Servo Hydraulic cylinder It can be equipped at the end with an internal piston, an external cylinder, or various sensing devices, and integrated with a servo valve and amplifier to achieve closed-loop control of position, force, and velocity. The key difference between a servo hydraulic cylinder and a conventional cylinder is that the former must meet the static accuracy and dynamic performance requirements of a servo system, demanding low friction, no stick‑slip, no dead zone, high responsiveness, and long service life. Consequently, its minimum starting pressure, leakage, and other performance parameters differ from those of standard cylinders. Moreover, servo hydraulic cylinders have specific requirements regarding their frequency response characteristics.

　　First, during design and calculation, the selection of the servo hydraulic cylinder must be considered in conjunction with that of the servo valve. In addition to choosing appropriate bore and rod diameters based on force requirements and speed—just as with a conventional cylinder—the servo hydraulic cylinder must also have its natural frequency verified to meet the system’s or the servo valve’s specifications. To enhance response speed, the servo valve should be mounted directly on the cylinder body whenever possible, thereby minimizing the piping between the valve and the cylinder; flexible hoses should be avoided.

　　In structural design, the sealing and guiding of servo hydraulic cylinders are of paramount importance; the sealing and support‑guiding solutions used for conventional hydraulic cylinders cannot be simply adopted. This is because servo hydraulic cylinders and standard cylinders have fundamentally different performance requirements. Servo hydraulic cylinders demand a low start-up pressure—i.e., minimal friction. Typically, the minimum start-up pressure for double‑acting piston rods does not exceed 0.2 MPa, while for single‑acting piston rods it is no more than 0.1 MPa. By contrast, conventional cylinders, depending on their sealing configuration and pressure class, exhibit a minimum opening pressure ranging from 0.1 to 0.75 MPa; under higher nominal pressures, this can rise as high as 1.8 MPa, as determined by percentage calculations. Only low friction between the seals and the guide rails can ensure compliance with critical performance criteria such as smooth operation without creep or stiction, rapid response, leak‑tightness, and extended service life—all of which are closely tied to the sealing and guiding system. In fact, the distinct sealing and guiding characteristics represent the most fundamental distinction between servo cylinders and ordinary cylinders. Today, numerous mature sealing products specifically designed for servo cylinders are available, offering both reliable sealing and low‑friction performance. Consequently, the key to designing a servo hydraulic cylinder lies in the careful selection and engineering of its sealing and guiding components.

　　In general, servo hydraulic cylinders outperform conventional cylinders in most respects, with internal leakage being the notable exception. For servo hydraulic cylinders, internal leakage is typically specified at 0.5 mL/min or as defined by dedicated technical requirements. By contrast, the leakage of standard cylinders can be as low as 0.03 mL/min, depending on cylinder bore size and sealing configuration. Thus, the internal leakage performance of servo hydraulic cylinders is not superior to that of conventional cylinders—and may even be lower. This is because servo systems usually incorporate closed-loop feedback control, allowing errors caused by internal leakage to be corrected and compensated through system feedback, even if the leakage is slightly higher. Moreover, internal leakage can affect dynamic performance metrics such as system stability and response speed; in some cases, a somewhat larger leakage is deliberately tolerated to enhance overall system stability.