WHAT IS A CAST-IRON GATE VALVE?

A Cast iron gate valve is a gate valve whose body and bonnet are made of cast iron material. Cast iron gate valves have been in use for hundreds of years. Cast iron gate valve has excellent resistance to temperature since it can withstand high temperatures of around 1150 oC. Cast iron gate valves also have high strength which makes them work at high pressure applications. However, the strength of the cast-iron gate valve will depend on the class of cast iron. Some cast-iron gate valves can withstand high pressures of around 500 psi. Cast iron gate valve as the name suggests, uses a gate to control fluid flow. Cast iron gate valves use the gate valve to either open or close fluid flow. These valves are bi-directional. The fluid flow and the gate in cast iron gate valves are perpendicular to each other. As such, the fluid flows in a straight line without taking direction in the cast iron gate valve which helps to reduce pressure loss. Cast iron gate valves have low fluid resistance as they are designed to enhance laminar flow (smooth flow/flow without turbulence). Cast iron gate valves are resistant to corrosion which makes them be used even in corrosive applications. These valves have high resistance to pressure and temperature. However, cast iron gate valves have a low resistance to impact damage since the material used to make them (cast iron) is of low ductility.

Components of cast iron gate valve

Valve body

The valve body in a cast-iron gate valve is the main component as it houses all internal parts of the valve. The valve body is always made very strong so that it can help the valve withstand high pressure and high temperature. In cast iron gate valves, the valve body is made of cast iron. With cast iron being a strong material and resistant to high temperatures, it helps cast iron gate valves to withstand thermal distortion.

Bonnet

Bonnet is a component of a cast-iron gate valve that is placed on top of the valve body to cover the internal components of the cast-iron gate valve. The bonnet is also made of cast iron material just like the valve body. The bonnet is connected to the valve body using screws or bolts and nuts. The screw-bonnet enhances tight-seal which is free from leakage and is used in medium to high-pressure applications. The bolted-bonnet connection enhances tight-seal free from leakage and is used in high-pressure applications. The bolted-bonnet connection tends to make the cast iron gate valve heavy relative to the screwed bonnet connection because of the bolts and nuts used.

Handwheel/actuator

The handwheel is a component used in manual cast iron gate valves. When the cast-iron gate valve is not manual, it is driven by an actuator. The handwheel/actuator is used to provide torque to another component called a stem. The stem transmits the torque to the gate to open/close the fluid flow. The actuators that can be used in the cast iron gate valve include hydraulic, pneumatic, and electric actuators.

Stem

The stem is the component in a cast-iron gate valve that is connected to the actuator/handwheel to provide force for opening/closing the gate. The stem is also made of strong material like cast iron or another material like brass or bronze. Cast iron gate valve manufacturers design the stem such that as it moves it cause movement effect on the gate to make it either close or open the valve for fluid flow.

Seat

The seat in a cast-iron gate valve is an interior component that makes contact with the gate to make a leakage free tight seal. In cast iron gate valves, the seat comes in contact with the gate when the valve is shut. In a cast-iron gate valve, the seat is integral to the valve body or employs a seat ring configuration. The seat ring configuration is pressed or threaded into the valve body. The pressed seat is used in higher pressure applications. The seat in the cast iron gate valve can be made of different materials other than cast iron. However, this material should be able to withstand temperatures meant for that application. Some of the reliable materials used in cast Iron Gate valve to make the seat include bronze and brass as well as PTFE. However, the PTFE cannot be used in high-temperature applications as it may be distorted by thermal heat.

Gate

The gate is the component in the cast iron gate valve which is used to close/open the fluid flow. The gate in a cast-iron gate valve is connected to the stem so that when the handwheel is rotated it can move linearly upwards or downwards to open or close the fluid flow respectively.

Trim

Trim is a collective name given to internal components of the cast-iron gate valve. These components include stem, valve body surface, bushing, gate sealing surface among others. These components work together to enhance effective operation of a cast-iron gate valve. Failure of one component affects the efficiency and life of the whole cast iron gate valve can be affected adversely.

