When procuring an ordinary manual valve, you can often get a price quote just by specifying the nominal size, pressure rating, material, and connection type. Procuring a control valve is different.
A control valve does not simply "open" and "close." Instead, it continuously changes its opening in response to commands from the control system, keeping flow, pressure, level, or temperature stable within the set range. Whether it controls accurately, shuts off tightly, and lasts long depends not only on valve quality, but also on whether the data provided at the selection stage is complete.
In real inquiry situations, people often send just one line:
Quote me a DN100, PN16 pneumatic control valve.
After receiving this, the manufacturer can only keep asking: what medium? what flow rate? what are the upstream and downstream pressures? what is the operating temperature? do you need air-to-open or air-to-close?
Customers may feel the manufacturer is asking too many questions, but these questions are not meant to make selection unnecessarily complicated. It is like buying shoes — you cannot just say "I want a pair of shoes"; you also need to know the size, purpose, and environment of use. Every important parameter of a control valve corresponds to a real-world question.
This article avoids piling up formulas and explains in plain language what you should provide when procuring a control valve, and what each parameter is actually for.
1. The Bottom Line: Provide at Least These Ten Items
If time is tight, tell the manufacturer at least these ten items:
- What medium flows through the pipe;
- Minimum, normal, and maximum flow rates;
- The pressure before the valve, i.e. the upstream pressure P1;
- The pressure after the valve, i.e. the downstream pressure P2;
- Normal, minimum, and maximum operating temperatures;
- Pipe size, pressure class, and connection standard;
- Whether the valve controls flow, pressure, level, or temperature;
- Whether to use a pneumatic or an electric actuator;
- Control signal, power supply, or air supply conditions;
- Whether the valve should open, close, or stay in position after a power loss, air loss, or signal loss.
If these ten items are provided completely, the manufacturer can usually begin basic selection. When the medium is special, the pressure differential is large, or safety requirements are high, add the information on solids, corrosion, leakage class, explosion protection, and noise mentioned later.
2. Medium: What Exactly Flows Through the Pipe?
This is the first step of selection.
Do not write only "liquid," "gas," or "chemical medium." It is best to write the specific name, for example:
- Tap water, circulating water, sewage;
- Steam, compressed air, nitrogen, natural gas;
- Hydrochloric acid, sulfuric acid, caustic soda, ammonia water;
- Heat transfer oil, resin, adhesive, slurry;
- Ethanol, methanol, or other solvents.
In Plain Language
The medium is what the valve contacts every day. Different media impose completely different requirements on the body, plug, seat, and packing.
Carbon steel behaves differently with water than with hydrochloric acid; clean air is different from dust-laden gas; ordinary liquid is different from slurry with solids. If the medium is not stated clearly, the manufacturer cannot decide whether to use carbon steel, stainless steel, or fluoroplastic lining, nor determine soft seal, metal seal, or special packing.
What if It Is a Mixed Medium?
Provide the main components and approximate proportions as far as possible, and especially state whether any of the following apply:
- Corrosiveness;
- Toxicity, flammability, or explosiveness;
- Solid particles, fibers, or crystalline matter;
- Tendency to solidify, polymerize, or adhere;
- Cleanliness or hygiene requirements.
Writing only "process material" is not very useful. The manufacturer does not need to know the customer's formulation secrets, but should at least know which components affect material and structure selection.
3. Medium State: Liquid, Gas, Steam, or Liquid-Gas Mixture?
The same substance can exist in different states at different temperatures and pressures. Water can be liquid water or steam; a liquefied gas may become a liquid-gas two-phase mixture after pressure drop through the valve.
In Plain Language
Liquids, gases, and steam are calculated differently when passing through a valve. Gas expands; liquid is usually not easily compressed; liquid under high differential pressure may also experience cavitation or flashing.
If the medium is actually a liquid-gas mixture but is calculated as a pure liquid, the valve size, outlet velocity, and noise judgment may all be wrong. Therefore, when bubbling, vaporization, or two-phase flow is seen in the pipe, tell the manufacturer in advance.
4. Flow Rate: Do Not Give Just One Number
For control valve selection it is best to provide three flow rates:
| Condition | Meaning |
|---|---|
| Minimum flow | The flow the valve must still control stably at low plant load |
| Normal flow | The flow used for the longest time and most frequently in normal operation |
| Maximum flow | The maximum flow that must pass under full load or special conditions |
Also state the unit clearly, for example:
- Water: m³/h;
- Steam: kg/h or t/h;
- Gas: Nm³/h or Sm³/h;
- Mass flow: kg/h.
In Plain Language
Flow rate is "how much medium must pass per hour." The maximum flow determines whether the valve can let so much medium through; the minimum flow determines whether the valve can still control stably at low flow; the normal flow determines at what opening the valve should normally work.
If only the maximum flow is given, the manufacturer may select an oversized valve. It is fine at maximum condition, but in normal operation it may only open 5% to 10%. A small movement then changes flow a lot, resulting in unstable control, repeated valve movement, and even the positioner repeatedly feeding and exhausting air.
The Most Common Mistake: A Number with No Unit
"Flow 50" cannot be calculated. 50 m³/h, 50 kg/h, and 50 t/h are completely different. Gas also requires distinguishing standard-state flow from actual-state flow. The unit must be provided together with the number.
5. Upstream Pressure P1: How Much Pressure Before the Medium Enters the Valve?
Upstream pressure is the pressure of the medium when it reaches the valve inlet.
For example:
Upstream pressure P1: 0.8 MPa normal, 1.0 MPa maximum.
