In industrial pipeline systems, stop valves play a vital role in controlling the flow of fluids. As the main operating component of the stop valve, the smoothness of the handwheel's operation directly affects the efficiency of the valve and the stability of the production process. Recently, many companies have reported that they have difficulty opening the hand wheel in the stop valve, and this issue has attracted widespread attention in the industry.
Table of contents
●Working principle and normal operation performance of Hand Wheel in Stop Valve
●Statistics of survey data on difficult opening
●In-depth analysis of the causes of difficult opening
1. Mechanical failure factors
2. Medium factors
3. Installation and maintenance factors
●Measures and suggestions for solving the problem of difficult opening
1. Target mechanical failures
2. Deal with media impacts
3. Strengthen installation and maintenance management
●Views of industry experts
Working principle and normal operation performance of Hand Wheel in Stop Valve
The stop valve drives the valve stem by rotating the handwheel, and the valve stem then drives the valve disc to move up and down to cut off and conduct the pipeline fluid. Under normal circumstances, the operator can easily open or close the valve by applying moderate force to turn the handwheel. According to relevant industry standards and a large amount of actual operation data statistics, when the valve is in good working condition, the handwheel operating torque should generally be between 50 and 80N・m to open an ordinary stop valve with a nominal diameter of DN100, and the rotation process should be smooth without obvious jamming or blocking. If the operating torque exceeds this range, or there are frequent jams during the rotation process, or multiple efforts are required to turn a certain angle, it may indicate that the valve is abnormal.
Statistics of survey data on difficult opening
In order to more intuitively understand the severity of the problem of difficulty in opening the Hand Wheel in Stop Valve, we conducted a questionnaire survey on 100 companies in different industries, covering chemical industry, electricity, oil and gas and other fields. The survey results are shown in the following table:
| Industry | Number of companies involved | Number of companies experiencing difficulties in starting up | Problem Occurrence Rate (%) |
| Chemicals | 30 | 18 | 60 |
| Electricity | 25 | 12 | 48 |
| Oil and gas | 20 | 10 | 50 |
| Other manufacturing | 25 | 11 | 44 |
| Total | 100 | 51 | 51 |
It is obvious from the data that as many as 51% of the surveyed companies encountered difficulties in opening the Hand Wheel in Stop Valve. This is by no means an isolated phenomenon, but has become a common problem affecting the production and operation of many companies.
In-depth analysis of the causes of difficult opening
1. Mechanical failure factors
Excessive friction between the valve stem and the stuffing box: The valve stem frequently moves up and down in the stuffing box. If the packing gland is too tight, the friction between the valve stem and the packing will increase sharply. According to statistics, about 30% of the cases of difficult opening are caused by this reason. In actual maintenance, it is found that some companies over-tighten the packing gland to prevent valve leakage, which greatly increases the movement resistance of the valve stem, and the operating torque can increase to 2-3 times the normal situation.
Adhesion between the valve flap and the valve seat: When the valve is in a closed state for a long time and the medium is corrosive or contains impurities, the valve flap and the valve seat are prone to adhesion. In the chemical industry, the problem of difficulty in opening caused by the adhesion of the valve flap and the valve seat due to medium corrosion accounts for 40% of the total number of problems in the industry. For example, in a pipeline that transports acidic media, if the valve is not operated for a long time, the surface of the valve flap and the valve seat will gradually be corroded, forming a layer of rust or crystals, which will stick the two tightly together, making it necessary to overcome great resistance when opening.
Loose connection between handwheel and valve stem: The handwheel and valve stem transmit torque through keys or other connection methods. If the connection part is loose, the handwheel cannot effectively drive the valve stem when it turns, resulting in difficulty in opening. This situation is more common in old valves, accounting for about 15% of the difficult opening problems. Inspections have found that some valves have been operated frequently for a long time, and the connection keys are severely worn or even fall off, causing the handwheel to rotate idly and unable to open the valve.
2. Medium factors
Medium crystallization or solidification: When the temperature of the medium in the pipeline changes greatly or in a low temperature environment, some media may crystallize or solidify. For example, in petrochemicals, in pipelines that transport waxy crude oil, when the temperature is low in winter, wax is easy to crystallize and adhere to the inside of the valve, blocking the gap between the valve disc and the valve seat, increasing the difficulty of opening. This type of difficult opening problem caused by the characteristics of the medium is particularly prominent in low temperature environments or working conditions where the medium is easy to crystallize, accounting for about 25% of the total number of problems.
