Valves and Clutches Commonly Used in Energy-Saving Systems

Abstract

In energy-saving systems, clutches and valves are used for equipment switching and load distribution.

In energy-saving systems, clutches and valves are used for equipment switching and load distribution.

5.1 Magnetic Powder Clutch and Magnetic Powder Brake

The magnetic powder clutch places magnetic powder between the active part and the passive part, and adjusts the attraction and distribution of the magnetic powder inside the magnetic powder clutch by changing the excitation voltage of the electromagnetic coil. Use magnetic powder to transmit torque between the driving shaft and the driven shaft. When the speed of the driving shaft is constant, the speed of the driven shaft can be controlled. The principle of the magnetic powder brake is the same as that of the magnetic powder clutch, except that it fixes the speed of the driving shaft to zero. The rotational speed and output torque of the driven shaft are adjustable.

Magnetic powder clutches and magnetic powder brakes can be used for breaking control and speed control.

Magnetic powder clutches and magnetic powder brakes are widely used in automatic production lines such as printing machines, die-cutting machines, paper machines, compound machines, wire drawing machines, coating machines, winding machines, metal sheets, strips, and films. They are mainly used for automatic tension control. For unwinding or rewinding control, generally the magnetic powder brake is used for unwinding control, and the magnetic powder clutch is used for rewinding control.

Magnetic powder clutches can also be used in power transmission mechanisms such as motors, engines, electric mechanisms, and reducers. One shaft of the magnetic powder clutch is connected to the motor side, and the other shaft is connected to the load side. Changing the excitation voltage of the magnetic powder clutch can adjust the torque and speed of the output shaft, or realize separate control of driving shaft and driven shaft.

A magnetic powder brake generally has only one output shaft, and a magnetic powder clutch has an input shaft and an output shaft. The appearance of the magnetic powder clutch and magnetic powder brake is shown in Fig. 5.1.

Fig. 5.1

Magnetic powder clutch and magnetic powder brake

5.2 Electromagnetic Clutch and Electromagnetic Brake

There are coils, passive friction plates and active friction plates inside the electromagnetic clutch and electromagnetic brake. There is an armature on the passive friction plate. The passive friction plate is an elastic disc structure. The active friction plate is connected to the rotating power shaft. When the coil is powered off, the passive friction plate separates from the active friction plate under the action of elastic force, and the clutch is in a separated state. The coil is energized to generate magnetic force, overcomes the elastic force of the shrapnel, the active friction plate and the active friction plate are attracted together, and they are in the engaged state. Some electromagnetic clutches and electromagnetic brakes are integrated. The appearance of the clutch and electromagnetic brake is shown in Fig. 5.2.

Fig. 5.2

Electromagnetic clutch and electromagnetic brake

5.3 Electro-Hydraulic Proportional Valve

By changing the duty ratio of the voltage applied to the solenoid valve coil, that is, changing the average voltage on the solenoid valve coil, the flow area of the valve or the elastic force of the constant pressure spring is changed. Such a device is an electro-hydraulic proportional valve. In the hydraulic system, the manually adjusted throttle valve uses people to change the throttle area of the valve to adjust the flow rate. The manually controlled pressure regulating valve uses people to change the spring force of the constant pressure spring to adjust the output pressure. Changing the average voltage on the solenoid valve coil can continuously change the flow area of the valve, thereby continuously controlling the flow of hydraulic oil. Such an electro-hydraulic proportional valve is an electro-hydraulic proportional speed control valve. The principle is shown in Fig. 5.3. The power supply voltage of the electromagnetic coil can use PWM (pulse Wide modulation) method to continuously adjust, changing the duty cycle of the electromagnetic coil voltage, that is, changing the average voltage of the electromagnetic coil. Changing the thrust of the valve stem on the throttle valve core means changing the pressure from the P1 oil inlet to the P2 oil outlet, changing the area of the oil port throttle surface, thereby changing the flow rate of the hydraulic oil outlet.

