The sealing of brass valvesis an important step in the manufacture of brass valves, which is used to prevent fluid leakage from the gap between the moving valve parts and the valve body. The choice of packing material and packing sealing structure is one of the important conditions to ensure that the brass regulating valve does not leak at the valve stem packing. The sealing of the brass ball valve mainly includes the sealing of the valve ball and the sealing of the valve stem.

Brass valves Includes brass ball valves, brass gate valves, brass angle valves, brass check valves, brass radiator valves, brass fittings and custom brass valves, sizes from DN8 to DN100, pressures from PN10 to PN40, which widely used for water, gas, oil and heating systems.

Sealing is preventing leakage, so the sealing principle of brass valve is also studied from preventing leakage. There are two main factors that cause leakage, one is the most important factor affecting the sealing performance, that is, there is a gap between the sealing pairs, and the other is the pressure difference between the two sides of the sealing pair. The sealing principle of brass valve is also analyzed from four aspects: liquid sealing, gas sealing, leakage channel sealing principle and sealing of brass valvespair.

The tightness of the liquid is carried out by the viscosity and surface tension of the liquid. When the leaking capillary of the brass valve is filled with gas, the surface tension may repel the liquid or introduce the liquid into the capillary. This forms a tangent angle. When the tangent angle is less than 90°, the liquid will be injected into the capillary, which will cause leakage. Leaks occur because of the different properties of the media. Experiments with different media will yield different results under the same conditions. Water, air or kerosene can be used. When the tangent angle is greater than 90°, leakage will also occur. Because it is related to the grease or wax film on the metal surface. Once the film on these surfaces is dissolved, the characteristics of the metal surface change, and the liquid that was originally repelled will wet the surface and leak. In view of the above situation, according to the Poisson formula, the purpose of preventing leakage or reducing leakage can be achieved under the condition of reducing the diameter of the capillary and the viscosity of the medium.

According to Poisson's formula, the tightness of a gas is related to the viscosity of the gas molecules and the gas. Leakage is inversely proportional to the length of the capillary and the viscosity of the gas, and proportional to the diameter of the capillary and the driving force. When the diameter of the capillary is the same as the mean degree of freedom of the gas molecules, the gas molecules flow into the capillary with free thermal motion. Therefore, when we are doing the sealing test of the brass valve, the medium must be water to play a sealing role, and air, that is, gas, cannot play a sealing role. Even if we reduce the diameter of the capillary below the gas molecules by plastic deformation, the flow of the gas still cannot be stopped. The reason is that the gas can still diffuse through the metal wall. So when we do gas test, we must be more strict than liquid test.

Brass valve seals are composed of two parts, the roughness that is scattered on the wave surface and the waviness of the distance between the wave crests. Under the circumstance that most of the metal materials in our country have low elastic strain force, if the sealing state is to be achieved, it is necessary to raise higher requirements for the compressive force of the metal material, that is, the compressive force of the material must exceed its elasticity. Therefore, when designing a brass valve, the sealing pair is matched with a certain hardness difference, and under the action of pressure, a certain degree of plastic deformation sealing effect will be produced. If the sealing surfaces are all metal materials, the uneven protruding points on the surface will appear first, and only a small load can be used to plastically deform these uneven protruding points at the beginning. When the contact surface increases, the unevenness of the surface becomes plastic-elastic deformation. At this time, the roughness on both sides of the recess will exist. When it is necessary to apply a load that can cause severe plastic deformation of the underlying material, and make the two surfaces in close contact, these remaining paths can be made close along the continuous line and hoop direction.

The brass valve seal pair is the part that closes when the valve seat and the closing member come into contact with each other. During use, the metal sealing surface is easily damaged by intercalated media, media corrosion, wear particles, cavitation and erosion. such as wear particles. If the wear particles are smaller than the unevenness of the surface, the surface accuracy will be improved without deterioration when the sealing surface is run-in. On the contrary, the surface accuracy will be deteriorated. Therefore, when selecting wear particles, factors such as their material, working conditions, lubricity and corrosion to the sealing surface should be comprehensively considered. Just like wear particles, when we choose seals, we must comprehensively consider various factors that affect their performance in order to play the function of preventing leakage. Therefore, materials that are resistant to corrosion, scratches and erosion must be selected. Otherwise, the lack of any one of the requirements will greatly reduce its sealing performance.

