In industrial refrigeration, petrochemical, energy, defense, and food & pharmaceutical applications, the difference between a successful valve specification and a costly misselection often comes down to terminology. A single misunderstood term—”rangeability” vs. “turndown,” “bubble-tight” vs. “ANSI Class VI,” or “fail-close” vs. “air-to-close”—can cascade into incorrect valve selection, premature trim failure, or safety incidents. At Dofun, from our modern facility of more than 30 acres in Liaocheng with over 10,000 square meters of workshop space​ and with more than 30 invention patents, we interact with engineers across energy & chemicals, defense & security, heavy industry & resources, public welfare & health, and thermal control & refrigeration​ sectors. This glossary of 50 essential terms is designed to give every engineer—from early-career designers to seasoned EPC specifiers—a authoritative reference grounded in industry-standard definitions and aligned with Dofun’s product portfolio.

💡 This glossary follows ISA, ANSI, and leading manufacturer (Emerson, Bray, GlobalSpec) terminology conventions. Definitions are synthesized from industry-standard sources to ensure technical accuracy and global applicability.

Category 1: Valve Types & Classifications (Terms 1–10)

Understanding valve family taxonomy is the foundation of all selection work.

1. Control Valve

A valve equipped with an actuator that responds to an external signal to modulate flow, pressure, temperature, or other process variables. Control valves are the “final control element” in a control loop. Dofun’s Pressure Regulating Valve Series​ and Motor Valve Series​ are prime examples, used in refrigeration and chemical processes where “continuous and safe operation under extreme operating conditions involving low temperature, high pressure, and strong corrosion” is mandatory.

2. Ball Valve

A quarter-turn valve using a spherical closure element with a central bore. When the bore aligns with the pipeline, flow passes; a 90° rotation blocks flow. Offers fast operation and excellent sealing.

3. Butterfly Valve

A quarter-turn rotary valve with a circular disc that rotates around a central axis. Known for compact design and low cost in large diameters, though the disc remains in the flow path even when open.

4. Gate Valve

A multi-turn linear valve that raises a wedge (gate) out of the flow path. Provides an unobstructed bore when fully open; not suitable for throttling.

5. Globe Valve

A linear-motion valve with a movable disk or plug that seals against a stationary seat ring. The preferred design for precise throttling control, though at higher pressure drop than ball or gate valves.

6. Check Valve

A self-actuating valve that permits flow in one direction only, automatically closing to prevent backflow. Critical in compressor discharge lines and parallel systems.

7. Solenoid Valve

An electromechanically operated valve controlled by an electric current through a solenoid coil. Dofun’s Solenoid Valve Series​ provides fast-acting on/off control for liquid lines, suction lines, and hot gas defrost applications.

8. Pressure Relief Valve (PRV)

A safety device that automatically releases excess pressure from a vessel or system when it exceeds a preset threshold. Mandatory on all pressure vessels per EN 378-2 and ASHRAE 15.

9. Expansion Valve

A valve that reduces refrigerant pressure while metering flow into an evaporator. Includes thermostatic (TXV), electronic (EEV), and float-type designs. Dofun’s Servo Main Valve Series​ includes pilot-operated configurations for precision pressure and flow management.

10. Three-Way Valve

A valve with three ports used to mix or diverge flow streams. Commonly used in process control where blending or diversion is required.

Category 2: Valve Body, Trim & Structural Components (Terms 11–20)

The physical anatomy of a valve determines its performance envelope.

11. Valve Body

The primary pressure-retaining shell that houses the internal flow passage and closure elements. Dofun bodies are manufactured using low-temperature alloy precision casting or forging, with our Stainless Steel Valve Series​ offering 316L construction for corrosive services.

12. Bonnet

The top portion of the valve, bolted or integral to the body, that contains the packing box, guides the stem, and provides the interface to the actuator. For cryogenic applications, Dofun offers Manual Operation Valve PN40/PN63 Long Neck Series—the extended structure keeps the stem packing accessible and protected from welding heat.

13. Valve Trim

The replaceable internal components that come into contact with the flow medium—including the stem, plug/disc, seat, and cage. Dofun’s proprietary NANO surface treatment​ achieves stem roughness (Ra) ≤ 0.03 μm with near-zero friction, and our six-level sealing structure​ uses imported materials to thoroughly prevent leakage.

14. Valve Seat

The internal surface that contacts the closure member to form a leak-proof seal. Seat design (soft vs. metal) dictates the valve’s leakage class.

15. Valve Stem

The component that transmits motion from the actuator to the closure member. Dofun’s 304 stainless steel stems undergo proprietary NANO treatment for exceptional durability.

16. Closure Member (Plug/Disc/Ball)

The movable element positioned in the flow stream to modify flow rate. In a globe valve, it is a plug; in a ball valve, a sphere; in a butterfly valve, a disc.