Fig. 5.3

Principle of electro-hydraulic proportional speed control valve

Change the duty ratio of the voltage applied to the solenoid valve coil, change the elastic force of the constant pressure spring, and continuously control the output pressure of the hydraulic oil. Such an electro-hydraulic proportional valve is an electro-hydraulic proportional pressure valve. The principle is shown in Fig. 5.4. Change The duty cycle of the electromagnetic coil voltage, that is, the average voltage of the electromagnetic coil is changed, and the thrust of the spring on the valve stem to the poppet valve is changed. The hydraulic oil is connected to the P port. When the pressure of the P port is greater than the thrust of the spring to the poppet valve, the poppet valve opens, the hydraulic oil is unloaded from the T port. The voltage of the electromagnetic coil is changed, that is, the pressure of the hydraulic oil is changed.

Fig. 5.4

Electro-hydraulic proportional pressure valve

The shape of the electro-hydraulic proportional valve is shown in Fig. 5.5.

Fig. 5.5

Electro-hydraulic proportional valve

The electro-hydraulic proportional valve has lower requirements on the cleanliness of the oil circuit than the electro-hydraulic servo valve. The control precision of the electro-hydraulic proportional valve is higher, reaching the servo control level, and it can also be used as an electro-hydraulic servo valve.

5.4 Electro-Hydraulic Servo Valve

Most of the electro-hydraulic servo valves use the amplification of the nozzle baffle to control the slide valve to perform power amplification, and use the weak electric signal sent by the automatic control system to control the precise movement of large parts of the hydraulic system. The weak electric signal controls the current of the electromagnetic coil. The change of the magnetic force of the electromagnetic coil brings about the change of the distance between the baffle and the nozzle, and at the same time changes the pressure in the space behind the nozzle. If this pressure is directly output, it is called a first-stage electro-hydraulic servo valve. The body is generally made of aluminum alloy, and its principle is shown in Fig. 5.6.

Fig. 5.6

First stage electro-hydraulic servo valve

The hydraulic oil is connected to the input port P on both sides. One end enters the space connected to port A through the throttle hole, this space communicates with the nozzle on the left side. One end enters the space connected to port B through the throttle hole, and this space communicates with the nozzle on the right side. The hydraulic oil through the nozzle flows out through the O port. After the electromagnetic coil is energized, assuming that the left end of the armature is an N pole, this N pole acts on the NS pole of the magnet to make the armature move downward. Similarly, the right end of the armature is shown as S pole, which interacts with the N S pole of the magnet, so that the armature moves upward. The baffle connected to the armature rotates counterclockwise, the baffle is close to the right nozzle, the pressure of port B increases. The baffle and the left side nozzle are far away, the pressure of A port decreases, which changes the pressure and flow of B port and A port. A port and B port are respectively connected to the oil holes on both sides of the hydraulic cylinder to control the push rod of the hydraulic cylinder for precise movement.

The 2-stage electro-hydraulic servo valve uses the 1-stage electro-hydraulic servo valve as the pilot valve to control a 4-way hydraulic cylinder for power amplification, so that the power of the output port A and B is greater. The principle is shown in Fig. 5.7. There is a small ball under the baffle connected to the center of the slide valve to form a joint. The left and right movement of the baffle drives the slide valve to move left and right. The left and right movement of the baffle changes the pressure of P1 cavity and P2 cavity, while the pressure of P1 cavity and P2 cavity pushes the spool valve to move in reverse, and finally the spool valve balances at one position. Changing the throttling area 1 of A port (or B port) and P port, and changing the throttling area 2 of B port (or A port) and O port. Port A and port B are respectively connected to the oil holes on both sides of the hydraulic cylinder to control the cylinder rod of the hydraulic cylinder for precise movement.

Fig. 5.7.

2-stage electro-hydraulic servo valve

The shape of the electro-hydraulic servo valve is shown in Fig. 5.8.