Components of a cast iron gate valve

How does a cast-iron gate valve work?

Cast iron gate valves work by using a gate to enhance fluid control through a pipeline. The gate in a cast-iron gate valve is connected to the stem. The stem is connected to the actuator/handwheel. When the actuator/handwheel is rotated it rotates the stem which transmits force to the gate. The force helps the gate to move linearly upwards or downwards to open or close the cast iron gate valve respectively. Cast iron gate valves are bi-direction and thus they can be used in any direction of choice. The rotation of the handwheel in the anticlockwise direction helps to open the valve while the direction of the handwheel in the clockwise direction helps to close the valve. The fluid flows through the gate in a cast-iron gate valve in a perpendicular direction which helps to reduce fluid resistance

Working of a cast iron gate valve

Rising stem and non-rising stem cast iron gate valves

Rising stem cast iron gate valves are also known as outside screw and yoke (OS&Y). The OS&Y name is given because these valves have exposed screw that extends above the top of the bonnet. Rising stem cast iron gate valves are used in different applications among them water pump stations. The rising stem cast iron gate valves is advantageous in that it is very easy to tell when the valve is open or closed by looking at the screw or stem position. Non-rising stem cast iron gate valves are designed such that the stem can revolve in the bonnet. In this type of cast iron gate valve, the gate is lowered or raised by employing threads on the end of the stem. Cast iron gate valve manufacturers design non-rising stem valves with a gage or pointer to indicate when the valve is closed or open.

Parallel disc cast iron gate valve

These are cast iron gate valves that consist of two discs mounted apart against parallel seats using spring at the closure point. Parallel disc cast iron gate valve has one of the most famous valve known as cast iron knife gate valve with two parallel seats and a gate between the seats to enhance fluid shut-off. In some cases,

Parallel disc cast iron gate valve

solid-wedge cast Iron Gate valve

A solid wedge cast iron gate valve is a valve mostly used in applications such as air services, gas, and oil. These valves use a wedge shape to enhance high additional seating load. Solid wedge cast iron gate valves can be installed in any direction suitable for the media being worked on. On certain occasions, it may be that the solid wedge cast iron gate valve cannot be opened till when the valve is reheated by system temperatures. Such a situation is known as thermal binding.

the parallel disc cast iron gate valves are limited to low-pressure drops and low-pressure applications.

Solid-wedge cast Iron Gate valve

Types of cast iron gate valves

Flexible wedge cast Iron Gate valve

A flexible wedge cast iron gate valve is a valve that uses a single flexible wedge gate with a cut around it. The cut is of various depths, shapes, and sizes. The flexible wedge cast iron gate valve has no problem with thermal contraction and expansion as the gate is designed to compensate for thermal changes and thus make it easy to open. With such enhanced thermal capabilities, flexible wedge cast iron gate valves are used in steam systems to help prevent thermal blinding.

Split wedge cast Iron Gate valve

Split wedge cast iron gate valves are valves with two separate halves. Such design helps to allow an angular wedge between the outer faces to fit the valve seat enhancing self-adjustment and self-alignment to both seating surfaces.

Slab cast iron gate valves

Slab cast iron gate valves are unitary valves with bore-sized holes. When slab cast iron gate valves are opened, the hole coincides with two seat rings. With such a design, the valve controls the fluid flow with small turbulence. The slab cast iron gate valve helps to reduce pressure drop in the fluid flow system. Slab cast iron gate valve manufacturers design this valve with a plug. The plug is used to expel dirt that may accumulate in the gate valve cavity. These valves need to be kept clean thus the need for the plug. Slab cast iron gate valves are used in different applications among them to transport crude oil and natural gas liquids.

