Hard sealing butterfly valve



The hard-sealed butterfly valve is also called the flap valve.

The hard sealing butterfly valve mainly plays the role of cutting off and throttling on the pipeline. The butterfly valve opening and closing part is a disc-shaped butterfly plate, which rotates around its own axis in the valve body to achieve the purpose of opening and closing or adjustment.

The hard-sealed butterfly valve is suitable for pipelines conveying various corrosive and non-corrosive fluid media in producer, coal gas, steam, natural gas, city gas, hot and cold air, chemical smelting engineering and power generation environmental protection system, for regulating and cutting off media flow.

Hard sealing butterfly valve can be divided into manual hard sealing butterfly valve, pneumatic hard sealing butterfly valve, electric hard sealing butterfly valve.

Also known as flap valve

On-off control of low-pressure pipeline medium

Cut-off and throttling on pipelines

Classification by structure

Classification by sealing surface material

Classification by sealing form

Classification by work pressure

Classified by operating temperature

Sort by connection

Elastic Structure Analysis and Problems

Overview

The hard sealing butterfly valve is an eccentric metal sealing structure, and the sealing form is metal-to-metal sealing.

Hard sealing butterfly valve(13 photos)

The plywood sealing ring is sealed to the metal. In addition to the electric drive, the hard seal butterfly valve also has: manual, worm gear drive, pneumatic, etc. This type of valve should generally be installed horizontally in the pipeline.

The disc of the hard-sealed butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation angle is between 0° and 90°. When it rotates to 90°, the valve is fully open.

working principle

The hard-sealed butterfly valve is a valve that realizes the opening or closing of the pipeline by the rotation of the circular butterfly plate (sealing piece) with the valve shaft.

At present, the use of hard-sealed butterfly valves in low-pressure large and medium-diameter pipelines is increasing.

The hard sealing butterfly valve is simple in structure, small in size and light in weight, and only consists of a few parts. And it only needs to rotate 90° to open and close quickly, the operation is simple, and the electric valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body, so the pressure drop generated by the valve is very small, so it has better flow control characteristics. Butterfly valves have two types of seals: elastic seal and metal seal. Elastic sealing valve, the sealing ring can be inlaid on the valve body or attached to the periphery of the disc.

If the butterfly valve is required to be used as flow control, the main thing is to correctly select the size and type of the valve. The structural principle of the hard-sealed butterfly valve is especially suitable for making large-diameter valves.

Hard-sealed butterfly valves are not only widely used in general industries such as petroleum, gas, chemical, and water treatment, but also in the cooling water system of thermal power plants.

Maintenance

1. The hard-sealed butterfly valve should always be kept clean during use, and the transmission thread must be lubricated regularly.

2. The bolts of the packing gland should be tightened evenly, and should not be pressed into a crooked state, so as to avoid bumping and hindering the movement of the valve stem or causing leakage.

3. During installation, the valve can be directly installed on the pipeline according to the connection method. Under normal circumstances, it can be installed at any position of the pipeline, but it needs to be easy to operate and repair. Note that the medium flow direction of the stop valve should be upward from the bottom of the vertical valve disc, and the lift check valve can only be installed horizontally.

4. When the hard-sealed butterfly valve is used, it is only fully open or fully closed, and it is not allowed to adjust the flow, so as to avoid erosion of the sealing surface and accelerated wear. There are inverted sealing devices in the gate valve and the upper threaded globe valve. The handwheel is turned to the upper position and tightened to prevent the medium from leaking from the packing.

5. The handwheel should be used when the hard-sealed butterfly valve is opened or closed. Do not use levers or other tools to avoid damage to the valve parts. Turn the handwheel clockwise to close, and vice versa to open.

6. Before installation, it is necessary to carefully check the pressure of the valve logo and whether the diameter meets the requirements for use, eliminate defects caused by the transportation process, and eliminate the dirt on the valve parts.

7. Valves that have been stored for a long time should be inspected regularly. The exposed processing surface should be kept clean and the dirt should be removed. During storage, both ends of the ball valve should be blocked and open, and both ends of the passage should be blocked and closed for pneumatic butterfly valves. Store neatly in a ventilated and dry place indoors, and it is strictly forbidden to stack or store in the open air.