There are many factors affecting the sealing of brass valves , mainly including the following:

Under the change of temperature or sealing force, the structure of the sealing pair will change. And this change will affect and change the force between the sealing pair, so that the performance of the brass valve seal is reduced. Therefore, when choosing a seal, be sure to choose a seal with elastic deformation. At the same time, pay attention to the width of the sealing surface. The reason is that the contact surfaces of the sealing pair cannot be completely matched. When the width of the sealing surface increases, the force required for the sealing should be increased.

The specific pressure of the sealing surface affects the sealing performance of the brass valve and the service life of the brass valve. Therefore, the specific pressure of the sealing surface is also a very important factor. Under the same conditions, if the specific pressure is too high, the brass valve will be damaged, but if the specific pressure is too small, the brass valve will leak. Therefore, we need to fully consider the appropriateness of the specific pressure when designing.

The physical properties of the medium also affect the sealing performance of brass valves . These physical properties include temperature, viscosity, and hydrophilicity of the surface, among others. The temperature change not only affects the slackness of the sealing pair and the change of the size of the parts, but also has an inseparable relationship with the viscosity of the gas. Gas viscosity increases or decreases with increasing or decreasing temperature. Therefore, in order to reduce the influence of temperature on the sealing performance of brass valves , when designing the sealing pair, we should design it as a brass valve with thermal compensation such as an elastic valve seat. Viscosity is related to the permeability of the fluid. When under the same conditions, the greater the viscosity, the less the penetrating ability of the fluid. The hydrophilicity of the surface means that when there is a film on the metal surface, the film should be removed. Because of this very thin oil film, it will destroy the hydrophilicity of the surface, resulting in blockage of fluid channels.

The quality of the sealing pair mainly means that we must check the selection, matching and manufacturing accuracy of materials. For example, the valve disc fits well with the valve seat sealing surface, which can improve the sealing performance. The characteristic of many circumferential waviness is that its labyrinth sealing performance is good.

Brass valve leakage is very common in life and production, and it will cause waste or bring danger to life, such as leakage of brass valves  in tap water, and serious consequences, such as toxic, harmful and flammable in the chemical industry. , explosive and corrosive medium leakage, etc., serious threats to personal safety, property safety and environmental pollution accidents. A brass valve that relies on external force to rotate and drive to open and close is designed with a sealing device, which is used to install a certain number of packing sealing rings in the packing culvert to achieve the sealing effect, but how is the sealing condition? The leakage at the packing of the brass valve is one of the most prone to leakage failures in the brass valve, but there are roughly two reasons for it.

Seals are also critical components in brass valves . The sealing performance of the brass valve refers to the ability of each sealing part of the brass valve to prevent the leakage of the medium, which is the most important technical performance index of the brass valve.

There are three sealing parts of the brass valve:

The contact between the opening and closing parts and the two sealing surfaces of the valve seat; the cooperation between the packing and the valve stem and the stuffing box; the connection between the valve body and the valve cover. The leakage in the former one is called internal leakage, which is commonly referred to as lax closure, which will affect the ability of the brass valve to cut off the medium. For shut-off valves, internal leakage is not allowed. The leakage in the latter two places is called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve.

External leakage will cause material loss, pollute the environment, and even cause accidents in severe cases. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so brass valves  must have reliable sealing performance.

Brass valves  run, run, drip, and leak. Next, we will discuss the dynamic sealing and static sealing problems of brass valves .

Brass valve dynamic seal, main finger stem seal. Preventing the medium in the valve from leaking with the movement of the valve stem is the central issue of the dynamic seal of the brass valve.

a) Stuffing box form

Brass valve dynamic seal, mainly stuffing box. The basic form of stuffing box is:

b) Gland type

This is the most used form.

The unified form can be distinguished by many details. For example, in terms of compression bolts, it can be divided into T-shaped bolts (for low-pressure brass valves  with a pressure of ≤16 kg/cm²), stud bolts and joint bolts. As far as the gland is concerned, it can be divided into integral type and combined type.

c) Compression nut type

This type of form has small dimensions, but the pressing force is limited, and it is only used for small brass valves .

2) Filler

In the stuffing box, the packing is in direct contact with the valve stem and is covered with the stuffing box to prevent the leakage of the medium. There are the following requirements for packing:

(1) Good sealing performance;

(2) corrosion resistance;

(3) The friction coefficient is small;

(4) Comply with the medium temperature and pressure.

