ASCO脉冲阀流量计算

阀门的性能指标计算公式阀门作为流体控制的重要设备，在工业生产中起着至关重要的作用。

为了保证阀门的正常运行和流体控制的准确性，需要对阀门的性能指标进行严格的计算和评估。

本文将介绍阀门的性能指标计算公式，并对其进行详细解析。

一、阀门的流量系数（Cv值）计算公式。

阀门的流量系数（Cv值）是衡量阀门流量特性的重要指标。

它表示在单位压差下，阀门能够通过的流体流量。

Cv值的计算公式如下：Cv = Q / (SG sqrt(ΔP))。

其中，Cv为流量系数，Q为流体流量，SG为流体相对密度，ΔP为压差。

二、阀门的流量系数（Kv值）计算公式。

Kv值是国际上通用的流量系数，用于表示阀门在单位压差下的流体流量。

Kv 值的计算公式如下：Kv = Q / sqrt(ΔP)。

其中，Kv为流量系数，Q为流体流量，ΔP为压差。

三、阀门的流体流速计算公式。

阀门的流体流速是指单位时间内流体通过阀门的速度。

流体流速的计算公式如下：V = Q / (A 3600)。

其中，V为流体流速，Q为流体流量，A为阀门的有效截面积。

四、阀门的流体动能损失计算公式。

阀门在流体流动过程中会产生一定的动能损失，影响流体流速和流量。

动能损失的计算公式如下：ΔP = (V^2 / 2g) (K1 + K2)。

其中，ΔP为动能损失，V为流体流速，g为重力加速度，K1和K2为阀门的局部阻力系数。

五、阀门的流体阻力计算公式。

阀门在流体流动中会产生一定的阻力，影响流体流速和流量。

流体阻力的计算公式如下：ΔP = f (L / D) (ρ V^2 / 2)。

其中，ΔP为流体阻力，f为摩擦阻力系数，L为阀门管道长度，D为管道直径，ρ为流体密度，V为流体流速。

六、阀门的流体压降计算公式。

阀门在流体流动中会产生一定的压降，影响流体流速和流量。

压降的计算公式如下：ΔP = f (L / D) (V^2 / 2)。

其中，ΔP为流体压降，f为摩擦阻力系数，L为阀门管道长度，D为管道直径，V为流体流速。

脉冲流量及计算公式哎呀，说起脉冲流量，这可真是个让人头疼的话题。

你可能会想，这玩意儿跟我有啥关系？别急，听我慢慢道来。

记得有一次，我去超市买东西，排队结账的时候，我前面有个阿姨，她买了一大堆东西，看起来像是要办个什么派对。

收银员开始一件一件扫码，然后屏幕上的数字就开始跳啊跳的，就像心电图一样，一会儿高一会儿低。

我在旁边看着，突然就想到了脉冲流量这个词。

脉冲流量，说白了，就是流量的突然变化。

就像那个阿姨买东西，一下买那么多，超市的流量就突然“噌”的一下上去了。

这跟我们平时上网的时候，突然有好多人同时在线，网络流量就会突然增加，是一个道理。

但是，这脉冲流量怎么计算呢？其实，这事儿也没那么复杂。

想象一下，你手里拿着一个秒表，然后你开始计时，从第一个人开始上网，到第N个人，你看看秒表，记下时间。

然后，你再数数这中间有多少人上网，这就是你的流量数据。

公式嘛，大概就是这样的：脉冲流量 = （总流量 - 平均流量） / 时间间隔。

这里的总流量，就是你在那个时间间隔里记录的所有人上网的流量总和；平均流量，就是那个时间间隔里，平均每人上网的流量；时间间隔，就是你计时的那个时间段。

举个例子，假设在5分钟的时间里，有100人上网，总流量是1000MB，而平时平均每人上网的流量是5MB，那么脉冲流量就是（1000MB - 5MB*100人）/ 5分钟 = 0MB。

