Faq

Double-sided forced sealing for gate valves:

This means that whether at the inlet or outlet end of the medium, the gate plate and valve seat sealing surfaces remain sealed. The sealing integrity is forcibly maintained by the axial force of the valve stem. When no medium is present, the positive pressure between the sealing surfaces must not be less than the sum of the medium's static pressure and the sealing force.

Single-face forced sealing for gate valves:

This means that no seal exists between the gate plate and the valve seat sealing surface at the medium inlet end. Here, either no pressure differential exists at all, or the pressure differential is less than the sealing pressure. On the medium outlet side, the seal between the gate plate and the valve seat sealing surface is forcibly maintained by the axial force of the valve stem and the medium pressure. When no medium is present, the pressure differential across the sealing surfaces must not be less than the sealing pressure.

(1) Classified into two types based on the structure of the gate plate

1. Parallel gate valves feature sealing surfaces parallel to the vertical centerline, meaning the two sealing surfaces are parallel to each other. Within this category, there are double-disc and single-disc types. They are further classified as having or lacking flow-through holes.
2. A wedge gate valve refers to a gate valve where the sealing surfaces form a wedge shape by being angled relative to the vertical centerline. Within this category, there are further distinctions between double-disc gate valves, single-disc gate valves, and elastic disc gate valves.

(2) Classified into two types based on valve stem construction

1. A rising stem gate valve is a type of gate valve where the valve stem nut is located on the valve bonnet or bracket. When opening or closing the gate, the valve stem is raised or lowered by rotating the valve stem nut.
2. A stemless gate valve is a type of gate valve where the valve stem nut is in direct contact with the medium inside the valve body, and the gate plate is opened or closed by rotating the valve stem.

The minimum stem diameter refers to the diameter of the portion of the stem that contacts the packing. The minimum stem diameter refers to the diameter of the stem thread relief groove.

The paint color of the handles and handwheels corresponds to the paint color of the sealing surface material, as detailed in the table below.

Valve handle and handwheel paint color：

The opening and closing directions for general valves are specified as follows: clockwise for closing and counterclockwise for opening.

The mandatory and optional markings for general-purpose valves are shown in the table below.

Valve markings：

Note: When the nominal pressure value cast on the valve body equals ten times the megapascal (MPa) figure and is positioned below the nominal pressure value, it is not preceded by the designation “PN”.

Marking method:

(1) Valve marking for nominal sizes greater than or equal to DN50:

1. Items 1 through 4 in the table are mandatory markings and should be affixed to the valve body.
2. Items 5 and 6 in the table are mandatory markings only when specified in the relevant valve standards. They should be marked on the valve body and flange, respectively.
3. Unless otherwise specified in various valve standards, items 7 through 19 in the table are optional markings. When required, they may be marked on the valve body or nameplate.

(2) Marking for valves with nominal sizes less than DN50:

1. Items 1 through 4 in the table are mandatory markings. Whether these markings appear on the valve body or on a label is determined by the product designer.
2. The marking of items 5 to 19 in the table shall comply with the provisions for markings 2 and 3 for nominal sizes greater than or equal to DN50.

(3) Additional markings:

1. Any marking from the table may be affixed at different locations. For example, any marking placed on the valve body may also be duplicated on the nameplate.
2. Any additional markings may be affixed provided they do not cause confusion with the markings on the form. For example: product model numbers, etc.

For pressure reducing valves, in addition to the 19 items specified for general valves, the markings on the valve body shall also include: date of manufacture, applicable medium, and outlet pressure.

For steam trap markings, in accordance with GB/T 12250-2005, the markings may be affixed to the valve body or displayed on a nameplate.

The marking of safety valves shall comply with the provisions of GB/T 12241-2005.

Ball valves, parallel gate valves, and plug valves shall be marked in accordance with API 6D-2014.

The sealing surface material code for surfaces machined directly from the valve body is denoted by “W”. Codes for other materials are listed in the table below.

Seat sealing surface or lining material code:

Note: When the sealing surfaces of a sealing pair are made of different materials, the designation code of the softer material shall be used.