Features

Features of the new high-life stainless steel butterfly valve

At present, as a component used to realize the on-off and flow control of the pipeline system, the hard-sealed butterfly valve has been widely used in many fields such as petroleum, chemical industry, metallurgy, hydropower and so on. In the known butterfly valve technology, the sealing form mostly adopts the sealing structure, and the sealing material is rubber, polytetrafluoroethylene, etc. Due to the limitation of structural characteristics, it is not suitable for industries such as high temperature resistance, high pressure, corrosion resistance and wear resistance.

A relatively advanced butterfly valve is a triple eccentric metal hard-sealed butterfly valve. The valve body and the valve seat are connected components, and the sealing surface layer of the valve seat is surfacing with temperature-resistant and corrosion-resistant alloy materials. The multi-layer soft stacked sealing ring is fixed on the valve plate. Compared with the traditional butterfly valve, this butterfly valve has high temperature resistance, easy operation, and no friction when opening and closing. When closing, the torque of the transmission mechanism increases to compensate the sealing, which improves the butterfly valve. The advantages of excellent sealing performance and extended service life.

Classification

Classification by structure

(1) Centerline type sealing butterfly valve

(2) Single eccentric sealing butterfly valve

(3) Double eccentric sealing butterfly valve

(4) Triple eccentric sealing butterfly valve

(1) Soft sealing butterfly valve.

a. The sealing pair is composed of non-metallic soft material to non-metallic soft material.

(2) Metal hard sealing butterfly valve. The sealing pair is composed of metal hard material to metal hard material.

(1) Forced sealing butterfly valve

a. Elastic sealing butterfly valve.The sealing specific pressure is generated by the elasticity of the valve seat or valve plate when the valve plate squeezes the valve seat when the valve is closed.

b. Additional torque seal butterfly valve.The seal specific pressure is generated by the torque applied to the valve shaft

(2) Pressurized sealing butterfly valve.The sealing specific pressure is generated by the charging of the elastic sealing element on the valve seat or valve plate

(3) Automatic sealing butterfly valve. The sealing specific pressure is automatically generated by the medium pressure.

Butterfly valve whose working pressure is lower than standard reactor atmospheric calendar.

Nominal pressure pn

Butterfly valve whose nominal pressure pn is 2.5–6.4mpa.

Butterfly valve with nominal pressure pn of 10.0–80.0mpa.

(1) High temperature butterfly valve: butterfly valve with t>450°c

(3) Normal temperature butterfly valve: -40°C

(4) Low temperature butterfly valve: -100°C

(5) Ultra-low temperature butterfly valve: t

There is a problem

1. Since the multi-layer soft and hard laminated sealing ring is fixed on the valve plate, when the valve plate is normally open, the medium forms a positive scouring on its sealing surface, and the soft sealing belt in the metal sheet interlayer is scoured, which directly affects the sealing performance.

2. Restricted by structural conditions, the structure is not suitable for valves with a diameter below dn200, because the overall structure of the valve plate is too thick and the flow resistance is large.

3. Due to the principle of the triple eccentric structure, the sealing between the sealing surface of the valve plate and the valve seat relies on the torque of the transmission device to press the valve plate to the valve seat. In the positive flow state, the higher the medium pressure, the tighter the seal squeezes.

When the medium in the flow channel flows back, the unit positive pressure between the valve plate and the valve seat is less than the medium pressure as the medium pressure increases, and the seal begins to leak.

High performance triple eccentric hard sealing butterfly valve,

It is characterized in that: the valve seat sealing ring is composed of multi-layer stainless steel sheets on both sides of the soft T-shaped sealing ring.

The sealing surface of the valve plate and the valve seat is an inclined conical structure, and the temperature and corrosion resistant alloy material is surfacing on the inclined conical surface of the valve plate; the spring fixed between the adjusting ring pressure plates and the adjusting bolts on the pressure plate are assembled together. This structure effectively compensates the tolerance zone between the shaft sleeve and the valve body and the elastic deformation of the valve stem under medium pressure, and solves the sealing problem of the valve during the two-way exchange of medium conveying.

