Gate Valve is the most widely used one among all types of valves. Gate Valve, whose disc or wedge moves vertically along the axis of the channel, has the same basic function of other valves, turning on or turning off channels. In the pipeline, it is used as a piece to connect and cut off the media inside. What is worthy to be noted is that an ordinary gate valve usually opens or close pipeline completely. In other words, it can’t be used as a controlling device to restrain the volume of the flow.

Gate valve can is designed to handle a wide range of situations: high temperature and high pressure or low temperature and low pressure. It also has the ability to deal with a handful of different media except those that are vicious, easy to precipitate or with granules.

Gate Valve has the following advantages:

1. small fluid resistance, safe and reliable;

2. small torque when turning it on or off;

3. it can be used in circular network pipelines where the medium flows in both directions. Namely, the flow direction of the medium is not restricted;

4. when it is fully open, gate vale’s sealing surface is less eroded than globe valve;

5. with a simple shape, it’s easy to cast and machining;

6. small face to face dimension.

Gate valves are widely used thanks to their many advantages mentioned above. Generally, the gate valve serves as the first choice to pick a cutting device for pipelines with DN≥50mm. And certain gate valves are still can be found even in some small size pipelines (such as DNV15 ~ 40mm).

Gate Valve also has its disadvantages:

1. relatively bigger space is required to install gate valves for their large size.

2. when open and close, abrasion occurs due to the relative friction between sealing surfaces;

3. gate valve’s two sea faces add difficulties to machining, grinding and maintenance.

4. long opening and closing time.

Gate Valves vary in structures. Generally, they differ from each other according to their seal components. Therefore, gate valves are usually divided into two types: parallel type and wedge type. What’s more, according to the structure of the stem, they also divided into rising stem and non-rising stem.

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The maintenance of valves is an important measure to ensure their long-term stable operation and extend their service life. Here are some key steps to note for valve maintenance:

1.Preservation and maintenance

a.Orderly storage: Valves should be stored in categories, with small valves placed on shelves and large valves neatly arranged on the ground to avoid disorderly stacking and damage caused by flange connection surfaces coming into contact with the ground.

b.Cleaning and Protection：

(1)Seal the inlet and outlet of the valve with wax paper or plastic sheets to prevent dirt from entering.

(2)Apply anti rust oil to the machined surface that can rust in the atmosphere for protection.

(3)Valves placed outdoors should be covered with oil felt or cloth to prevent dust and rain.

c.Regular inspection:

(1)For valves that are not used for a long time, asbestos packing should be removed to avoid chemical corrosion.

(2)The valves newly added to the warehouse should be checked for rainwater or dirt and wiped clean in a timely manner.

2.Usage and maintenance.

a.Keep clean: Regularly keep the valve clean and lubricate the transmission threads regularly.

b.Correct operation:

(1)The valve stem thread needs to be coated with lubricant (such as yellow dry oil, molybdenum disulfide, or graphite powder) to reduce wear.

(2)Valves that are not frequently opened or closed should also have their handwheel turned regularly to prevent the valve stem threads from biting.

(3)Outdoor valves require protective sleeves for the valve stem to prevent rain, snow, dust, and rust.

c.Inspection and maintenance

(1).Regularly check the sealing performance and operational flexibility of the valve to ensure no leakage or blockage.

(2).Check whether the connecting components (such as bolts and nuts) are loose or damaged, and tighten or replace them in a timely manner.

d.Packing maintenance

(1).Packing is the key to valve sealing and requires regular inspection and timely replacement of failed packing.

(2).After the valve is installed in the pipeline, if there is leakage, the packing gland nut should be tightened, but it should not be tightened all at once to avoid losing elasticity.

3.Lubrication and grease injection

a.grease injection volume and pressure:

(1)When injecting grease, the amount should be accurately calculated based on the sealing capacity of the valve type to avoid excessive or insufficient grease.

(2)The grease injection pressure needs to be lost. If it is too high, it may block the grease injection port, and if it is too low, the sealing effect will be poor.

b.Injection timing:

(1)During the use of valves, due to the loss and drying of lubricating grease, regular replenishment is required.

(2)Especially during the process of valve opening and closing, the lubrication condition of the transmission parts should be checked in a timely manner.

4.Special maintenance for different valves

a.Gate valve

(1)When fully open, the operating pressure loss of the medium is minimized, making it suitable for situations that do not require frequent opening and closing.

(2)Not suitable for use as a regulator or throttle to avoid damaging the sealing surface.

b.Globe valve

(1)After opening, there is no contact between the valve seat and the sealing surface of the valve disc, and the wear of the sealing surface is small.

(2)Attention should be paid to the flow direction of the medium during installation, generally from bottom to top.

c.ball valve

(1)The structure is simple, the operation is convenient, and it is suitable for situations with fast opening and closing.

(2)When in use, only fully open or fully closed, not used to regulate flow.

According to their structural form, cast iron gate valves can be divided into rising stem gate valves and hidden stem gate valves. Further research is needed on the specific structural characteristics and application scenarios.

The opening and closing component of a gate valve is the gate plate, and the direction of movement of the gate plate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and fully closed, and cannot be adjusted or throttled. The gate valve has two sealing surfaces, and the most commonly used mode gate valve has two sealing surfaces that form a wedge shape. The wedge angle varies with the valve parameters, usually 50 degrees, and 2 ° 52 'when the medium temperature is not high.

The gate of a wedge gate valve can be made as a whole, called a rigid gate; It can also be made into a gate that can produce slight deformation to improve its processability and compensate for the deviation of the sealing surface angle during the processing. This type of gate is called an elastic gate.

When the gate valve is closed, the sealing surface can be sealed solely by the medium pressure, that is, the sealing surface of the gate is pressed against the valve seat on the other side by the medium pressure to ensure the sealing surface is sealed, which is called self sealing.

Most gate valves use forced sealing, which means that when the valve is closed, external force must be used to forcefully press the gate plate against the valve seat to ensure the sealing performance of the sealing surface.
The gate of a gate valve that moves in a straight line with the valve stem is called a rising stem gate valve (also known as a lift stem gate valve). Usually, there are trapezoidal threads on the lifting rod, which convert rotational motion into linear motion through the nut at the top of the valve and the guide groove on the valve body, that is, convert operating torque into operating thrust.

Some valves have valve stem nuts installed on the gate plate, and the handwheel rotates to drive the valve stem to rotate, thereby lifting the gate plate. This type of valve is called a rotary stem gate valve or a concealed stem gate valve.