DMS SEALS TECHNOLOGY CO.,LIMITED
DMS Seals-Mechanical Seals and Oil Ring Seals Manufacturer
The Professional Sealing Solution Supplier(O Ring Suppliers & Oil Seal Manufacturers).
It is suitable for valves suitable for medium temperature -40℃～-196℃. It is called low temperature valve. Low temperature valve includes low temperature ball valve, low temperature gate valve, low temperature globe valve, low temperature safety valve, low temperature check valve, low temperature butterfly valve, low temperature needle valve, low temperature valve Throttle valve, low temperature pressure reducing valve, etc., mainly used in ethylene, liquefied natural gas plant, natural gas LPG LNG storage tank, receiving base and satellite station, air separation equipment, petrochemical tail gas separation equipment, liquid oxygen, liquid nitrogen, liquid argon, Carbon dioxide low-temperature storage tanks and tankers, pressure swing adsorption oxygen production and other devices. The output liquid low-temperature medium, such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, etc., is not only flammable and explosive, but also needs to be gasified when heated up, and its volume expands hundreds of times when gasified.
The material of liquefied natural gas valve is very important. If the material is not qualified, it will cause external leakage or internal leakage of the casing and sealing surface; the comprehensive mechanical properties, strength and rigidity of the parts cannot meet the requirements of use or even break. Leakage of liquefied natural gas medium causes explosion. Therefore, in the process of developing, designing and developing LNG valves, the material is the primary and key issue. After many years of manufacturing, it has accumulated rich experience, and has become more and more mature from design, technology to manufacturing, and has developed a series of low-temperature valve products.
1. Product specifications and design parameters of cryogenic valves:
1. Pressure rating: 150, 300, 600Lb, 900LB, 1500LB (45MPa)
2. Valve diameter: 15～1200 mm (1/2～48").
3. Connection form: flange type, welding type, thread.
4. Valve material: LCB, LC3, CF8.
5. Working temperature: -46°C, -101°C, -196°C, -253°C
6. Applicable medium: LNG, ethylene, propylene, etc.
7. Drive mode: manual, bevel gear drive, electric.
2. Low temperature valve standard and product structure:
1. Design: API6D, JB/T7749
2. Valve routine inspection and test: according to API598 standard.
3. Valve low temperature inspection and test: according to JB/T7749.
4. Drive mode: manual, bevel gear drive and electric drive.
5. Valve seat form: The valve seat adopts a welded structure, and the sealing surface is surfacing with cobalt-based hard alloy to ensure the sealing performance of the valve.
6. The gate adopts an elastic structure, and a pressure relief hole is designed at the pressure inlet end.
7. The valve body with one-way seal is marked with the flow direction mark.
8. Low temperature ball valve, gate valve, globe valve, butterfly valve adopt long neck structure to protect packing.
9. Ultra-low temperature ball valve standard: JB/T8861-2004
3.low temperature valve material selection:
1. Valve body and bonnet adopt: LCB(-46℃), LC3(-101℃), CF8(304)(-196℃)
2. Gate: stainless steel surfacing cobalt-based cemented carbide
3. Seat: stainless steel surfacing cobalt-based carbide
4. Stem: 0Cr18Ni9
4. Manufacturing and testing of cryogenic valves:
Maezawa has formulated strict manufacturing processes and special equipment for the cryogenic valves produced, and carries out strict quality control on the processing of parts. After special low temperature treatment, the rough machined parts are placed in the cooling medium for several hours (2-6 hours) to release the stress, ensure the low temperature performance of the material, and ensure the finishing size to prevent the valve from being damaged due to low temperature conditions. Leaks caused by deformation due to temperature changes. The assembly of the valve is also different from that of ordinary valves, and the parts need to be strictly cleaned to remove any oil stains to ensure the performance.
5. Low temperature valve test equipment:
1. Low temperature valve test device
2. Liquid nitrogen storage device
3. Low temperature treatment tank
4. Low temperature test bench to ensure the performance of the valve under low temperature conditions 5. Others
6. Low temperature valve test and inspection: The main parts of the low temperature valve are treated at low temperature and each batch is sampled for low temperature impact test to ensure that the valve is not brittle under low temperature conditions and can withstand the impact of low temperature media.
The following tests are performed on each valve:
1. Normal temperature shell strength test;
2. Normal temperature and low pressure upper sealing test;
3. Normal temperature and low pressure sealing test;
4. Low temperature upper sealing air tightness test (when there is upper sealing);
5. Low-temperature gas sealing test, etc., to ensure that the entire low-temperature valve meets the requirements of the standard;
6. The main parts of the low-temperature valve are treated at low temperature and each batch is sampled for low-temperature impact test to ensure that the valve is not brittle under low temperature conditions and can withstand the impact of low-temperature media;
Other parameters of cryogenic valve:
The valve body is light and small in size. In order to reduce the heat loss of the valve body, especially to ensure the use of the valve under ultra-low temperature, the valve body is specially designed to be light in weight and small in size.
The long-shaft valve has a valve through which low-temperature fluid flows, and adopts the form of a long valve stem, which can avoid the effect of external heat and keep the gland at normal temperature to prevent the performance of the cover seal from being degraded. This length is obtained by calculation and experimentation.
Ideal valve seat soft sealing structure: In SW and BW forms, the valve body cannot be removed from the piping, in order not to replace the valve body valve seat, a soft contact valve seat is used. The valve core seal is made of Teflon or Teflon containing 15% glass fiber with good low-temperature characteristics and stability, and can also be replaced according to needs. Hard metal seal structure: metal seals are used on gate valves and valves with fire protection requirements. It is to add a stellite metal bushing to the contact surface of the valve seat to improve the surface hardness and improve the anti-burn and wear resistance.
The gasification and boosting structure gate valve adopts a flexible structure and is completely sealed. Therefore, at this time, the liquefied gas inside the valve body is sealed, and when the temperature rises after absorbing external heat, the phenomenon of regasification will occur, causing the internal pressure of the valve to rise. In order to prevent this phenomenon, a structure in which a decompression hole is opened in the valve body is adopted. The gland packing with excellent durability adopts Nanchang Teflon ring packing with good durability in the gland part. This packing has self-pressure sealing properties depending on the internal pressure, so it can be easily controlled with a small tightening torque. And the friction is small, so the operation is easy.
Gasket Gasket is made of Teflon material containing ceramic filler material with stable sealing performance. In addition, a gasket with a scroll-shaped metal surface is also used, which has frequent switching at normal temperature and low temperature and sealing stability against temperature changes.
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