# A Method of Two-Stage Pressure Control Based on Multistage Orifices
## 1 Introduction  
Multiactuator systems are widely used in engineering, e.g., in bionic robots, engineering machinery, and turbine electrohydraulic control systems. When a single oil source serves the hydraulic control system with multiple actuators, the actions of each actuator are restrained due to the mutual influence of pressure and flow in the circuit; therefore, independent and stable pilot control pressure is often needed in the system to meet the specific operating requirements of the actuators. Taking the electrohydraulic control system of steam turbines in power plants as an example, the opening and closing actions of multiple hydraulic motors in the steam turbine system are controlled by pilot pressure. When providing higher pilot pressure, all actuators work normally, and the change in external load force of the actuator has little influence on pilot pressure. When the turbine functions abnormally, lower pilot pressure is provided to make the main control actuator close quickly and realize an emergency shutdown. At present, there are two main methods for the formation of pilot pressure. The first method is to provide two-stage pilot pressure through an independent pump source system, which makes the overall hydraulic system structure more complex and costlier to maintain. The second method is to directly takesystem pressure oil as the pilot oil source. This has pilot oil pressure closely related to the working pressure of the actuator, which can cause the system with a single pump source and multiple actuators to run incorrectly. It is difficult for this method to provide low pressure for emergency stops under normal conditions. In engineering systems, the throttling principle of an orifice is often adopted to realize single pressure control, such as using orifices to reproduce pressure conditions encountered at the inlet of steam generator tube bundles in nuclear power plants [1], installing an orifice in the pilot tube to retain pressure in the control chamber of the main valve in the pilot valve system of gas regulators [2], or controlling the fuel mixing and jet spray breakup of a liquid ejector by reducing pressure of the orifice [3]. When a single orifice is used to achieve large pressure drops, its diameter is too small and may cause problems such as liquid flash, flow blockage (in the gas flow), or serious erosion; therefore, a series of orifices with a large diameter are often adopted in engineering applications instead of a single orifice with a small diameter [4; 5], such as an orifice tube with six pressure-drop stages in the process line of power plants [6] and dimethyl ether flash-boiling spray discharged through a vertical twin-orifice injector [7]. [PERSON] et al. pointed out that when two orifice plates were connected in series, the distance between the two had a great influence on the overall pressure drop before and after the series connection as well as the upstream flow field of the second orifice [5]. [PERSON] et al. analyzed the damping characteristics of a two series orifices and the influence of their structural parameters on the pressure change of the control oil circuit by MATLAB [8]. [PERSON] et al. investigated the thermal fluid-flow transport phenomena of twin concentric orifices with different radii installed in an axially rotating passage [9]; however, no attention was paid to the effect of the series combination of orifice plates with different diameters on the pressure at a certain point. If more than two orifices are connected in the series, and solenoid valves are used to change the direction of oil flow, the pressure control of different levels can be realized. From the perspective of the engineering implementation of this method, components can be installed on the manifold block, and desired oil path can be obtained by drilling holes in the block to realize tubeless connection.