Commonly used fillers are:

(1) Asbestos packing: Asbestos packing has good temperature and erosion resistance, but when used alone, the sealing effect is not good, and it is always impregnated or added with other materials. Oil-immersed asbestos packing: It has two basic structural forms, one is twisting and the other is knitting. It can be divided into round and square.

(2) PTFE braided packing: The PTFE tape is braided into packing, which has excellent corrosion resistance and can be used for cryogenic medium.

(3) Rubber O-ring: Excellent sealing effect under low pressure. The use temperature is limited, such as natural rubber can only be used for 60 ℃.

(4) Plastic molding filler: generally made into three pieces, but also can be made into other shapes. The plastics used are mostly polytetrafluoroethylene.

In addition, for example, in the 250 ℃ steam brass valve, the asbestos packing and the lead ring are alternately superimposed, and the steam leakage will be alleviated; there is a brass valve, and the medium is often changed, such as asbestos packing and polytetrafluoroethylene. The sealing effect is better when used in conjunction with the material belt. In order to reduce the friction on the valve stem, molybdenum disulfide (MOS2) or other lubricants can be added in some places.

What is a static seal called?

A static seal usually refers to a seal between two stationary surfaces. The main method of sealing is to use gaskets.

1) Gasket material

(1) Non-metallic materials: such as paper, hemp, cowhide, asbestos products, plastics, rubber, etc.

Paper, linen, cowhide, etc. have capillary pores and are easy to penetrate. When using, they must be impregnated with oil, wax or other impermeable materials. Generally, brass valves  are rarely used.

Asbestos products, there are asbestos belts, ropes, boards and asbestos rubber sheets. Among them, the asbestos rubber sheet has a compact structure, good pressure resistance and good temperature resistance.

Plastic products have good corrosion resistance and are widely used. Varieties are polyethylene, polypropylene, soft PVC, PTFE, nylon 66, nylon 1010 and so on.

Rubber products, soft in quality, all kinds of rubber are divided into certain acid resistance, alkali resistance, oil resistance and seawater resistance. Varieties are natural rubber, styrene-butadiene rubber, nitrile rubber, neoprene rubber, isobutylene rubber, polyurethane rubber, fluorine rubber and so on.

(2) Metal materials: Generally speaking, metal materials have high strength and strong temperature resistance. But lead is not like this, only its resistance to dilute sulfuric acid is taken. Commonly used varieties are brass, copper, aluminum, low carbon steel, stainless steel, Monel, silver, nickel, etc.

(3) Composite materials: such as metal sheathed (internal asbestos) gaskets, combined wave gaskets, entangled gaskets, etc.

2) Frequent use of gasket performance

When using a brass valve, it is often necessary to replace the original gasket. Common gaskets are: rubber flat washer, rubber O-ring, plastic flat washer, teflon-coated washer, asbestos rubber washer, metal flat washer, metal special-shaped washer, metal sheathed washer, wave washer, entangled gasket, etc.

(1) Rubber flat gasket: easy to deform, not difficult to press, but poor pressure and temperature resistance, only used for low pressure and low temperature. Natural rubber has a certain acid and alkali resistance, and the operating temperature should not exceed 60 °C; neoprene rubber can also withstand certain acids and alkalis, and the operating temperature is 80 °C; nitrile rubber is oil-resistant and can be used up to 80 °C; Fluorine rubber has good corrosion resistance and is resistant to The temperature performance is also stronger than that of general rubber, and it can be used in 150 ℃ medium.

(2) Rubber O-shaped washer: The cross-sectional shape is a perfect circle, and it has a certain self-tightening effect. The sealing effect is better than that of the flat washer, and the pressing force is smaller.

(3) Plastic flat washer: The biggest feature of plastic is good corrosion resistance, and most plastics have poor temperature resistance. PTFE is the crown of plastics, with excellent corrosion resistance, wide temperature resistance range, and can be used for a long time within -180℃～+200℃.

(4) PTFE-wrapped gasket: fully display the advantages of PTFE, and at the same time make up for its poor elasticity, and make PTFE-wrapped rubber or asbestos rubber gaskets. In this way, it is not only as resistant to erosion as the PTFE flat gasket, but also has excellent elasticity, which enhances the sealing effect and reduces the pressing force.

