Why is a needle valve installed on the pressure gauge of a gas storage tank?

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Relevant regulatory provisions: “Safety Technical Inspection Regulations for Stationary Pressure Vessels” TSG 21–2016, 9.2.1.3 Installation of pressure gauges: (1) The installation location should be such that it is easy for operators to observe and clean; it should also be protected from adverse effects such as radiant heat, freezing, or vibration. (2) Between the pressure gauge and the pressure vessel, a three-way cock or needle valve must be installed (the three-way cock or needle valve should have an open indicator and a locking mechanism); no other fittings or pipes intended for other purposes may be connected. (3) For pressure gauges used with steam media, a water trap must be installed between the pressure gauge and the pressure vessel. (4) For pressure gauges used with corrosive or highly viscous media, a buffer device capable of isolating the medium must be installed between the pressure gauge and the pressure vessel. Why install a needle valve? It is mainly to facilitate the maintenance and replacement of pressure gauges; can other types of ball valves be used as well? First, it does not comply with the specifications; second, when opened, the needle valve and three-way cock allow the medium to flow at a relatively slow rate, thus preventing damage to the pressure gauge.