In Plain Language
It can be understood as the starting pressure with which the medium "pushes the valve forward." Upstream pressure affects flow calculation, body pressure class, and the force on the plug and actuator.
Note that pump discharge pressure is not necessarily equal to upstream pressure. If there is still a long pipe, heat exchanger, or filter between the pump and the valve, the pressure may have dropped by the time it reaches the valve. It is best to provide the pressure near the valve installation location.
6. Downstream Pressure P2: The Item Most Easily Omitted
Downstream pressure is the pressure in the downstream pipe after the medium passes through the valve.
For example:
Downstream pressure P2: 0.3 MPa normal, 0.1 MPa minimum.
In Plain Language
Knowing upstream pressure but not downstream pressure, you do not know how much differential pressure the valve must bear.
For example, saying only "working pressure 1.0 MPa" could mean two completely different situations:
- Upstream 1.0 MPa, downstream 0.9 MPa, differential only 0.1 MPa;
- Upstream 1.0 MPa, downstream 0.1 MPa, differential as high as 0.9 MPa.
The first is gentle; the second may involve high velocity, noise, cavitation, flashing, and larger actuator thrust. The two conditions may lead to completely different valves.
What if You Do Not Know Downstream Pressure?
You can provide the downstream equipment situation, for example:
- Discharging into an atmospheric storage tank;
- Entering a pipe network at 0.3 MPa;
- Connecting to a reactor downstream;
- Discharging directly to atmosphere;
- A heat exchanger or long-distance pipe further downstream.
The manufacturer can help judge from this, but key items should be confirmed by process personnel.
7. Differential Pressure ΔP: Not Another Data for the Customer to Fill In
Differential pressure is upstream pressure minus downstream pressure:
ΔP = P1 - P2
In Plain Language
Differential pressure can be understood as the pressure the valve must "consume." It determines how much flow capacity the valve needs, and also affects internal velocity, noise, cavitation, flashing, and actuator force.
The customer usually does not need to calculate complex formulas; just provide P1 and P2 clearly for each condition, and the manufacturer can calculate. Accurate upstream and downstream pressures are more reliable than writing an unconfirmed differential pressure directly.
8. Temperature: Do Not Just Write "Ambient"
It is best to provide:
- Normal operating temperature;
- Minimum operating temperature;
- Maximum operating temperature;
- Whether it frequently alternates hot and cold.
In Plain Language
Temperature determines whether the material can withstand it, and whether the seal will soften, harden, age, or lose elasticity.
An ordinary PTFE seat seals well at room temperature, but that does not mean it suits all high-temperature conditions; low-temperature media may require an extended bonnet and low-temperature material; heat transfer oil, molten material, or easily solidifying media may require a jacketed insulation structure.
"Room temperature" is best replaced with an actual range, such as 15°C to 40°C. If the temperature is low at start-up and high after operation, state that too, because temperature change affects valve torque, packing, and seat life.
9. Pipe Size: It Is Not Necessarily Equal to the Control Valve Size
The customer needs to provide the upstream and downstream pipe sizes, for example DN100, and state whether reduced-bore installation is allowed.
In Plain Language
A DN100 pipe does not mean the control valve must be DN100. The control valve size is calculated from flow, differential pressure, and allowable velocity.
Sometimes a DN100 pipe may use a DN80 control valve; high-velocity gas or flashing conditions may use a larger valve outlet. The manufacturer must first calculate Cv, then determine the valve size.
So when procuring, tell the manufacturer "how big is the pipe," do not directly specify "the valve must be this big," unless the design institute has already completed the calculation and defined the valve size.
10. Pressure Class and Connection Standard: Decide Whether It Can Be Installed
Common pressure classes include PN10, PN16, PN25, PN40, as well as Class 150, Class 300, etc. Connection forms include flange, wafer, threaded, and welded.
Writing only "DN100 flange" is still incomplete; it is best to state the flange standard, for example:
- GB/T 9119;
- HG/T 20592;
- ASME B16.5;
- EN 1092-1.
In Plain Language
Even with the same name DN100, PN16, flange dimensions, sealing faces, and bolt holes may differ between standards. If the standard does not match, the valve may not fit on site when it arrives.
If the customer does not know the flange standard, provide the original valve nameplate, flange photo, and the outer diameter, number of holes, bolt circle diameter, and sealing face type, so the manufacturer can help verify.
11. Control Objective: What Is This Valve Actually Managing?
State that the control valve is used to control:
- Flow;
- Pressure;
- Level;
- Temperature;
- Ratio or other process parameters.
In Plain Language
Different control objects give the valve different working characteristics.
A valve controlling steam temperature may move frequently; a valve controlling tank level usually responds more slowly; a pressure-reducing valve needs to focus on high differential pressure, noise, and stability; fine low-flow dosing cares more about rangeability and small-opening control.
Also state whether the valve is "continuous regulation" or "only open and close." If it is only fully open and fully closed, a shut-off valve with an on-off actuator should be selected, rather than making an ordinary shut-off task into a regulating configuration.
12. Pneumatic or Electric: Depends on Site Conditions, Not Which Is Absolutely Better
Pneumatic Control Valve
Need to provide:
- Instrument air pressure, e.g. 0.4 to 0.7 MPa;
- Whether the air supply is dry and clean;
- Control signal, e.g. 4 to 20 mA;
- Whether solenoid valve, filter regulator, and limit switch are needed.
Pneumatic actuators respond quickly and can reach a safe position through the spring after air loss. They are commonly used in chemical, petrochemical, and frequent-regulation applications, but require a stable air source on site.
