Linear Flow Characteristics A valve with an ideal linear flow characteristic produces a flow that is directly proportional to the spool travel over the travel range. For example, at 50% of the nominal stroke, the flow is 50% of the maximum flow; at 80% of the nominal stroke, the flow is 80% of the maximum flow; and so on. As the spool travel changes, the flow rate changes are constant. Valves with linear characteristics are often specified for fluid level control as well as fluid control applications that require constant gain. Equal Percent Flow Characteristics - Ideally, for equal increments of spool travel, the change in flow for travel can be expressed as a constant percentage of the flow at change. The observed flow rate changes for stroke are relatively small when the valve spool approaches the valve seat and relatively large when the valve spool is nearly fully open. As a result, valves with inherent equal flow characteristics provide precise, regulated control over the lower limit of the travel range and rapidly increase flow as the valve spool approaches the fully open position. Valves with equal percent flow characteristics may be used in pressure control applications where most of the pressure drop is normally absorbed by the system and a relatively small portion is left to the control valve and where a highly variable pressure drop is expected. In most real systems, inlet pressure decreases with increasing flow rate, and an equal percentage characteristic is appropriate. For this reason, equal percentage becomes the most common valve characteristic. FAST FLOW CHARACTERISTICS A valve with quick-open flow characteristics provides maximum flow change at low stroke positions. The flow curve is essentially linear over the first 40% of the spool travel, with a clear flattening behind, indicating a small increase in flow as the stroke approaches full open. Control valves with quick open flow characteristics are commonly used for on / off applications. In the open / close situation, as the valve begins to open, a huge amount of flow must be quickly established. The result is that they are often used in valve release applications. Quick open valves can also be used for many of the same applications where linear flow characteristics are recommended, as the quick release feature is linear up to 70% of the maximum flow rate. The linearity decreases abruptly when the flow area produced by the spool stroke is equal to the flow area of ​​the valve seat. For a typical quick-open control valve, this occurs at a valve seat diameter that is equal to a quarter of the spool travel. Regulating valve flow characteristics of the inherent refers to the valve when both ends of the differential pressure constant flow through the valve with the opening rate of change. From a physical point of view, the inherent flow characteristics of the valve shows how effective the flow area of ​​the valve varies from gambling to gambling. There are several types of quick opening, linearity, equal score and parabola, while the three most widely used . (1) Quick-opening characteristic The rate of change of flow rate with opening degree is the highest in the opening range of the school, and the rate of change of the flow rate decreases sharply as the opening degree increases. (2) Linearity The rate of change of the flow rate with opening is constant within the range of 0--100%. (3) Equal Percentage Within the range of the school opening, the rate of change of flow rate with opening degree increases very little, but with the increase of valve opening, the rate of change increases sharply. Control valve role: Control valve (controlvalve) is used to regulate the flow of media, pressure and level. According to adjust the position of the signal, the valve automatically control the opening, so as to achieve the media flow, pressure and liquid level adjustment. Regulating valve sub-electric control valve, pneumatic control valve and hydraulic control valve. Regulating valve by the electric actuator or pneumatic actuator and control valve of two parts. Regulated and usually divided into two types of direct-through single-seat and direct two-seat, the latter has the ability to circulate large, uneven and small operation stability characteristics, it is generally particularly suitable for large flow, high pressure drop and leakage less occasions. Flow capacity Cv is one of the main parameters to select the control valve, the control valve flow capacity is defined as: When the control valve is fully open, the pressure drop across the valve is 0.1MPa, the fluid density of 1g / cm3 hourly flow path The number of flow control valve, known as the flow capacity, also known as flow coefficient, in Cv, said t / h, liquid Cv value calculated according to the following formula. According to the size of flow capacity Cv check the table, you can determine the nominal valve DN. Flow characteristics of the control valve, the pressure drop at both ends of the valve to maintain a constant condition, the medium flow through the control valve and the relative flow of its relationship between the opening. Regulating valve flow characteristics of linear characteristics, such as percentage characteristics and parabolic characteristics of three. The significance of the three kinds of fluency features are as follows: (1) Equal Percentage Characteristics (Logarithmic) The relative and relative flow rates of equal percentage characteristics do not have a linear relationship, and the change of the flow rate caused by the unit stroke change at each point of the stroke corresponds to this point Of the traffic is proportional to the percentage of traffic changes are equal. So it has the advantage of small flow, small changes in traffic, traffic flow, the flow changes, that is, in different degrees, with the same regulation accuracy. (2) Linearity (Linearity) Relativeness and linearity of linearity are linear. Changes in unit stroke caused by changes in the flow is unchanged. When the flow rate is large, the relative value of the flow rate changes little, and when the flow rate is small, the relative value of the flow rate changes greatly. (3) Parabolic characteristics The flow rate varies proportionately with the two sides of the travel, and generally has the intermediate characteristics of linear and equal percentage characteristics. From the analysis of the above three characteristics can be seen, in terms of its regulatory performance, with equal percentage characteristics for the best, stable regulation, good regulation performance. The parabolic characteristics than the linear properties of the regulatory performance is good, according to the different requirements of the occasion, select any one of the flow characteristics. This article Keywords: regulating valve
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