1. Classification

1.1. By Power Source

Automatic valves: Valves that operate using the energy of the fluid itself, such as check valves, pressure-reducing valves, steam traps, and safety valves.

Actuated valves: Valves operated by external forces such as manual power, electricity, hydraulic power, or pneumatic power. Examples include globe valves, throttling valves, gate valves, butterfly valves, ball valves, and plug valves.

1.2. By Structural Characteristics

1.3. By Function

On/off valves: Used to shut off or allow flow through a pipeline, such as globe, gate, ball, and plug valves.

Control valves: Used to regulate fluid pressure or flow, such as pressure-reducing valves and regulating valves.

Check valves: Prevent reverse flow.

Diverter valves: Change the direction of flow to distribute the medium, such as three-way plug valves and three-way globe valves.

Safety valves: Discharge excess medium when pressure exceeds a set limit to protect equipment; examples include safety and emergency relief valves.

Steam traps: Retain steam while discharging condensate.

1.4. By Method of Operation

Manual valves: Operated by hand using handwheels, handles, levers, chain wheels, gears, worm gears, or similar mechanisms.

Electric valves: Operated by electrical power.

Pneumatic valves: Operated by compressed air.

Hydraulic valves: Operated by external force transmitted through liquids such as water or oil.

1.5. By Pressure Rating

Vacuum: Valves for absolute pressures below 1 kgf/cm².

Low pressure: Valves with a nominal pressure below 16 kgf/cm².

Medium pressure: Valves with a nominal pressure of 25–64 kgf/cm².

High pressure: Valves with a nominal pressure of 100–800 kgf/cm².

Ultra-high pressure: Valves with a nominal pressure of 1,000 kgf/cm² or higher.

1.6. By Medium Temperature

General-purpose valves: For medium temperatures from −40 to 450°C.

High-temperature valves: For medium temperatures from 450 to 600°C.

Heat-resistant valves: For medium temperatures above 600°C.

Low-temperature valves: For medium temperatures from −40 to −70°C.

Cryogenic valves: For medium temperatures from −70 to −196°C.

Ultra-low-temperature valves: For medium temperatures below −196°C.

1.7. By Nominal Size

Small-bore valves: Nominal size below 40 mm.

Medium-bore valves: Nominal size from 50 to 300 mm.

Large-bore valves: Nominal size from 350 to 1,200 mm.

Extra-large-bore valves: Nominal size above 1,400 mm.

These classifications are not absolute; valves can also be classified from other perspectives. Understanding these basic categories is nevertheless very helpful when dealing with the wide variety of valves available.

2. Valve Model Designation

According to the valve model designation method, a valve model number consists of seven elements:

Note: Elements five and six are separated by a hyphen.

2.1. The first element is the valve type code, represented by a Chinese phonetic letter:

For low-temperature valves used below −40°C, jacketed insulated valves, and valves with bellows (instead of a stuffing box), the letters D, B, and W, respectively, are placed before the type code.

2.2. The second element is the actuation-method code, represented by an Arabic numeral:

Pneumatic or hydraulic valves are generally classified as normally open or normally closed. Normally open types use 6K or 7K; normally closed types use 6B or 7B.

2.3. The third element is the connection-type code, represented by an Arabic numeral:

2.4. The fourth element is the structural-type code, represented by an Arabic numeral:

For lever-operated safety valves, the letter G is placed before the type code. The current standard does not specify numerical codes. Under the old standard: 1 = single-lever low-lift; 2 = single-lever full-lift; 3 = double-lever low-lift; 4 = double-lever full-lift; 6 = pulse type.

2.4.1. The fifth element is the code for the seat sealing-surface or lining material, represented by a Chinese phonetic letter.

If the sealing surface is machined directly into the valve body, the code W is used.

2.5. The sixth element indicates the nominal pressure value.

Nominal pressure is the pressure a valve is designated to withstand. Its actual pressure capacity may be higher, but for safety it should be operated within its nominal rating. Under standard JB 74-59, nominal pressure values are: 1, 1.5, 4, 6, 10, 16, 25, 40, 64, 100, 200, 250, 320, 400, 500, 640, 800, and 1,000. Values above 1,000 are not specified.

2.6. The seventh and final element is the valve-body material code, represented by a Chinese phonetic letter:

This code may be omitted for grey cast-iron valve bodies at the specified nominal pressure and for carbon-steel valve bodies at the specified nominal pressure.

As these classifications show, valves come in many varieties. A unified model-numbering system is therefore needed so purchasers and users can identify a valve’s structure, characteristics, and materials from its nameplate.

3. Marking and Identification

3.1. Purpose of Valve Identification

Valve identification is especially important when drawings and documentation are unavailable, nameplates have been lost, or valve parts are missing. It helps ensure correct operation, weld repair, refurbishment, and replacement of valve components. The following sections describe valve marking, material identification, and valve identification.

Using the basic valve knowledge covered above, the nameplate, markings, and paint colors can help identify a valve’s type, construction, material, nominal size, nominal (or operating) pressure, service medium, temperature range, and closing direction.