Fig. 5.8

Electro-hydraulic servo valve

5.5 Electro-Hydraulic Digital Valve

The electro-hydraulic digital valve uses the number and direction of digital pulses to control the hydraulic valve. Uses the step** motor and ball screw to adjust the flow area of the valve or the spring force of the constant pressure spring to obtain more accurate flow or pressure. Using the motor and ball screw, changing the rotary motion of the step** motor into a linear motion to continuously change the flow area of the valve or the elastic force of the constant pressure spring, thereby continuously controlling the flow of hydraulic oil, or continuously controlling the pressure of hydraulic oil. Its principle is shown in Fig. 5.9. The step** motor drives the ball screw to rotate, the nut on the screw drives the valve stem to produce linear motion, and the valve stem pushes the valve core, thereby changing the pressure from P1 oil inlet to P2 oil outlet, the area of the throttle surface of the port changes the flow rate of the hydraulic oil outlet. The sensor is used to determine the zero position at the beginning, or to determine the zero position after the valve stem reaches one end.

Fig. 5.9

Electro-hydraulic digital valve

5.6 Pneumatic and Hydraulic Directional Solenoid Valves

When it is required to control the on–off and reversing of multi-channel gases, it is necessary to use a multi-position multi-pass pneumatic reversing solenoid valve. The valve uses a slider as the valve core to switch channels. The pneumatic reversing solenoid valve is controlled by an electromagnetic coil and has two working positions. The electromagnetic coil is energized to one valve position, and the internal spring is used to reset to the other valve position. When the pneumatic reversing solenoid valve is controlled by two electromagnetic coils, there can be two working positions. The coil 1 is energized, working position 1, coil 2 is energized to change to another working position. There can also be three working positions, coil 1 is energized to working position 1, coil 2 is energized to change to another working position, both coil 1 and coil 2 are powered off in the middle bit.

Commonly used reversing solenoid valves: 2-position 2-way (2/2), 2-position 3-way (3/2), 3-position 3-way (3/3), 2-position 4-way (4/2), 3-position 4-way (4/3), 2-position 5-way (5/2), 3-position 5-way (5/3).

Generally, on the valve body, use P to represent the input port of compressed air, A to represent the output port, O to represent the exhaust port, B to represent another output port, O1 and O2 to represent two exhaust ports. The valve with 2 states is a 2-position reversing valve, and the reversing valve with 3 states is a 3-position reversing valve. With 2-position 3-way normally close (P and A disconnected) reversing solenoid valve and 3-position 4-way normally closed in the middle (P, A, B, O are all blocked) reversing solenoid valve is given as an example, as shown in Fig. 5.10. In the figure, the positions marked with letters are the normal working positions after power off.

Fig. 5.10.

3-position 4-way intermediate closed reversing solenoid valve

Figure 5.10a is a 2-position 3-way (normally open) solenoid valve, single electromagnetic coil (mark on the left), spring return (mark on the left), in the normal (power-off) position, the compressed air input port P and output Port A is disconnected, A is connected to exhaust port O, after reversing, the spool moves to the right position, P is connected to A, and exhaust port O is disconnected from A.

Figure 5.10b is a 3-position 4-way (normally closed in the middle) solenoid valve, double solenoid coils (one on the left and one on the right), in the middle position of the normal state (power-off), compressed air input port P and output port A, output port Both B and exhaust port O are disconnected.

After the left solenoid valve is energized, the input port P is connected to the output port A, and the output port B is connected to the exhaust port O.

After the right solenoid valve is energized, the input port P is connected to the output port B, the output port A is connected to the exhaust port O.

The switching frequency of some direct-acting high-speed 2-position 2-way solenoid valves with pneumatic reset can reach thousands of hertz. This kind of valve is often used for high-speed sorting. The switching frequency of the direct-acting high-speed 2-position 3-way switching valve with spring return can also reach several hundred Hz.

When the pressure of the compressed gas is high, the force required for the spool reversing is relatively large. In order not to use a more powerful electromagnetic coil, the pilot valve can be used to control the reversing valve. The working process is: first use the electromagnetic coil to control a smaller reversing valve, this valve is called the pilot valve. The electromagnetic power required by the pilot valve is small, and then the output port of the pilot valve is used to control the larger spool of the large reversing valve, and the switching control is performed after the power is amplified. The principle is shown in Fig. 5.11.

Fig. 5.11

Pilot valve controls reversing valve

Figure 5.11a is a direct-acting type, directly using the electromagnetic coil to push the spool of the reversing valve, the electromagnetic coil is powered off, and under the action of the spring, the A port and the O port are connected, and the P port is disconnected, as shown in Fig. 5.11b, the electromagnetic coil is energized, the P port and the A port are connected, and the O port is disconnected.

