API 600 Gate Valve

What is API 600 gate valve?

API 600 gate valve is an on and off type of gate valve used. This valve is used for opening and closing the flow of fluid in a pipeline. API gate valve is a bidirectional flow valve. This means that the flow of fluid through the valve can take place in either direction. API gate valve manufacturers design the valve such that one end can act as the inlet enabling the fluid to enter in any direction. An API 600 gate valve is characterized by a large diameter size (between 2 and 80 inches), a cast steel body, heavy wall thickness, and a flat sealing surface between the gate and the seat. API 600 gate valves are mostly used in the petroleum and gas industry, especially in applications where the minimum pressure drop is desired for smooth operation. This kind of valve is not used for the regulation of flow rate. The term “API 600” represents an American standard for the design of gate valves meant for petroleum industry applications. This standard specifies the design criteria for cast steel (carbon and alloy steel) gate valves and also dictates the geometry and sizes of the gate valve in terms of body and bonnet thicknesses, dimensions, joint, yoke, and bolting, and auxiliary connections. 

Figure 1: API 600 gate valve

Components of API 600 gate valve

The API 600 is an assembly of several components which include the following:

Figure: Diagram showing the parts and assembly of a standard API 600 gate valve

Valve body 

This is the part of the API 600 gate valve which is used to house internal parts of the valve. The valve body also acts as the main pressure barrier of an API 600 gate. To make the body withstand high pressure and high temperatures it is made of strong metallic materials such as stainless steel and carbon steel. 

Gate

The gate is part of an API 600 gate valve responsible for effective sealing. API gate valve manufacturer modify the gate to suit a variety of applications. Some of the most common types of gates used in API 600 gate valves include slide gates, wedge gates, knife gates, and parallel gates. 

Bonnet

Bonnet is the part of an API 600 gate valve that houses the internal components of a gate valve. It contains the moving components and is attached to the valve’s body using screws or bolts to create a tight seal.

Stem  

This is the part of an API 600 gate valve that serves to raise and lower the gate. This role is achieved by turning the threaded stem manually or by actuation. API 600 gate valve manufacturers design the stem such that it can be rising or non-rising type depending on the threaded stem end. 

Seat 

The seat is the component of an API 600 gate valve which is used to support the gate and prevent fluid leakage. API 600 gate valve’s manufacturer either provides the seats integrated within the body of the gate valve or as a separate seat ring design. The seat rings that are already attached to the gate valve must be constructed using the same material as the valve body.

Design variation of API 600 gate valve

 The design of the API 600 gate valve may vary depending on the bonnet and end connections, type of wedge, stem, or valve operation. For example, the bonnet can have either a bolted connection or a pressure seal connection. The gate also provides a great area for API 600 gate valve design variation as gates can be designed in different configurations such as a solid wedge gate, Flexible wedge gate, parallel-slide wedge gate, and split-wedge gate. A solid wedge gate is manufactured from a piece of steel. The design of a flexible wedge is such that it can adjust to the changes in the angle between seats. A split wedge features a two-disc construction to help with the wedge alignment on the valve seats. As earlier indicated, the stem of an API 600 gate valve can be designed as either rising or non-rising type, while valve operation can be manual, gear, or pneumatic/ electric/ hydraulic actuation.

How does the API 600 gate valve work? 

The API 600 gate valves are handwheel-operated or they are automated. API 600 gate valves work by inserting a gate or disc into the fluid’s flow path through a threaded stem. The stem links the handwheel and the gate valve. When the handwheel is rotated in the anti-clockwise direction, the vertical movement of the stem causes the gate to open. Conversely, rotation of the handwheel in the clockwise direction causes the gate to move downwards, and thus the API 600 gate valve to shuts off. API 600 gate valve manufacturers design these valves for use in on and off applications but not for throttling. When the valve is fully open, the gate valve is free from obstruction in the flow path and, therefore, it experiences a very slight drop in the flow pressure. Operation of the gate valve while partially open results in a huge loss of pressure. The gate valve must be used strictly with less corrosive fluids and fluids that do not leave sediments because they can prevent the gate from closing fully. Also, API 600 gate valve cannot be used for flow regulation because the flow of fluid through a partly closed gate can generate a lot of vibration which may cause the valve to move from its designed position. Additionally, the valve seats and the gate can be heavily eroded when the valve is partially open.

Types of API 600 gate valves

The API 600 gate valve manufacturers offer a few different types to choose from. Such types include the following.

API 600 gate valve with knife gate

This is a special type of API 600 gate valve that is used for highly viscous fluids. The valve is designed to eliminate the water hammer effect by opening and closing at a very low speed. API 600 gate valve with knife gate can be constructed from a range of materials including ductile iron and stainless steel. This type of API 600 gate valve is available in a variety of sizes ranging between 2 inches and 24 inches and it also has several variants including the soft-seat, the metal seat, and bonneted types. One major limitation of an API 600 knife gate valve is that it has a low-pressure rating.

