) Water spray, acid mist or salt mist environment.

Attention must be paid to its impact on the sealing system, material properties of each component, surface treatment of the piston rod and protection of the product.

Selection Of Seal Quality

There are specific working conditions and specified quality requirements as mentioned above. The consequences of failure of the sealing system of the hydraulic cylinder are serious (such as affecting safety, difficult to replace, large economic losses, etc.). For special requirements such as the sealing system of the hydraulic cylinder for export, it is recommended that the professional engineers of the manufacturer recommend the use of well-known sealing qualities with good interchangeability and easy procurement based on the working conditions.

alt. Hydraulic Cylinder Seal

Other Feature Options

Exhaust Valve

Depending on the working position of the hydraulic cylinder, it is normally set at the highest point where the air finally accumulates in the two end chambers. After the air is exhausted, it can prevent creeping, protect the seal, and slow down the deterioration of the oil.

 Leakage Port

In a working environment where oil leakage is strictly prohibited, due to the long stroke of the hydraulic cylinder or certain working conditions, the oil accumulates behind the dust ring during its reciprocating operation. To prevent leakage after long-term operation, a leakage port must be set at the location where the oil accumulates.

Conclusion

Selecting the right hydraulic cylinder requires balancing load, pressure, stroke, and environmental factors. By following these guidelines—from bore sizing to mounting configurations—you can optimize performance, reduce downtime, and extend service life.