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Valves’ sealing requirements and daily maintenance

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

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

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 Check the wear of the trapezoidal thread of the valve stem and the valve stem nut, whether the packing is out of date and invalid, etc., and replace it if necessary.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

TH Valve is a professional manufacturer of butterfly valvegate valvecheck valveglobe valveknife 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

Related news/knowledge:
Reasons and solutions for leakage of valve sealing surface;
Application of low temperature butterfly valve;
Ball valve installation and maintenance methods;

What is the material of the main parts of the butterfly valve?-(2)

Selection of valve sealing material:

Sealing surface material: The sealing surface is the most critical working surface of the valve. The quality of the

marine valve seat

marine valve seat

sealing surface is related to the service life of the valve. Generally, the sealing surface material should consider factors such as corrosion resistance, scratch resistance, erosion resistance, and oxidation resistance. Usually divided into two categories:

(1) Soft materials of butterfly valve:

  • Rubber (including nitrile rubber, fluorine rubber, etc.)
  • Plastics (polytetrafluoroethylene, nylon, etc.)

(2) Hard sealing material of butterfly valve:

  • Copper alloy (used for low pressure valves)
  • Chrome stainless steel (used for ordinary high and medium pressure valves)
  • Stellite alloy (used for high temperature and high pressure valves and strong corrosion valves)
  • Nickel-based alloy (used for corrosive media)

Tianjin Tanghai Valve Manufacturing Co., Ltd. is one of the largest butterfly valve manufacturers in China, main products are butterfly valves, check valves, gate valve and globe valves. Key words:  butterfly valve, lug type butterfly valve, wafer type butterfly valve, U-type butterfly valve, double flange butterfly valve, gate valves, check valves, globe valves, valve parts (Valve body, Valve disc, Valve shaft, Valve seat…)

What is the material of the main parts of the butterfly valve?-(1)

Selection of butterfly valve parts materials:
There are many materials for manufacturing butterfly valves, including ferrous and non-ferrous metals and their

16 U-type-flange-butterfly-vlave-body

16 U-type-flange-butterfly-vlave-body

alloys of different brands, and various non-metallic materials. The materials for manufacturing valve parts should be selected based on the following factors:

1. Pressure, temperature and characteristics of working medium.

2. The force of the part and its function in the valve structure.

3. It has better manufacturability.

4. If the above conditions are met, there must be a lower cost.

The material of the valve body, bonnet and disc (disc) The body, bonnet and gate (disc) are one of the main parts of the valve, which directly bear the pressure of the medium, and the material used must meet the “pressure and temperature rating of the valve” Provisions.

Commonly used material types for butterfly valves:

1. Gray cast iron: Gray cast iron is suitable for water, steam, air, gas, oil and other media with a nominal pressure of PN≤1.0MPa and a temperature of -10℃~200℃. The commonly used grades of gray cast iron are: HT200, HT250, HT300, HT350.

2. Malleable cast iron: Suitable for water, steam, air and oil media with a nominal pressure

17 center-line-butterfly-valve-plate-disc-parts-4

17 center-line-butterfly-valve-plate-disc-parts-4

of PN≤2.5MPa and a temperature of -30~300℃. Commonly used grades are: KTH300-06, KTH330-08, KTH350-10.

3. Ductile iron: suitable for water, steam, air and oil with PN≤4.0MPa and temperature of -30~350℃. Commonly used grades are: QT400-15, QT450-10, QT500-7. In view of the current level of domestic technology, the plants are uneven, and users are often not easy to inspect. According to experience, it is recommended that PN≤2.5MPa, and the valve should be made of steel for safety.

4. Acid-resistant high-silicon ductile iron: suitable for corrosive media with nominal pressure PN≤0.25MPa and temperature below 120℃.

5. Carbon steel: suitable for water, steam, air, hydrogen, ammonia, nitrogen and petroleum products with a nominal pressure of PN≤32.0MPa and a temperature of -30~425℃. Commonly used grades are WC1, WCB, ZG25 and high-quality steel 20, 25, 30 and low-alloy structural steel 16Mn. Six, copper alloy: suitable for water, sea water, oxygen, air, oil and other media with PN ≤ 2.5MPa, and steam media with a temperature of -40 to 250 ℃, commonly used brands are ZGnSn10Zn2 (tin bronze), H62, Hpb59-1 (Brass), QAZ19-2, QA19-4 (aluminum bronze).

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

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

7. High temperature steel: suitable for steam and petroleum products with nominal pressure PN≤17.0MPA and temperature≤570℃. Commonly used grades are ZGCr5Mo, 1Cr5M0. ZG20CrMoV, ZG15Gr1Mo1V, 12CrMoV, WC6, WC9, etc. The specific selection must be in accordance with the valve pressure and temperature specifications. 8. Low temperature steel, suitable for nominal pressure PN≤6.4Mpa, temperature≥—196℃ ethylene, propylene, liquid natural gas, liquid nitrogen and other media, commonly used grades) ZG1Cr18Ni9, 0Cr18Ni9, 1Cr18Ni9Ti, ZG0Cr18Ni9.

9. Stainless acid-resistant steel, suitable for nitric acid, acetic acid and other media with nominal pressure PN≤6.4Mpa and temperature≤200℃. Commonly used grades are ZG0Cr18Ni9Ti, ZG0Cr18Ni10<nitric acid>, ZG0Cr18Ni12Mo2Ti, ZG1Cr18Ni12Mo2Ti<acid and urea>.

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