When a burst disc and a safety valve are used in series, what is the function of the vent valve in between? Where should I go
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When a burst disc and a safety valve are used in series, a pressure gauge and a vent valve should be installed between them. The pressure gauge is used to check whether the burst disc has ruptured; but what is the purpose of the vent valve located in between? How large does this vent valve need to be? Should this vent also be connected to the flare?
This vent valve must serve the purpose of draining liquid; once the burst disc ruptures, it is necessary to drain the liquid, and the vent valve functions as a regular drain, allowing the liquid to flow back directly into the tank.
Mine is on a liquefied hydrocarbon sphere tank; there shouldn’t be any liquid coming out, right?
There is a nitrogen seal at the top; even without it, the upper part is in a gaseous state
I checked other posts on the forum as well: “A pressure gauge, stopcock, vent hole, or alarm indicator should be installed between the rupture disc device and the safety valve, in order to check whether the rupture disc has ruptured or is leaking”； Measures should also be taken between the rupture disc and the safety valve to ensure that no pressure buildup occurs in the space, thereby preventing the structural components on the pressure-bearing side of the rupture disc from having an increased capacity to withstand pressure. ”I think it’s the latter reason.
This explosion-proof disc and safety valve should be installed in parallel, and equipped with a three-way plug for replacing the explosion-proof disc or for carrying out repairs after it ruptures. As for whether the discharged materials are recycled or released into the atmosphere, that is another matter. A pressure gauge cannot be used as a monitoring instrument for blast discs.
It is recommended to leave a short pipe between the rupture disc and the safety valve, as there is molecular-level diffusion at the cracks in the rupture disc. Without this short pipe, the diffusing molecules will quickly fill the space between the rupture disc and the safety valve, thereby affecting the back pressure of the rupture disc.
When a burst disc is connected in series at the inlet of a safety valve, the calibration pressure of the burst disc must be the same as the set pressure of the safety valve. The diameter of the burst disc shall be no smaller than the diameter of the safety valve inlet, and a pressure gauge and a vent valve must be installed between the burst disc and the safety valve. When selecting a rupture disc, one should choose one that does not produce fragments upon rupture. In many cases, due to space constraints, it is possible to make holes in the holder behind the rupture disc in order to connect a pressure gauge and a zero-venting device; however, it is recommended to leave a short pipe between the rupture disc and the safety valve. This is because there is molecular-level diffusion at the cracks in the rupture disc, and without such a short pipe, the diffused molecules will quickly fill the space between the rupture disc and the safety valve, thereby affecting the back pressure of the rupture disc.
The main reason is that safety valves generally do not provide a perfect seal; if there is backpressure in the outlet pipe of the safety valve, fluid will flow back into its inlet. Therefore, a pressure gauge and a vent valve are installed between the safety valve inlet and the burst disc. It is necessary to measure the pressure on the gauge; otherwise, the burst pressure of the rupture disc will not be accurate.