Figure 5.11c is the pilot type. The solenoid coil is used to control the spool of the pilot valve first. When the pilot valve is powered off, the spool is connected to O1. Under the action of the spring, the A port and the O port are connected, and the P port is disconnected. In Fig. 5.11d, the pilot valve is energized, the P port of the pilot valve communicates with the spool, the spool moves to the left, the P port communicates with the A port, and the O port disconnects. Since the pilot valve bore is small, the power can be less.

The shape of the common pneumatic reversing solenoid valve is shown in Fig. 5.12.

Fig. 5.12

Pneumatic reversing solenoid valve

When the on–off control of multiple liquids is required, a multi-position multi-pass hydraulic reversing solenoid valve is used. The hydraulic output power is greater than that of the air pressure. The shape of the common hydraulic reversing solenoid valve is shown in Fig. 5.13.

Fig. 5.13

Hydraulic reversing solenoid valve

5.7 Solenoid Valve and Pneumatic Valve

Solenoid valve is a device that uses coil power on and off to control liquid, gas and steam on and off. The solenoid valve acts after power is turned on, and resets by spring or hydraulic pressure after power is turned off. Generally, the valve is marked with the direction of the fluid. The closing and opening of the solenoid valve are relatively fast, and are generally used in small-diameter pipelines. The solenoid valve is divided into two types: energized to close and energized to open. When the power is turned on, the medium must be shut off (such as gas), while other control processes may require that it is safe to open after a sudden power failure. There are two types of power supply voltages: AC and DC., air conditioners, water heaters, and IC water meters have many applications, and the shapes of common solenoid valves are shown in Fig. 5.14.

Fig. 5.14

Solenoid valve

The pneumatic valve uses compressed air to control the diaphragm, bellows or cylinder, and controls the diaphragm, bellows or cylinder to drive the valve stem to move, push the valve core to close and open. Drive the valve stem to move, the valve stem is connected to the valve core to open or close. The bellows type is single-port air intake, the cylinder type can be single-port air intake or double-port air intake. The push rod of the cylinder is connected to the valve stem, and the valve stem is connected the valve core makes it open or close. Pneumatic valves are divided into two types: air-to-close and air-to-open. In flammable and explosive occasions, pneumatic valves are safer than solenoid valves because they do not have the problem of accidental ignition, and are generally used to control pneumatic valves with higher fluid pressure or larger pipe diameters. They have pilot valves inside, which amplify the force of switching valves. The shape of common pneumatic valves is shown in Fig. 5.15.

Fig. 5.15

Pneumatic valve

5.8 Electric Regulating Valve and Pneumatic Regulating Valve

When the position of the valve is only fully open and fully closed, which cannot meet the process requirements. We need to control the opening of the valve. At this time, an electric control valve or a pneumatic control valve is required.

The difference between the electric regulating valve (or electric valve, driven by an electric motor) and the solenoid valve is that the valve opening of the electric regulating valve can be controlled, rather than simply realizing on and off. The power of the electric control valve is the electric motor, and there is a process of closing and opening. It can be used in large-diameter pipelines or occasions where flow or pressure needs to be adjusted. The electric control valve with a valve positioner can use standard signals (0–5 V, 4–20 mA, etc.) to control the opening of the valve in the control system. The electric valve without valve regulator uses the forward and reverse of the valve motor and the feedback signal of the valve opening to control the opening of the valve. The appearance of the electric regulating valve is shown in Fig. 5.16. The electric damper (or louver) that regulates the low-pressure air duct (such as the air supply and induction of the boiler) has a larger volume and a different shape.

Fig. 5.16

Electric regulating valve

Motors, reducers or linkages form more commonly used linear strokes, angular strokes (0–90°) and multi-rotation (>360°) electric actuators, and the reducers are mostly worm wheel and gear structures. The electric actuator is mainly used for the control of various valves (gate valve, disc valve, ball valve, globe valve, etc.), and it is the actuator of the electric control valve, and its appearance is shown in Fig. 4.3.

