Hard sealed ball valves are much more stringent in operating conditions than soft sealed ball valves. High temperature, strong corrosion, and media such as dust, particles, and mud pose significant obstacles to the continuous use of hard sealed ball valves. During the use of hard sealed ball valves, valve failures often occur due to operating conditions or human factors, forcing maintenance. Understanding the causes of valve failures and finding ways to prevent them is necessary and effective for valve industry workers and product users.

From the perspective of product usage, hard sealed ball valve faults can be roughly divided into the following two categories: non technical faults and technical faults.

1. Non technical faults

This type of failure is not related to technology, that is, it is not a problem with the internal structure of the valve or a malfunction in the operation of internal components. Therefore, the cause of its failure is generally caused by external conditions.

1.1 Errors in valve selection

Some customers, when choosing a valve model, lack understanding of the product's operating conditions or consider cost, and the selected valve cannot meet the requirements for working temperature, working pressure, medium corrosiveness, and erosion under the operating conditions, resulting in rapid valve failure once put into use.

Therefore, in the selection process, the customer or design institute must prioritize the reliability of the product's use, as choosing too low-end products due to cost reasons may result in failures and damage, which may not be worth the loss. This is particularly important in the selection of hard sealed ball valves with harsh operating conditions.

1.1.1 Incorrect material selection for spraying hard alloy surface on ball seat sealing surface

The key to the performance of hard sealed ball valves lies in the surface hardening treatment of steel balls and valve seats. In order to ensure the sealing of metal to metal, the sealing pressure between hard sealed ball seats is much higher than that of ordinary ball valves, which makes it easy for the metal materials to bite or pull, both of which can directly cause the ball valve to not function properly. At present, the most widely used and effective method for surface hardening of ball seats is the spraying of hard alloy technology (mainly nickel based alloys and chromium based alloys). The steel ball and valve seat coating of hard sealed ball valves largely determine the performance and lifespan of the sealing surface of the ball seat. Therefore, in complex working conditions, the selection of hard alloy layer should be based on the actual situation.

There are generally two directions for selecting hard alloy layers: one is to pursue their hardness. High hardness alloy layers have strong wear resistance and erosion resistance, and are commonly used in working conditions with small and hard solid particle media (such as coal chemical and polycrystalline silicon industries); The second is to pursue its corrosion resistance. In some highly corrosive media, the corrosion resistant alloy layer can effectively protect the internal substrate of the ball socket, thereby extending its lifespan. It is commonly used in highly corrosive media conditions (such as the petrochemical and paper industries). In the selection of materials for hard sealed ball valves, the material for spraying a hard alloy layer on the sealing surface of the ball seat is of utmost importance, and hard alloys that do not match the working conditions and medium conditions must not be selected.

1.1.2 Material selection of some internal components of the valve does not match the operating temperature

In hard sealed ball valves, the selection of some internal components is closely related to their operating temperature or medium temperature, such as fillers, sealing washers, valve stem sheaths, etc. There are generally two reasons for choosing hard sealed ball valves. One is that the operating temperature is high, and the soft sealed valve seat cannot withstand it. The other is that the medium has strong abrasive and erosion ability, and the soft sealed valve seat is not hard enough. It can be seen that hard sealed ball valves are not equal to high-temperature ball valves. In some operating conditions, Its usage temperature may not be very high.

When the medium temperature is below 200 ℃, synthetic plastic can be selected for packing, sealing gaskets (including body cover sealing gasket, lower valve stem sealing gasket, middle flange sealing gasket, etc.), and valve stem sheath. This configuration is similar to the configuration of related accessories in soft sealed ball valves.

When the medium temperature is above 200 ℃, graphite needs to be selected as the filler (graphite has strong temperature resistance, and its performance remains basically unchanged at high temperatures

1.2 Selection failure of accessories



The accessories of the valve include the driving device, the supporting device of the driving device, and accessories such as brackets and connecting shafts that connect the driving device. The driving devices of hard sealed ball valves can be divided into lever handles, steel pipe handles, turbine actuators, handwheel clutch reducers (used to switch between manual or automatic operations), and automatic actuators (including pneumatic actuators, electric actuators, electro-hydraulic actuators, etc.) based on their power sources.

For manually operated driving devices such as lever handles, steel pipe handles, and gear mechanisms, the torque can be calculated based on the working torque value of the product, and appropriate lengths or specifications can be selected. Of course, the torsional and tensile strength of the material also needs to be considered.

The selection of automatic actuators is relatively complex. Taking pneumatic actuators as an example, they are divided into single acting and double acting types. Double acting pneumatic actuator switches all have spring force and consistent torque. Single acting pneumatic actuators need to overcome the spring force when opening and rely on spring force to close. As a result, their output torque is within a range of torque values, which increases the difficulty of selection. Generally, when installing pneumatic actuators, it is necessary to multiply the working torque value of the valve by a safety factor, To prevent the occurrence of insufficient operating force due to the output torque of the actuator due to range changes.