这说明在这5分钟里，流量并没有突然增加。

你看，这脉冲流量其实挺有意思的，它就像我们生活中的小插曲，突然给你来个惊喜，或者给你来个措手不及。

就像那次在超市，我看着那个阿姨的购物车，心想她家肯定有个大派对，结果她结账的时候，突然说“哎呀，我忘了带钱包了”，然后就开始手忙脚乱地把东西放回去。

这脉冲流量，不就像是她突然增加的购物车，然后又突然减少一样嘛。

所以说，脉冲流量这东西，虽然听起来挺高大上的，但其实它就在我们身边，无处不在。

下次你再看到超市结账屏幕的数字跳来跳去，或者上网的时候感觉网速突然变慢，不妨想想，这可能就是脉冲流量在作怪呢。

200 1.46 1.61 1.68 1.77 1.85 1.95 2.00 2.07
300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1600 1800 2000 2500 3000 4000 5000 6000
1.21 1.30 1.38 1.46 1.52 1.60 1.65 1.71
公式1 FORMULA 1 流速：磅/小时(蒸汽或水) FLOW RATE LBS/HR (Steam or Water)
在此： Where:
dp = 压降，单位：PSI dp = pressure drop in PSI
F = 流速，单位：磅/小时 F = flow rate in lbs./hr.
例子 EXAMPLE 1. 通过DN350, 压力等级Class 900的压力密封闸阀，水温 400oF，压力为1500 PSIG，流速为5,000,000磅/小时的压降 是多少？ What is the pressure drop through a 14" Class 900 pressure seal gate valve with 400oF water, 1500 PSIG, and 5,000,000
F = 500,000 = 0.785 (来自900oF, 1200 PSIG蒸汽表) = 0.785 (from chart for steam at 900oF, 1200 PSIG) =
= 2.24
最接近的、较大的Cv是DN250压力等级Class 2500闸阀，其Cv是 3130。这里是压降小于5 PSIG的最小的阀门。 The closest higher Cv is a 10" Class 2500 gate with a Cv of 3130. This is the smallest valve with a pressure drop less than 5 PSIG.

