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In a pilot valve system, the pressure in the control chamber of the main valve is straightforwardly affected by pressure oscillation in the downstream pipeline or the pilot tube. To solve this problem, an orifice is generally installed in the pilot tube to restrain the oscillation. However, the orifice is a nonlinear flow resistance; the amplitude of the oscillation alters the gain curve of the control pressure response. In this study, a linear flow resistance such as a porous material is employed to stabilize the pilot valve system. A test pilot valve was manufactured, and a pilot valve system was developed in the laboratory of the authors of this article. A mathematical model of the pilot valve system using linear and nonlinear flow resistances was simulated in MATLAB. The linearity of the P-Q characteristics of the linear flow resistance was confirmed, and a series of frequency response experiments were performed to examine the dynamic characteristics of the pilot valve system with various flow resistances. The experimental results were in accord with the simulation results. This implied that when porous materials were used in the pilot valve system, the gain of the pressure response did not vary regardless of the varying pressure vibration amplitude. Therefore, porous materials are suitable to be used in the pilot valve system instead of an orifice to enhance its stability.

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In a gas governor unit, gas pressure vibration often occurs in the tube that connects the diaphragm chamber of the pilot valve to the downstream pipeline. Generally, placing a restriction such as an orifice in the tube can curb the vibration. However, because of the nonlinear flow rate characteristics of an orifice, the gain of the pressure response changes with changing amplitude of the pressure vibration. This paper proposes a method that employs porous materials for improving the characteristics of the gas pressure control system on account of their linear flow rate characteristics. A static flow rate characteristics experiment was performed and the linear flow rate characteristics of the porous materials were confirmed. Then, a series of dynamic pressure response experiments, in which an isothermal chamber replaced the diaphragm chamber, were performed to examine the dynamic characteristics of the porous materials and an orifice. The experimental results revealed that the gain of the pressure response in the isothermal chamber with the porous materials remained unchanged irrespective of changes in the pressure vibration amplitude, and they were in close agreement with the simulation results. They also indicated that the pressure gain of porous materials is smaller than that of an orifice when the amplitude of pressure vibration is small. These results demonstrate that porous materials can be employed instead of an orifice in the gas governor unit in order to improve the unit's stability.

In pneumatic systems, the volume of a pressure vessel can be assumed to be analogous to pneumatic capacitance, and is an important parameter that governs the pressure response of the system. Therefore, an accurate and high-fidelity volume measurement is an indispensable requirement for a high-precision pressure response system. However, in measurement of the volume of pneumatic pressure vessels, the conventional drainage method is inefficient, and may cause damage to the surfaces of the vessel. This paper proposes a new method that uses compressed-air discharge for volume measurement of pneumatic pressure vessels. The primary measurement equipment merely comprises an orifice and a pressure sensor. A formula that calculates the measured volume is obtained based on curves demonstrating the change in pressure derived as part of the experimental analysis conducted in this study. To demonstrate the effectiveness of the proposed method, volumes of three test tanks, considered as pneumatic pressure vessels, were measured using this method. The measurement exercise was performed using three orifices, the effective areas of which were measured in advance. Through use of the proposed method, the error in volume measurement is found to be maintained below approximately 4% by selecting an appropriate shut pressure and orifice diameter. Additionally, the method offers other advantages of being convenient to use, fast, and low cost, as well as non-damaging and non-corrosive to the pressure vessel.