Electric Control Valve
Need to provide:
- Power supply, e.g. AC220V, AC380V, or DC24V;
- Control signal, e.g. 4 to 20 mA or 0 to 10 V;
- Whether bus communication is needed;
- Stroke time and protection requirements.
Electric actuators do not need compressed air and work once wired. They suit sites without air supply or with relatively low action frequency. Large valves, fast action, and fail-safe requirements need separate evaluation.
13. Control Signal: How Does the Control Room Command the Valve?
The most common regulating signal is 4 to 20 mA. 4 mA usually corresponds to 0% opening and 20 mA to 100% opening, but it can also be set in reverse.
Other possibilities include:
- 0 to 10 V;
- Discrete (on/off) signal;
- HART;
- Modbus, Profibus, or Foundation Fieldbus communication.
In Plain Language
The control signal is like the "language" the control room uses to speak to the valve. If the PLC or DCS speaks 4 to 20 mA while the actuator only listens to 0 to 10 V, the two cannot cooperate directly.
If unsure, confirm the PLC/DCS output signal with instrumentation or automation personnel.
14. Fail Position: Where Should the Valve Go After Air or Power Loss?
This is a very important item in safety selection. Common choices are:
| Fail Position | Plain Meaning |
|---|---|
| FC, Fail Close | Valve automatically closes after air loss, power loss, or signal loss |
| FO, Fail Open | Valve automatically opens after a fault |
| FL, Fail Last | Valve tries to hold its current position after a fault |
In Plain Language
Do not ask "what does the industry usually choose"; ask "which position is safer when a fault occurs."
Fuel gas and hazardous chemical feed valves usually tend to fail closed; cooling water valves may tend to fail open to prevent loss of cooling; some circulation or ratio systems need fail-last. The final position should be determined by process and safety specialists.
Pneumatic valves also need to state air-to-open or air-to-close. The manufacturer will determine the actuator type, spring direction, and positioner action based on the fail position.
15. Leakage Class: Allow a Little Passage, or Must It Shut Tight?
The main task of a control valve is regulation, not all control valves require zero leakage. The allowable seat leakage class or process requirement should be stated when procuring.
In Plain Language
Higher leakage class means stricter sealing requirements, and also higher requirements on plug-seat structure, actuator thrust, and cost.
Ordinary flow regulation may allow a little seat leakage; hazardous medium isolation, shutdown protection, or batch production may require stricter shut-off performance. If the process must achieve reliable shut-off, sometimes consider "control valve plus independent shut-off valve" rather than requiring one valve to do all tasks.
When the customer does not know the specific class, describe the need directly, for example:
- A little dripping allowed after closing;
- Downstream pressure must not keep rising after closing;
- Medium is toxic, require it as tight as possible;
- This valve only regulates, with a separate shut-off valve downstream.
16. Body and Trim Material: State the Medium Condition First When Unsure
Common body materials include cast iron, ductile iron, WCB carbon steel, CF8 stainless steel, CF8M stainless steel, and various alloys. The material of plug, seat, stem, and packing must also be selected based on corrosion, temperature, and wear.
In Plain Language
The customer can state existing material requirements, but when not confident, do not just write "all 304" or "all 316" out of habit. Some media still corrode 316; some slurries need more attention to hardness and wear resistance rather than blindly raising the stainless grade.
The most valuable information is still medium composition, concentration, temperature, particles, and the corrosion experience of existing equipment.
17. Action Frequency and Speed: Moving Once a Day Is Not the Same as Moving Once a Minute
State roughly how often the valve acts, and how long you want it to take from fully open to fully closed.
In Plain Language
Action frequency affects the life of the actuator, seal, guide, and positioner. A valve that acts a few times a year and one that regulates dozens of times per minute have completely different structural requirements.
Faster action is not always better. Closing too fast may cause water hammer, pressure shock, and pipe vibration; too slow may fail to meet interlock or process requirements. The customer should provide the allowable time, and the manufacturer determines a reasonable speed combined with the valve and system.
18. Site Environment: Usable Indoors Does Not Mean Usable Outdoors or in Explosion-Proof Zones
State:
- Indoor or outdoor;
- Minimum and maximum ambient temperature;
- Whether there is rain, dust, salt spray, or corrosive gas;
- Whether it belongs to an explosion-proof zone;
- Explosion-proof and protection level requirements;
- Whether there are underwater, underground, or high-altitude installation conditions.
In Plain Language
This information mainly determines the enclosure, explosion-proof, and protection configuration of the positioner, solenoid valve, limit switch, and electric actuator. Ordinary indoor products installed directly in the open air, coastal, or corrosive environment will have significantly shortened life.
"Require explosion-proof" is also incomplete; it is best to provide the explosion-proof mark, gas group, and temperature group specified by the project.
19. Are There Cavitation, Flashing, Noise, or Particle Erosion?
These are special conditions, but it is best to state them at the inquiry stage.
In Plain Language
- Cavitation: liquid produces bubbles when passing through the valve, then the bubbles burst violently, like countless tiny impacts continuously hitting the plug;
- Flashing: liquid continues to vaporize after pressure drop, and the downstream becomes high-velocity liquid-gas two-phase flow;
- High noise: common in steam and high-pressure gas with large pressure drops;
- Particle erosion: solid particles in the medium wear the trim like sandpaper.
If the site already shows abnormal noise, vibration, plug pitting, downstream pipe erosion, or very short valve life, provide photos and operating conditions together. The manufacturer may need multi-stage pressure reduction, anti-cavitation, low-noise, angle-flow, or wear-resistant materials, rather than continuing with ordinary trim.
