Gate valves ? open and close flows in demanding applications
Gate valves regulate flow by means of a plate or flap that is raised or lowered over an opening in the pipe. Vimab mainly works with wedge gate valves, a type of gate valve with a wedge at the bottom that makes the flap seal tightly against the seat. This type of valve is suitable for shutting off high pressure and high temperature flows.
In a gate valve, the flow is regulated by a plate or flap that slides into place, top to bottom, over an opening. It seals by a wedge or slide at the bottom of the flap resting against its seat. The valve type is used for shut-off. The advantage is that it has a straight flow path and thus allows maximum flow when fully open. It is operated by a knob or actuator.
A slide valve should only be used when it is fully closed or fully open. If it is left partially open during operation, the valve may be damaged.
The most common types of gate valves are wedge gate valves and gate valves. In a wedge gate valve, the plate is wedge-shaped at the bottom, which allows it to press firmly against the sealing element and prevents leakage. In a gate valve, the seal is missing a wedge, which means it does not seal as well. Gate valves are therefore used in low pressure applications, such as water and sewage.
The wedge gate valve, on the other hand, can handle high pressures and high temperatures. A steam flow with a temperature just above 500 degrees and a pressure of 100 bar, for example, is not an unusual application for a wedge gate valve. The valve is tight in both directions. It is often used for different types of applications in the power industry.
Another type is the parallel slot valve. Instead of a wedge, this has a round seal that seals against one seat in the inflow and one in the outflow to the valve. The advantage of this type is that it opens and closes very quickly and seals very well. It is widely used in the oil and gas industry.
High pressure
If a wedge gate valve is operating under very high pressure, you may need to reduce the pressure to open it. Otherwise the flap will be too tight against the valve body. To reduce the pressure, there is often a bypass valve, a small pipe with a valve that directs part of the flow past the wedge, thus reducing the pressure.
In terms of size, wedge gate valves start at 25 mm and can be virtually any size.
Wedge gate valves should not be used in applications with particles in the media, as the particles can get trapped under the wedge and cause leakage.
It is important that the flap slides easily against the valve body. To minimise friction, there are many different materials to choose from for both the clapper and the valve body, such as stainless steel, cast iron or ductile iron. As different materials have different properties at different pressures, temperatures and in different media, material selection can be a delicate task. Here, you need to consult the manufacturer to get a combination of properties that works.
Regular maintenance
The wedge gate valve needs to be exercised from time to time so that the wedge does not get stuck. In addition, the threaded spindle needs to be lubricated and care should be taken to ensure that no debris is trapped in the spindle.
If the valve leaks, it is necessary to grind the wedge and seat surface. Valves with flanged mounting can be disassembled and transported to Vimab for refurbishment. In the case of welded mounting, the valve is renovated on site with portable equipment. There are a large number of makes of wedge gate valves. For the most demanding applications, Vimab recommends valves from KSB, Persta and Sempell.
Click here to see which wedge gate valves are currently in stock. http://ventillager.vimab.se/