Section 1: OverviewThis application enables the quick calculation of flow coefficient (Cv), pressure drop, or flow rate for 2 way general service valves.It should be used in conjunction with ASCO publication "Flow Rating of ASCO Valves Cv Method", commonly known as the Red Hat Flow Book. Parts of thefollowing were taken from the ASCO publication:Almost every conceivable fluid is being handled today by automatic or semi -automatic electrically operated control valves. Applications of hydraulic and fluidmechanics are so extensive that almost every engineer has found himself faced with the responsibility to select and size a control valve for one process or another.ASCO is greatly interested in this subject because of the wide variety of solenoid valves they manufacture,and has developed aids to properly select a valve size capable of handling the required flow. This flow information has been published based on the Cv concept.Definition of Cv:The valve flow coefficient, Cv, is a capacity index, and is defined as the number of U.S. gallons of water per minute that will flow through a valve with a pressure dropof one pound per square inch. The Cv method is widely used & is very adequately serving its purpose in solenoid valve applications. The Fluid Control Institute has published standards for its use, such as FCI 62-1, 58-2 and 61-1.Testing of solenoid valves is performed within the rangeof variables usually handled. The simplicity of determining the Cv rating for eachdesign has proven invaluable. The Cv of a valve does not change. Once assigned to a valve, it can be used to solve flow problems involving any media; air, gas, liquid or vapor.Importance of Properly Sizing Valves:It is very important to properly size a valve. There are undesirable effects inboth undersizing and oversizing.Undersizing may result in:A. Inability to pass desired flow requirements.B. Flashing of liquids to vapors on outlet side of valve.C. Lowering desired outlet pressure.D. Creating a substantial pressure loss in a piping system.Oversizing may result in:A. Unnecessary cost in oversize equipment.B. Variable flow through the valve or erratic control of the flow.C. Shorter life of some valve designs through oscillating of internal parts, caused by lackof flow to maintain required internal pressure differentials.D. Erratic operation of some designs, such as failure to shift position due to lack ofrequired flow to do so.E. Erosion or wire drawing of seats in some designs, because they operate at nearlyclosed position.Conditions to be Known:In general, we must obtain as many of the conditions surrounding the application as possible, but it is never necessary to know all of them. In the case of liquids, at least two ofthe following conditions must be known. When solving flow problems concerning air, gases and vapors, at least three of the following conditions must be known.1. Flow required in gallons per minute (GPM) as used for liquids, standard cubic feet per hour (SCFH) as used for gases, or pounds per hour (lb/hr) as used for steam. This can be obtained by merely asking the customer's requirements, from nameplates on pumping equipment, boiler room charts or calculations.2. Inlet Pressure (P1).This is usually known or readily obtained by placing a gage near the valve inlet.3. Outlet Pressure (P2). This can be obtained by the gage observation, but usually is tied in with restrictions regarding allowable system pressure drop.If we know the inlet pressureand the pressure drop, we, of course, know the outlet pressure.4. Pressure Drop ( P). In large or complicated systems, it is desirable to keepthe pressure drop across a valve to a minimum. Often, the customer will have definite specifications concerning this factor. Of course, if the valve is discharging to atmosphere, the pressure drop is equal to the inlet pressure when dealing withliquids. With gases and steam, although the valve may be discharging to atmosphere, when sizing a valve, only 50% of the absolute inlet pressure (PSIA)* can be used for the pressure drop used in the formulas (commonly called critical pressure drop). In all other cases, the pressure drop is, of course, the difference between inlet and outlet pressures. This information is needed to size the valve. If this is not specified, a rule of thumb is to take 10% of the inlet pressure as pressure drop.* PSIA (absolute pressure psi) = [PSIG (gage pressure psi) + 14.7]Valves Requiring A Minimum Operating Pressure Differential:It is often difficult to understand the meaning of the term "Minimum OperatingPressure Differential". Some valves have been assigned such a figure becausethey are not direct acting valves. These valves work by differential pressures created internally by pilot and bleed arrangements.This differential, of course, is measured as the differencebetween inlet and outlet conditions on all valve constructions. In the case of 2 -way valves, a minimum differential under flowing conditions less than that assigned would mean that the orifice might not be fully open. In the case of 3 and 4 way valves, if the minimum differential is not maintained when shifting position, there is a possibility of improper operation. The minimum operating pressure differential concerns only the condition between inlet and outlet on 3 and 4 way valves, and not between inlet and cylinder connections.If pressure conditions are not known, but flow information can be obtained, we can solve the resulting pressure drop under the known flow conditions. If the drop is less than the assigned minimum differential, the valve is oversized. In these situations, it is advisable to offer a valve having a lower assigned minimum operating pressure differential, or go to a smaller size or another valve having a closer Cv to that desired.Estimating Cv or Orifice Size:The following table can be used to estimate a Cv if the orifice size is known or relate the approximate orifice if the Cv is known. The chart is based on the ASCO designs of in-line globe type valves. The flow charts must be used for precise sizing and converting Cvfactors to actual flow terms. The catalog must be consulted for the actual Cv of a particular valve.Terminology:Before we can attempt to size any valve or solve any flow problems, we must be inaccord regarding the terms used. The following are simple explanations of the most common ones along with their symbols.Useful Conversions1 PSI = 2.036021 inches of Mercury (Hg)1 PSI = 27.68 inches of water column1 Bar = 14.5 PSI1 FT3/HR = 471.6 cm3/minuteSee / for the unit conversion tool. Back to ContentsSection 2: Liquids Governing Equation:(For Viscosity > 300 SSU) Cv corrected = Viscosity correction Factor x Cv uncorrectedCv = flow coefficientGPM = Gallons per MinuteS.G. = Specific Gravity (in most cases, defaults to 60°F). See the Specific Gravity Section. P = Pressure Drop (Pinlet – Poutlet)Viscosity Effects:The viscosity of most fluids in the program database will be entered automatically once the liquid and flowing temperature are defined. As a general rule, for most liquids, viscosity goes up as the temperature goes down.If the viscosity is greater than 300 SSU, then the flow through the valve (Cv) will be affected. In this case, a correction factor is calculated in order to determine the higher Cv required to achieve a specified flow at the specified pressure drop.Note: When viscosity is greater than 300 SSU, the program