17. Cage

A hollow cylindrical trim element that guides the plug, retains the seat ring, and can be configured to characterize flow, attenuate noise, or prevent cavitation. Multi-stage cages are the gold standard for anti-cavitation trim.

18. Y-Passage (Y-Shaped Flow Passage)

Dofun’s patented Y-structured flow passage reduces flow resistance, avoids calorification, eddy, and effusion, and decreases refrigerant supplementation—a structural innovation that enhances both performance and efficiency.

19. Handwheel

A manually operated wheel that drives the stem via threads to open or close a valve. Used on Dofun’s Manual Operation Valve Series (PN40, PN63, Long Neck).

20. Fixed-Torque Bolting

A Dofun design principle where each bolt on the valve has a fixed torque specification, effectively avoiding leakage due to unreasonable installation torque when reassembling. This embodies our craftsmanship philosophy of carving every valve into “a metal artwork.”

Category 3: Actuation & Control Accessories (Terms 21–30)

Modern valves rarely operate in isolation—they are part of an automated system.

21. Actuator

A device (pneumatic, electric, hydraulic, or electro-hydraulic) that provides the force and motion to operate a valve. Dofun’s Motor Valve Series​ and Gas Powered Valve Series​ integrate actuators tailored to specific service conditions.

22. Positioner

A device mounted on a control valve actuator that ensures the valve reaches the exact position demanded by the control signal (typically 4–20 mA). Essential for precise modulating control.

23. Fail-Safe

A valve’s predetermined action upon loss of actuating energy. Three modes exist:

• Fail-Close (FC):​ Closure member moves to closed position
• Fail-Open (FO):​ Closure member moves to open position
• Fail-In-Place (FIP):​ Closure member remains in last position

For ammonia refrigeration ESD applications, fail-safe closed (spring-return) solenoids are mandatory, with closure within ≤5 seconds.

24. Air-To-Open / Air-To-Close

A pneumatic actuator configuration: “air-to-open” means increasing air pressure opens the valve (fail-closed); “air-to-close” means increasing air pressure closes the valve (fail-open).

25. Pneumatic Actuator

An actuator that uses compressed air to position the valve. Offers fast response and reliability in hazardous areas.

26. Electric Actuator (Motor Operator)

An electro-mechanical actuator that drives valve motion via an electric motor. Dofun’s Motor Valve Series​ provides electric actuation for precise modulation in refrigeration and process control.

27. Pilot Valve

A small valve that controls a larger valve, often used in pilot-operated relief valves or large-diameter solenoid systems. Dofun’s Servo Main Valve Series​ includes pilot configurations (IPV, OPV, DPV, PHV) that enable mechanical control without PLC dependency.

28. Bench-Set

The calibration of an actuator’s spring range to account for in-service process forces, ensuring the valve strokes correctly across its full travel.

29. Topworks

The assembly above the valve body, including the actuator, yoke, and stem coupling. Houses all components that translate control signals into valve motion.

30. Travel Indicator

A visual or electronic indicator showing the valve’s current position. Critical for operator awareness and control system feedback.

Category 4: Flow, Sizing & Hydraulic Terminology (Terms 31–40)

The mathematics of valve selection separates competent engineers from exceptional ones.

31. Flow Coefficient (Cv)

The number of US gallons of 60°F water that flows through a valve per minute with a 1 psi pressure drop. The primary sizing parameter for all control valves. Higher Cv = greater flow capacity.

32. Vena Contracta

The point in a flow stream where velocity is at its maximum and static pressure is at its minimum—typically just downstream of the physical restriction. Critical for understanding cavitation onset.

33. Cavitation

A two-stage destructive phenomenon: (1) vapor bubbles form when local pressure drops below vapor pressure at the vena contracta, and (2) bubbles violently collapse as pressure recovers downstream. The implosion generates micro-jets exceeding 1.5 GPa, eroding metal surfaces. Dofun’s multi-stage anti-cavitation trim and DOFUN-CTP modular platform​ address this through engineered pressure reduction.

34. Choked Flow

A condition where further valve opening does not increase flow because the velocity at the vena contracta has reached sonic (for gases) or the vapor formation is maximal (for liquids). The valve loses control authority.

35. Rangeability (Turndown Ratio)

The ratio of maximum controllable flow to minimum controllable flow while maintaining accurate control. Higher rangeability enables precise adjustments across varying flow conditions.

36. Flow Characteristic

The relationship between valve travel and flow capacity. Two primary types:

• Linear:​ Equal increments of travel yield equal increments of flow
• Equal Percentage:​ Small flow changes near closed position, larger changes as valve opens

Dofun’s technical articles provide in-depth analysis of these characteristics in “How to Read Valve Flow Characteristic Curves (Equal Percentage, Linear): Impact on System Control Explained.”

