What is a Ductile Iron Gate valve?
A Ductile Iron Gate valve is a type of gate valve which is made using ductile iron material. Ductile iron is also known as nodular cast iron or ductile cast iron. Ductile Iron Gate valves have high fatigue and impact strength due to use of ductile iron material. Ductile Iron Gate valves are more ductile due to the use of “ductile iron” material. This ductility makes the ductile Iron Gate valve have excellent ductility which helps to resist impact and bending. Ductile Iron Gate valve manufacturers design these valves for use in high temperatures such as 730 oC. These valves are also meant for use in high-pressure applications of around 640 psi. Ductile Iron Gate valves have excellent corrosion resistance. One of the main challenges of ductile Iron Gate valves is that they are a bit expensive relative to other types of gate valves such as cast iron gate valves. The high cost is due to its complex chemical makeup.
Figure: Ductile Iron Gate valve.
Components and construction of a ductile Iron Gate valve
Ductile Iron Gate valves are made of ductile iron material. Ductile Iron Gate valves are connected to the pipeline using bolts, threads, or welding. The ductile material is used to make the body, gate the bonnet of the valve. The body and bonnet are used to protect the internal components of the valve and act as the main pressure barrier. Other parts of the ductile Iron Gate valve such as the stem can be made of different materials such as stainless steel and bronze while the seats can be metallic or soft materials. Metallic seats are made of metallic materials like steel and bronze while soft seats are made of plastic or rubber materials. The material used to make the seat in a ductile Iron Gate valve determines the application of the valve. Valves made of soft seats are not recommended for use in high temperatures since the seats can be damaged. In a ductile Iron Gate valve the gate is connected to the handwheel through the stem. The bonnet is placed on top of the valve body and the two are connected using bolts or screws, pressure seal, and or union connection. The bolts connection is used when the application needs high pressure, unlike the screw connection. The union connection is preferred where the ductile Iron Gate valve needs to be inspected and cleaned. The pressure seal bonnet connection is preferred where the ductile Iron Gate valve is meant for high-pressure application.
Figure: Construction and components of a ductile Iron Gate valve.
How does a ductile Iron Gate valve work?
A ductile Iron Gate valve works by raising or lowering a gate to close or open fluid flow. The gate is connected to the actuator or handwheel via the stem. Ductile Iron Gate valve manufacturer design the stem with threads. When the handwheel is rotated, it rotates the stem which makes the stem move straight up or down. Since the stem is connected to the gate, when the stem moves down, it moves together with the gate. As such, to open a ductile Iron Gate valve, the handwheel is turned in the anticlockwise direction several times. This rotation of the handwheel makes the stem rotate in the same direction. Rotation of the stem makes it move upwards together with the gate. When the gate moves upwards it leaves the valve open which allows fluid to flow through the valve. To close a ductile Iron Gate valve, the handwheel is rotated in the clockwise direction. This makes the stem rotate in the same direction as it moves linearly downwards. The movement of the stem downwards makes the gate also move downwards which blocks fluid flow through the valve. The Manual ductile Iron Gate valve is operated using the handwheel while the automatic one is operated using actuators.
Figure: Working of a ductile Iron Gate valve.
Types of ductile Iron Gate valve
Parallel slide ductile Iron Gate valve
This is a ductile Iron Gate valve that is made with a parallel-faced gate for opening and closing fluid flow. The closing gate can have one or two discs that have a spreading mechanism between them. The gate is pressed against the seat by using force controlled by fluid pressure that acts on a floating seat or floating disc. Ductile Iron Gate valve manufacturers make the gate slide across the seat which makes these seats to be able to handle fluids carrying solid particles. Other Parallel slide ductile Iron Gate valves have springs meant to keep the downstream and upstream seats in sliding contact which improves seat load at low fluid pressure. Parallel slide ductile Iron Gate valve has low operating torque and low maintenance cost. However, this valve has the advantage of slight pressure loss across the valve.
Figure: Parallel slide ductile Iron Gate valve.
