A Guide to Gate Valves and Sluice Valves
Also sometimes called sluice valves, gate valves are designed to open and close flow within a piping system. The linear valves feature a barrier that is either lifted or dropped with a manual actuator that is connected to the unit via a stem. They are commonly used in water supply systems when a section of a pipeline needs to be isolated for repairs, maintenance or cleaning. Gate valves can be used to block flow in both directions without causing major pressure losses. On the downside, gate valves cannot be used to throttle flow and can be slow to open or close.
What are the Applications of Gate Valves?
Perhaps the most common valve type on the market, gate valves are utilised in a variety of industries including water treatment facilities, food and factory production, oil and gas, as well as medical and laboratory facilities.
Despite their simple design, gate valves are fire-safe and can be used in both extreme temperatures and high-pressure environments. However, unlike some other valve types such as butterfly valves or globe valves, gate valves can only be used to open or close the flow of liquid. In other words, they cannot be partially lowered to reduce the flow rate.
How do gate valves work?
Gate valves feature a barrier or a gate that is lifted to open flow in a pipeline and lowered to stop it. The barrier is moved manually by turning a handwheel. Most gate valves are made from stainless steel, brass or iron for maximum durability. Gate valves are different from non return check valves, which are specifically designed to only allow flow in one direction. While gate valves have a similar function to ball valves, they tend to have tighter seals.
Different types of gate valves
Despite their similar appearance, gate valves are not all the same. Here are the different types of gate valves available on the market.
Wedge gate valves
One of the most popular gate valve types out there, wedge gate valves utilise two inclined seats and an inclined barrier to achieve a tight seal. Wedge gate valves are further classified into solid taper wedges, split wedges and flexible wedges. Also referred to as plain wedge valves, solid taper wedges are the most common type of wedge gate valve. They are simple, affordable and feature decent mechanical strength. In addition, solid taper wedges feature one-piece construction, which makes them ideal for turbulent flows.
Parallel gate valves
Also called parallel disk gate valves, parallel gate valves come with two discs positioned at a 90-degree angle to the direction of the flow of liquid. They are often used in high temperatures since they are less likely to lead to thermal binding.
Split gate valves
Often used with corrosive substances and non-condensing gases, split gate valves are made from two parts and a spring or a spacer. This construction allows split gate valves to self-adjust and create a relatively tight seal.
Knife gate valves
Usually used with viscous fluids, knife gate valves feature discs that are tapered, or sharpened, at one end. Knife gate valves are often used with thick fluids such as powder-currying liquids.
How to use gate valves
Operating gate valves is very simple. Rotating the handwheel 360 degrees to one side raises the barrier and opens the valve. Meanwhile, rotating the handwheel 360 degrees to the other side lowers the barrier and closes the valve.
How to tell if a gate valve is open or closed
While for most valves a handle that is perpendicular to the flow line indicates that it is open, the situation is not as easy when it comes to gate valves. This is because gate valves feature handwheels that rotate 360 degrees. Most gate valves are opened by turning the handwheel anticlockwise and closed by turning it clockwise. As a rule of thumb, you should stop turning a handwheel on a gate valve when you feel resistance — pushing the handwheel too hard can break the valve.
Other valve types
While gate valves are one of the most commonly used valve types on the market, they are by no means the only go-to option. With this in mind here are some other popular valve types.
Ball valves are used to open and shut the flow of fluid. They come with balls with a hole in them that are manually rotated with a lever to open or close the valve. When the hole opening is parallel to the flow line, the valve is open. When the hole opening is perpendicular to the flow line, the valve is closed.
Similar to ball valves, butterfly valves come with a disc instead of a ball. Rotating the disc 90 degrees either opens or closes the valve. Unlike most ball valves, butterfly valves can be used to regulate flow rather than just open or close it completely.
Non return check valves
Also called reflux valves or retention valves, non return check valves let liquid or gas through in only one direction, preventing it from returning back up the piping system. Non return check valves have two openings, one that lets fluid into the valve and the other through which the fluid exits the valve.
Pressure relief & safety valves
While both protect systems from excessive pressure, pressure relief valves and safety valves have slightly different functions. Just like their name suggests, pressure relief valves control pressure to protect equipment. Safety valves, on the other hand, release pressure immediately (or open completely) if there is an emergency.
While both ball valves and gate valves are used to open and close flow, they function in slightly different ways. Gate valves use a barrier that is lifted to open the flow and lowered to shut it off. It takes a 360-degree rotation of a handwheel to either open or close a gate valve. Ball valves, on the other hand, feature a ball with a hole in it. The ball is attached to a stem, which, in turn, is attached to a lever. When the hole in the ball lines up with the pipe, the valve lets flow through. When the lever is moved 90-degrees, the valve shuts off the flow.
Just like most other valves, gate valves remain operational for between 10 and 25 years. Gate valves need to be used on a regular basis, however. This is because valves not used for substantial periods of time can freeze in the open or closed position.
Butterfly valves are more compact, lightweight and inexpensive than gate valves. Instead of a solid barrier that is either lifted or lowered to open or close flow, butterfly valves come with a revolving disc that regulates flow. This means that even if a butterfly valve is fully opened, the flow will remain somewhat obstructed. Gate valves are suitable for use in high-pressure environments whereas butterfly valves are not.
While relatively sturdy, gate valves do experience wear and tear over time. There is also the risk of corrosion. If affected, the disc can get stuck in the same position, making the opening or closing of the flow impossible. A stuck disc can lead to a broken lever if the user applies too much force when trying to manually open or close the valve.