1. The nameplate is attached to the valve body or handwheel. It contains key information about the valve’s basic characteristics. Use the manufacturer’s details on the nameplate to request drawings and documentation for wearing parts. The manufacturing date can help guide repair planning. Use the stated service conditions to select the materials and types of replacement gaskets, packing, and other components.
2. Markings are applied to the valve body by casting, stamping, or other methods to indicate nominal pressure, working pressure, nominal size, and the direction of medium flow
3. Another type of marking is the position indicator, which may have a scale or arrows showing open and closed positions. Throttling valves and non-rising-stem gate valves may have position indicators at the top. An arrow on the handwheel indicates the closing direction. A straight groove on the end of the stem aligned with the valve passage indicates that the valve is open; when the groove is at 90° to the passage, the valve is closed.
4. Paint on valves is not merely decorative or for rust prevention; it can also help identify materials. Different paint colors may indicate the valve-body material or the sealing-surface material.

To identify a valve’s construction, material, and basic characteristics visually, the valve body should be cast or stamped with the model, nominal diameter, flow direction, and manufacturer name, or be fitted with a nameplate. Specified paint colors are also applied to the body, handwheel, and outer edges of the flanges.

For lined valves, an additional identification paint should be applied to the outer circumference of the connecting flanges, using the colors specified below:

3.2. Examples of Valve Markings

DN stands for nominal diameter (nominal size) of a valve and is usually followed by a number. For example, a nominal size of 250 mm is marked DN250. In general, the valve passage diameter corresponds to the nominal size. However, for valves with welded-pipe construction or valves connected to piping through standard steel-pipe flanges, the actual passage diameter may differ from the DN value.

WCB indicates the valve-body material; other valve components may be made from different materials. WCB is a grade of carbon-steel casting under ASTM A216. In the designation, W refers to weldability, C to cast steel, and B to the mechanical-property grade. Thus, WCB is a weldable cast-steel grade with Class B mechanical properties. It is a common carbon steel, broadly comparable to carbon steels such as grades 25 or 35.

PN denotes the nominal pressure rating, followed by an integer. In China, the unit is often stated as MPa for clarity. For example, PN100 denotes a nominal pressure of 10 MPa, equivalent to 100 kgf/cm².

3.3. Key Requirements for Valve Marking

1. Unless otherwise specified, valves to American standards should have permanent markings in accordance with API 600, API 6D, or MSS SP-25; valves to Chinese national standards should follow GB/T 12220. Markings should include the casting heat number or the manufacturer’s casting mark.
2. The nameplate must be securely attached in a clearly visible location. Its information must be neat and accurate and comply with GB/T 13306. Nameplates should be made of stainless steel, copper alloy, or aluminum alloy.
3. If the required marking cannot practicably be applied to the valve body, it may be placed on the nameplate. However, the flow-direction marking must be applied to the valve body regardless of the standard followed.
4. Paint used for color coding and marking must not contain harmful metals or metal salts—such as zinc, lead, sulfur, copper, tin, or chlorides—that may cause corrosion at elevated temperatures. The paint must also resist corrosion from salt water, tropical environments, and similar conditions.
5. For small components that are difficult to mark, use a stainless-steel tag secured with stainless-steel wire.
6. Nameplate information generally includes the model, material, pressure rating, applicable standard, service temperature, service medium, and manufacturing date. These details help users procure parts for maintenance and replacement.

3.4. Methods of Applying Markings

1. If the valve body is formed by casting or die casting, its markings should be cast or die-cast as part of the body.
2. If the valve body is formed by forging in a die, markings may be forged or die-cast together with the body, or stamped onto it. For bodies machined from forgings, or fabricated from steel pipe or rolled and welded steel plate, markings may be stamped or applied by another method that does not impair body performance.

3.5. Marking Format

Markings include the nominal-size value, pressure code or working-pressure code, and flow-direction indicator. The pressure code is positioned above the nominal-size marking.

3.6. Marking Location

1. Markings should generally be placed where they are easy to see on the valve body, preferably near the center of the body’s vertical centerline.
2. If there is insufficient space on one face of the valve body, markings may be placed on another face near the center.
3. Markings must be clear, legible, and neatly arranged.

3.7. Marking Dimensions

1. Cast markings should have raised profiles. The size and arrangement of the lettering and arrows should be designed accordingly.
2. The dimensions of stamped markings and arrows are specified in the design drawings.
3. The character size for each product marking may also be specified in the design drawings according to the product’s overall size.

3.8. Understanding Valve Nameplates

Nameplates are usually attached to the valve body, flange, or handwheel. They provide key information about the valve’s basic characteristics, although the information shown varies by valve type.

3.9. Valve Painting

1. The external surfaces of cast-iron, carbon-steel, and alloy-steel valves must be painted before delivery. A suitable powder-coating process may be used for the internal and external surfaces instead.
2. The coating should be durable and attractive, while keeping markings clear and legible. Use paint that is suitable for the service temperature and is non-toxic and non-polluting.
3. The paint finish on handwheel components should comply with the contract or the manufacturer’s standard.
4. The pressure-containing body surfaces of copper-alloy valves are not painted.
5. The pressure-containing body surfaces of acid-resistant steel and stainless-steel valves are not painted. If painting is required by the contract, follow the contractual requirements.
6. Paint colors for valve actuators should generally follow the manufacturer’s standards. For manual gear operators, the surface color should follow the applicable standard; pneumatic, electric, and hydraulic actuators should also follow the manufacturer’s standard unless the purchase contract specifies a customer-selected color.