will only calculate corrected Cv. For instance, one cannot input Cv and flow to determine pressure drop (as on liquids with low viscosities ).The corrected Cv will always be higher than the calculated Cv without viscosity effects. In this case, a larger capacity valve might be required.Note: Not all ASCO valves can properly handle highly viscous fluids. Some arebetter suited than others. Some valves have been designed to handle heavy oils, etc. Contact ASCO for further details.Viscosity Database:For liquids listed, not all viscosity values are available. When the viscosity of a listed li quid is either unknown or not available, a message will appear to that effect.At this point, the following can be done:1. Assume the viscosity is less than 300 SSU and calculate the Cvwithout any viscosity effects.2. If the user has a value for viscosity (from a reference, customer specs,etc.), thencalculate the Cv using "Any liquid (user defined)". The user enters specific gravity and viscosity.3. Try using another temperature that may be in the available viscosity data range. (Thismay not help solve for the correct Cv if it is a fluid with a viscosity that changes rapidly with temperature.)For some liquids, limited viscosity data is available. In this case, large interpolation estimates will be used. When applicable, a message will appear to that effect.Specific Gravity:To be precise, the specific gravity should be that at the flowing temperature ; however, the gravity of many liquids varies very little with temperature (an exception would be liquid refrigerants ). For all practical purposes, the value at 60°F can be used for most temperature ranges with minor error.This program uses the 60°F specific gravity value, regardless ofthe temperature entered (except cryogenic fluids,liquid O2, N2, CO2 @ - 320°F).The flowing temperature entered will be used for viscosity purposes.Cryogenic Fluids:Liquid Oxygen, Liquid Nitrogen and Liquid CO2 are cryogenic fluids. The specific gravity value is at -320°F (-190°C ,140 Ranking,77.6 Kelvin). The calculations will be made with the (correct) assumption that viscosity is less than 300 SSU.Mass Flow Rates:Very often, flow requirements are given in mass units (LB/SEC) rather than GPM. The following conversion formulas are to be used to find GPM:EXAMPLE:A valve is required to pass 2 LB/SEC of #3 Fuel Oil. What is the flow rate in GPM?S.G. = .89Section 3: Air / GasGoverning Equation:T = Absolute temperature Ranking (°F + 460)P1 = Inlet pressure (PSIA)P2 = Outlet pressure (PSIA)∆P = Pressure drop (P1–P2) (psi)S.G. = Specific gravity @ 60°F and 14.7 PSIA(standard atmosphere pressure)Cv = Valve Flow coefficientFlow = Volumetric Flow in SCFH (standard cubic feet per hour)Important: When using this formula / computer program, do not use a ∆ P greater than 50% of the absolute inlet pressure, and consequently, aP2 less than 50% of the absolute inlet pressure.The computer program requires the following information to be entered:∙Fluid temperature∙Gage inlet pressure (PSIG)Specific Gravity and Temperature Considerations:This program will use the 60°F specific gravity value from the air/gas database,regardless of the (flowing) temperature entered.The temperature entered will be used for a temperature correction thatis automatically used in the flow calculations. This correction is almost negligible for temperatures between 20°F and 150°F ( -7°C and 65°C); however, it is programmed in for all temperatures.Note: With "Any gas (user defined) ", the user enters the specific gravity ( should be at or near 60°F, standard atmospheric conditions for proper conversion between SCFH or LB/HR flow entered ) and the flowing temperature. The temperature correction is still in effect.Example, Natural Gas:Published specific gravity values of natural gas vary from 0.56 to 0.78. Use "Any Gas (User Defined)" when inputting a specific gravity other than the program database value.Temperature Range:For most gases, the default temperature range (to enter) is -40 to 302 degrees Fahrenheit.Note: This is a default range and does not imply the actual temperature range for each individual gas in the database.Rate of Flow:This program allows the user to enter air / gas flow either in SCFH or lb/hr (see volumetric and mass flow details below).Volumetric Flow (SCFH):The most common means of expressing compressible (gas) flow is Standard Cubic Feet Per Hour ( SCFH ). This is defined as the number of cubic feet per hour of gas at 14.7 PSIA and 70°F that the unit is passing. "Free air or gas" is another means of designating SCFH. If the flow is not designated as "Standard" or "Free", it is very possible that the value is that of compressed air and not free air. If this is the case, refer to theASCO Publication "Flow Rating of ASCO Valves, Cv Method" (ASCO Flow Book), or contact ASCO.Mass Flow Rates (lb/hr):Gas flow rates are often stated in mass per unit time ( lb/sec, lb/hr, etc. ). If this is the case, the conversion to SCFH is made quite readily by multiplying the flowvalue times the specific volume at standard conditions.SCFH = lb/hr x (S.V. @ Standard Conditions)If specific volume cannot be found,and specific gravity or density is known, the following conversion equations can be used:Gas Combustion SystemsAll flow problems dealing with combustion systems can be handled as any other gas.Flow rates can be designated directly as FT3/MIN or LBS/HR. Additionally, it can be expressed indirectly as output capacity of the system (BTU/HR).It is not uncommon to have the flow rate given indirectly as the output capacity (BTU/HR). The program will accept this value and convert it (in the background) into flow by the following equation:SCFH= output capacity (BTU/HR) / heating value (BTU/ FT3)The heating values of common combustion gases are listed below. These values are the same that are loaded in the program’s database.HEATS OF COMBUSTIONMeasured at 68F and 14.7 PSIA ( standard atmoshepric conditions ).*Propane is commercial grade per Suburban Propane, March 1986Note: If the values for a particular gas conflict with the customer data provided, then select the gas "any gas (user defined)" and manually enter the gas values.Section 4: SteamGoverning Equation:Flow = (lb/hr)Degrees SH = degrees of superheat (°F)∆P = (P1-P2) pressure drop (psi)P1 = Inlet Pressure (psia), PSIG + 14.7P2 = Inlet Pressure (psia), PSIG + 14.7This section calculates Cv flow coefficient, pressure drop or flow rate for saturatedand superheated steam.For determining steam flow in terms of boiler capacity (BTU/hr) or boiler horsepower, consult the ASCO Flow Book Publication or contact ASCO.The computer program requires the following information to be entered:∙Gage inlet pressure (PSIG)∙Superheat temperature (if applicable, see below)Superheated Steam:Further application of heat to saturated steam vapor produces a rise in the temperature of the vapor under the same given pressure. Such a vapor is called superheated vapor. The quantity of superheat is equal to the difference between the superheated vapor temperature and the temperature of its saturated vapor at the same pressure. For example, superheated vapor at 120o F above its saturated vapor temperature is said to contain 120o superheat.Note:When using this formula / program, do not use a ∆ P greater than50% of the absolute inlet pressure; and consequently, a P2 less than 50% of the absolute inlet pressure (PSIA).。