37. Installed Characteristic

The actual flow vs. travel relationship when the valve operates in a system where pressure drop across the valve varies with flow—as opposed to the “inherent characteristic” measured at constant pressure drop.

38. Pressure Recovery Factor

A dimensionless coefficient that accounts for pressure increase downstream of a control valve. High-recovery valves (butterfly, ball) induce cavitation at lower pressure drops than low-recovery valves (globe).

39. Piping Geometry Factor

A correction factor that accounts for the effect of pipe bends, fittings, and adjacent geometry on flow behavior near the control valve. Influences accurate valve sizing.

40. Sizing

The process of selecting an appropriately sized valve based on flow requirements, pressure drop, fluid properties, and operating conditions. Proper sizing ensures optimal control authority while avoiding excessive energy loss.

Category 5: Sealing, Leakage & Performance Standards (Terms 41–45)

Sealing integrity defines valve reliability.

41. Bubble-Tight

A term describing zero measurable seat leakage. In ANSI/FCI 70-2 seat leakage classifications, Class VI​ (with rubber or soft seats) is considered bubble-tight, allowing only a specified number of air bubbles per minute during testing. Dofun’s six-level sealing structure​ using imported materials achieves this level of integrity.

42. Seat Leakage Class (ANSI/FCI 70-2)

A six-tier standard for measuring control valve seat leakage:

• Class I:​ Permissive (no test required)
• Class II:​ 0.5% of rated capacity
• Class III:​ 0.1% of rated capacity
• Class IV:​ 0.01% of rated capacity (standard for metal-seated valves)
• Class V:​ 0.0005 mL/min per psi differential per inch of orifice diameter (water test)
• Class VI:​ Bubble-tight (air test, soft seats)

43. Hydrostatic Test

A pressure test using water to verify shell and seat integrity. Dofun valves undergo rigorous hydrostatic and pneumatic testing on globally advanced platforms, with a documented record of no leakage after 5,000 operations.

44. Double Block and Bleed (DBB)

A valve configuration with two sealing elements providing isolation from both upstream and downstream pressure, with a bleed valve between them to verify seal integrity. Used in critical isolation applications.

45. Anti-Cavitation Trim

Specialized valve trim geometry (multi-stage, tortuous-path, or drilled-hole cage) that reduces pressure gradually to prevent vapor bubble formation. Dofun’s Pressure Regulating Valve Series​ incorporates these principles through the DOFUN-CTP modular platform.

Category 6: Refrigeration-Specific & Material Terminology (Terms 46–50)

Terms unique to industrial refrigeration and material science.

46. Refrigerant

The working fluid in a refrigeration cycle. Common industrial refrigerants include:

• R717 (Ammonia):​ Natural refrigerant, high efficiency, toxic/flammable—requires steel bodies, no copper components
• R744 (CO₂):​ Transcritical cycle, high pressure—requires specialized valves
• R404A / R507:​ HFC blends for medium/low-temperature applications

Dofun valves are engineered for all these refrigerant types across our product range.

47. Back-Seating

A design feature where the stem seals against the bonnet when fully open, allowing packing replacement under pressure without refrigerant release. Critical for 24/7 industrial refrigeration operations.

48. Extended Bonnet (Long Neck)

A bonnet design that elevates the packing gland away from cryogenic temperatures, keeping stem packing accessible and preventing ice buildup. Dofun’s Manual Operation Valve PN40/PN63 Long Neck Series​ is specifically designed for this purpose.

49. NANO Surface Treatment

Dofun’s proprietary patented process applied to 304 stainless steel stems, achieving surface roughness (Ra) ≤ 0.03 μm with near-zero friction. This extends stem and seal life far beyond industry norms, contributing to our 5,000-cycle no-leakage test record.

50. DOFUN-CTP Modular Shared Platform

Dofun’s revolutionary modular manufacturing platform that enables component sharing while supporting customization in appearance and connection dimensions. Through this platform:

• Standardized parts​ effectively reduce inventory costs
• Different functions​ are achieved through quick switching of modules without pipeline disassembly
• Selection and maintenance​ are simplified with increased flexibility
• Globally compliant products​ are delivered with market responsiveness

This platform embodies Dofun’s core value of “Technology Leadership”—pioneering the next generation of valve technology through continuous R&D and innovation.

