Could you provide a detailed analysis of how the pneumatic valves FO/FC/FB(L) function?

This post was last edited by s4685565 on 2011-9-28 09:01: FO fault = open, ventilation = off; loss of pressure = open. FC fault = closed, ventilation = on, loss of pressure = closed. Single-action spring actuators can generally achieve this function directly, while double-action actuators require a air tank for reset. . . FB should be fail-safe; a holding valve is required for single-acting types, while double-acting cylinders can achieve this directly.

This post was last edited and replied to by YPDI FWJ on 2011-9-28 at 11:49. Reply to 2# s4685565: 1. For a single-acting FL valve, what type of solenoid valve should be used? And the pressure maintaining valve, how is it connected to the air circuit? 2. For double-acting FL valves, what type of solenoid valve should be used? How to connect it on the gas line?

FO/FC/FB (L): FO – Fault Open, meaning the valve is in the open position due to a fault; FC – Fault Close, meaning the valve is in the closed position due to a fault; FL – Fault Lock, meaning the valve remains in its current position due to a fault. FB – It’s not clear what this means, but it’s likely also related to maintaining the valve’s position. Since it’s a pneumatic valve, the ways in which the valve can switch between open and closed positions vary depending on whether there’s a power loss, air loss, or signal loss – three different types of faults that result in different switching methods. First, let’s talk about switch valves, which are a set consisting of solenoid valves, cylinders, and valves. Cylinders are further divided into single-acting and double-acting types. A single-acting cylinder is equipped with a two-position three-way solenoid valve; in the single-acting configuration, it is very simple to operate either in the off state when power is lost or in the fault state when air supply is interrupted – there is merely a difference between the forward and reverse action of the cylinder. The loss-of-pressure position retention valve is installed before the air supply connected to the solenoid valve. Its function is quite simple: it uses the main air supply as a signal – as long as the main air supply is active, the flow remains unblocked; once the air supply is cut off, the position retention valve locks itself, preventing the gas inside the cylinder from escaping and thus ensuring position retention. For loss-of-power position retention, a dual-control solenoid valve can be used; by examining the internal structure of the solenoid valve, it becomes clear that it is capable of maintaining the position. Double-acting cylinder: A double-acting cylinder is equipped with a two-position five-way solenoid valve. Due to its structure, it lacks a spring for return, so it stays in place when the air supply is cut off. However, this cannot be considered true position holding, as the valve position can change depending on the flow direction and speed of the fluid in the pipes. If strict control over the valve position is required, an air lock valve must be installed (and the air lock valve used with three-way or five-way solenoid valves is different), which enables position holding even when the air supply is interrupted. Turn on when air is cut off, turn off when air is cut off: Of course, double-acting cylinders are generally not used for this purpose; single-acting cylinders are employed instead. If the design requirements call for a double-acting cylinder to achieve this function, there’s nothing else to do but call such a design stupid and use an air tank instead. Air tanks work well for small cylinders, but not for large ones, as the amount of gas stored and the pressure it can generate aren’t sufficient. Power-off position retention: Only dual-electrovalve control can keep the valve in an open or closed state, but this is not true position retention in principle. Positioner: Positioners can achieve signal loss retention, full open, and full closed states; the specific functionality depends on each individual positioner. This is the simplest fault switch retention mechanism; no further explanation is needed for complex gas circuit analysis

Reply to 3# YPDI FWJ: Add a single-acting solenoid valve, a two-position three-way solenoid valve, and a pressure reducing valve. The output from the pressure reducing valve is divided into two paths – one path supplies air to the solenoid valve, while the other path supplies air to the position maintaining valve. The output from the solenoid valve serves as a signal for the position maintaining valve, and the output from that valve is connected to the cylinder. This configuration enables the function of maintaining the position even when power is lost. Stop breathing, hold position. For the two-action type, add a two-position five-way solenoid valve; the valve closes when power is lost, ensuring position retention under air loss conditions.

Double-acting cylinder: A double-acting cylinder is equipped with a two-position five-way solenoid valve. Due to its structure, it lacks a spring for return, so it stays in place when the air supply is cut off. However, this cannot be considered true position holding, as the valve position can change depending on the flow direction and speed of the fluid in the pipes. If strict control over the valve position is required, an air lock valve must be installed (and the air lock valve used with three-way or five-way solenoid valves is different), which enables position holding even when the air supply is interrupted.