On the location of valve failures as well
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In fact, the fault location should be determined first, before discussing which suitable valve to use. Pneumatic single-acting types with spring return are generally chosen. For processes that require shutdown in the event of a fault, a gas-open valve can be selected; otherwise, a gas-close valve should be chosen. Here, a fault generally refers to a problem with the gas supply. If it is a pneumatic double-acting type without a spring, it becomes more complex. At this time, the opening and closing of the valve is achieved through a complex air circuit, and it usually comes equipped with an air tank.
Agree with the person above. The selection of a valve for air-operated opening or closing should be based on the process requirements, in order to protect the equipment. Both terms refer to air; this air serves as the power source for the valve, which is why they are referred to as pneumatic valves. By \"air-operated opening,\" it means that the valve opens when there is air supply, and by extension, it closes when there is no air. A situation with no air supply is usually indicative of a fault (such as a broken air supply line, etc.). In such cases, it is necessary for the valve to return to a safe state, and the safe state without control is generally the initial state.
What is the status of a pneumatically double-acting valve when it malfunctions?
In the case of a double-action failure, it generally remains in place
Everything discussed above is great. When selecting a pneumatic valve nowadays, it is generally necessary to determine the state of the valve in case of a failure. Failures can include issues with the air supply or the power supply; sometimes the required state may differ in these two scenarios, but in most cases it remains the same. Yes, whether it should be turned on or off in the event of a fault is not determined by the instrumentation specialists; it should be decided by the process engineering team, with the instrumentation used to implement that decision.
May I ask the original poster, what are the fault conditions of a pneumatic double-acting type?
Double-action failure: remain in place if there is no safety gas cylinder. If so, depending on the gas circuit settings, it can be fully open or fully closed
Double-acting retention. One solenoid valve operation is ineffective; it is also known as double-cylinder operation.
Double-acting types also come with spring return; it depends on the position it is in when it fails – whether it is in FO or FC mode