How Dofun’s Product Portfolio Maps to These Terms

To make this glossary actionable, here is how Dofun’s seven core product series align with the terminology above:

Dofun Product Series	Primary Valve Types	Key Terminology Applied
Pressure Regulating Valve Series​	Control valves, servo valves	Cv, rangeability, flow characteristic, anti-cavitation trim, positioner
Motor Valve Series​	Control valves with electric actuators	Actuator, fail-safe, bench-set, travel indicator
Solenoid Valve Series​	Solenoid valves (EPV-NC, EPV-NO)	Fail-close, fail-open, response time, solenoid coil
Gas Powered Valve Series​	Gas-actuated valves	Actuator, pilot valve, fail-safe
Servo Main Valve Series​	Pilot-operated main valves (IPV, OPV, DPV, PHV)	Pilot valve, back-seating, extended bonnet
Valve Station Series​	Integrated multi-function manifolds	DBB, modular design, Cv matching
Manual Operation Valve Series​ (PN40, PN63, Long Neck)	Gate/globe-style stop valves	Handwheel, back-seating, extended bonnet, fixed-torque bolting
Stainless Steel Valve Series​	Ball, globe, and check valves in 316L	Bubble-tight, seat leakage class, NANO treatment

The Dofun Terminology Philosophy: Engineering Precision Through Language

At Dofun, we believe that “the true meaning of Dofun is not just to achieve what we want in our hearts, but to finely carve every Dofun product into a metal artwork.” This craftsmanship extends to how we communicate with engineers. Precise terminology is not pedantry—it is the foundation of precise engineering.

Our four core values frame every technical interaction:

• Quality as Foundation:​ We integrate precision into every valve we manufacture, ensuring unmatched reliability and performance
• User as Priority:​ We build lasting partnerships by providing tailored solutions and exceptional service that exceeds expectations
• Environmental Friendliness:​ Our sustainable practices and energy-efficient products contribute to a greener industrial future
• Technology Leadership:​ Through continuous R&D and innovation, we pioneer the next generation of valve technology

With 30+ invention patents​ and a facility producing approximately 300,000 sets of industrial refrigeration valves annually, Dofun’s engineering team speaks this terminology fluently across all five application sectors:

💡 Energy & Chemicals:​ “Under extreme operating conditions involving low temperature, high pressure, and strong corrosion, our valves ensure continuous and safe operation.”

💡 Defense & Security:​ “We provide specialized valves with exceptional performance and absolute reliability under extreme conditions for the defense and military sectors.”

💡 Heavy Industry & Resources:​ “Facing the heavy-load and high-wear challenges of the mining and metallurgy industries, we provide robust and durable product solutions.”

💡 Public Welfare & Health:​ “We provide precision valves that meet stringent hygiene standards for the food and pharmaceutical industries, safeguarding safety and health from the production line to the end consumer.”

💡 Thermal Control & Refrigeration:​ “As a core component in the refrigeration field, our products are dedicated to achieving precise temperature control and energy efficiency management.”

Conclusion: Mastery of Terminology as Engineering Competence

The 50 terms in this glossary represent more than vocabulary—they are the conceptual toolkit that enables engineers to:

• Specify the correct valve family for each duty
• Size valves accurately using Cv, rangeability, and flow characteristics
• Define fail-safe actions that protect personnel and equipment
• Select materials compatible with refrigerants and process media
• Validate sealing performance against ANSI/FCI leakage classes
• Engineer anti-cavitation solutions through multi-stage trim
• Leverage modular platforms like DOFUN-CTP for lifecycle flexibility

When you specify Dofun valves, you are not just purchasing hardware—you are partnering with a team that lives these terms daily. From the NANO-treated stem achieving Ra ≤ 0.03 μm, to the six-level sealing structure delivering bubble-tight integrity, to the DOFUN-CTP modular platform enabling rapid configuration, every Dofun valve embodies the precise engineering that correct terminology makes possible.

Our clients confirm this value:

“In our low-temperature, high-pressure core unit, Dofun’s products have been operating stably for over three years. Their exceptional reliability has completely eliminated our concerns about unplanned downtime.”

“Dofun’s control valves achieve exceptional precision, playing an instrumental role in ensuring our cold chain safety and energy efficiency management.”

“The mining environment is devastatingly abrasive to equipment. The solution provided by Dofun, with its remarkable durability, has significantly reduced our maintenance frequency and spare parts costs.”

As you specify your next valve—whether a pressure regulating valve for an ammonia refrigeration system, a motor valve for precise modulation, a solenoid valve for emergency shutdown, or a stainless steel valve for corrosive chemical service—remember that the terminology in this glossary is your engineering compass. Master these 50 terms, and you master the language of valve specification.

Engage Dofun’s application engineering team​ to discuss how our products and the DOFUN-CTP modular platform can translate this terminology into tailored solutions for your specific application. Whether you are designing a new refrigeration system, upgrading a petrochemical process line, or specifying valves for defense applications where absolute reliability is non-negotiable, our engineers will guide you through every term, every specification, and every stage—from RFQ to commissioning and beyond.

💡 Dofun’s Terminology Commitment:​ Precision in language enables precision in engineering. By mastering these 50 essential terms, engineers unlock the full potential of Dofun’s valve technology—transforming abstract concepts into tangible reliability, efficiency, and safety. This is how we carve every valve into a metal artwork worthy of your most critical application.