What’s dome valve?

In the field of power, metallurgy, chemical, food, pharmaceutical and other industries, there are often need to transfer high-temperature particles or powder raw materials to the specified container, where a quick cut-off valve, dome valve is needed can be used here to cut off the medium and obtained sealing.

It can cut off the flowing material into the pressure tank or close to achieve sealing so as to ensure the filling rate of the pressure tank is 100% without a material level gauge, safe and reliable. The inflatable pressure sealing ring embedded in the dome seat ensures the working pressure difference between upstream and downstream of the valve and avoids the abrasion of the sealing ring. The dome valve is mainly operated by pneumatic actuators, the linear cylinder or sector cylinder is fully closed driven, which offers a large output torque. When the valve is opened and closed, there is no contact between the valve core and the inflatable rubber sealing ring, reliable sealing performance and can work under severe working conditions.

Working principle:

The ball valve is opened/closed with a gap of about 2mm between the spool and the rubber seal ring, allowing them to move in a contactless manner without causing or reducing wear. Fully sealed straight or sector cylinder drives the dome valve to rotate, effectively preventing dust caused by wear, leakage, etc. When the dome valve is closed, the rubber seal ring inflates, expands, and presses tightly against the spherical dome spool, forming a reliable seal ring band that prevents material flow.

Features of the dome valve:

1. Lightweight, fast action, switch only 5~8 seconds, valve drive pneumatic, is the ideal part in the pipeline automation system;

2. The ball has no friction with the sealing ring in the whole process of opening and closing, which improves the service life of the valve to a limited extent;

3. Upper and lower stem bushings are self-lubricating, with small friction coefficient, flexible opening and closing, and reliable sealing performance;

4. The valve switch signal device can realize remote automatic control. Integrated and quick connector for easy operation.

 

Specifications:

DN, mm 50 80 100 150 200 250 300
Working pressure, MPa ≤1.0
Working temperature ℃ ≤200
Air source Pressure, MPa 0.4~0.6
Gas consumption, L/time 1~3
Medium Granule, dry ash, dry powder materials, etc
Material Valve body: WCB;

Doom: WCB+Chromeplate/Ni60

Seat: Butyl rubber/Viton

Stem/bonnet/York: A105

Cylinder: Aluminum alloy

Notes: The filling pressure of the rubber sealing ring should be 0.30 ~ 0.60MPa and higher than the conveying pressure 0.15MPa, the working pressure of the cylinder should be 0.45 ~ 0.65MPa, and the compressed air should be clean, dry and oil-free.

 

What’s pinch valve?

Pinch valve, also known as hose valve, is a unique structure of the valve that consists of aluminum alloy/cast steel body, rubber sleeve, valve stem gate, guide pillar and other parts. With the features of convenient opening, good sealing performance and cost-saving, the pinch valve is an economical alternative to a gate valve, globe valve and regulating valve, which can extend the5-10 times of service life than that of conventional valves, suitable for conveying system of granular slurry or chemical medium in low-pressure pipeline.

The rubber sleeve is the core part of the pinch valve, which can be replaced regularly, saving cost, with excellent corrosion resistance, wear resistance and good bearing pressure. There are several sleeve materials can be selected according to the corrosiveness and abrasiveness of the flow media, and the operating temperature. The EPDM rubber pinch valve is designed for the higher temperature environment, which needs to be within the limit of the polymer. In addition, electric, pneumatic, manual or hydraulic actuator drives the sleeve to achieve opening, close and adjusting action.

 

 

The principle of pinch valve

For a manual pinch valve, when the handwheel turns, the stem forces the internals to force the rubber sleeve and the gate to reciprocate between the guide pillars to close the valve. Similar principle for the pinch valve with actuator, the force pushing down onto the rubber sleeve which fully collapses and closes tightly.

 

The features of pinch valve

  • Full port or bore, no obstruction
  • Low flow resistance, sleeve self-cleaning
  • Zero leakage can be closed when there are residual particles;
  • No clogging or dead spots to prevent valve operation
  • Simple design, not affected by the external environment.
  • Replaceable elastomer sleeve, low and easy maintenance cost.

 

The applications of pinch valve

Pinch valves are commonly used in the pipeline transportation of some corrosive chemical media, or abrasive solid or liquid products such as particles, fibers, powders and mortar. It can also be used in sewage processing such as sludge treatment, gravel cleaning, raw sewage, lime, charcoal. The typical application including:

Power plant: FDG system, ash removal system, coal transport;

Mining: Tailings filling, flotation control, mud line, or other slurries;

In addition, it is also widely used in cement, glass, paper manufacturing, electronics industry, food industry, and industrial sewage and other fields.

 

The extraction check valve for high pressure turbine

In the last article, we introduced the ventilator valve, blowdown valve and reverse flow valve for turbine system, here today we will continue talking about the extraction check valve for high-pressure turbine When the valve opens, the cylinder takes steam, the flowing medium pushes the valve plate to open the valve, the greater the medium flow, the greater the spool opening; When the valve is closed, the solenoid valve quickly loses power and expunges the air in the cylinder. In addition to the dead weight of the valve plate and the auxiliary closing force of the cylinder, the valve is quickly closed.

