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Introduction of the function of check valve and the analysis of the reason why check valve doesn’t work

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Function of check valve
The fluid resistance of swing check valve is generally less than that of lift check valve, which can be divided into three types: single disc swing, double disc swing and multi disc swing. Swing check valve is suitable for large caliber occasions. For the swing check valve larger than 80mm installed at the pump outlet, the horizontal installation method shall be adopted to reduce the valve disc seating and impact. For the pipeline with the diameter of the check valve at the pump outlet greater than or equal to 150 mm, the bypass shall be set before and after the check valve to prevent the damage to the sealing surface of the check valve caused by the high pressure rise in front of the valve.
The reason why the check valve does not work

  1. The check valve is installed reversely. It shows that the pipeline medium flows, and the check valve blocks the flow.
  2. Wrong selection or installation of check valve, such as vertical installation of check valve in vertical pipeline. For example, the flange connected lift check valve itself is installed vertically with the pipeline. The medium enters from the water inlet and pushes up the disc. The medium flows through the valve seat to another outlet of the check valve. The thrust to push the disc is less than the disc gravity, and the disc will fall naturally to the valve seat. If the valve is installed vertically, the gravity of the valve disc is all borne by the flange connected lift check valve, and the medium pushes the valve disc, only pushes the valve disc horizontally, and the valve disc cannot fall back to the valve seat naturally, causing the flange connected lift check valve to lose its function.
  3. The internal parts of the check valve are rusted. It is shown as the connection parts inside the swing check valve.
  4. The valve disc is not closed tightly due to the blockage of foreign matters
  5. Valve disc is broken or has sand hole.
  6. The check valves produced by  Stv Valve Technology Group  Co.,limited include swing check valve, lift check valve, ANSI check valve, DIN check valve, cast steel check valve, forged steel check valve and other materials.

150LB Stainless Steel Double Window Sight Glass

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PartsMaterialsMax.Pressure or Temperature
Body & Covers304 Stainless Steel-112°F to 797°F
316 Stainless Steel-320.8°F to 1202°F
316L Stainless Steel-320.8°F to 1472°F
WindowsTempered Soda Lime Glass235psig@212°F
Tempered Borosilicate Glass290psig@248°F
Tempered Quartz Glass362psig@392°F
Sealing GasketsNBR-4°F to 248°F
Viton-13°F to 400°F
PTFE(Teflon)-40°F to 500°F
Flange StandardANSI 150Lb/300Lb/DIN/JIS 5K/10K/Ghost/GB

What is the difference between Hard seal and soft seal of valve？

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Soft seal valve
The sealing form is different, and the place of use is also different! In a nutshell
Soft seal is generally used for normal temperature and pressure pipelines, while hard seal is widely used for high temperature and pressure!
Hard seal valve

 

  1. In the structural mechanism, the hard seal is the seal between metal and metal, and the sealing ball and valve seat are all metal. Machining accuracy and technology are relatively difficult, generally used in high pressure. Soft seal is the seal between metal and non-metal, such as nylon tetrafluoroethylene, the manufacturing standard is the same.
  2. The soft and hard seal on the sealing material is for the sealing material of the valve seat. The hard seal is precisely processed with the valve seat material to ensure the matching accuracy with the valve core (ball), generally including stainless steel and copper. Soft seal means that the sealing material embedded in the valve seat is non-metallic material. Because the soft sealing material has certain elasticity, the requirements for machining accuracy are relatively low for hard seal.
  3. In terms of manufacturing technology, due to the complex working environment of many chemical and mechanical industries, many of them are high temperature and high pressure, with high friction resistance and strong corrosiveness of the medium. Now the technology has improved, the application of various materials is better, and the processing and other aspects can keep up with it, so that the hard sealed ball valve can be widely promoted. In fact, the principle of hard seal ball valve is the same as that of soft seal ball valve, only because of the sealing between metals, the hardness relationship between metals, working condition and medium should be considered. Generally, it is required to do hardening treatment, and the ball and valve seat should be continuously ground to achieve sealing. The production cycle of hard seal ball valve is long and the processing is complex. It is not easy to make hard seal ball valve.
  4. Generally, the soft seal can reach a high level, while the hard seal can reach a high level according to the requirements; the soft seal needs fire protection, because under high temperature, the material of the soft seal will leak, while the hard seal does not; the hard seal can generally do a high pressure, but the soft seal cannot; the soft seal cannot be used in some occasions due to the problems of the flowing medium Finally, hard sealed ball valves are generally more expensive than soft sealed ones. As for manufacturing, there is little difference between the two, mainly the difference between the valve seat. The soft seal is non-metal, and the hard seal is metal.
  5. The selection of soft and hard sealing ball valves is mainly based on the process medium, temperature and pressure. Generally, the medium containing solid particles or with wear or temperature higher than 200 degrees is the best choice for hard sealing. When the diameter is greater than 50, the valve pressure difference is large, and the valve opening torque is also considered. When the torque is large, the fixed hard sealing ball valve should be selected. The sealing grade of soft and hard sealing can reach 6 Class.

