A valve is defined as a controlling device that controls the flow of fluid or air through pipes or ducts, especially an automatic device that allows the direction of fluid in one direction only. A proportional valve is one that deals with a change in the pressure of output flow upon a change in the pressure of input flow. For example, if input is double the output of pressure will also be double.
A proportional valve can change the output when a change in electrical signal is received at the input. They work in response to variations in electrical input signals. These valves are sometimes called electrohydraulic valves because, in hydraulic servo valves, the valve is controlled by electrical signals.
The spool of a valve is controlled by an electrical signal which is produced by the solenoid.
A spool valve is almost found in every industry. It can perform a wide range of tasks. It is used in the oil and energy sector or air as an energy source (pneumatic system). Its job is to control the flow of direction of energy sources by combining or routing the path through which oil or air is traveling. A basic type of proportional valve used is proportioning solenoid valve which is widely known throughout the world.
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Servo vs proportional valve
Servo valves are used in closed-loop systems and with more sophisticated electronics. Therefore servo valves are much more expensive. The difference between servo and proportional valves is proportional valves can be used in both open and closed-loop systems but servo is used only in closed-loop systems.
A proportional control valve can be used to improve control of machines without investing much in servo control systems. Proportional valves are used as direction control or pressure control valves but usually, they are direction control valves. Their actuation is done with the help of electric signals. Electric signals decide the direction and flow rate of the valve.
Features of proportioning solenoid valve
These types of valves are used in a close loop control system and hence the valves are controlled with the help of electrical input signals from sensors. It is because of this feature the proportioning solenoid valve is used for many applications. Proportioning solenoid valves provide various safety features in case of power shutdown or interruption of supply the valve will automatically close immediately. These types of valves have a long life and need less maintenance. Hence the maintenance of a valve will also decrease.
Construction of proportioning solenoid valve
The body of a proportioning solenoid valve is made up of a high-grade hydraulic casting and the spool is made up of a hardened steel. The valve is painted and the solenoid is zinc-coated. The housing of electronics is made up of aluminum. The proportional spool slides in the cast body. Like a directional control valve, the construction of a valve is quick and short. They are economical and provide a high flow capacity to flow through them. The throttle area of the valve is formed by making notches cut into the spool. The size and geometry of the notch determine the flow capacity of a given housing.
Working of Proportional valve
Based on the electrical signal input, a proportional directional control valve would modify the fluid flow. The output of these valves is proportionate to the electronically controlled input. The output will take one of three forms: direction, pressure, or flow. The coils in the valves generally function in direct current (DC) and may be powered by varied voltages. This produces a changing force, which is utilised to shift the spool. These valves have excellent efficiency and accuracy, and they can also be activated remotely. These valves can operate cylinders or other hydraulic motors.
The outside device such as a PLC, computer, or potentiometer provides a signal so that the valve operates according to given instructions and this will automate the device. The control device provides an electrical signal to the card driver and sends a current signal to the solenoid valve. The spool shifts because of the force acting on it. A flow path is created between the pump and the actuator port. A transducer checks the spool movement.
Proportional valves are widely used in analytics and test instrumentation. They have applications in medical and foundry as well. They are also used in process applications of an industry such as tensioning, spraying, and blow molding.