For gate, globe, and check valves, as well as ball and butterfly valves, the sealing specific pressure qMF must be less than the sealing specific pressure q, and the sealing specific pressure is less than the sealing allowable specific pressure [q] (i.e., qMF < q < [q]).

The shell test pressure for general-purpose valves is 1.5 times the rated working pressure of the material at 38°C. The high-pressure seal test is 1.1 times the rated working pressure of the material at 38°C. Low-pressure seal test requirements vary by standard.

Among these:

GB/T 13927-1992, ISO 5208:2008, EN 12266.2-2012 is 0.6MPa±0.01MPa;

GB/T 26481-2011, API 598-2009 is 0.4MPa~0.7Mpa;

MSS SP61-2013 is 0.56 MPa;

API 6D-2014 for Type I: 0.034MPa~0.1MPa, Type II: 0.55MPa±0.69MPa;

ISO 14313:2007 for Type I: 0.05MPa~0.1MPa, Type II: 0.55MPa±0.07MPa;

API 6A (idt ISO 10423:2003) for PSL3G: first: rated pressure, second: 2.0MPa ± 0.2MPa; PSL4: first: rated pressure, second: 2.0MPa ± 0.2MPa.

The specific test pressures for shell tests, high-pressure sealing tests, and high-pressure upper sealing tests are shown in Tables 1-1 and 1-2.

Classification of valves based on their purpose or primary structural characteristics.

General classification categorizes valves by both operating principle and structure, representing the most widely used classification method domestically and internationally. Common types include: gate valves, globe valves, plug valves, ball valves, butterfly valves, diaphragm valves, check valves, throttle valves, safety valves, pressure reducing valves, steam traps, and control valves.

Valve model designations are composed of codes representing valve type, actuation method, connection type, structural configuration, sealing surface material or lining material type, pressure rating or working pressure at operating temperature, and valve body material.

The valve model consists of seven parts, with their meanings shown in the diagram.

NPS：

Combined alphanumeric size designation for piping system components consisting of the letters NPS followed by a dimensionless integer number. This number is directly related to a characteristic dimension such as the bore or outside diameter of the end connection. The dimensionless number may be used as a dimensional designation for valves without the prefix “NPS”. Dimensionless size numbers do not represent measured values and cannot be used for calculations.

Class：

A combination of letters and numbers used to identify the pressure/temperature capability of a valve in relation to the mechanical and dimensional properties of the valve material. It consists of the letter Class followed by a dimensionless integer. The number following the letter Class does not represent a measured value and should not be used in calculations. The permissible pressure of piping elements depends on the Class value, the material and the permissible working temperature, unless otherwise specified in the respective standard. The permissible pressures are given in the pressure-temperature rating tables of the respective standards.

DN:

A combination of letters and numbers used to identify the size of piping system components. It consists of the letter DN followed by an integer number without a factor. This number is directly related to the characteristic dimensions of the end connection, such as the bore diameter or the outside diameter (expressed in mm).

Note:

1. Unless otherwise specified in the relevant standards, the numbers following the letters DN do not represent measured values and cannot be used for calculation purposes.
2. Those standards that utilize a DN marking system should give the DN in relation to the size of the pipe element, e.g. DN/OD or DN/ID.

PN:

A combination of letters and numbers used for reference purposes in connection with the mechanical and dimensional properties of piping system components. It consists of the letter PN followed by a non-factorized number.

Note:

1. The numbers following the letter PN do not represent measured values and should not be used for calculation purposes, unless otherwise specified in the relevant standard.
2. The term PN has no meaning except in connection with the relevant pipe component standard.
3. The permissible pressure of a piping element depends on the PN value, material and design of the element as well as the permissible working temperature, etc. The permissible pressure is given in the pressure-temperature rating table of the respective standard.
4. All piping components with the same PN and DN values and their mating flanges should have the same mating dimensions.

Valves commonly used in pipelines across various industrial enterprises.

A general term for mechanical products with movable mechanisms used to control the flow of media within pipelines.