20. Installation Space and Orientation: Selected Right Also Means Fitted In
Large pneumatic actuators, electric actuators, and control valves with handwheel, positioner, and accessories may be significantly larger than the body.
State:
- Whether the valve is installed horizontally or vertically;
- Stem up, side-mounted, or other restrictions;
- Whether there are platforms, walls, pipes, or insulation around;
- Available height and width;
- Whether extended bracket or remote-mounted accessories are needed.
In Plain Language
A position on the drawing does not mean there is maintenance space on site. The valve must fit in, and also consider whether the positioner can be removed, packing replaced, and actuator lifted later. When space is tight, site photos and dimensions are more effective than verbal description.
21. The Customer Does Not Need to Provide the Cv Value
Many customers see Cv or Kv in the selection table and worry they cannot calculate it.
In fact, Cv or Kv is usually calculated by the valve manufacturer based on flow, pressure, temperature, and medium properties. The customer's most important task is to provide the original conditions accurately.
In Plain Language
Cv can be understood as the valve's "ability to let medium pass." A larger number usually means more flow can pass at the same differential pressure.
But bigger Cv is not always better. Too small leads to insufficient flow; too large causes the valve to stay at small opening for a long time with unstable control. Therefore, the manufacturer should calculate the required Cv and select the appropriate size combined with valve characteristics.
22. Five Common Ineffective Inquiry Styles
1. "Quote a DN100 pneumatic control valve"
Lacks medium, flow, P1, P2, temperature, and control requirements; can only give a very rough budget.
2. "Pressure 1.0 MPa"
Unclear whether this is design pressure, upstream pressure, or differential pressure, and no downstream pressure known.
3. "Flow 100"
No unit, and no minimum, normal, or maximum condition.
4. "Material 304, everything else per standard"
No single configuration of control valve covers all "standard" conditions. At least the medium and temperature must be known.
5. "Same as before"
This is meaningful only if the original valve nameplate, model, data sheet, and site problems are provided. Sending only a distant photo usually cannot reveal the trim, Cv, or fail position.
23. An Inquiry Template You Can Copy Directly to the Manufacturer
This template can be copied directly into WeChat, email, or an inquiry form. For uncertain items, write "to be confirmed" rather than guessing.
Control Valve Inquiry Parameters
1. Project or equipment name:
2. Control object: flow / pressure / level / temperature / other
3. Medium name and main components:
4. Medium state: liquid / gas / steam / liquid-gas two-phase
5. Corrosive, with particles, crystalline, or high viscosity:
6. Minimum flow: unit:
7. Normal flow: unit:
8. Maximum flow: unit:
9. Normal upstream pressure P1:
10. Normal downstream pressure P2:
11. Maximum shut-off differential pressure:
12. Normal operating temperature:
13. Minimum / maximum temperature:
14. Upstream and downstream pipe size:
15. Pressure class:
16. Connection form and flange standard:
17. Actuator: pneumatic / electric / per manufacturer suggestion
18. Control signal: 4-20mA / 0-10V / discrete / bus
19. Air supply pressure or power supply:
20. Fail position: Fail Close FC / Fail Open FO / Fail Last FL
21. Leakage class or shut-off requirement:
22. Body and trim material requirement:
23. Explosion-proof and protection level:
24. Desired full-stroke time:
25. Positioner, solenoid valve, limit switch and other accessory requirements:
26. Installation orientation and space restriction:
27. Other special requirements: noise / cavitation / flashing / hygiene / oil-free, etc.
28. Whether original valve nameplate, data sheet, and site photos are available:24. A Complete Filled Example
Control object: reactor steam flow, for temperature control
Medium: saturated steam
Min / normal / max flow: 500 / 1800 / 2600 kg/h
Upstream pressure P1: 0.8 MPa normal, 1.0 MPa maximum
Downstream pressure P2: 0.3 MPa normal, 0.2 MPa minimum
Operating temperature: 175°C normal, 190°C maximum
Pipe: DN80
Pressure class and flange: PN16, HG/T 20592
Actuator: pneumatic diaphragm or piston, selected by manufacturer
Control signal: 4-20mA
Air supply pressure: 0.4-0.6 MPa
Fail position: fail closed FC on air loss
Accessories: smart positioner, filter regulator
Installation: outdoor, non-explosion-proof zoneThis data is not many more words than "one DN80 steam control valve," yet it is enough for the manufacturer to calculate Cv, noise, opening, and actuator thrust, and the quotation will be closer to the final supply scope.
25. Check These Before Ordering
Before placing a formal order, it is recommended that procurement, process, instrumentation, and the manufacturer jointly confirm:
- Whether the flow unit is correct, and whether gas notes the standard state;
- Whether P1 and P2 correspond to the same operating condition;
- Whether the maximum shut-off differential pressure covers start-up, shutdown, and accident states;
- Whether the valve size is a calculation result or just copied from the pipe size;
- Whether control signal, power, or air supply matches the site;
- Whether the fail position has been confirmed by process and safety specialists;
- Whether flange standard, sealing face, and face-to-face dimension match the site;
- Whether the valve and actuator have enough installation and maintenance space;
- Whether the scope of positioner, solenoid valve, limit switch, and handwheel accessories is defined;
- Whether the parameters in the data sheet, quotation, and final order are consistent.
Conclusion
When procuring a control valve, the manufacturer repeatedly asking for parameters is not complicating a simple matter, but because every piece of data affects the actual use result.