Applications of cast iron gate valves

Cast iron gate valves are used in steam power plants.
Cast iron gate valves are used in salty fluid applications.
Cast iron gate valves are used in transporting crude oil and natural gas liquids.
They are used in controlling flow of slurries.
They are used in control of gas, steam, and liquids flow.
Cast iron gate valves are used in chemical plants.
Cast iron gate valves are used in high pressure and high-temperature applications.
Cast iron gate valves are used in the food processing and beverages industries.
They are used in pharmaceutical industries.

Advantages of cast iron gate valves

Cast iron gate valves have a low-pressure drop.
Cast iron gate valves have low fluid resistance since the fluid flow is perpendicular to the valve gate.
Cast iron gate valve can withstand high temperatures as high as 1150 oC.
These valves have high strength to withstand high pressure.
Cast iron gate valves can be used as bi-directional valves.
These valves are energy efficient because the fluid flow has very small turbulence as the fluid flows perpendicular to the valve gate.
Cast iron gate valves have a simple body design which helps in repair, cleaning, and maintenance of the valve.
Cast iron gate valves are used when fully open or fully closed which helps to reduce erosion on sealing surfaces.

Disadvantages of cast iron gate valves

Cast iron gate valves are susceptible to impact damage since their ductility is low.
Cast iron gate valves are slow to open/close.
Cast iron gate valves need a large area for their operation, maintenance, and installation.
Cast iron gate valves are not meant for throttling applications.

Troubleshooting cast Iron Gate valves

Leakage in the valve seat

Clogged materials in the valve seat. Open the valve high enough to get a high velocity to flush the clogged dirt. Repeat the same process several times to ensure all dirt/debris is removed.
This could also be due to a damaged seat. Check the seat seal and replace it if damaged.
Leakage in the stem

O-rings damaged. Replace the O-rings.
Loose packing gland bolts. Tighten gland packing bolts. If it persists, replace the gland packing system.
Leakage in the valve body

The valve body may be cracked or damaged. This could be due to cast iron material used to make the valve body which is of low ductility and thus prone to impact damage. For damaged cast iron gate valve body, replace the body.
Leakage in the connections

Loose bolts and nuts. Tighten the bolts and nuts.
Worn out gaskets. Replace the gaskets.
The handle is not working

It could be due to foreign particles clogged. Clean the foreign materials.
The handle could be damaged. Replace the handle as necessary.
The cast-iron gate valve is not operating

Broken stem. Replace the stem.
Gate and stem engagement are broken. Replace the product as necessary.
Misaligned stem. Check the stem and align it.

Summary

Cast iron gate valves are gate valves made of cast iron material. These valves have bonnet and the valve body made of cast iron material. The use of cast iron material to make cast iron gate valves is preferred because these material has high resistance to temperature. Cast iron gate valves are preferred because of their high strength which makes them withstand high pressure.

As the name suggests, cast iron gate valve manufacturers design these valves to block fluid flow with a gate. The gate is connected with the valve stem and then to the handwheel. When the handwheel is rotated, it makes the stem move upwards or downwards to open and close the fluid flow respectively. Cast iron gate valves are valves preferred not only for their high thermal and mechanical strength but also for their low-pressure drop. Cast iron gate valves have the gate perpendicular to the fluid flow which reduces pressure drop and fluid resistance. With low-pressure drop and low fluid resistance cast iron gate valves are energy efficient.

Cast iron gate valves are used in different applications such as HVAC, steam power plants, food and beverages processing, pharmaceuticals, water supply applications among others. Cast iron gate valves are of several types which include slab cast iron gate valve, wedge cast iron gate valve, rising stem cast iron gate valve, non-risings stem cast iron gate valve, parallel disc cast iron gate valve, solid-wedge cast iron gate valve, flexible wedge cast iron gate valve, and split wedge cast iron gate valve. The advantages of cast iron gate valves are low fluid resistance, low-pressure drop, and high resistance to fluid pressure, high thermal resistance, bi-directional fluid flow, energy-efficient, corrosion resistance, and minimal erosion. However, cast iron gate valves tend to get damaged easily by impacts because their ductility level is low.