Question 1

What is a gate valve and when should it be used?

Accepted Answer

A gate valve uses a flat or wedge-shaped gate that moves perpendicular to the flow direction to open or close. When fully open, the gate is completely withdrawn from the flow path, providing minimal pressure drop and maximum flow capacity. Gate valves are designed for on-off service only and should never be used for throttling. They are ideal for pipelines requiring full bore flow with minimal turbulence, such as crude oil transmission lines, refined product pipelines, and raw water intake systems in Saudi Arabian oil fields and UAE desalination plants.

Question 2

What are API 600 gate valve pressure/temperature ratings?

Accepted Answer

Supreme Valves API 600 gate valves are available in Class 150, Class 300, Class 600, and Class 900 ratings for sizes from 2 inches to 48 inches. The Class 150 and 300 cast steel valves (WCB) are most common for general oil and gas service. For high-pressure Saudi Arabian gas pipelines and steam distribution systems, Class 600 forged steel valves (A105, F22) are specified. API 602 compact steel gate valves are available for smaller sizes up to 4 inches in Class 150-1500 ratings.

Question 3

What's the difference between WCB and CF8M gate valve materials?

Accepted Answer

WCB (ASTM A216 Grade WCB) is a carbon steel casting material suitable for general service up to 425°C with good strength and machinability. CF8M (ASTM A351 Grade CF8M) is a stainless steel casting (316 SS) offering superior corrosion resistance, especially against chlorides and sour service. For seawater cooling systems in GCC countries, CF8M or Nickel Aluminium Bronze (NAB) is preferred. WCB with FBE coating is used for buried pipeline service where corrosion protection is provided externally.

Question 4

How does a flexible wedge gate valve work in high-temperature steam?

Accepted Answer

A flexible wedge gate valve features a one-piece disc with a split stem connection that allows slight angular movement of the wedge seat faces. This flexibility compensates for thermal expansion and contraction during steam service, maintaining a tight seal throughout temperature cycles. The design prevents binding and ensures reliable shut-off in steam distribution lines up to 260°C. For superheated steam applications above 260°C, solid wedge design with hardfaced seats is recommended.

WCB Gate Valve Class 150