The most critical information can be summed up in one sentence:
What medium, at what temperature, how much per hour, from what pressure down to what pressure, what signal and power on site, and where the valve should stop after a fault occurs.
State this sentence clearly, and the control valve selection is more than half done.
The customer does not need to know how to calculate Cv, nor decide in advance whether to use a single-seat valve, cage valve, V-ball valve, or butterfly valve. Just provide the real conditions accurately, and the manufacturer can further calculate size, valve type, material, and actuator.
A complete parameter sheet may take only ten-odd minutes to fill in, yet it avoids problems after the valve arrives on site such as not fitting, insufficient flow, long-term small opening, excessive noise, actuator unable to close, or wrong fail position. Clarifying issues at the selection stage is usually more time-saving and cost-saving than retrofitting after commissioning.
Wuxi Quankong Valve & Fluid Control Co., Ltd.
Industrial Valves | Control Valve Selection | Actuator Integration | Fluid Control Solutions
Technical inquiries: [email protected]
采购普通手动阀时，知道口径、压力、材质和连接方式，很多时候就能先报出价格。但采购调节阀不一样。
调节阀不是简单的“打开”和“关闭”，而是要根据控制系统的命令，不断改变开度，把流量、压力、液位或温度稳定在设定范围内。它能不能调得准、关得住、用得久，不只取决于阀门质量，还取决于选型时提供的数据是否完整。
实际询价中，经常有人只发一句：
给我报一台DN100、PN16的气动调节阀。
厂家接到这句话以后，只能继续追问：什么介质？流量多少？阀前压力和阀后压力是多少？工作温度多高？需要气开还是气关？
客户可能觉得厂家问得太多，其实这些问题并不是故意把选型复杂化。就像买鞋不能只说“我要一双鞋”，还要知道尺码、用途和使用环境。调节阀的每一个重要参数，都对应着一个实际问题。
这篇文章不堆公式，尽量用大白话讲清楚：采购调节阀时应该提供什么，以及这些参数到底有什么用。
一、先说结论：最少要提供这十项
如果时间比较紧，至少先把下面十项告诉厂家：
- 管道里流的是什么介质；
- 最小、正常和最大流量；
- 阀门前面的压力，也就是阀前压力P1；
- 阀门后面的压力，也就是阀后压力P2；
- 正常、最低和最高工作温度；
- 管道口径、压力等级和连接标准；
- 这台阀门要控制流量、压力、液位还是温度；
- 采用气动执行机构还是电动执行机构；
- 控制信号、电源或气源条件；
- 断电、断气或失去信号以后，阀门应该开、关还是保持原位。
这十项能提供完整，厂家通常就可以开展基本选型。介质比较特殊、压差比较大或安全要求比较高时，还要补充后文提到的颗粒、腐蚀、泄漏等级、防爆和噪声等信息。
二、介质：管道里到底流的是什么？
这是选型的第一步。
不要只写“液体”“气体”或“化工介质”，最好写出具体名称，例如：
- 自来水、循环水、污水；
- 蒸汽、压缩空气、氮气、天然气；
- 盐酸、硫酸、烧碱、氨水；
- 导热油、树脂、胶黏剂、浆料；
- 乙醇、甲醇或其他溶剂。
大白话解释
介质就是阀门每天要接触的东西。不同介质对阀体、阀芯、阀座和填料的要求完全不同。
水对碳钢的影响和盐酸不一样；干净空气和含粉尘气体不一样；普通液体和带颗粒浆料也不一样。介质不说清楚，厂家就无法判断用碳钢、不锈钢还是衬氟，也无法确定软密封、硬密封或特殊填料。
如果是混合介质怎么办？
尽量提供主要成分和大致比例，尤其要说明有没有以下情况：
- 腐蚀性；
- 毒性、易燃或易爆；
- 固体颗粒、纤维或结晶物；
- 容易凝固、聚合或黏附；
- 对洁净度或卫生有要求。
只写“工艺物料”意义不大。厂家并不需要知道客户的配方秘密，但至少要知道哪些成分会影响材料和结构选择。
三、介质状态：是液体、气体、蒸汽，还是气液混合？