In flammable and explosive occasions, the safety of the pneumatic control valve is higher than that of the electric control valve. The pneumatic control valve uses compressed air to control the diaphragm, bellows or cylinder, and the diaphragm, bellows or cylinder then drives the valve stem to push the valve core. The opening of the valve is controlled through the valve position feedback. The pneumatic control valve has two types: air opening and air closing. The choice of air opening and air closing will affect the positive and negative selection of the controller's control function. The shape of the pneumatic control valve is shown in Fig. 5.17.

Fig. 5.17

Pneumatic regulating valve

5.9 Electric/Pneumatic Converter

Since the calculation and processing of the automatic control system are electrical signals, and some pneumatic systems require continuously adjustable air pressure, a device that converts electrical control signals into pneumatic control signals is required.

The electric/pneumatic converter converts the 4–20 mA control signal into a standard air pressure control signal of 0.2–1 kg/cm² by using nozzles, baffles, pneumatic amplifiers, signal control coils, iron cores, magnetic steel and levers. The principle of the electric/pneumatic converter is shown in Fig. 5.18. The signal coil is fed with a 4–20 mA control signal. The greater the signal current, the greater the repulsion between the coil and the magnet, the closer the distance between the baffle and the nozzle, and the greater the outlet pressure. The smaller the signal current, the smaller the repulsive force between the coil and the magnet, the farther the distance between the baffle and the nozzle, the smaller the outlet pressure, so the current in the signal coil is proportional to the outlet pressure. The outlet air pressure is fed back into the Bellows, if the outlet pressure is too high, the bellows will push the lever to make the baffle close to the nozzle, so that the outlet pressure will decrease. Adjust the zero adjustment screw, so that 4 mA corresponds to the standard air pressure of 0.2 kg/cm².

Fig. 5.18

Principle of electric/gas converter

In fact, the electric/pneumatic converter can also be obtained by combining a small motor, a pressure regulating valve and a pressure sensor. The appearance of the electric/pneumatic converter is shown in Fig. 5.19.

Fig. 5.19

Electrical converter

5.10 Self-operated Regulating Valve

In some automatic control occasions, precise control is not required, and a self-operated regulating valve can be used to complete simple automatic constant pressure, constant temperature or constant current control without using PLC, PID and other controllers. There are many applications in gas, liquid and steam control in metallurgy, metallurgy and other occasions.

When using a self-operated regulating valve to control the temperature, a temperature ball is inserted into the pipe and the temperature ball is filled with a certain amount of liquid. The volume of the liquid expands and contracts at different temperatures, and the expanded and contracted liquid pushes the diaphragm or piston. After the movement of the diaphragm or piston is balanced with the internal spring force, the valve stem of the regulating valve is determined to rise or fall, and finally the opening of the valve is controlled to realize automatic temperature control.

The pressure control self-operated regulating valve uses the pressure of the liquid at the valve output port (or inlet) to push the diaphragm or piston to drive the valve stem up and down, and finally realizes the control of the opening of the valve, and automatically controls the pressure.

The self-operated regulating valve that controls the flow rate uses the pressure of the liquid at the input port and the output port of the valve, and the pressure difference between the two sides of the valve. The movement of the disc or piston drives the valve stem to rise and fall, and finally realizes the control of the opening of the valve and the automatic control of the flow rate.

The shape of the self-operated regulating valve is shown in Fig. 5.20.

Fig. 5.20

Self-operated regulating valve

5.11 Relays and Contactors

The on–off of the power supply and the device needs to be controlled by the contacts of the contactor. The start/stop, forward/reverse, function switching and other actions in the control circuit need to use the contacts of the relay for on–off control. These two devices are commonly used in energy-saving systems, as shown in Fig. 5.21.

Fig. 5.21

Relay and AC contactor

5.12 Other Electric Devices

Motors, reducers and linkages can form complex movements, which can be applied to various automatic control occasions, such as fans driven by motors, water pumps, belt conveyors, scraper conveyors, impeller feeders, screw conveyors, etc.

General machinery includes feeders, oil pumps, quantitative pumps, peristaltic pumps, etc., and these mechanisms are widely used in automation systems as a whole or as non-standard products, and will not be listed here.