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Section 2: Sealing surface material
The sealing surface is the most critical working surface of the valve. The quality of the sealing surface is related to the service life of the valve. Generally, the sealing surface material considers factors such as corrosion resistance, scratch resistance, erosion resistance, and oxidation resistance. Generally, sealing surface materials are divided into two categories:
1. Soft materials

soft sealing marine valve, rubber sealing, valve seat parts

1. Rubber (including nitrile rubber, ethylene propylene rubber, fluorine rubber, etc.)
2. Plastics (polytetrafluoroethylene, nylon, etc.)
2. Hard sealing material
1. Copper alloy (for low pressure valve)
2. Chrome stainless steel (used for ordinary high and medium pressure valves)
3. Stellite alloy (used for high temperature and high pressure valves and strong corrosion valves)
4. Nickel-based alloy (used for corrosive media)

Section 3: Valve Stem Material
During the opening and closing of the valve, the valve stem bears tensile, compressive and torsional forces, and is in direct contact with the medium. At the same time, there is relative frictional movement with the packing. Therefore, the valve stem material must ensure sufficient strength at the specified temperature And impact toughness, a certain degree of corrosion resistance and abrasion resistance, and good manufacturability. Commonly used valve stem materials are as follows:
1. Carbon steel: For water with low temperature and medium temperature not exceeding 300°C, when steam

18 buttefly-valve-stem-shaft-parts-1

medium, A5 ordinary carbon steel is generally selected (now Q275, A3 is Q235)
2. Alloy steel: For medium pressure and high pressure, when the medium temperature does not exceed 450°C, 40Cr (chromium steel) is generally used when the medium temperature does not exceed 450°C. Water, the medium temperature does not exceed 540°C For steam and other media, 38CrMoAlA nitriding steel can be selected; for high-pressure steam media with a medium temperature not exceeding 570°C, 25Cr2MoVA chromium molybdenum vanadium steel is generally selected.
3. Stainless and acid-resistant steel: used for medium and high pressure, non-corrosive and weakly corrosive media with a medium temperature not exceeding 450°C. 1Cr13, 2Cr13, 3Cr13 chromium stainless steel can be selected; when used in corrosive media, it can be used Use Cr17Ni2, 1Cr18Ni9Ti, Cr18Ni12Mo2Ti, Cr18Ni12Mo3Ti and other stainless acid-resistant steels and PH15-7Mo precipitation hardening steels.
4. Heat-resistant steel: 4Cr10Si2Mo martensitic heat-resistant steel and 4Cr14Ni14W2Mo austenitic heat-resistant steel can be used for high-temperature valves whose medium temperature does not exceed 600°C.

Section 4: Valve Stem Nut Material
The stem nut directly bears the axial force of the stem during the opening and closing of the valve, so it must have a certain strength. At the same time, it and the valve stem are threaded transmission, which requires a small coefficient of friction, no rust and avoid seizure. The main materials are as follows:
1. Copper alloy: Copper alloy has a small friction coefficient and does not rust. It is one of the commonly used materials. For low pressure valves with Pg<1.6Mpa, ZHMn58-2-2 cast brass can be used.
2. Steel: When the working conditions do not allow the use of copper alloys, high-quality carbon steels such as 35, 40, 2Cr13, 1Cr18Ni9, Cr17Ni2 and other stainless and acid-resistant steels can be selected. The working conditions do not allow the following:
For electric valves, stem nuts with gua-shaped clutches require heat treatment to obtain high hardness or surface hardness.
When the working medium or the surrounding environment is not suitable for copper alloys, such as ammonia medium that is corrosive to copper.
When selecting steel stem nuts, pay special attention to thread seizure.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

The sealing performance of the valve refers to the ability of each sealing part of the valve to prevent the leakage of the medium. It is the most important technical performance index of the valve. There are three sealing parts of the valve:

marine valve seat

the contact between the opening and closing parts and the two sealing surfaces of the valve seat; the matching place between the packing and the valve stem and the stuffing box; the connection between the valve body and the valve cover. One of the previous leakage is called internal leakage, which is commonly referred to as lax closure, which will affect the valve’s ability to cut off the medium. For shut-off valves, internal leakage is not allowed. The latter two leaks are called external leakage, that is, the medium leakage from the valve to the outside of the valve will cause material loss, pollute the environment, and cause accidents in severe cases. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.

Daily maintenance of the valve:
1. Pay attention to the storage environment of the valve. It should be stored in a dry and ventilated room, and both ends of the passage should be blocked.

2. The valve should be inspected regularly, the dirt on it should be removed, and anti-rust oil should be applied to its surface.

ductile iron, DI, butterfly valve, manufacturer, center line, TH valve

3. The valve after installation and application should be overhauled regularly to ensure its normal operation.

4. Check whether the sealing surface of the valve is worn or not, and repair or replace it according to the situation.

5. Check the wear of the trapezoidal thread of the valve stem and the valve stem nut, whether the packing is out of date and invalid, etc., and replace it if necessary.

6. The sealing performance of the valve should be tested to ensure its performance.

7. The valve in operation should be intact, the bolts on the flange and the bracket are complete, the threads are not damaged, and there is no looseness.

8. If the handwheel is lost, it should be prepared in time and cannot be replaced with an adjustable wrench.

9. The packing gland is not allowed to be skewed or without pre-tightening clearance.

10. If the valve is used in a harsh environment and is easily contaminated by rain, snow, dust, sand and other dirt, a protective cover should be installed for the valve stem. 11. The ruler on the valve should be complete, accurate and clear, and the valve should be sealed and capped.

12. The insulation jacket should be free of dents and cracks.

13. Avoid hitting the valve during operation, or supporting heavy objects.

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Valve material and valve standards-(3)-sealing material

Valves’ sealing requirements and daily maintenance

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