同一种物质在不同温度和压力下，可能处于不同状态。水可以是液态水，也可以是蒸汽；液化气通过阀门降压后，可能变成气液两相。
大白话解释
液体、气体和蒸汽通过阀门时的计算方法不同。气体会膨胀，液体通常不容易被压缩；液体在高压差下还可能出现气蚀或闪蒸。
如果介质实际是气液混合，却按纯液体计算，阀门口径、出口速度和噪声判断都可能出错。因此，看到管道里有冒泡、汽化或两相流时，要提前告诉厂家。
四、流量：不要只给一个数字
调节阀选型最好提供三组流量：
| 工况 | 含义 |
|---|---|
| 最小流量 | 装置低负荷时，阀门仍需要稳定控制的流量 |
| 正常流量 | 平时运行时间最长、最常用的流量 |
| 最大流量 | 满负荷或特殊工况下需要通过的最大流量 |
同时一定要写清单位，例如：
- 水：m³/h；
- 蒸汽：kg/h或t/h；
- 气体：Nm³/h或Sm³/h；
- 质量流量：kg/h。
大白话解释
流量就是“每小时要通过多少介质”。最大流量决定阀门能不能让这么多介质通过，最小流量决定阀门在小流量时还能不能调得稳，正常流量决定阀门平时应该工作在什么开度。
如果只给最大流量，厂家可能选出一台“大阀门”。它在最大工况下没问题，但正常运行时可能只开5%至10%。稍微动一点，流量就变化很多，结果是控制不稳、阀门来回动作，甚至定位器反复进气排气。
最常见的错误：流量有数字却没有单位
“流量50”无法计算。50m³/h、50kg/h和50t/h完全不是一回事。气体还要区分标准状态流量和实际状态流量。单位必须与数字一起提供。
五、阀前压力P1：介质进阀门前有多大压力？
阀前压力就是介质到达阀门入口时的压力。
例如：
阀前压力P1：正常0.8MPa，最高1.0MPa。
大白话解释
它可以理解为介质“推着阀门往前走”的起始压力。阀前压力会影响流量计算、阀体压力等级，也会影响阀芯和执行机构受到的力。
要注意，泵出口压力不一定等于阀前压力。如果泵和阀门之间还有很长的管道、换热器或过滤器，压力走到阀门前可能已经下降了。最好提供阀门安装位置附近的压力。
六、阀后压力P2：这项最容易被漏掉
阀后压力就是介质通过阀门以后，下游管道中的压力。
例如：
阀后压力P2：正常0.3MPa，最低0.1MPa。
大白话解释
知道阀前压力，却不知道阀后压力，就不知道阀门到底要承担多大压差。
比如只说“工作压力1.0MPa”，可能有两种完全不同的情况：
- 阀前1.0MPa，阀后0.9MPa，压差只有0.1MPa；
- 阀前1.0MPa，阀后0.1MPa，压差达到0.9MPa。
前一种比较温和，后一种可能涉及高流速、噪声、气蚀、闪蒸以及较大的执行机构推力。两种工况选出来的阀门可能完全不同。
不知道阀后压力怎么办？
可以提供下游设备情况，例如：
- 排入常压储罐；
- 进入压力为0.3MPa的管网；
- 阀后连接反应釜；
- 直接对大气排放；
- 下游还有换热器或长距离管道。
厂家可以据此帮助判断，但关键项目最好由工艺人员确认压力数据。
七、压差ΔP：不是让客户再填一个新数据
压差就是阀前压力减去阀后压力：
ΔP = P1 - P2
大白话解释
压差可以理解为阀门要“吃掉”的压力。压差决定阀门需要多大的通流能力，也影响阀内流速、噪声、气蚀、闪蒸和执行机构力量。
客户通常不需要自己计算复杂公式，只要把各工况下的P1和P2分别提供清楚，厂家就可以计算。比起直接写一个未经确认的压差，准确提供阀前、阀后压力更可靠。
八、温度：不能只写“常温”
最好提供：
- 正常工作温度；
- 最低工作温度；
- 最高工作温度；
- 是否经常冷热交替。
大白话解释
温度决定材料能不能承受，也决定密封件会不会变软、变硬、老化或失去弹性。
普通PTFE阀座在常温下密封很好，但不代表适合所有高温工况；低温介质可能要求加长阀盖和低温材料；导热油、熔融物料或容易凝固的介质可能需要夹套保温结构。
“常温”最好换成实际范围，例如15℃至40℃。如果开车时温度低、运行后温度高，也要说明，因为温度变化会影响阀门扭矩、填料和阀座寿命。
九、管道口径：它不一定等于调节阀口径
客户需要提供上游和下游管道口径，例如DN100，同时说明是否允许变径安装。
大白话解释
管道DN100，不代表调节阀一定要选DN100。调节阀口径是根据流量、压差和允许流速计算出来的。
有时候DN100管道可能使用DN80调节阀；高流速气体或闪蒸工况，也可能采用较大的阀体出口。厂家需要先计算Cv，再确定阀门口径。
所以采购时应当告诉厂家“管道多大”，不要直接规定“阀门必须多大”，除非设计院已经完成计算并明确了阀门口径。
十、压力等级与连接标准：决定能不能装得上
常见压力等级包括PN10、PN16、PN25、PN40，以及Class 150、Class 300等。连接形式包括法兰、对夹、螺纹、焊接等。
仅写“DN100法兰”仍然不完整，最好说明法兰标准，例如：
- GB/T 9119；
- HG/T 20592；
- ASME B16.5；
- EN 1092-1。
大白话解释
同样叫DN100、PN16，不同标准的法兰尺寸、密封面和螺栓孔可能不同。标准没对上，阀门运到现场可能装不上。
如果客户不知道法兰标准，可以提供原阀铭牌、法兰照片以及外径、孔数、孔中心距和密封面形式，让厂家协助核对。
十一、控制目标：这台阀到底要管什么？
需要说明调节阀用于控制：
- 流量；
- 压力；
- 液位；
- 温度；
- 配比或其他工艺参数。