Figure: Knife gate API 600 gate valves with knife gate.

Rising and non-rising stem API 600 gate valve

In a rising stem type of API 600 gate valve, the stem rises above the handwheel when the valve is opened. On the other hand, the non-rising stem type consists of a stem that does not rise above the handwheel when the valve is opened. The rising stem API 600 gate valve makes it easy for the valve operator to know when it is being opened or being closed by checking the raising or lowering of the stem. The non-rising API 600 gate valve manufacturers produce the valve with closing and opening indicators. 

Figure: Rising and non-rising stem API 600 gate valves.

API gate valve with expanding gate

This is the type of API 600 gate valve designed with a wedge gate and segment. It is best suited for highly abrasive liquids under high temperatures and pressure. In an API 600 gate valve with expanding gate, positive sealing is achieved through mechanical expansion of the gate and segment against the seal. Expansion of the gate and segment occurs when the stem exerts a thrust on them. In either closed or open positions, the expansion creates a tight seal against the upward stream and downstream sides. This unique design helps to prevent wear of the seats and gate.

Figure 5: API 600 gate valve with expanding gate.

Applications of API 600 gate valve

API 600 gate valves are used in a wide variety of applications which include the following:

• Used in the transportation of petroleum.
• They are used in oil and gas refinery industries. 
• These valves are used in petrochemical applications.
• Chemical industries
• Metallurgy applications. 
• Steam power generation plants. 

Advantages of API 600 gate valve 

• Easy to assemble, repair, and maintain.
• They result in a modest pressure drop in the pipeline.
• Can work effectively with viscous fluids.
• Versatile. 
• They are durable. 
• Fire-safe.
• Zero fluid leakage.
• Tolerate high pressure and temperature.

Disadvantages of API 600 gate valve 

• Tedious to open and close
• Poor throttling characteristics
• Prone to the valve and seat erosion

Troubleshooting API 600 gate valve 

The operating nut not turning in either direction

• Interference between valve box and the operating key. Inspect for interference by locking down the valve box to see if it is close to the operating nut; reposition.
• Uneven tightening of the stuffing box bolts and nuts during assembly. Loosen and evenly retighten the stuffing box bolt and nuts.
• Corrosion may have taken place between the stuffing box and stem. Inspect; clean or replace both the stuffing box and stem if necessary; apply operation or gritty backfill. 
• Wedging of debris under the gate. Remove the bonnet and clean the debris.

When closing the API 600 gate valve, you don’t get the right number of turns

• Accumulation of debris in the seating area. Create a flow through the valve and exercise the valve to get rid of debris.

The operating nut does not stop turning even after the right number of turns

• The operating nut may have been subjected to excessive torque. Inspect the stem and step nut; Replace the nut if necessary. 
• The valve has a bevel or sour gear to help during operation. Inspect to find out if the API 600 gate valve was installed with a gear. 

Leakage between the body and bonnet flange

• Damaged or pinched O-ring or gasket. Remove the bonnet and replace the gasket.
• Cracked/broken body or bonnet flange. Inspect and replace the body or bonnet as necessary. 
• Loosen bonnet bolts and nuts. Tighten the bonnet bolts and nuts.

Fluid leaking from the stuffing box area

• Stuffing box packing and stem O-ring are worn out. Replace packing or stuffing box or O-ring as necessary. 

Leakage from the seat

• Damaged seats. Replace the seats.
• Foreign materials are stuck under the gate. Remove the foreign materials.

Summary 

An API 600 gate valve is an on-off bidirectional valve. They are constructed to the standards of the American Petroleum Institute (API 600), mainly through the casting method using steel material. The casting method is preferred as guarantees zero fluid leakage. These valves can be operated manually or using hydraulic, pneumatic, or electric actuators. API 600 gate valve manufacturers design these valves with extra-large diameters, heavy wall thickness, and a sealing surface between the gate and the seat. The valves are widely used in the petroleum and gas industries because they are fire-safe and they provide a minimal drop in fluid flow pressure. These valves are also used for the transfer of high pressure and high-temperature fluids in heavy-duty steam industries and petrochemical and chemical industries. The manufacturers of API 600 gate valves avail several different types in the market including API 600 gate valves with knife gate, rising and non-rising stem API 600 gate valves, and API 600 gate valves with expanding gate among others. An API 600 gate valve offers numerous advantages in its applications including versatility, durability, zero leakage, high strength, fire-safe, and low-pressure drop. However, API 600 gate valves are unsuitable for throttling applications and operate slowly.