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1. Hydraulic cylinder barrel tube design
2. Piston design
3. Piston rod design
4. Piston rod guide sleeve (cylinder sleeve), seal and dustproof
5. Piston Rod Spacer
In long-stroke hydraulic cylinders, due to the mounting method and load guidance conditions, the piston rod guide sleeve may be subjected to excessive lateral forces, resulting in severe wear. Therefore, a spacer ring (also called a stop ring or support ring) must be installed between the piston and the rod-side end cap to ensure sufficient support length for the piston rod when fully extended. The minimum support length L of the piston rod in the cylinder should satisfy the following formula:
L > D + d / 2 (m)
Determining the Spacer Ring Length LT: (For reference) When the stroke length S exceeds 8 times the cylinder bore diameter D, a spacer ring with an L = 100 mm can be installed. For every 700 mm of excess length, the spacer ring length L increases by 100 mm, and so on.
When 1000 < S < 2500 mm, the required spacer lengths are as follows: S = 1001-1500 mm, L = 50 mm; S = 1501-2000 mm, L = 100 mm; S = 2001-2500 mm, L = 150 mm.
6. Exhaust Valve
If the exhaust valve is improperly set or not set, air will remain inside the hydraulic cylinder after the pressurized oil enters it. Due to the compressible and subsequently expansive nature of air, this can cause vibration and creep in the hydraulic cylinder and the entire hydraulic system during operation, affecting its proper function.
To prevent this, in addition to preventing air from entering the hydraulic system, an exhaust valve must be installed on the hydraulic cylinder. Because the hydraulic cylinder is the final actuator in the hydraulic system, it directly reflects the harmful effects of residual air.
The exhaust valve should be positioned appropriately. For horizontally mounted hydraulic cylinders, it should be located above the ends of the cylinder body chambers; for vertically mounted hydraulic cylinders, it should be located above the end caps. Both valves should be connected to the pressure chamber to facilitate the removal of air from the cylinder after installation and before commissioning. Since air is lighter than oil, it always floats upward, preventing air from accumulating in dead corners.
7. Oil Ports
Oil ports consist of port holes and port connection threads. The inlet and outlet ports of a hydraulic cylinder can be located on the end cap or the cylinder barrel. Most port holes are thin-walled (those with a length-to-diameter ratio (L/d) greater than 0.5). The flow rate through a thin-walled hole is calculated as follows:
Q = CA√[(2/p)(PI – P2)] = CA√[(2/p)ΔP (m³/s)]
C – Flow coefficient. When the ratio of the large to small hole at the joint is greater than 7, C = 0.6-0.62; when it is less than 7, C = 0.7-0.8.
A – Cross-sectional area of the oil hole (m²)
p – Density of the hydraulic oil (kg/m³)
P – Pressure in the chamber before the oil hole (Pa)
P2 – Pressure in the chamber after the oil hole (Pa)
AP – Pressure difference between the chambers before and after the oil hole (Pa)
C and p are constants. The factor that most affects flow rate is the area A of the oil hole. The above formula can be used to calculate the hole diameter to meet the required flow rate and thus ensure the hydraulic cylinder’s normal operating speed.