The high-pressure turbine steam-exhaust check valve is installed in the horizontal pipeline of the steam turbine reheating and cooling section to prevent water and steam from pouring back into the high-pressure cylinder and affecting the safety of the steam turbine. Specially designed for steam turbine exhaust protection, their fast and tight closure ensures that water or steam can be quickly isolated from the steam turbine while the generator is tripped or the main steam valve is closed. The valve will close automatically when the high water level of heating equipment in the turbine tripping or all levels of extraction steam pipelines. As a protective device, the extraction check valve must be reliable.

 

High-pressure cylinder exhaust steam pressure: Reheater inlet pressure

High-pressure cylinder exhaust temperature: ≤420℃

Extraction pressure of each section: vacuum ~10MPa

Extraction temperature of each section: 200~510 ℃

Valve pressure range:

ASME B16.34 1996 –150 Class

ASME B16.34 1996 – 300 Class

ASME B16.34 1996 –400 Class

ASME B16.34 1996 –600 Class

Valve body: Cast steel

ASTM A216-WCB

ASTM A217-WC6/WC9(1# /3#extraction)

Actuator:

For large units, the steam extraction reverse check valve is mainly driven by pneumatic, while it is hydraulic for small and medium-sized units.

 

 

The type of extraction check valve 

According to the opening /closure parts:

  1. Self-weight closing. Self-weight close (close): Check valve closed by the self-weight or counterweight of the trim or depending pressure of medium and counterweight of trim to keep it in the open position of the valve.
  2. Power-assisted closing. The actuator provides a pulse point action to make the spool overcome the initial inertia caused by being in the closed position for a long time or external causes and complete the rest travel by itself to close the valve.
  3. Power closing. During the closing process, the actuator always provides power to complete all the travel of the spool and close the valve.

According to its structure:

  • Steam extraction reverse check valve without a hammer

IBS internal balancing shaft steam extraction reverse check valve without a hammer. Internal balance refers to the internal balance of the dead weight of the spool. The spool is supported by the shaft and rotates freely around the shaft. They are not connected directly but are connected with the piston of the side working cylinder. The actual opening inside the valve cannot be confirmed.

  • Steam extraction check valve with a heavy hammer

A large diameter valve offers heavy trim, then a heavy hammer can be used in the extraction steam check valve, hammer can offset part of the trim weight (about half of the spool). The valve trim is directly connected to the shaft, and the actual opening inside can be seen from the angle changes of the exterior tumbler. If the inside is not fully open, it can be observed from the outside. The valve is a free swing, gravity closed check valve, when the inlet pressure is higher than the outlet valve trim open, while the valve closed on the contrary.

The pressure reducing valve VS overflow valve

Both the pressure reducing valve and overflow valve can be used to regulate the pressure and maintain the safety of the pipeline. The pressure reducing valve is a pressure regulating valve that makes the valve outlet pressure lower than the inlet pressure, mainly used to reduce the pressure of a branch oil line in the hydraulic system to make the branch pressure is lower than the main pressure and stable. The disc of pressure reducing valve in the valve body reduce the medium pressure and adjust the opening degree under the downstream pressure, so that the downstream pressure remains in a certain range, to keep the outlet pressure in the set range in the case of constant changes in the inlet pressure.

The overflow valve, also known as the relief valve, an automatic pressure relief device driven by the static pressure in front of the valve. It opens proportionally as the pressure exceeds the opening force, mainly used for fluid applications. It is mainly used for constant pressure,overflow and safety protection in the hydraulic system.

Quantitative pumps provide constant flow in the throttling control system. When the system pressure increases, the flow decreases. At this point, the overflow valve is opened to make the excess flow overflow back to the tank, ensuring that the inlet pressure of the overflow valve constant, that is, the pump outlet pressure. When it is used to limit the pressure, it can be used as a safety valve. When the system is working normally, the overflow valve is in the state of closure and started when the system pressure is greater than its set pressure, which offers overload protection for the system. The differences are:

  1. Different working purposes. The overflow valve is usually connected in parallel with the branch of the system to prevent system overload and ensure safety. Pressure-reducing valves are generally connected in series on a certain road to reduce pressure under the premise that the system cannot be loaded. It can be said that the former is passive work, and the latter is active work.
  1. The pressure reducing valve maintains the pressure at the outlet unchanged, while the overflow valve maintains the pressure at the inlet unchanged;
  2. The pressure reducing valve is normally operated, reducing pressure through the narrow channel. The overflow valve is normally closed and only acts when the system is overpressurized.

 

Titanium and titanium alloy valve

Titanium alloy valve is a broad concept, refers to the valve that the body and internal parts are made of titanium alloy or valves that the body material is carbon steel or stainless steel, and internal parts are made of titanium alloy valve. As well as we knew, Titanium is a reactive structural metal that reacts easily with oxygen to form a dense, stable oxide film on the surface, which can react with oxygen to regenerate the oxide film even if it is damaged. It can resist the erosion of a variety of corrosive mediums and provides a better corrosion and strength solution than that made of stainless steel, copper or aluminum valves.