Through conduit ductile Iron Gate valve
This is a ductile Iron Gate valve made as one unit with bore-sized ports. Ductile Iron Gate valve manufacturers make these valves such that when the valve is opened, the bore-sized hole aligns with two seat rings creating smooth fluid flow at minimal turbulence. As such, through conduit ductile Iron Gate valve has minimal pressure loss and is suitable for transporting natural gas and crude oil over long distance. The seats of a through conduit ductile Iron Gate valve should remain clean although the gate cavity can have foreign materials. As such, ductile Iron Gate valve manufacturers ensure the valve has a built-in plug used for removing accumulated dirt.
Figure: Through conduit ductile Iron gate valve.
Knife ductile Iron Gate valve
This is a type of ductile Iron Gate valve with a specially designed gate for handling fluids with suspended particles. As such, ductile Iron Gate valve manufacturers design these valves so that they can effectively control flow even in slurry, corrosive, viscous and abrasive media. The ability of the valve to handle such media is due to the knife-edged gate which can cut through solid materials. This type of ductile Iron Gate valve is designed with a short face length relative to other gate valves. As a result, knife Gate valve has lightweight relative to other gate valves. These valves are used in applications such as pulp and paper, metals, mining, petrochemicals, chemicals, thermal power plants, and steel plants among others.
Figure: Knife ductile Iron Gate valve.
Wedge Ductile Iron Gate valve
This is a ductile Iron Gate valve that uses a wedge-shaped gate. Ductile Iron Gate valve manufacturers design these valves with wedge gates to help enhance the high seating load. With a high seating load, these valves can seal against high and low fluid pressure. The extent of seat tightness that is achieved using this type of ductile Iron Gate valve is higher than that in the parallel slide gate valve. There are three designs of wedge gates which include solid wedge gate, flexible wedge gate, and split wedge gate.
Figure: Wedge ductile Iron Gate valve.
Rising stem and non-rising stem ductile Iron Gate valve
As the name suggests, the rising stem ductile Iron Gate valve manufacturers design it so that the valve operator can see the movement of the stem when the valve is being closed or opened. The rising stem ductile Iron Gate valve stem rises upwards when the valve is being opened and it moves downwards when the valve is being closed. This helps the valve operator to easily know when he/she is closing or opening fluid flow. This helps to prevent damage to the valve by the valve operator. A rising stem valve takes a lot of space and is thus installed where space is not limited. Non-rising stem ductile Iron Gate valve is a type of valve in which the stem does not rise or move downwards like in the rising stem type. In this type of ductile Iron Gate valve, the gate travels along the valve stem when the handwheel is rotated. Non-rising stem ductile Iron Gate valve does not take up a lot of space compared to the rising stem version which makes it suitable for use where space is limited. Non-rising stem version has a closing and opening indicator to help know when the valve is being rotated for closure or opening.
Figure: Rising and non-rising stem ductile Iron Gate valve.
Applications of ductile Iron Gate valves
Advantages of Ductile Iron Gate valves
Disadvantages of ductile Iron Gate valves
Troubleshooting ductile Iron Gate valves
High operating torque
The Ductile Iron Gate valve does not open
Valve not opening completely
The ductile Iron Gate valve does not close completely
Leakage through bolts and nuts connection
Leakage through the seats
Leakage through stem packing
Summary
A Ductile Iron Gate valve is a type of gate valve that is made of ductile iron material. Ductile iron material is a strong metallic material compared to cast iron material in terms of strength and impact resistance. Ductile Iron Gate valve manufacturers design these valves for use in on and off applications where there is high temperature and high pressure. Ductile Iron Gate valves are more expensive relative to other gate valves due to their complex chemical makeup. Ductile Iron Gate valves use a gate to close and open fluid flow. The gate is raised or lowered to open or close fluid flow respectively. Ductile Iron Gate valves are operated manually using a handwheel or they are automated using actuators. Ductile Iron Gate valve manufacturers produce different types of ductile Iron Gate valves such as rising and non-rising stem, wedge gate, through conduit, parallel slide gate, and knife gate valves among others. Ductile Iron Gate valves are used in different applications such as mining, chemicals, paper and pulp, foods and beverages, pharmaceuticals, water supply, steam power plants, natural liquid gas, and crude oil among others. Advantages of using Ductile Iron Gate valves are versatility, durability, bi-directional fluid flow, low-pressure loss, zero leakage and high strength among others.
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