What is a servo valve and how does it work

What is a servo valve and what is the function of a servo valve

A servo valve can be considered as a directional control valve, basically, it is a pneumatic or hydraulic actuator that can connect more ways through which a fluid circulates. These valves are simple and rugged in design, and they are capable of infinitely variable positioning. Servo valves are capable to control the direction of the flow and they can also control the amount of the flow. Servo valves have certain sensing devices that would allow the perfect positioning and velocity of an actuator. Servo valves are used in hydraulic systems because these valves have internal feedback which is capable to provide better valve operation with high reliability.

What are the characteristics of servo valve

  • Higher oil capacity
  • Accurate position control
  • Closed-loop control system
  • The closed-loop control system has feedback sensor, command sensor, and digital or analog controller
  • It can give a continuous variation of flow with changing input signal
  • Highly responsive
  • High repeatability
  • Frequency response is high
  • Flow changes are handled very perfectly

What are the factors that must be considered while selecting a servo valve

  • Select the valve that has the proper pressure rating for the application
  • Temperature ratings must be checked
  • Flow rate of the servo valve must be checked
  • Rated pressure must be checked
  • Rated current must be checked and all this data could be known by the catalog data
  • Valve material must be checked as if it is suitable for the application and the material should able to resist corrosion and other environmental issues
  • Interaction of the closed-loop system must be done
  • The electrical connector that is used in the valve must be of a high standard so that it can prevent deterioration in service.

What is the difference between the servo valve and proportional valve

Proportional valves are used for general electrical control systems, while the servo valves are used for high-frequency applications. Proportional valves have, either open or closed-loop circuits, while the servo valves have closed-loop circuits. Servo valves have high accuracy and reliability when compared to a proportional valve. In order to get a high-frequency response from the servo valve, higher pressure must be given. Servo valves have a feedback system that can control the actuator and the feedback system consist of sensing devices and this is the major difference from the proportional valve. The controller can control the actuator by the help of the feedback system

How servo valves are constructed

The servo valves have three major parts they are the control motor, hydraulic amplifier, and the main slide valve. The electrohydraulic servo valves have a motor and the motor consists of coils, magnets, and armature. Flexure tube is used to support the armature for small movements, this tube also provides a fluid seal between the hydraulic and electromagnetic portions. In the center of the armature, a flapper is attached and this flapper is extended towards the flexure tube. A nozzle can be seen on both sides of the flapper and the nozzle opening is dependent on the flapper motion.

What is a Moog valve and how does it work

How does a servo valve work

Servo valves are mostly used for accurate position control and an electrical signal is used to control the servo valves. These valves are widely used in electrohydraulic systems because it has the advantage of using small power electrical signals to position the actuator or motor. A feedback system is used to ensure that the actuator does what the controller asks it to do. This feedback is achieved with the help of some electronic device mostly it is a transducer. This transducer is capable to produce the signal according to the direction and speed of the flow and this will be given to the feedback system and the flow direction and speed can be changed according to the need. The fluid will enter through the inlet and then it will reach the orifices after that it travels through the two spools and after that to the nozzle and then to the return line. The operation of the valve starts with an electrical signal and this will make the armature push the flapper from one nozzle and this flapper would be closer to the other nozzle. This would create an increase in pressure at one end of the spool and decrease at the other end and the spool will change its position from higher pressure according to the armature rotation the spool movement can be controlled.

What are the types of servo valves

  • Mechanical type servo valve
  • Electro-hydraulic servo valve

Mechanical type servo valve

This valve is a mechanically operated servo valve and it will control the flow of fluid in an actuator. This type of valve can be considered as a force amplifier that is used to control the position. The spool is shifted to the required direction with the help of a small input force. The oil will flow through one of the ports and the direction of the hydraulic cylinder is changed too. The flow to the hydraulic cylinder is blocked by a sliding sleeve. So by the input signal, we could get a required output motion. This system is known as a closed-loop system in which the output is given to the input to change the input.

Electro-hydraulic servo valve

In this type of servo valve the operation is done with the help of analog or digital input and this input is used for the required movement in a hydraulic cylinder. The important components in a servo valve are torque motor, flapper nozzle, and spools. If the input is given to the torque motor then the motor will be powered, the input will be electric power. Because of the input, the torque motor will move the spool of the servo valve according to the requirement. The direction of the flow can be controlled by shifting the spool direction. If the flow direction needs to be changed then the spool is shifted to the other direction

What are the applications of servo valve

  • Servo valves are used in many industrial applications
  • These valves are used in earth moving vehicles
  • In articulated arm devices
  • It is used in cargo handling cranes
  • Farm machinery and steel mill controls
  • Fire trucks and servicing vehicles
  • Logging equipment and utility construction