Water treatment systems utilize different types of gate valves to achieve fluid control based on the media characteristics and operating requirements. Commonly used gate valves in water treatment are classified into the following categories based on the gate disc structure, stem type, actuation method, and sealing technology:
Rigid Wedge-Type: The gate disc is a one-piece wedge-shaped casting. While simple and robust, it requires extremely high machining accuracy and fit of the valve seat sealing surface angle, otherwise it can easily cause sticking or leakage under high temperatures or temperature fluctuations. It is commonly used in clean water applications with relatively stable temperature and pressure.
Elastic Wedge-Type: The gate disc has a central groove or is designed as a two-piece structure, offering a certain degree of elastic deformation. It can better compensate for minor deviations in the valve seat sealing surface caused by temperature fluctuations or manufacturing errors, resulting in more reliable sealing performance and a wider range of applications (e.g., in applications with large temperature fluctuations).
Parallel Single Disc: The gate is a single flat plate that relies on external force (usually downward pressure during the final closing stage) to press against the valve seats to achieve a seal. While its structure is simple, it requires high sealing force and is susceptible to wear.
Parallel Double Disc: The gate consists of two flat plates with a wedge mechanism (spring or cam) installed between them. During closing, the wedge forces the two gates outward, tightly fitting the valve seats. It offers excellent sealing performance, is insensitive to seat angle deviation, has relatively low opening and closing torque, and has a certain degree of automatic compensation capability for wear. It is widely used in water treatment, particularly in large-diameter pipelines and applications requiring reliable sealing.
Rising Stem Gate Valve: The stem nut is fixed to the valve cover or bracket. Turning the handwheel (or actuator) drives the stem nut, causing the valve stem (threaded connection) to move linearly upward and downward. Advantages: The valve stem’s raised and lowered position is intuitively visible, making it easy to determine the valve’s open or closed state. The valve stem threads are located outside the valve body, out of contact with the medium and less susceptible to corrosion or sticking. Maintenance and packing replacement are also simplified. Disadvantages: The opening height is large, requiring a large installation space (this should account for the fully raised valve stem height). Widely used in water treatment plants, particularly at ground level or in locations where operation is easily observable.
Non-rising-stem gate valve: Threads at the lower end of the valve stem engage the gate nut. Turning the handwheel (or actuator) rotates the valve stem, and the gate rises and falls along a guide groove driven by the stem threads (the stem only rotates, not rises or falls). Advantages: The valve stem maintains its height when open, requiring minimal installation space. This valve is particularly suitable for underground manholes or other locations with limited space. Disadvantages: The open or closed state cannot be directly determined from the valve stem position. The valve stem threads are exposed to the medium for extended periods, making them susceptible to corrosion and abrasion from solid particles, requiring high maintenance. Commonly used in clean water pipe networks and manholes with limited space.
Manual gate valve: Operated by a handwheel, handle, or gearbox. Simple in structure, economical and reliable, suitable for applications with low operating frequency and moderate operating torque (common for sizes below DN300).
Electric gate valve: Driven by an electric motor. Suitable for applications requiring remote control, frequent operation, or excessive operating torque (large diameter, high pressure). It is a key valve type for automated control in water treatment plants. However, its relatively long opening and closing times are important.
Pneumatic/hydraulic gate valve: The actuator is driven by compressed air or hydraulic oil. Suitable for explosion-proof environments or specific applications requiring rapid actuation (less common than electric gate valves).
Metal-sealed gate valve: Both the gate and seat are made of metal (such as stainless steel or alloy steel). They are resistant to high temperatures and high pressures and have excellent wear resistance. However, they require a high sealing pressure ratio to achieve zero leakage and are sensitive to particulate matter, which can easily scratch the sealing surface. They are primarily used for raw water, high-temperature water, or special operating conditions.
Elastomeric-sealed (soft-sealed) gate valve: The valve seat or disc is inlaid with an elastomeric material (such as EPDM, NBR rubber, PTFE, etc.). They are the most widely used in water treatment. Advantages: Excellent sealing performance (reaching bubble-proof seal), low opening and closing torque, a certain tolerance for tiny solid particles in the medium, and the ability to compensate for installation deviations. Disadvantages: Due to the temperature and chemical resistance of the elastic material, it is not suitable for extremely high temperatures or highly corrosive media. Common “resilient-seated gate valves” fall into this category, with a valve seat entirely covered in rubber.
Gate valves are key fluid control devices in water treatment systems. WEIZIDOM, drawing on years of experience and project-specific recommendations, can provide the following: wedge valves are suitable for stable operating conditions, parallel double-disc gate valves are resistant to impurity impact, and resilient-sealed valves achieve zero leakage for clear water. Rising-stem valves facilitate condition monitoring, while concealing-stem valves save installation space. Scientifically selecting a valve type requires matching the media characteristics with operational requirements to ensure reliable shutoff and long-term operation.
A: Gate valves are categorized by disc structure into wedge-type and parallel-type valves; by stem structure and movement, into rising-stem and non-rising-stem valves; by actuation method, into manual, electric, and pneumatic/hydraulic gate valves; and by sealing technology, into metal-sealed and resilient-sealed gate valves.
A: Resilient-sealed gate valves offer bubble-level sealing performance, low opening and closing torque, tolerance for fine particles, and compensation for installation misalignment. They are suitable for non-extreme environments such as clean water and are widely used in water treatment.
A: For high-temperature and high-pressure water treatment, hard-seal wedge-type gate valves or power station-specific gate valves are preferred. Made of stainless steel or chrome-molybdenum steel, they can withstand temperatures of 540°C and pressures of 320 MPa, ensuring a reliable seal.
A: Maintenance and care require monthly lubrication of the valve stem threads (using grease or graphite powder), regular inspection of packing leaks, and symmetrical tightening of the gland. The valve should be inspected every six months to prevent sticking. When not in use, any accumulated water should be drained and the valve stem should be protected.