Impurity accumulation in the medium: If the medium contains granular impurities, rust, etc., these impurities may accumulate between the valve disc and the valve seat sealing surface during the valve closing process, hindering the normal rise of the valve disc and causing difficulty in opening. In some old industrial pipeline systems, due to the lack of effective filtering devices, this situation often occurs, accounting for about 20% of the difficult opening problems. For example, in some factories that do not regularly clean the pipelines, a large amount of rust and impurities can often be found inside the valve, seriously affecting the normal opening of the valve.
3. Installation and maintenance factors
Improper valve installation: If the valve is not installed in accordance with the correct installation specifications, such as excessive vertical deviation of the valve stem, reverse installation of the valve inlet and outlet directions, etc., it may cause the valve to be difficult to open during use. According to installation case analysis, about 10% of the difficult opening problems are caused by improper installation. For example, if the vertical deviation of the valve stem exceeds the specified range, the valve stem will be subjected to additional lateral force during movement, increase the friction with the stuffing box and other components, and then cause difficulty in opening.
Lack of regular maintenance: After long-term use, if the valve is not regularly maintained, the internal components will gradually be damaged due to wear and corrosion, affecting the normal operation of the valve. Statistics show that in enterprises that have not established a complete valve maintenance system, more than 60% of the valves have varying degrees of difficulty in opening. If the valve stem is not lubricated in time, the friction coefficient between the valve stem and the stuffing box will increase, and the operating torque will increase significantly; if the damaged seals are not regularly inspected and replaced, it may also cause the valve disc and the valve seat to be loosely sealed, which will cause difficulty in opening.
Measures and suggestions for solving the problem of difficult opening
1. For mechanical failures
Regularly check the matching of the valve stem and the stuffing box, adjust the tightness of the packing gland, and ensure that the valve stem moves flexibly and does not leak. It is generally recommended to check and adjust once a quarter.
For valves that are prone to adhesion, apply an appropriate amount of anti-adhesion lubricant to the sealing surface of the valve disc and the valve seat, and regularly open and close the valve to prevent adhesion caused by long-term static. For valves that have already adhered, you can try to separate the valve disc and the valve seat by soaking in solvent or lightly knocking, but pay attention to the operating force to avoid damaging the sealing surface.
Strengthen the inspection of the connection between the hand wheel and the valve stem, and tighten or replace the connection parts in time if loose. Every time the valve is maintained, the connection parts should be checked in detail.
2. Dealing with the influence of the medium
For media that are easy to crystallize or solidify, heating and insulation measures can be taken to ensure that the medium always remains in liquid state in the pipeline to prevent crystallization or solidification. At the same time, when designing the pipeline system, it should be considered to add necessary media filters to remove impurities and reduce the impact of impurity accumulation on the valve.
Clean the pipes and valves regularly to remove the impurities accumulated inside. The cleaning cycle can be determined according to the cleanliness of the medium and the frequency of use. It is generally recommended to perform a comprehensive cleaning every six months to one year.
3. Strengthen installation and maintenance management
Install the valve strictly in accordance with the valve installation instructions to ensure that the installation position is correct and the verticality of the valve stem meets the requirements. After the installation is completed, strict debugging and inspection should be carried out to ensure smooth operation of the valve.
Establish a complete valve maintenance system, clarify the maintenance cycle, maintenance content and responsible person. Regularly lubricate the valve, check the sealing performance, detect component wear and other maintenance work to promptly discover and solve potential problems. At the same time, strengthen the training of operators to improve their skills in correct operation and maintenance of valves.
Hangzhou Xiaoshan Chuangye Metal Processing Co., Ltd. said that the difficulty in opening the Hand Wheel in Stop Valve is not a normal phenomenon, which will seriously affect production efficiency and even bring safety hazards. For example, a chemical company loses more than one million yuan every year. Enterprises need to establish a full life cycle valve management system, and the industry should also improve relevant standards. "As a deep cultivator in the industry for more than ten years, our company can solve this problem in all aspects: in terms of design and selection, the professional team customizes the solution to reduce friction and adhesion with high-precision technology; during installation and commissioning, the technicians provide on-site guidance to ensure accurate installation and smooth operation; in daily maintenance, the exclusive service package covers inspection, maintenance, and testing, and the replacement of wearing parts is quickly responded to 24 hours. Free operation and maintenance training is also provided to help enterprises scientifically manage valves and escort production operations.
