How to Tell If a Valve Is Open or Closed: A Complete Guide
Introduction
A valve is a mechanical device used to control the flow direction, pressure, flow rate and other parameters of a fluid. It is usually composed of a valve body, a start-stop component and a drive device. Valves play a very important role in pipeline systems and are used to connect, cut off, regulate, divert, prevent backflow, divert or overflow pressure relief and other functions.
This article will share how to determine the switch status of ball valves, butterfly valves, stop valves, and gate valves, as well as how to determine whether the drive valve (i.e., the valve without a manual operating handle) is closed or open, and introduce the advantages of smart valves in switching and regulation.
Opening and closing status of ball valve and butterfly valve
Ball valves and butterfly valves are both simple and intuitive to judge. When closed, the handle and the pipe are perpendicular, visually it is blocking the flow of fluid in the pipe; when open, the handle and the pipe are parallel, which is the case for almost all ball valves.
It should be noted that plastic valves with T-shaped handles are still ball valves, so the above principles apply. In addition, the handle of the ball valve should point in the direction of flow when it is open, which is a more intuitive indicator of which side of the valve still has water after the valve is closed.
The butterfly valve handle is slightly different from the ball valve. The butterfly valve has a latching mechanism. This latching mechanism can be positioned somewhere between closed and open to adjust the flow. Ball valves are usually used only in the open or closed position. The latch on the butterfly valve handle prevents water flow from pushing the valve to the fully open position. As with the ball valve, the handle should point in the direction of flow through the pipe.
Open/close status of gate valve/stop valve
Compared with ball valves/butterfly valves, valves with handwheels (such as gate valves) are more complicated. Not only can the on/off status of the valve not be seen intuitively, it is also difficult to determine whether the valve is completely closed or open. Manual rotation is required to know.
To determine the on/off status of this type of valve, you need to know its correct rotation direction. Generally speaking, if you turn it clockwise until the handwheel can no longer turn, the valve is completely closed; if you turn it counterclockwise until the handwheel can no longer turn, the valve is open. Of course, there are some rare exceptions that open or close by turning in the opposite direction, but this is very rare and is generally marked out.
Today, most gate valves and stop valves have rising stems, which means that the handwheel will extend further from the valve body when it is opened, and will retract to the bottom when the valve is closed. Although this can also be judged by visual inspection, this method is not rigorous, and manual confirmation is the safest. In addition, some valves with handwheels have dark stems. This means that it is impossible to judge whether the valve is open or closed by the naked eye, and manual confirmation is required.
Opening and closing status of valves with actuators
In the previous tweet, we learned about valve selection, which mentioned that there is a distinction between drive types in valve models. Models that control the opening and closing of valves by electrical or pneumatic forces are usually equipped with actuators and no manual handles, so it is almost impossible to confirm whether the valve is open or closed by visual or manual methods.
The driven valve is connected to the control system and indicates whether the pipeline is open or closed. The best way to determine whether the driven valve is working properly is to install a flow meter downstream.
It should be noted that although many driven valves are also equipped with manual handles as a backup device in case of emergency, these valves are not adjusted in normal operation. Therefore, it is difficult to determine whether these types of valves are open or closed by visual or manual methods.