大白话解释
控制对象不同，阀门的工作特点也不同。
控制蒸汽温度的阀门可能动作频繁；控制储罐液位的阀门响应通常较慢；减压阀需要重点考虑高压差、噪声和稳定性；小流量精细加料则更看重可调比和小开度控制。
还应说明阀门是“连续调节”还是“只开只关”。如果只是全开和全关，应选择切断阀和开关型执行机构，不必把普通切断任务做成调节型配置。
十二、气动还是电动：看现场条件，不是谁一定更好
气动调节阀
需要提供：
- 仪表风压力，例如0.4至0.7MPa；
- 气源是否干燥、洁净；
- 控制信号，例如4至20mA；
- 是否需要电磁阀、过滤减压阀和限位开关。
气动执行机构响应快，失气后可以通过弹簧到达安全位置，常用于化工、石化和频繁调节场合，但现场必须有稳定气源。
电动调节阀
需要提供：
- 电源，例如AC220V、AC380V或DC24V；
- 控制信号，例如4至20mA或0至10V；
- 是否需要总线通讯；
- 开关时间和防护要求。
电动执行机构不需要压缩空气，布线后即可工作，适合没有气源或动作频率相对较低的场合。大型阀门、快速动作和故障安全要求需要单独评估。
十三、控制信号：控制室用什么方式指挥阀门？
最常见的调节信号是4至20mA。4mA通常对应0%开度，20mA对应100%开度，但也可以设置成反向。
还可能使用：
- 0至10V；
- 开关量信号；
- HART；
- Modbus、Profibus或Foundation Fieldbus等通讯方式。
大白话解释
控制信号就像控制室对阀门说话的“语言”。PLC或DCS说的是4至20mA，而执行机构只听0至10V，双方就没法直接配合。
如果不清楚，向仪表或自动化人员确认PLC/DCS输出信号即可。
十四、故障位置：断气断电以后，阀门应该去哪儿？
这是安全选型中非常重要的一项，常见选择有：
| 故障位置 | 通俗含义 |
|---|---|
| FC，故障关 | 断气、断电或失去信号后，阀门自动关闭 |
| FO，故障开 | 发生故障后，阀门自动打开 |
| FL，故障保位 | 发生故障后，阀门尽量保持当时位置 |
大白话解释
不要问“行业通常怎么选”，要问“发生故障时，哪个位置更安全”。
燃料气、危险化学品进料阀通常倾向故障关闭；冷却水阀可能倾向故障打开，防止设备失去冷却；有些循环或配比系统需要故障保位。最终位置应由工艺和安全专业确定。
气动阀还要说明气开还是气关。厂家会根据故障位置确定执行机构形式、弹簧方向和定位器动作方式。
十五、泄漏等级：是允许少量通过，还是必须严密切断？
调节阀的主要任务是调节，不是所有调节阀都要求完全无泄漏。采购时应说明允许的阀座泄漏等级或工艺要求。
大白话解释
泄漏等级越高，密封要求越严，对阀芯阀座结构、执行机构推力和成本的要求也越高。
普通流量调节可能允许少量阀座泄漏；危险介质隔离、停机保护或批次生产可能要求更严格的关闭性能。如果工艺必须做到可靠切断，有时应考虑“调节阀加独立切断阀”，而不是要求一台阀同时承担所有任务。
客户不知道具体等级时，可以直接描述需求，例如：
- 关闭后允许少量滴漏；
- 关闭后下游不能继续升压；
- 介质有毒，要求尽可能严密；
- 这台阀只调节，后面另有切断阀。
十六、阀体和阀内件材质：不确定时先说介质条件
常见阀体材质有铸铁、球墨铸铁、WCB碳钢、CF8不锈钢、CF8M不锈钢和各种合金材料。阀芯、阀座、阀杆及填料的材质还要根据腐蚀、温度和磨损情况选择。
大白话解释
客户可以提出已有的材料要求，但没有把握时，不建议只凭习惯写“全部304”或“全部316”。某些介质对316仍有腐蚀，某些浆料更需要考虑硬度和耐磨，而不是一味提高不锈钢牌号。
最有价值的信息仍然是介质成分、浓度、温度、颗粒和现有设备的腐蚀经验。
十七、动作频率和速度：一天动一次与一分钟动一次不是一回事
需要说明阀门大致多久动作一次，以及希望从全开到全关需要多长时间。
大白话解释
动作频率影响执行机构、密封、导向和定位器的寿命。阀门一年动作几次，与每分钟调节几十次，对结构的要求完全不同。
动作速度也不是越快越好。关闭过快可能引起水锤、压力冲击和管道振动；动作过慢又可能不满足联锁或工艺要求。客户应提供允许时间，由厂家结合阀门和系统确定合理速度。
十八、现场环境：室内能用，不代表室外和防爆区也能用
需要说明：
- 室内还是室外；
- 环境最低和最高温度；
- 是否有雨水、粉尘、盐雾或腐蚀性气体；
- 是否属于防爆区域；
- 防爆等级和防护等级要求；
- 是否有水下、井下或高空安装条件。
大白话解释
这些信息主要决定定位器、电磁阀、限位开关和电动执行机构的外壳、防爆及防护配置。普通室内产品直接装在露天、沿海或腐蚀环境中，寿命会明显缩短。
“要求防爆”也不够完整，最好提供项目规定的防爆标志、气体组别和温度组别。
十九、是否存在气蚀、闪蒸、噪声或颗粒冲刷？
这些属于特殊工况，但最好在询价阶段说明。
大白话解释
- 气蚀：液体通过阀门时产生气泡，随后气泡猛烈破裂，像无数微小冲击不断打击阀芯；
- 闪蒸：液体降压后持续汽化，阀后变成高速气液两相流；
- 高噪声：常见于蒸汽和高压气体大幅降压；
- 颗粒冲刷：介质中的固体颗粒像砂纸一样磨损阀内件。
现场如果已经出现异常噪声、振动、阀芯麻点、下游管道冲蚀或阀门寿命很短，应把照片和运行情况一起提供。厂家可能需要采用多级降压、抗气蚀、低噪声、角式流道或耐磨材料，而不是继续使用普通阀内件。
二十、安装空间和方向：选得对还要装得下
