Gate Valve Types: Wedge, Parallel Slide, and Slab Gate Valve — Complete Guide
Quick Answer: Gate valves are primarily classified into three main types based on disc design: wedge gate valves (solid, flexible, or split wedge), parallel slide gate valves, and slab gate valves (through-conduit). Each type serves specific pressure, temperature, and media requirements in industrial piping systems.
Gate Valve Comparison Table
| Feature | Wedge Gate Valve | Parallel Slide Gate Valve | Slab Gate Valve |
|---|---|---|---|
| Disc Design | Single wedge or split wedge | Two parallel discs | Single flat slab |
| Sealing | Metal-to-metal wedge action | Spring-loaded or pressure-energized | Floating seat design |
| Pressure Range | Up to 2500 LB (Class 150-2500) | Up to 1500 LB | Up to 2500 LB, API 6A |
| Temperature Range | -29°C to 540°C | -29°C to 400°C | -46°C to 250°C |
| Typical Standard | API 600, API 602, BS 1414 | API 600, MSS SP-80 | API 6A, API 6D |
| Best For | General isolation, high-temp steam | Frequent operation, dirty media | Pipeline, wellhead, critical service |
1. Wedge Gate Valve
The wedge gate valve is the most common type and derives its name from the wedge-shaped gate that seals against two angled seats. Available in three sub-types:
- Solid Wedge: Single-piece gate, simple and strong. Best for moderate temperatures and non-corrosive services. Performs well in turbulent flow conditions.
- Flexible Wedge: A cut around the perimeter allows the gate to flex under thermal expansion. Preferred for high-temperature steam services where thermal binding is a concern.
- Split Wedge: Two-piece gate that self-aligns to the seats. Used for corrosive media or when seat alignment cannot be guaranteed.
Wedge gate valves are widely used in oil refineries, petrochemical plants, power stations, and water treatment facilities. They are available in bolted bonnet, pressure seal, and welded bonnet designs. Browse our full range of wedge gate valves and other gate valve products.
2. Parallel Slide Gate Valve
Parallel slide gate valves use two parallel discs that are pressed against the seats by springs or line pressure. Unlike wedge valves, they do not rely on a wedging action for sealing. Key advantages include:
- Bi-directional sealing: Seals equally well in both flow directions
- Self-cleaning action: Discs slide across seats, wiping debris away
- Low operating torque: Requires less force to open and close
These valves are ideal for high-temperature steam services and applications where thermal cycling is frequent. They are commonly specified for power plant main steam and feedwater isolation.
3. Slab Gate Valve (Through-Conduit)
Slab gate valves, also known as through-conduit gate valves, use a flat slab that moves perpendicular to the flow path. When fully open, the bore is unobstructed — allowing pigging and flow scraping operations. This makes them essential in:
- Oil and gas pipeline transmission
- Wellhead and Christmas tree systems (API 6A)
- Subsea and offshore applications
- Hydrocarbon storage and transport
Slab gate valves typically comply with API 6A or API 6D standards and are available with floating or expandable seat designs. See our slab gate valve products for pipeline and wellhead applications.
Gate Valve Materials and Trim Selection
| Service Condition | Body Material | Trim Material | Seat Hardness |
|---|---|---|---|
| General service (water, air, oil) | WCB, WCC | 13Cr (410 SS) | 250 BHN |
| Sour service (NACE MR0175) | LCC, LC2 | 316 SS, F6NM | 200 BHN max |
| High-temperature steam | WC6, WC9 | Stellite-faced | 350 BHN min |
| Corrosive service | CF8M, CF3M | 316L, Alloy 20 | Varies |
| Cryogenic service | LCB, LCC | F304, F316 | 200 BHN |
Proper material selection is critical for gate valve performance and longevity. Incorrect trim selection can lead to galling, corrosion, or seat leakage within months of service. Contact our engineering team for material and trim recommendations for your specific application.
Gate Valve vs Globe Valve: Quick Comparison
Engineers often confuse gate valves with globe valves since both are common isolation valves. The key difference: gate valves are designed for fully open or fully closed service (isolation), while globe valves can handle throttling and flow regulation. See our globe valve products for flow control applications.
Frequently Asked Questions
Q: What is the difference between API 600 and API 602 gate valves?
A: API 600 covers bolted bonnet steel gate valves for petroleum and natural gas industries. API 602 covers compact, forged steel gate valves (typically smaller sizes, NPS 4 and under).
Q: Can a gate valve be used for throttling?
A: No. Gate valves should only be used in fully open or fully closed positions. Using them for throttling causes wire drawing of the seat and disc, leading to leakage and premature failure.
Q: How do I know if I need a rising stem or non-rising stem gate valve?
A: Rising stem valves provide visual indication of valve position and are preferred for above-ground installations. Non-rising stem valves are used where vertical space is limited, such as underground installations.
Q: What is the maximum pressure rating for a standard gate valve?
A: Standard gate valves are available from Class 150 (20 bar) to Class 2500 (420 bar). For higher pressures, API 6A slab gate valves can handle up to 20,000 psi (1,380 bar) for wellhead applications.
Q: How often should gate valves be exercised?
A: For emergency isolation valves, quarterly full-stroke operation is recommended. For valves in clean service, annual exercise is typically sufficient. Valves in dirty or scaling service may require more frequent operation.
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