Start switch valve control mode

Pneumatic on-off valves generally operate in two modes: supplying power to the solenoid valve in the control air circuit and cutting off the power, with no digital output. Pneumatic valves that require digital signals do not belong to on-off valves; they should be classified as instrument control valves.

It’s the pneumatic valve that controls the switch; our teacher told us to use a pneumatic one for our graduation project, but he didn’t tell us anything else. Then it must be using solenoid valves; turning power on and off corresponds to digital signals, right? In other words, an input of 1 means the solenoid valve is open and air is supplied continuously, while 0 means the valve is closed with no air flow?

The last edit to this post was made by shiwendong on 2016-5-29 at 22:32. Control principle and steps of the FBVAA two-stage pneumatic ball valve: 1. Control principle: The control principle is shown in Figure 3. Taking loading as an example, the process involves the solenoid valve 1 being activated, which causes the valve to open fully for loading. When the desired flow rate is approached, the solenoid valve 2 is activated while solenoid valve 1 deactivates (note that solenoid valve 1 deactivates 3 seconds after solenoid valve 2 is activated), and the valve enters a low-flow state. Once the flow rate reaches the set value, solenoid valve 2 deactivates and the valve closes completely. Under normal conditions, the solenoid valve of the emergency shut-off valve should be de-energized and in an open state, while the valve body should remain closed in the absence of air supply. When operating with an air source, it is first necessary to ensure that the adjustment screw and lock nut of the manual mechanism are disengaged. During operation, first turn on the air supply; when the pressure of the instrument air supply exceeds 0.3 Mpa, the piston rod moves forward under force, compressing the spring and simultaneously causing the rotating shaft and valve stem to rotate, which in turn opens the valve core and fully opens the valve. 　　To close the shut-off valve, the host computer issues a closing command, which causes the solenoid valve to be activated and closed; as a result, the gas inside the cylinder is released. When the pressure of the instrument air supply drops below 0.1 Mpa, the spring force becomes greater than the pressure of the air supply, causing the piston rod to move backward and the rotating shaft to start moving in the opposite direction. When the pressure drops to zero, the shut-off valve is completely closed. When operating with a manual mechanism, the air supply should first be cut off to drain the air from the cylinder, thereby reducing the instrument air pressure to zero. At this time, the shut-off valve should be in a closed state due to the lack of air pressure. To open the shut-off valve, turn the handle on the side of the spring cylinder counterclockwise; when the adjustment screw has protruded about 8 cm from the spring cylinder, resistance can be felt clearly. At this point, the screw of the manual mechanism is locked by the lock nut; continue to turn the handwheel in a counterclockwise direction until the adjustment screw stretches the spring, causing the piston rod to move forward. When the adjustment screw has moved about 21 cm out of the spring cylinder, the rotating shaft has completed a 90° rotation. At this point, the shut-off valve is fully opened. 　　To close the shut-off valve, turn the handwheel in a clockwise direction; this causes the spring to slowly return to its original position, pushing the piston rod backward and causing the shaft to rotate in the opposite direction. When the adjusting screw is moved to a position where the length of the spring cylinder is 8 cm, the spring is fully reset at this point. The cut-off valve is closed. Continue to turn the handwheel in a clockwise direction; when no resistance is felt at all, the screw of the manual mechanism becomes disengaged from the locking nut. During manual control, it is strictly prohibited to turn on the air supply. When the cut-off valve is in the normally open position, the adjustment screw of the manual mechanism cannot be locked by the lock nut. 2. Control steps: Taking the scenario of opening at one stage, closing at two stages, and controlling flow at a low level as an example, the specific control steps are as follows: (1) Charge stages ① and ②; open all valves to proceed with loading ； 　(2) As it approaches low-flow control, ⑧ and ④ become charged ； 　(3) After 3 seconds, ① and ② lose power, and the valve closes to a low-flow state ； 　(4) When loading is completed, ⑧ and ④ lose power, and the valves close completely. 　(5) If reloading, repeat steps (1) to (3). 3. Low-flow opening adjustment: The VAA pneumatic two-stage ball valve can pause once during the opening or closing process, allowing for precise control of flow rate based on system requirements. It is particularly suitable for use in chemical or oil loading systems; for example, the valve is opened fully to start the loading process, and when the flow rate approaches the set value, the valve is closed to a low-flow state. Once the set value is reached, the valve is completely closed. The low flow rate can be set on-site within the range of 0 to 45%, such as 5%, 8%, 10%, 15%, etc., to achieve precise control. The low-flow setting is already configured at the time of factory exit; if adjustment is needed on-site, follow these steps: (1) Loosen the protective sleeves at both ends ； 　(2) Use an Allen key to loosen the positioning pin on the copper shaft ； 　(3) Rotate a copper shaft by hand: turn it clockwise to set a lower flow rate, and turn it counterclockwise to set a higher flow rate. After making the adjustment, secure the positioning pin in place. Conduct a ventilation test to check whether the requirements are met; if not, repeat the adjustments several times until the requirements are satisfied. 　(4) In the fourth control step, during step 2, manually rotate the other copper shaft so that both ends press tightly against the cylinder end caps at the same time in step 3 of this fourth control step; under this applied force, tighten the positioning pins. 　(5) Cover the protective end caps at both ends.

Pneumatic on-off valves are controlled by switching the solenoid valve; all that is needed is to turn the solenoid valve on or off. What you mentioned – the valve opening when the solenoid valve is powered and closing when it is turned off – refers to single-acting cylinders, and this can also be achieved using a two-position three-way solenoid valve. There are also double-acting cylinders, which use two-position five-way solenoid valves; with these types, the valve opens or closes when the solenoid valve is powered, and then it closes or opens again when the power is turned off. To control an on-off valve, it is sufficient to turn the solenoid valve on or off. If there is a control system in place, a control box is required to facilitate operation. The control valve receives the control signal directly.