The sealing ring is composed of multi-layer stainless steel sheets on both sides of the soft T-shaped, which has the dual advantages of metal hard sealing and soft sealing, and has zero leakage sealing performance under low temperature and high temperature conditions. The test proves that when the pool is in a positive flow state (the direction of medium flow is the same as the direction of rotation of the butterfly plate), the pressure on the sealing surface is generated by the torque of the transmission device and the action of the medium pressure on the valve plate. When the positive medium pressure increases, the tighter the oblique conical surface of the valve plate and the sealing surface of the valve seat are, the better the sealing effect will be.

When the flow is reversed, the sealing between the valve plate and the valve seat depends on the torque of the driving device, so that the valve plate is pressed against the valve seat. With the increase of the reverse medium pressure, when the unit positive pressure between the valve plate and the valve seat is less than the medium pressure, the deformation stored by the spring of the adjusting ring after being loaded can compensate the tight pressure between the valve plate and the valve seat sealing surface play an automatic compensation role.

Therefore, the utility model does not install the soft and hard multi-layer sealing ring on the valve plate as in the prior art, but is directly installed on the valve body, and adding an adjusting ring between the pressure plate and the valve seat is an ideal two-way hard sealing method . It will replace gate valves and ball valves.

Structural features

The unique design of the three-way eccentricity enables frictionless transmission between the sealing surfaces and prolongs the service life of the valve.

An elastic seal is produced by torque.

The clever wedge-shaped design enables the valve to have the automatic sealing function of closing and tightening, with compensation and zero leakage between the sealing surfaces.

Small size, light weight, light operation and easy installation.

Pneumatic and electric devices can be configured according to user requirements to meet the needs of remote control and program control.

The material of the replacement parts can be applied to various media, and the lining can be anti-corrosion.

Diversified continuous structures: wafer, flange, butt welding.

the difference

The difference between hard sealing butterfly valve and soft sealing butterfly valve

Hard-sealed butterfly valve: Both sides of the sealing pair are made of metal materials or other hard materials, which are called “hard seals”. This kind of seal has poor sealing performance, but has high temperature resistance, wear resistance and good mechanical properties. For example: Steel + steel; steel + copper; steel + graphite; steel + alloy steel; (the steel here may also be cast iron, cast steel, alloy steel may also be surfacing, sprayed alloy).

Soft sealing butterfly valve: one side of the sealing pair is made of metal material, and the other side is made of elastic non-metallic material, which is called “soft seal”. This kind of seal has better sealing performance, but it is not resistant to high temperature and easy to wear. , poor mechanical properties. Such as: steel + rubber; steel + tetrafluoroethylene[wiki]polyethylene[/wiki]; and other rotor pumps.

The advantage of soft sealing butterfly valve is good sealing performance, but the disadvantage is easy aging, wear and short service life.

The hard seal butterfly valve has a long service life, but the sealing performance is relatively poorer than that of the soft seal.

With the development of my country’s capital construction and the implementation of large-scale national projects, the number of valves in electric power, petroleum, chemical, urban water supply and drainage systems has increased, especially butterfly valves. The metal hard sealing butterfly valve produced in my country can be divided into two categories from the sealing structure, one is the elastic hard sealing structure, and the other is the multi-level hard sealing butterfly valve.

The production diameter of elastic hard sealing butterfly valve is generally dn500

Below, the large-caliber mostly adopts a multi-level structure.

The following butterfly valves are used in large quantities, so there are many problems encountered by users when using them. Here, we will summarize the common problems and guide the correct installation and use.

The elastic structure hard sealing butterfly valve is composed of main parts such as valve body, valve plate, valve stem, elastic valve seat and pressure ring.

The structure and function of the pressure ring: the side of the pressure ring is the sealing surface of the valve body and the sealing surface of the pipe flange becomes the sealing pair, and there are bolt holes on the side. Connected together to form the total structural length of the valve.

