Principle of operation and types of steel wedge gate valves
Gate valves with a steel wedge are the most common design of shut-off and control valves and are widely used due to their simplicity and strength.
Classification and design features
There are the following types of steel gate valves ZKS:
- With a solid wedge;
- With a flexible wedge;
- With an all-welded body;
- With a cast body.
The steel gate valve with a solid wedge can be installed in any position – vertical or horizontal, besides it is suitable for almost all liquids. It can be used for both laminar and turbulent flow of the working medium. This type of gate valves are used, as a rule, at moderate and low pressures and temperatures, since their opening / closing under significant loads on the wedge is very laborious.
The flexible wedge is a one-piece steel disc having a cut along the entire perimeter. These incisions vary in size, shape, and depth. For example, a shallow, narrow cut along the perimeter of the wedge is characterized by reduced flexibility, but retains the strength of the valve. On the contrary, a deeper and wider incision along the entire perimeter of the wedge increases flexibility, but reduces the strength of the reinforcement unit in question. This design improves the alignment of the seats and provides better tightness. The disadvantage of flexible valves is that the fluid pumped in the pipeline tends to accumulate in the grooves of the disc, which can cause corrosion and, ultimately, reduce the durability of the valve.
The production technology of the housing depends on its complexity and requirements for operating pressure values: all-welded housings are designed for less intensive operating conditions than those made of steel casting.
Operational problems and solutions
In the process of pumping heated liquids at high speeds, as well as with a complex flow configuration, the transported medium is heated. This process is accompanied by the corresponding heating of the elements of the steel gate valve ZKS and its thermal expansion.
The presence of a steel wedge improves transportation performance, but cannot compensate for changes in the alignment of the seat due to the load on the pipe or its thermal expansion. Therefore, leaks are possible in valves with a solid wedge.
At particularly high temperatures (for example, in steam pipes), thermal wedge blocking may occur – a phenomenon in which the wedge gets stuck between the seats due to the expansion of the metal. Thermal expansion of the steam line causes distortion of the valve housings, which can lead to thermal jamming of a part of the pipeline. The flexible gate allows the valve to bend when the valve seat is compressed due to thermal expansion of the steam line and prevents such an emergency. In such cases, ZKS wedge steel gate valves with parallel spring-loaded discs are used. They are always in contact with the seats and provide a two-way seal.
The considered fittings are supplied according to the standards of TU 3741-094-07538145-99 and are calculated for a pressure range of 8 ...160 at, at temperatures from -60 to +4500C.