Normally off selection for solenoid valves
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When selecting solenoid valves for the cut-off valves of FC and FO, should it be a normally open or normally closed type? Is it usually okay to disconnect? Should we still consider whether it’s a live fault or a loss-of-pulse fault? Must the air supply for the cut-off valve come from above the cylinder? Could it be the location where the spring is installed? If the on-site shut-off valve is installed backwards, it will now close instead of opening at 4 milliamps. What should I do? Are there several solutions? Which solutions will change the fault bits FC/FO, and which will not? Automatic control instruments
1. The solenoid valve should be set to a fail-safe configuration, meaning it loses power in the event of a fault; this can be configured during the setup of the air circuit. It has two air output ports. 2. Springs can be installed; those with air intake at the top are generally used with direct-acting actuators, while those with air intake at the bottom are used with reverse-acting actuators. 3. Since it is a shut-off valve, the control signal should not be a 4mA change, but rather a change in power status. This change in power status can be achieved by adjusting the air circuit. For control valves, the positioner settings can be modified to use reverse action; additionally, the system configuration can be inverted
Thank you for the guidance! Point 3 is understood. I’m a bit confused about point 1: normally, shut-off valves and control valves are designed to be fail-safe, but is the same true for solenoid valves? Changing to the on-constant and off-constant modes can also be combined with cut-off valves and control valves to achieve a fail-safe position. However, the electric and de-energized operations of the solenoid valve will change as a result. Does this have an impact? It still needs to be set as a loss-of-power action. Then, select the normally open or normally closed type based on the requirements of the control valve or shut-off valve. Point 2: If it is a cut-off valve with spring return, should the air circuit of the solenoid valve be connected to the upper air inlet of the cylinder? Can it be connected to the lower air inlet instead? I have quite a few doubts; I’m not sure if I’ve explained it clearly There is an example, but I won’t upload a picture; I’m not sure if this description is clear enough Thank you
Generally, for two-way three-port solenoid valves, NC is chosen; that is, when the coil is energized, air is supplied to the cylinder； The coil loses power, and the air in the cylinder is released.
1. When the solenoid valve is operating under powered conditions, it is possible to determine whether it is functioning properly; safety also needs to be taken into consideration. The solenoid valve is required to reach the fault position in the event of a power loss; the valve will operate whether there is power or not. 2. In piston-type valves, when the spring force is insufficient, air can be introduced from below to increase the pushing force; this is not possible in diaphragm-type valves. As a result, there is only one direction of force, and it is not possible to control the downward movement of the valve stem
The general principle in the petrochemical industry is fail-safe operation; here, by \"failure\" is meant a situation of loss of air or power supply, in which the valve can be placed in the safe position required by the process specifications. In other words, when the device is operating normally, the solenoid valve is energized and the valve is in its normal position; in case of a fault, interlock, power loss, or similar situations that require the valve to assume a corresponding fault state, it should be configured accordingly.