Due to the screw hole on the side of the pressure ring, the effective sealing surface diameter will be reduced. From the user’s use of flanges, most of them use flat-welded flanges, and their inner diameters are also known as 10~20mm larger. In this way, the effective sealing surface will be reduced. If the valve and the pipe flange are not concentric during the installation process, they will be dislocated and pressed on the bolt hole diameter. At this time, the bolt hole diameter will be exposed inside the inner hole of the pipe flange, causing leakage here. The leak is characterized by the flow of media from the back of the pressure ring.

At present, the country has no corresponding special standards for flanges for elastic hard-sealed butterfly valves. According to the current national standards, we use the socket type for the inner diameter of the flange under the condition that the standard size specified by the flange remains unchanged. The inner diameter of the flange is basically the same as the nominal diameter, which is to increase the effective sealing surface, and also provide favorable convenience for installation, and at the same time ensure the normal use of the valve.

Here, users are reminded that when using elastic hard sealing butterfly valves, the paired reverse flanges must use special flanges, especially the pipeline flanges that match the pressure ring surface of the valve body, must use special flanges.

The direction of the arrow on the valve body refers to the pressure direction of the medium

Usually, the direction of the arrow cast on the valve body refers to the flow direction of the medium. After the user sees the arrow, it is logical to install it according to the direction of the flow and the arrow. This installation has become a habit, and the installer can easily accept this instruction. There is nothing wrong with the standard. However, for butterfly valves with eccentric structure, some problems may arise in this installation. Here is an example: the eccentric butterfly valve is installed in the same direction as the flow direction of the medium, and the medium in the pipe is liquid. When it is reduced or zero, the medium at the outlet will flow back and forth. If it is supplied from a high level, the medium is at a high level and the pressure is generated. When the pressure is greater than the inlet pressure, the valve will bear the effect of reverse pressure. Use the valve for one-way use, which is not conducive to the tightness of the butterfly valve, and there will be leakage.

From the above example, it can be concluded that the arrow direction of the butterfly valve body refers to the pressure direction of the medium.

Before installation, the user should clearly know the direction of the medium pressure after the valve is closed. The arrow direction of the free valve body is consistent with the direction of the medium pressure to achieve correct use, and the sealing performance is kept in good condition.

Precautions for acceptance of elastic hard sealing butterfly valve to the user

It is very necessary for the user to sample or inspect all the valves at the place of purchase. The sampling inspection of the product quality is as follows: one is to check the quality of the product, and the other is to reduce the unnecessary maintenance and update of the valve after installation, and the success rate of one-time installation is high. However, there are some points that the user did not pay attention to in the test of the hard-sealed butterfly valve during the random inspection, resulting in doubts about the quality of the valve or rejection as unqualified. There are 4 screws on the pressure ring according to the diameter

The diameter of the bolts shall not exceed m10. These screws are mainly used to fix the elastic valve seat, which cannot bear all the medium pressure. When the valve is installed in the pipeline and pressed by the outer flange bolts, it can bear all the medium force. Due to structural reasons, it is common for users to notify the manufacturer on the grounds that they are unqualified due to differences in the inspection operations. Leakage occurs during acceptance. Therefore, here are the matters that should be paid attention to, so that users can better understand and communicate with the elastic hard sealing butterfly valve.

When testing the elastic hard-sealed butterfly valve, lay the side of the pressure ring flat, and place a pressure plate on this plane that is basically the same size as the outer circle of the flange and the valve passage. This pressure plate makes the pressure evenly distributed on the pressure ring on one side of the valve body.

If the blind plate is used for the test, generally the wafer-type elastic hard-sealed butterfly valve is tested with two flanges clamped to the clip. Sometimes the flange-type elastic hard-sealed butterfly valve only uses one flange below for convenience. It is fixed with the valve bolts. At this time, the fixing screws on the pressure ring on the valve body will bear the full pressure of the medium. As mentioned above, these screws cannot bear the pressure of the entire medium, so use a blind plate. The valve does not leak during the test, and it is basically the same as the actual use state.

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