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The Procedure To Produce The Valves
Mar 18, 2019

The procedure to produce the valves


At first glance, the valve has few parts, simple structure and general precision. It belongs to simple parts in the mechanical industry, but the core sealing parts of the valve are particularly demanding. Valve manufacturing process is complex and difficult. What process characteristics should we pay attention to?

1. Manufacturing materials

Because of the variety and specifications of valves, they are used in various fields of the national economy, and their application occasions vary greatly, such as high temperature and high pressure, low temperature and deep cooling, flammable and explosive, highly toxic, strong corrosive media and other working conditions, which put forward stringent requirements for the material of valves.

In addition to cast iron, carbon steel and alloy structural steel, CrNi stainless steel, CrMoAl nitriding steel, CrMoV heat-resistant steel, CrMnN acid-resistant steel, precipitation hardening steel, duplex stainless steel, low temperature steel, titanium alloy, Monel alloy, Inconel alloy, Hastelloy alloy and G0CrW cemented carbide are widely used. The casting, welding and processing properties of these high alloy materials are very poor, which makes the manufacturing process very difficult. In addition, most of these materials are precious materials with high alloy, high strength and high hardness. There are many difficulties in material selection, preparation and procurement. Some materials are difficult to purchase and supply because of their small usage.


2. Structure of casting blank

Most of the valve blanks are thin shell castings with complex structure, which require not only good appearance quality, but also compact internal quality and good metallographic structure, and can not have defects such as porosity, shrinkage, sand inclusion, cracks and so on. Therefore, its casting process is complex and heat treatment technology is difficult. In the mechanical industry, the casting difficulty of the thin shell casting blank of the valve is much more complex and more difficult than that of other mechanical components.


3. Machining Technology

Because the cutting performance of most high strength, high hardness and high corrosion resistant materials is not good, such as high alloy stainless steel and acid resistant steel, which have some shortcomings such as high toughness, high strength, poor heat dissipation, high chip stickiness and strong tendency to work hardening, it is difficult to achieve the required dimensional accuracy and smoothness, which brings some difficulties to the machined tools, processes and equipment. In addition, the requirements of valve sealing surface in processing accuracy, matching angle, smoothness and matching sealing pairs are also very high, which brings great difficulties to mechanical processing.


4. Process Arrangement of Valve Parts

The main parts of the valve are few, the structure is relatively simple, the processing accuracy of most sizes is not high, and the outside is rough, which gives the impression that it belongs to simple machinery. In fact, the heart sealing part of the valve is extremely precise. The "three degrees" (smoothness, smoothness, hardness) of the sealing surface is required to be very high, and the coincidence degree of the sealing pair composed of two sealing faces must reach zero to zero, so as to meet the zero leakage of the gas tightness test. This kind of zero-to-zero requirement, which guarantees the precision of heart parts with rough benchmarks, is the biggest technological difficulty in valve processing.


5. Valve Testing and Inspection

Valve is an important opening and closing and regulating element of pressure pipeline, and the working conditions of pressure pipeline are different, such as high temperature, high pressure, low temperature, cryogenic, flammable, explosive, highly toxic and corrosive. However, the test and test conditions of valve manufacturing can not meet the same requirements of working conditions. Various international and domestic valve test standards stipulate that the gas or water is used as the medium to test under the condition of near normal temperature. There is a fundamental hidden danger, that is, the valves which are qualified for normal factory test may be difficult to meet the application requirements due to material selection, casting quality and sealing damage under harsh actual working conditions, and major quality accidents will occur.


Step 1: Valve body manufacturing

Valve body (casting, surfacing of sealing surface)

Purchase of castings (according to standards), Inspection in factory (according to standards), Surfacing trough, ultrasonic flaw detection (according to patterns), Surfacing and post-weld heat treatment, finishing, grinding sealing surface, hardness testing and colouring inspection.


Step 2: Valve internals manufacturing process

A. Internals such as discs, seats, etc. that require surfacing of sealing surfaces

Purchase of raw materials (according to standards)Inspection in factory (according to standards)Production of blanks (round steel or forgings, according to the requirements of drawing process)Rough processing of ultrasonic flaw detection surface (when required by drawings) Rough processing of surfacing trough Surfacing and post-weld heat treatment Finishing of various parts Grinding of sealing surface Hardness testing and color detection.


B, stem

Purchase of raw materials (according to standards)Inspection in factory (according to standards)Manufacturing of blanks (round steel or forgings, according to the requirements of drawing process) Rough surfacing trough Surfacing and post-weld heat treatment Finishing of various parts Grinding of outer circle Valve stem surface treatment (nitriding, quenching, chemical coating) Final treatment (polishing, grinding, etc.) Grinding of sealing surface Hardness test of sealing surface, staining detection.


C. Internal parts without surfacing seals, etc.

Purchase of raw materials (according to standards)Inspection in factory (according to standards)Production of blanks (round steel or forgings, according to the requirements of drawing technology) Rough processing of ultrasonic flaw detection surface (when required by drawings) Finishing of various parts.


Step 3: Fastener Manufacturing

Fastener Manufacturing Standard DL439-1991.

Purchase of raw materials (according to standards)Inspection in factory (according to standards)Production of blanks (round steel or forgings, according to drawing process requirements) and sampling for necessary inspection_Rough processing Finishing_Spectral inspection.


Step 4: Assembly

Receiving parts, cleaning, rough assembly (according to drawings), hydraulic test (according to drawings, processes), qualified, disassembly, erase, final assembly, debugging with electrical or actuator (for electric valves), painting packaging, shipping.


Step 5: Product Production and Inspection Process

1. Raw materials of various specifications purchased by the company.

2. Material testing of raw materials is carried out by spectral analyzer, and the material testing report of raw materials is printed out for backup.

3. Cutting raw materials with cutting machine.

4. Inspectors inspect the cutting diameter and length of raw materials.

5. The forging workshop processes the raw materials by forging.

6. Inspectors inspect the various sizes of the blanks.

7. The worker is cutting the waste edge of the blank.

8. Sandblasting worker carries out surface sandblasting treatment on the blank.

9. Inspectors conduct surface treatment inspection after sand blasting.

10. The worker processes the blank.

11. Valve body sealing thread processing - Employees in the process of self-inspection inspectors after processing products for post-processing inspection.

12. Valve body connection thread processing.

13. Medium hole processing.

14. Inspectors conduct general inspection.

15. Qualified semi-finished products are sent to semi-finished warehouses

16. Electroplating of semi-finished products.

17. Surface treatment inspection of semi-finished electroplating products.

18. Inspection of various accessories (ball, stem, sealing seat).

19. The assembly workshop carries out product assembly-assembly line inspectors to inspect the products.

20. The assembled products are tested by pressure and dried to the next process.

21. The general assembly workshop inspects the sealing, appearance and torsion of the product by inspectors on the packaging line. Unqualified products are never allowed to be packaged.

22. Qualified products are packed in bags and sent to finished products warehouses.

23. All inspection records will be classified and stored in the computer for inquiry at any time.

24. Qualified products are sent toChinaand abroad through containers.

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