Instruction for choosing right type of servo valves
1.Servo valve for position servo system
(1)For position system such as servo control cylinder and servo control motor, general-purpose servo valve should be fine.
(2)For applications with large load inertia, small actuator support and rigidity of load connection, small system damping, high system static rigidity and high frequency response, a specially designed dynamic pressure feedback web, general-purpose servo valves may be used instead of dynamic pressure feedback ones.
(3)Should there is strict requirement for system static control precision, a servo valve with zero lap and high threshold and pressure gain is recommended.
(4)Nozzle-flapper, jet deflector servo valves or nozzle-flapper servo valves with high dynamic response are recommended for systems with dynamic response requirement.
(5)When choosing right types of servo valves, please bear in mind that normally tolerance for servo valves’ rated current is 10%. Once rated current of servo valve is chosen, flow gain of servo valve is also fixed. Users can get desired servo system gain by adjusting gain of electrical controller. As long as tolerance of symmetry, linearity and null bias sticks to American Military standard or our national standard, they are applicable to control precision of most position servo systems.
2.Servo valve for force servo system
(1)Normally flow control servo valves with relatively big underlap or pressure control servo valves are recommended for force (load) servo systems. For applications with high rigidity like material test machines, electrohydraulic pressure control servo valves are recommended. For force servo systems with flow control servo valves or pressure control servo valves, system should minimize load chamber, because load chamber will affect system dynamic performance greatly. Should servo valves are mounted to servo cylinder directly, pipeline is not recommended, especially the way in which two load ports of servo valve are connected to two load chambers of servo cylinder through hose.
(2)Servo force system is aimed at precision control of output force, During the process of loading, the movement of actuator and load chamber change caused by compressibility of fluid work together to create flow required to output by the valve. For this reason valves used in the servo force system, whether it is a flow control servo valve or pressure control servo valve, its necessary to accurately work out load flow of valves. Amd allow for bigger rated flow.
3.Tips for choosing other types of servo valves
(1)When choosing jet pipe or jet deflector servo valves to be used in a hydraulic system whose fluid cannot clean by itself, please pick up servo valves which can be installed in horizontal or vertical direction. For important hydraulic systems or fuel servo systems, ordinary jet pipe or jet deflector servo valves cannot be mounted in horizontal or vertical direction, because they cannot resist fluid contamination when hydraulic pump is not working.
(2)In case system design picks up single chamber of servo valve load output, you can work out no-load flow rate required by servo valve through movement speed of actuator, then the flow rated is divided by square root of 2, you will get no-load flow rate of servo valve with two chamber output.