Generally, when leaving the factory, the actual working torque value cannot be accurately measured before reaching the actual working condition. The commonly used standard is to estimate the working torque value based on multiplying the no-load torque value by a dielectric coefficient. For hard sealed ball valves, the medium coefficient should be selected according to different working conditions. If it is a particle, dust, or mud medium, the coefficient should be as large as possible, usually within the range of 1.5-2.

In addition to the selection of the actuator itself, its accessories should also be selected according to the actual situation, such as related solenoid valves, pressure reducing valves, valve position switches, etc. For example, a pneumatic actuator with a large intake volume is equipped with a solenoid valve with a small air flow rate, which will slow the intake of the pneumatic actuator, slow the valve closure, and prolong the time for the sealing surface to be eroded, which is not conducive to the service life of the valve. Moreover, the significant advantage of valves in automatic devices lies in their fast opening and closing time. Many customers require the opening and closing action to be completed within N seconds, which puts higher demands on the reasonable configuration of related accessories.

1.3 Other non-technical faults

In addition to the non-technical faults caused by common selection errors mentioned above, during the actual use of hard sealed ball valves, installation direction and steps may not follow the specifications, which can also cause usage faults. Therefore, during the use of the valve, it is necessary to follow the instructions and connect the connection position properly to ensure safety.

2. Technical faults

The non-technical faults mentioned earlier are all caused by human factors, originating from subjective reasons. If they are sufficiently cautious or experienced, they can be completely avoided, and their causes are not related to the internal structure of the valve. And technical faults. As the name suggests, it is caused by the current imperfect technology of hard sealed ball valves, and often we can only try to minimize the impact it brings, which is difficult to completely eliminate. Of course, if a hard sealed ball valve with a service life of 3 months can be extended to six months after troubleshooting or prevention, even if the fault cannot be completely eliminated, it can still be considered successful.


2.1 Leakage caused by sealing surface damage

For ball valves, and even for valves, the sealing surface is the most important part that affects the operation of the entire valve. From the working principle of a ball valve, it is an opening and closing component, and its operation process is the process of the steel ball opening or closing on the valve seat. If the sealing surface is damaged during the opening or closing process, the sealing surface may leak, causing internal leakage of the valve, and the valve is considered invalid.


2.1.1 Reasonable selection of valve seat springs

The biggest difference between hard sealed ball valves and soft sealed ball valves is that the steel ball and valve seat are both metal materials, unlike soft sealed steel balls that are metal while valve seats are non-metallic. Therefore, the sealing mechanism is also different. The sealing principle of a soft sealing ball valve is that the sealing force between the steel ball and the valve seat causes deformation of the non-metallic valve seat, transforming the uneven line contact between the valve seat and the steel ball into contact. At the same time, the soft sealing valve seat is squeezed and deformed, and further fits with the surface of the steel ball to compensate for the uneven areas on the surface of the steel ball. If the compression deformation between the steel ball and the valve seat is greater or smaller, Has little impact on sealing performance; The sealing principle of hard sealed ball valves is that the sealing force between the steel ball and the valve seat is difficult to deform the metal valve seat. Therefore, greater sealing force (compared to soft sealed ball valves) is needed to deform the sealing surface of the valve seat, in order to achieve the fit between the steel ball and the valve seat and achieve sealing. However, this deformation is only minor, and if there is a slight change in the extrusion pressure of the steel ball valve seat, it may not be able to seal. It is not difficult to draw two conclusions from the differences in the two mechanisms: firstly, the squeeze pressure between the hard sealed ball valve steel ball and the valve seat is greater; 2、 The adjustment function of hard sealed ball valves for sealing is weaker than that of soft sealed ball valves.


Due to the greater squeezing force between the hard sealed ball valve steel ball and the valve seat, sliding friction occurs between the metal steel ball and the metal valve seat during the opening and closing transition of the ball valve. According to material mechanics, sliding friction between metals with similar hardness is likely to strain the sealing surface (causing scratches on the sealing surface). In hard sealed ball valves, a spring (disc spring or column spring) is generally added after the valve seat to compare the pressure for fine adjustment. In this way, to a certain extent, the sealing force can be achieved within a certain range.

2.1.2 Adjustment effect of valve seat pressure ring

The previous article analyzed the regulating effect of springs. The elasticity and compression of springs are linear or quadratic functions, and the effective value range is very short, so adjustments are only made within a very small range. When the valve leaks

3. Conclusion

In summary, the production accuracy requirements for hard sealed ball valves are high, and the working conditions are harsh. To ensure that hard sealed ball valves can have fewer failures and maintain a longer service life, the following aspects need to be grasped:

① Design and selection should be based on actual working conditions, selecting appropriate materials and structures.

② During the production process, precision must be strictly controlled and every step of testing must be done well before leaving the factory.

③ Strictly follow the product production manual during use.

④ Regularly conduct inspections and maintenance, and promptly repair or replace any problems to avoid safety accidents.