大口径气动执行机构、电动执行机构以及带手轮、定位器和附件的调节阀，外形可能明显大于阀体。
需要说明：
- 阀门水平安装还是垂直安装；
- 阀杆朝上、侧装还是有其他限制；
- 周围是否有平台、墙壁、管道或保温层；
- 可用高度和宽度；
- 是否需要加长支架或远程安装附件。
大白话解释
图纸上有位置，不代表现场一定有检修空间。阀门装得进去，还要考虑以后能不能拆定位器、换填料和吊装执行机构。空间紧张时，现场照片和尺寸比口头描述更有效。
二十一、客户不需要自己提供Cv值
很多客户看到选型表中有Cv或Kv，就担心自己不会计算。
其实Cv或Kv通常由阀门厂家根据流量、压力、温度和介质性质计算。客户最重要的任务是把原始工况提供准确。
大白话解释
Cv可以理解为阀门“让介质通过的能力”。数字越大，通常表示同样压差下能通过的流量越大。
但是Cv不是越大越好。太小会导致流量不够，太大又会造成阀门长期小开度、控制不稳。因此，应由厂家计算所需Cv，并结合阀门特性选择合适规格。
二十二、常见的五种无效询价方式
1. “报一台DN100气动调节阀”
缺少介质、流量、P1、P2、温度和控制要求，只能做非常粗略的预算。
2. “压力1.0MPa”
不知道这是设计压力、阀前压力还是压差，也不知道阀后压力。
3. “流量100”
没有单位，也没有最小、正常和最大工况。
4. “材质304，其他按常规”
调节阀没有一种配置能覆盖所有“常规”工况。至少要知道介质和温度。
5. “和原来一样”
如果能提供原阀铭牌、型号、数据表和现场问题，这句话才有意义。只发一张远距离照片，通常看不出阀内件、Cv和故障位置。
二十三、可直接复制给厂家的询价模板
下面这份模板可以直接复制到微信、邮件或询价单中。不确定的项目可以写“待确认”，不要随意猜测。
调节阀询价参数
1. 项目或设备名称：
2. 控制对象：流量 / 压力 / 液位 / 温度 / 其他
3. 介质名称及主要成分：
4. 介质状态：液体 / 气体 / 蒸汽 / 气液两相
5. 是否腐蚀、含颗粒、易结晶或高黏度：
6. 最小流量： 单位：
7. 正常流量： 单位：
8. 最大流量： 单位：
9. 正常阀前压力P1：
10. 正常阀后压力P2：
11. 最大关断压差：
12. 正常工作温度：
13. 最低 / 最高温度：
14. 上下游管道口径：
15. 压力等级：
16. 连接形式及法兰标准：
17. 执行机构：气动 / 电动 / 待厂家建议
18. 控制信号：4-20mA / 0-10V / 开关量 / 总线
19. 气源压力或电源：
20. 故障位置：故障关FC / 故障开FO / 保位FL
21. 泄漏等级或关闭要求：
22. 阀体、阀内件材质要求：
23. 防爆和防护等级：
24. 希望的全行程时间：
25. 定位器、电磁阀、限位等附件要求：
26. 安装方向和空间限制：
27. 其他特殊要求：噪声 / 气蚀 / 闪蒸 / 卫生 / 禁油等
28. 是否有原阀铭牌、数据表和现场照片：二十四、一个完整的填写示例
控制对象：反应釜蒸汽流量，用于温度控制
介质：饱和蒸汽
最小 / 正常 / 最大流量：500 / 1800 / 2600 kg/h
阀前压力P1：正常0.8MPa，最高1.0MPa
阀后压力P2：正常0.3MPa，最低0.2MPa
工作温度：正常175℃，最高190℃
管道：DN80
压力等级及法兰：PN16，HG/T 20592
执行机构：气动薄膜或气动活塞，由厂家选型
控制信号：4-20mA
气源压力：0.4-0.6MPa
故障位置：失气关闭FC
附件：智能定位器、过滤减压阀
安装环境：室外，非防爆区这份数据比“DN80蒸汽调节阀一台”多不了多少字，却足以让厂家开展Cv、噪声、开度和执行机构推力计算，报价也会更接近最终供货范围。
二十五、采购前最后核对这几件事
在正式下单前，建议采购、工艺、仪表和厂家共同确认：
- 流量单位是否正确，气体是否注明标准状态；
- P1和P2是否对应同一个运行工况；
- 最大关断压差是否覆盖启动、停车和事故状态；
- 阀门口径是计算结果，还是直接照搬管道口径；
- 控制信号、电源或气源是否与现场一致；
- 故障位置是否经过工艺和安全专业确认；
- 法兰标准、密封面和结构长度是否与现场匹配；
- 阀门及执行机构是否有足够安装和检修空间；
- 是否明确定位器、电磁阀、限位和手轮等附件范围；
- 数据表、报价单和最终订单中的参数是否一致。
结语
采购调节阀时，厂家反复询问参数，并不是把简单事情复杂化，而是因为每一项数据都会影响实际使用结果。
最关键的信息可以归纳成一句话：
什么介质，在什么温度下，每小时要通过多少，从多大压力降到多大压力，现场用什么信号和动力，发生故障以后希望阀门停在哪个位置。
把这句话说清楚，调节阀选型已经完成了一大半。
客户不需要自己会算Cv，也不需要先判断应该用单座阀、套筒阀、V型球阀还是蝶阀。只要把真实工况提供准确，厂家就能进一步计算口径、阀型、材料和执行机构。
一份完整的参数表，可能只需要十几分钟填写，却能避免阀门到现场以后出现装不上、流量不够、长期小开度、噪声过大、执行机构关不动或故障位置错误等问题。选型阶段把问题问明白，通常比投运后再改造更省时间，也更省成本。
无锡泉控阀门流体控制有限公司
工业阀门 | 调节阀选型 | 执行机构配套 | 流体控制解决方案
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