Lines with liquid and gaseous media are equipped with fittings in the form of shut-off equipment. The main task that the shut-off valve performs is to exclude the development of consequences in the event of a malfunction in the pipeline. In particular, deformation of highways, leakage, overflow of tanks. Devices are distinguished by response speed, durability, purpose, design and installation.
Shut-Off Valve Overview
A shut-off valve is installed for mechanical intervention in the free movement of liquids and gases through the pipeline. Stopping and freeing the line from the contents may be necessary due to leaks, depressurization, critical temperature or pressure drops. That is, the content is either completely driven out of the area, or its movement is blocked.
Devices are installed on the highway with gases, oil products, hot and cold water. These can be both household utilities, gas stations, and more industrial-scale structures or, for example, a city heating network.
There are disposable devices that are equipped with replaceable valves or must be completely replaced after operation. They are usually made from plastic. Reusable metal equipment is in great demand, as it is characterized by a long service life.
The device is based on a cast body, seat and cover. They are made of cast iron, galvanized steel, brass or polymer materials with high strength. The second element is designed to install the valve in the pipeline.
The shutter mechanism is presented as follows:
- a spring that drives the device (shutter and return);
- the stem responsible for the dynamics of the valve;
- absorbent pad to prevent condensation and leaks.
Electric or pneumatic actuators are responsible for the operation of the device. The valve is controlled in two ways: manually by a service operator or automatically. Without human intervention, operation occurs, as a rule, due to built-in sensors.
Principle of operation
The functionality of the cut-off device is to ensure that the contents of the pipeline stop their movement in a particular section or along the highway as a whole. The shut-off valve must shut off the flow promptly to minimize the risk of accidents. Here are a few reasons why they happen:
- violations of the technology of installation of pipelines, filters;
- non-compliance with safety requirements;
- end of service life of constituent components;
- various kinds of malfunctions;
- unexpected change in pressure or temperature within structures.
More practical are devices equipped with special sensors. This is due to automatic operation within a short period of time (from fractions of a second to minutes). The speed depends on the characteristics of the sensors and the quality of the equipment settings. The latter is the responsibility of trained service personnel.
Benefits of using a shut-off valve
Compared to valves, which initially performed the task of shutting off the movement of liquids and gases, valves are equipped with various kinds of automatic response mechanisms. It consists either in giving signals to operators, or directly blocking the free passage through the pipeline.
Today, instruments eliminate some of the shortcomings of prototype equipment. For example:
- due to mud flows and impurities, false alarms are excluded;
- tighter housings are better able to handle small pressure drops;
- response speed is minimized to a few seconds.
In addition, modern shut-off valves block movement in both directions. And in the designs there are additional elements. For example, silicone spring gaskets or shims.
Main types of devices
Pipe fittings differ in design and purpose. So, normally open devices are distinguished. They are responsible for dealing with flow in relation to movement. Normally closed shut-off devices are usually manually operated and open in an emergency to release the contents of a tank or line.
Separately, devices for water, oil products and gas are considered. The actuation can be realized by means of a mechanical load, a spring mechanism, a pneumatic or magnetic actuator. The devices are also different in terms of characteristics, connection methods, work in one or two directions. And depending on the materials used, manufacturers offer disposable and reusable shut-off valves.
The scope includes lines for liquid products flowing under high pressure. The body of the equipment is made of high-strength steel. The equipment has a piston hydraulic drive. The principle of operation is designed for incoming and distributing movement.
It is relevant to install a direct-acting shut-off valve in pipelines where there is a risk of leakage. The content in this case can be both clean and with impurities or impurities, bubble inclusions. At the same time, microparticles do not settle and do not accumulate in nodal joints. With regard to materials, the main criteria are impact resistance, wear resistance and protection against corrosion damage.
This device has two landing saddles and a plunger. Installation is allowed on pipelines with a large cross-section and high pressure drops. Double-seated shut-off valves are used in conditions of explosion hazard and active chemical reactions.
Such a locking device is installed on pipelines of relatively small diameter. The same applies to the amplitude of low pressure drops. The device has a single plunger that blocks the flow in one direction.
Shut-off valves of this type usually have a steam damper. It works within 1.5–10 seconds after a malfunction occurs. They are also characterized by durability and minimal susceptibility to deformation. For greater efficiency, devices are equipped with special controllers. They respond to changes in pressure, temperature, in the composition of the content, which must remain constant.
Shut-Off Valve Selection Guidelines
One of the main criteria is the speed of response of the device. Especially if the flow of liquid or gas occurs under high pressure. However, this is not the only option. The following is also important:
- Application area. Under this concept, flowing substances, their composition, and the degree of aggressiveness are hidden.
- Operating conditions include pressure and temperature.
- Throughput means the cross section of the line.
- Tightness. The reliability of the equipment depends on this indicator.
- Strength affects the durability of devices.
When choosing a shut-off valve, design features and action in one or two directions are taken into account. Regarding materials, not only the body is considered, but also gaskets, seals, seals.
Shut-off valve installation rules
The locking device is installed according to the manufacturer’s instructions. Self-installation is allowed only for water supply in the private sector. At the same time, warranty service and operation of the device may not correspond to the declared one due to the inexperience of the installer. Therefore, it would be right to entrust the work to specialists.
Mount gate valves in accessible places for maintenance or replacement of equipment. At the same time, areas in which stagnation and hydraulic “bags” can form should be excluded. There are also rules regarding the place:
- on vertical tanks, the upper bottom (or on the helmet tube) is considered;
- on horizontal ones — in the vapor phase zone (the upper generatrix of the cylinder).
An important point is the exclusion of freezing of the contents of the pipeline in the nodal connections. And the cross section of the branch pipe should be 1.25 times greater than the total analogous indicator relative to the valves installed on it.
Operations Expert Tips
Use of equipment to control the flow of the contents of the main is prohibited. Therefore, the valves must be in the fully open or closed position. During installation and maintenance work, it is important to exclude any clogging of the internal surface of the housing and the ingress of foreign objects. Operation is feasible only in strict observance of the instructions, another purpose is unacceptable.
Moments related to safety are prescribed in GOST 12.2063–2015 and 32569–2013, in the norms established by organizations such as Rostekhnadzor, the Customs Union, the Eurasian Commission. It is also important to use personal protective equipment. And only trained specialists with tolerances are allowed to service devices, replace them.
Shut-off valves are widely used due to their purpose. Thanks to these devices on highways, there is a chance to localize the consequences of malfunctions, correct them and put them back into operation. This is true both for utility networks and for large-scale pipelines.