Is a pressure relief valve or a flow control orifice plate better for nitrogen sealing to reduce pressure in storage tanks?
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This post was last edited by Liangshuibei on 2015-6-17 09:08. I have a question and would appreciate guidance from those with more experience. If a combination of a vent valve and a nitrogen seal is needed on a storage tank, and a flow-limiting orifice plate is used for pressure reduction, then it’s necessary to install a vent pipe to allow exhaust gases to be collected or treated in a sealed manner. Isn’t this a waste of nitrogen? If a self-acting pressure regulator is used, a lot of nitrogen can be saved. Which one is better? This storage tank is an intermediate buffer tank, of the fixed-roof type
A self-acting control valve would be better.
I’ve never seen anyone use a flow-limiting orifice plate; generally, self-acting control valves are used instead. I’m not sure how the idea of using a flow-limiting orifice plate came about
Well, I think it’s a self-acting control valve; as for pressure, the control valve can have its settings adjusted, but that’s not possible with an orifice plate, right?
For filling a atmospheric-pressure sewage storage tank with nitrogen, we use orifice plates, and the gas outlet is controlled by a pressure-high/low interlock switch. In terms of design, I have also seen combinations of orifice plates filled with nitrogen and water seal tanks, from the drawings of Luoyang Institute.
What are the advantages of each approach? When a flow-limiting orifice plate is used, nitrogen is continuously fed in and then exhaust gas is continuously removed; it’s not possible to control the pressure. With a flow-limiting orifice plate, there’s no need for pressure sensing tubes, so there’s no risk of those tubes getting blocked. However, this method results in a waste of nitrogen, so it’s likely not used in large tanks
The operating condition for the orifice plate is that a pressure reduction effect can be achieved only at a certain flow rate; if the exhaust is closed, the pressure inside the tank will gradually equalize with the pressure at the front end of the orifice plate. At this time, control is achieved by using a switch valve in front of the pressure control orifice plate to maintain a certain nitrogen seal pressure, but this is generally not done. For simple cases, a self-acting valve is sufficient.