(5) Asbestos rubber gasket: cut from asbestos rubber sheet. Its components are 60-80% asbestos and 10-20% rubber, and fillers, vulcanizing agents, etc. It has good heat resistance, cold resistance, chemical stability, abundant supply and low price. When using, the pressing force does not need to be very large. It can adhere to metal, and it is best to apply a layer of graphite powder on the surface to avoid strenuous disassembly.

(6) Metal flat heating ring: lead, temperature resistance 100℃; aluminum 430℃; copper 315℃; low carbon steel 550℃; silver 650℃; nickel 810℃; Monel (nickel-copper) alloy 810℃, stainless steel 870℃ . Among them, lead has poor pressure resistance, aluminum can withstand 64 kg/square centimeter, and other materials can withstand high pressure.

(7) Metal heterosexual gasket:

Lens Gasket: Self-tightening for high-pressure brass valves .

Oval washers: also belong to high pressure self-tightening washers.

Conical double gasket: used for high pressure inner self-care sealing.

In addition, there are square, diamond, triangle, tooth, dovetail, B, C, etc., which are generally only used in high and medium pressure brass valves .

(8) Metal-clad gasket: Metal has both excellent temperature and pressure resistance and excellent elasticity. Foreskin materials include aluminum, copper, low carbon steel, stainless steel, Monel alloy, etc. The filling materials are asbestos, PTFE, glass fiber and so on.

(9) Wave washer: It has the characteristics of small pressing force and good sealing effect. Often in the form of a combination of metals and non-metals.

(10) Surrounding entanglement washer: It is a thin metal belt and a non-metallic belt that are closely attached together, and are entangled into a multi-layer circle, with a wave-shaped section, which has good elasticity and tightness. Metal strips can be constructed of 08 steel, 0Cr13, 1Cr13, 2Cr13, 1Cr18Ni9Ti, copper, aluminum, titanium, Monel, etc. Non-metallic belt materials include asbestos, polytetrafluoroethylene, etc.

Above, when describing the performance of sealing gaskets, some figures are listed. It must be noted that these numbers are closely related to the flange form, medium conditions and installation and repair technology, etc., which can be crossed, not reached, and the pressure and temperature resistance performance are also mutually transformed. For example, when the temperature is high, the pressure resistance capacity tends to decrease. , These subtle issues can only be experienced in practice.

Sealing of brass valves material is an important part of the brass valve seal, which acts as the direct contact surface of the brass valve seal. What are the sealing of brass valves materials? We know that the sealing of brass valves ring materials are divided into two categories: metal and non-metal.

sealing of brass valves material is an important part of the brass valve seal, which acts as the direct contact surface of the brass valve seal. What are the sealing of brass valves materials? We know that the sealing of brass valves ring materials are divided into two categories: metal and non-metal. The following is a brief introduction to the use conditions of various sealing materials, as well as the commonly used types of brass valves 

1 Synthetic rubber

The comprehensive properties of synthetic rubber, such as oil resistance, temperature resistance and corrosion resistance, are better than those of natural rubber. Generally, the use temperature of synthetic rubber t≤150℃, natural rubber t≤60℃, rubber is used for brass globe valve, brass gate valve, diaphragm valve, butterfly valve, brass check valve, pinch valve with nominal pressure PN≤1MPa and other brass valve seals.

2 nylon

Nylon has the characteristics of small friction coefficient and good corrosion resistance. Nylon is mostly used for brass ball valves and brass globe valves with temperature t≤90℃ and nominal pressure PN≤32MPa.

3 Teflon

PTFE is mostly used for brass globe valves, brass gate valves, brass ball valves, etc. with temperature t≤232℃ and nominal pressure PN≤6.4MPa.

4 cast iron

Cast iron is used for brass gate valve, brass globe valve, plug valve, etc. for temperature t≤100℃, nominal pressure PN≤1.6MPa, gas and oil.

5 Copper alloy

Commonly used materials for copper alloys are 6-6-3 tin bronze and 58-2-2 manganese brass. Copper alloy has good wear resistance and is suitable for water and steam with temperature t≤200℃ and nominal pressure PN≤1.6MPa. It is often used in brass gate valve, brass globe valve, brass check valve, plug valve, etc.