STV Delivery A lot of Carbon Steel Y Strainer

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We finished and delivered Ansi 150, Carbon Steel Y Strainer 
Purchase Order Number: STV20191005
Requested the valve inside & outside to be done painting

Product description:
Available in PN16/40 or ANSI 150lb  flanged,JIS Flange
sizes: 1/2″ to 24″
Temperature range: -29 to 560°C .
Pressure rating: DIN PN16-PN40 or ANSI 150LB-1500LB,JIS10K-30K
Body Material,WCB,CF8,CF8M,WC6 AND WC9 Etc.

Materials:
Body: ASTM A216 WCB
Trim: 304
SRCEEEN: 316L
GASKET: 304 + Graphite
Stud/Nut: A193 B7 / A194 2H
Connection: RF acc. to ASME B16.5
Size: 4 Inch
Class: 150 LB
Qty: 60 PCS

STV big size Swing check valve tested and Delivery to Customer

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We delivered a Big Size Swing Check valves to one of European customers.

ASTM A351 CF8 304 Stainless Steel Body, Cover and Disc.
304 Stainless Steel Trim.
PTFE Cover Seal. Bolted Cover Design.
Face to Face dimensions in accordance with ANSI B16.10
Class 300 pressure rated. -20 / +200 deg C Temp rated.
Flanged ANSI 300 end connections.
Size:3″Painting: Inside and outside not painted.
Bolts and nuts between the body and bonnet and also the gland nuts and gland eye bolts made of steel A193-B8/A194-8
Material:
Body/bonnet CF8
Pressure:300LB
Stem packing graphite.
Size:32 Inch

How to Selection and installation of forged steel gate valve

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Forged steel gate valve is mainly used to cut off or connect the medium in the pipeline, not for regulating or throttling. According to different methods, gate valve can be divided into parallel gate valve, wedge gate valve, lifting gate valve, rotary rod gate valve, quick opening and closing gate valve, necking gate valve, flat gate valve, etc.

  1. The installation position, height, inlet and outlet direction shall meet the design requirements, and the connection shall be firm and tight.
  2. The handle of all kinds of manual valves for installation of thermal insulation pipeline shall not be downward.
  3. Visual inspection shall be carried out before the installation of the valve. The nameplate of the valve shall comply with the provisions of the current national standard “general valve mark” GB 12220.
  4. The gate valve with transmission mechanism shall be installed according to the product instructions.
  5. The hand wheel, handle and transmission mechanism are not allowed to be used for lifting and collision is strictly prohibite
     Stv Valve Technology Group  Co.,limited is the Forged Steel Valve professional Manufacture.

How to Repair a Gate Valve

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For stainless steel gate valves, the valve is disconnected from the valve stem and the spool due to corrosion, wear or improper operation during opening and closing. After the valve is closed, it cannot be opened. It can only be replaced after it is cut out from the system. If it cannot be cut out from the system, only another process or device will be shut down.

When the stainless steel gate valve spool is detached and cannot be cut out, the valve cover, the valve stem, the bushing and the packing can be changed without changing the valve body, the valve core and the valve seat while the sealed medium is sealed. After the gland is assembled, the valve core is exposed, and the valve stem is reconnected to the valve core by a conventional method, so that the three seals of the valve can be continuously maintained and the valve can be reopened. After the valve cover of the stainless steel gate valve is disassembled, except for the special valve, the wedge angle of the valve spool is in the friction angle range. No matter how the pressure on both ends of the valve core changes, the valve core will not be squeezed out from the valve seat under the self-locking condition. For flat valve spools, there is no more extrusion.

what is the causes of ball valve leakage

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There are many kinds of stainless steel ball valves, each of which has different uses. When choosing ball valves, we should know what kind of Ball Valves we need. Ball valve is essential, and there will be some leakage problems such as failure. Today I will tell you the reasons for the leakage of ball valve.

Causes of internal leakage
1. The casting quality of iron castings is not high, and there are sand holes, loose structures, slag inclusions and other defects on the valve body and bonnet body.
2. The bolt is loose due to thermal shock, and the pre tightening force of the bolt is not good. Or the nonuniformity of bolt is higher than that of flange.
3. The contact between gasket and flange becomes weak due to aging failure or mechanical vibration. Touch surface with low precision (with grooves, ridges, etc.) and medium
4. Poor welding, slag inclusion, no welding, stress crack and other defects
5. The cast iron valve is damaged after being hit by heavy objects.

External leakage cause
1. The packing is not selected correctly, is not resistant to medium corrosion, and is not resistant to the use of high pressure or vacuum, high temperature or low temperature of the valve.
2. The filler has aged and lost elasticity after the service life.
3. The number of packing rings is insufficient, and the gland is not pressed tightly.
4. The gland is skewed, and the gap between the gland and the valve rod is too small or too large, which causes the valve rod to wear.
5. Improper operation and excessive force