Is the dual-valve setup one in use and one as a backup, or are both valves closed?
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1. The sampling valve switches frequently and is prone to damage; therefore, two valves are generally installed on the sampling tube. In production, are both valves closed, or are they kept open near the equipment valves with the second one used as a switch for sampling? 2. To completely drain/empty high-pressure pipelines, dual valves are generally required. In production, are both valves closed, or is the valve near the equipment kept open while the second one serves as the normally operating switch valve? 3. The drain pipes of towers and vessels should be equipped with double valves for normal operation. In production, are both valves closed, or is the valve near the equipment kept open while the second one serves as the normally operating switch valve? 4. When draining/emptying hazardous materials, a double valve system should be used, with both valves closed. In production, should it be kept open near the equipment valves, with the second one serving as the normally operated switch valve?
As I understand it, they are all turned off. I don’t know who could help give some guidance.
Double valves are installed for both discharge and sampling of various pipes or equipment, as both processes take place at atmospheric pressure and the valves are opened and closed frequently; the medium can erode the valve components and cause leaks. Replacing such valves would inevitably lead to production shutdowns； In practice, the first valve closest to the equipment is normally kept fully open; it is this second valve that is operated. If leakage occurs in the second valve, the first valve can be closed to allow for the replacement or repair of the second valve.
The dual valves used in sampling operations have different modes of operation; this also depends on the volume of the pipeline between the two valves, and it is possible to switch them on and off alternately