A gas pressure regulator, commonly known as a pressure reducing valve, is a device that maintains the outlet gas at a specified pressure by automatically adjusting the flow of gas through the regulating valve. It is usually divided into two types: direct-acting and indirect-acting.
The direct-acting regulator consists of a measuring element (diaphragm), a transmission component (valve stem), and a control mechanism (valve) (Figure 1). When the gas consumption after the outlet increases or the inlet pressure decreases, the outlet pressure drops. At this point, the pressure reflected by the pilot tube causes the force acting on the underside of the diaphragm to be less than the force exerted by the weight on top of the diaphragm (or spring), causing the diaphragm to drop. The valve disc also moves down with the valve stem, opening the valve wider, increasing the gas flow, and restoring the outlet pressure to the originally set value. Conversely, when the gas consumption after the outlet decreases or the inlet pressure rises, the valve closes slightly, reducing the flow while still restoring the outlet pressure. The outlet pressure value can be set by adjusting the weight of the weight or the spring force. Small liquefied petroleum gas pressure reducing valves and user regulators are all direct-acting.
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The indirect-acting regulator works on the principle shown in Figure 2. It consists of a main regulator, a pilot, and an exhaust valve. When the outlet pressure p2 is lower than the set value, the diaphragm of the pilot drops, opening the pilot valve. Gas throttled to a pressure of p3 is supplied to the space below the diaphragm of the main regulator. Since p3 is greater than p2, the valve of the main regulator opens wider, increasing the flow, and p2 returns to the set value. Conversely, when p2 exceeds the set value, the diaphragm of the pilot rises, closing the valve. Simultaneously, due to the force acting on the underside of the exhaust valve diaphragm, the exhaust valve opens, discharging some of the gas at pressure p3 into the atmosphere, reducing the force acting on the underside of the diaphragm of the main regulator. Since p2 is too high, the valve of the main regulator closes slightly, and p2 returns to the set value.
In China, the safe operating gas pressure for water heaters and stoves using liquefied petroleum gas is 2800Pa. The gas pressure inside bottled liquefied petroleum gas cylinders is generally 4kg. After passing through the pressure reducing valve in front of the cylinder, the gas pressure is reduced to 0.028kg (i.e., 2800Pa) for use by water heaters or stoves.
Gas storage and distribution stations, regional pressure regulating stations, and large user dedicated pressure regulating stations mostly adopt indirect-acting regulators.