A gate valve is a valve that moves up and down in a straight line along the valve seat (sealing surface), with the opening and shutting part (gate) being powered by the valve stem.

1. What a gate valve does

A type of shut-off valve called a gate valve is used to connect or disconnect the medium in a pipeline. The gate valve has many different uses. The commonly used gate valves made in China have the following performance characteristics: nominal pressure PN1760, nominal size DN151800, and working temperature t610°C.

2. Features of a gate valve

① Benefits of gate valve

A. There is little fluid resistance. The medium does not change its flow direction when it passes through the gate valve since the medium channel inside the gate valve body is straight through, which reduces fluid resistance.

B. There is little resistance during opening and shutting. Comparatively speaking to the globe valve, the opening and closing of the gate valve is less labor-saving since the direction of the gate movement is perpendicular to the flow direction.

C. The medium’s flow direction is unrestricted. Since the medium can flow in any direction from either side of the gate valve, it can serve its intended purpose and is more suited for pipelines where the media’s flow direction may change.

D. It is a shorter structure. The globe valve’s structural length is shorter than that of the gate valve because the globe valve’s disc is positioned horizontally in the valve body while the gate valve’s gate valve is vertically positioned within the valve body.

E. Effective sealing capabilities. The sealing surface is less degraded when fully open.

② Drawbacks of gate valve

A. It’s simple to harm the sealing surface. The sealing surface of the gate and the valve seat experience relative friction when they open and close, which is easily damaged and reduces the sealing performance and lifespan.

B. The height is substantial and the opening and closing times are lengthy. The stroke of the gate plate is large, a certain amount of space is needed for opening, and the exterior dimension is high because the gate valve must be fully opened or fully closed while opening and closing.

Complex structure, letter C. In comparison to the globe valve, there are more parts, it is more complex to manufacture and maintain, and it costs more.

3. The gate valve’s construction

The valve body, bonnet or bracket, valve stem, valve stem nut, gate plate, valve seat, packing circle, sealing packing, packing gland, and transmission device make up the majority of the gate valve.

A bypass valve (stop valve) can be linked in parallel on the inlet and outlet pipelines next to large-diameter or high-pressure gate valves in order to lessen the opening and shutting torque. Open the bypass valve before opening the gate valve when utilizing to equalize the pressure on either side of the gate. The bypass valve’s nominal diameter is DN32 or more.

① The valve body, which forms the pressure-bearing portion of the medium flow channel and is the main body of the gate valve, is attached directly to the pipeline or (equipment). It is crucial for putting the valve seat in place, mounting the valve cover, and joining the pipeline. The height of the inner valve chamber is relatively big because the disc-shaped gate, which is vertical and moves up and down, needs to fit within the valve body. The nominal pressure largely determines how the valve body’s cross-section is shaped. For instance, the low-pressure gate valve’s valve body could be flattened to shorten its structural length.

In the valve body, the majority of the medium passageways have a circular cross-section. Shrinkage is a technique that can also be used on gate valves with large diameters to lower the size of the gate, the opening and closing force, and the torque. When shrinkage is employed, the fluid resistance in the valve increases, causing a pressure drop and rising energy costs. The channel shrinkage ratio should therefore not be excessive. The busbar of the narrowing channel’s inclination angle to the center line should not be more than 12°, and the ratio of the valve seat channel’s diameter to its nominal diameter should typically be between 0.8 and 0.95.

The connection between the valve body and the pipeline, as well as the valve body and the bonnet, is determined by the gate valve body’s structure. Cast, forged, forged welding, cast welding, and tube plate welding are all options for valve body roughness. For diameters under DN50, casting valve bodies are typically used, forged valve bodies are typically used, cast-welded valves are typically used for integral castings that fall short of specifications, and cast-welded structures can also be used. Forged-welded valve bodies are typically used for valves that have problems with the overall forging process.

②The valve cover has a stuffing box on it and is attached to the valve body, making it the major pressure-bearing component of the pressure chamber. The valve cover is equipped with a machine surface supporting components, like stem nuts or transmission mechanisms, for medium and small diameter valves.

③The stem nut or other components of the transmission device are supported by the bracket, which is attached to the bonnet.

④The valve stem is directly connected with the stem nut or the transmission device. The polished rod part and the packing form a sealing pair, which can transmit torque and play the role of opening and closing the gate. According to the position of the thread on the valve stem, the stem gate valve and the hidden stem gate valve are distinguished.

A. A rising stem gate valve is one whose transmission thread is located outside the body cavity and whose valve stem can move up and down. The stem nut on the bracket or bonnet must be rotated in order to lift the valve stem. The stem thread and the stem nut are not in contact with the medium and are therefore unaffected by the medium’s temperature and corrosion, which makes them popular. The stem nut can only rotate without up and down displacement, which is advantageous for the lubrication of the valve stem. The gate opening is also clear.

B. Dark stem gate valves have a transmission thread that is located inside the body cavity and a rotating valve stem. Rotating the valve stem drives the stem nut onto the gate plate, causing the valve stem to rise and fall. The valve stem can only spin, not move up or down. The valve is difficult to manage because of its tiny height and difficult opening and closing stroke. Indicators must be included. It is suited for non-corrosive medium and situations with unfavorable climatic conditions because the temperature and corrosion of the medium effect the contact between the valve stem thread and stem nut and the medium.

⑤The part of the kinematic pair that can be directly attached to the transmission device and transmit torque is made up of the valve stem nut and the valve stem thread group.

⑥The valve stem or stem nut can be directly supplied with electric power, air force, hydraulic force, and labor via the transmission device. Long-distance driving in power plants frequently makes use of handwheels, valve covers, transmission components, connecting shafts, and universal couplings.

⑦valve seat Rolling, welding, threaded connections, and other techniques are used to secure the valve seat to the valve body so that it can seal with the gate.

⑧Depending on the needs of the customer, the sealing ring can be surfaced directly on the valve body to create a sealing surface. The sealing surface can also be treated directly on the valve body for valves made of materials like cast iron, austenitic stainless steel, and copper alloy. In order to prevent the medium from leaking along the valve stem, packing is placed inside the stuffing box (stuffing box).