The features of titanium alloy valve

  • Good corrosion resistance, lightweight and high mechanical strength.
  • It is almost noncorrosive in the atmosphere, freshwater, seawater, and high-temperature water vapor.
  • It has good corrosion resistance in royal water, chlorine water, hypochlorous acid, wet chlorine gas and other media.
  • It is also very resistant to corrosion in alkaline media.
  • It is highly resistant to chlorine ions (CI) and has excellent corrosion resistance to chloride ions.
  • Corrosion resistance in organic acids depends on the degree of reduction or oxidation of the acid.
  • Corrosion resistance in reducing acids depends on the presence of a corrosion inhibitor in the medium.

 

The applications of titanium valve

  • Aerospace

Titanium and titanium alloy valves can be widely used in the aerospace field because of high strength ratio, corrosion resistance. The pure titanium and titanium alloy Ti-6Al-4V control valve, stop valve, check valve, needle valve, plug valve, ball valve, butterfly valve, etc. are widely used in aircraft pipelines.

  • Chemical industry

Sometimes in Chlor-alkali, salt, synthetic ammonia, ethylene, nitric acid, acetic acid and another strong corrosion environment, titanium alloy valve that has better corrosion resistance can replace common metals such as stainless steel, copper, aluminum, especially in the control and regulation of the pipeline.

  • Warships

Russia is one of the first countries in the world using titanium alloy for warships. From the 1960s to the 1980s, Russia produced a series of attack submarines of which used a large number of titanium alloy pipes and valves in its seawater system.

  • Power plant

Most nuclear power plants are built on the coast and titanium valves are used in nuclear power projects due to their excellent corrosion resistance to seawater. The types include a safety valve, pressure reducing valve, globe valve, diaphragm valve, ball valve, etc.

In addition, as a special medium and environment fluid control equipment, titanium valves are also used in the paper industry, food and pharmaceutical manufacturing and other fields.

 

 

 

The globe valve in ammonia application

Ammonia is an important raw material for the manufacture of nitric acid, ammonium salt and amine. Ammonia is a gas at room temperature and can be liquefied under pressure. Most metals such as Stainless steel, Aluminum, Lead, Magnesium, Titanium, etc. have excellent corrosion resistance to ammonia gas, liquid ammonia and ammonia water. Cast iron and carbon steel also have good corrosion resistance to ammonia gas or liquid ammonia, the corrosion rate is generally less than 0.1mm/year, so ammonia production and storage equipment is generally made of steel from the perspective of cost.

The check valve, globe valve, ball valve, and other valves can be used in ammonia and liquid ammonia piping system. These valves bring the gas pressure down to a safe level and pass it through other valves to the service system. Among them, the most commonly used is the globe valve. Ammonia globe valve is a kind of force-sealing valve, that is, when the valve is closed, the pressure must be applied to the disc so that the sealing surface are leak-free.

When the medium enters the valve from below the disc, it is necessary to overcome the friction of the stem and packing and the pressure from the medium. The force of valve closure is greater than that of valve opening, so the diameter of the stem should be large or the stem bending. The flow of self-sealing ammonia gas globe valve is generally from top to bottom, that’s the medium into the valve cavity from the top of the disc, then under the pressure of the medium, the force of valve closing is small and the valve opening is big, the diameter of the stem can be correspondingly reduced. When the globe valve is open, when the opening height of the disc is 25% ~ 30% of the nominal diameter, the flow has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the fully open position of the globe valve shall be determined by the travel of the disc. So what are the characteristics of globe valves for ammonia application?

  • Copper reacts with ammonia gas and ammonia water to form soluble complexes and produce dangerous stress corrosion cracking. In the ammonia-environment, even trace amounts of ammonia can cause stress corrosion in the atmosphere. Valves made of copper and copper alloy are generally not suitable for ammonia applications.
  • Ammonia globe valve is ono-rising-stem cone design compared with the common globe valve. Its sealing surface is mostly Babbitt alloy and the valve body is made of stainless steel CF8 or high-quality carbon steel WCB to be used to the maximum requirements, can be resistant to ammonia corrosion, low-temperature resistance to -40℃.
  • The tongue and groove face design of flange connection ensures reliable sealing performance even when pipeline pressure fluctuates.
  • Multi-layer PTFE (PTFE) or Babbitt alloy sealing material and a composite soft packing made of PTFE+ butanol + spring) ensure that the valve packing box is free of leakage during the service life.
  • PTFE plain gaskets, stainless steel + graphite wound gaskets, stainless steel + PTFE wound gaskets are also recommended for ammonia valves.

 

The handwheel of the ammonia globe valve is generally painted yellow to distinguish it from valves for other applications. In addition, vertical check valves and lift check valves are also available for ammonia applications. Their discs rise and fall depending on the differential pressure of the fluid and their own weight, automatically stopping the medium against the current and protecting the upstream equipment, suitable for most ammonia tank on the horizontal pipeline.