1. What is a Gate Valve used for?
Gate valves are commonly used for all types of applications especially water supply systems. It is suitable for underground and above-ground installation. The gate valve represents a linear-motion isolation valve and has a function to fully open or fully close function. Gate valves act like a gate that has the closure element sliding into the flow stream to provide shutoff function. The gate valve is used to separate specific areas of the water supply network during new system installation, repair and maintenance works, and reroute water flow throughout the pipeline. It is not applicable in control or regulating flow design.
The gate operates with a handwheel handle and it can be either CTO (clockwise to open) or CTC (clockwise to close) rotating motion of the stem. The gate moves upward or downward on the threaded stem when operating the valve stem by turning the handwheel. The gate valves are designed as full port valves which the port has the same size as the inner diameter of the connecting pipe. Compare to reduce ball design, the full bore gate valve passes the fluid flow without obstacle and by remaining the internal piping pressure. It helps in cost-saving and increases system flow efficiency. The valve has to turn the handwheel handle multiple times to go from close to open position and open to close position. The slow operation prevents water hammer effects.
2. How does Gate Valve work?
A gate valve is a combination of body, seat, gate, stem, and bonnet. The primary operation mechanism is simple and straightforward. The gate moves up and down via the stem thread by turning the gate valve handwheel rotation. They require more than one round 360-degree turn to get the valve in an open or closed position. When lowering down the component gate, the valve is in a closed sealing position.
Gate valves are used in various system applications and it has a wide variety of designs.
Bonnets: The bonnet is screwed in or bolted inside the gate valve body to create a leak-proof sealing and it is used to protect the internal components. It is flexible to remove for repair or maintenance purposes. It is available in screw-in, union, or bolted design and is subject to different application types. A Screw-in bonnet is the most common design in construction lines and it is used for small size valves. It provides durable leak-proof sealing. A union nut is used to install union bonnets in the gate valve body and it sits on the lower edge of the bonnet. Next, it screws into the valve body’s threads. It is common to use for that application that requires regular inspection or service maintenance. Bolted cover bonnets are commonly used for larger valve and higher pressure applications. The bonnet and valve body are flange and bolted together to form a tight sealing.
Gates: The most common gates are wedge and parallel slides. The wedge gate sits on two inclined seats and it is a primary force created by fluid pressure. The stem’s tightening assists with reliable sealing to create a high wedging force on the gate valve seats. In the case of high fluid differential pressure, the wedge shape does not stick to the seat. It has an increased service life due to less “rubbing” on the seats. The parallel side gate is flat and the seats are parallel. It uses line pressure and positioning to form a tight sealing. It consists of two pieces of flat gates with a spring in the middle. The spring pushes the flat gate towards the seats for enhanced sealing. Parallel gate valves have a safety advantage when it works in higher temperature application due to their inherent design. The seat with an additional compression load may result in thermal binding. Since there is no wedging action in the parallel gate, the closing torques are comparatively smaller and resulting in a lesser manual effort. Parallel gates keep dirt away from the seating surfaces due to the sliding position.
Stem: The valve gate is raised and lowered by the manual handwheel to spin the internally threaded stem. The stem can be either a rising or non-rising stem and it decides the stem location either raises or stays in place when spinning.
3. Is the Gate Valve better than the ball valve?
Gate valve and ball valves are the most common valve design to control flow. They are basically applied in different mediums such as liquid and gasses. Although both valves have a similar function, there are still fewer important differences between these two valves. A ball valve uses a rotary ball to control the flow. The ball valve handle is parallel to the piping direction when the valve is open and the handle is perpendicular to the pipe when the valve is closed. The quarter-turn function is to allow or block the fluid flow through the valve body.
A gate valve uses a gate mechanism to control the fluid flow. The gate is a solid plate structure that is connected to the stem. The gate is lifted to open the valve. The valve returns to closing position when the gate is back to the original place. Gate valve is known as a multi-turn handwheel valve as it takes more than a 360-degree turn to fully operate the valve.
Here is the comparison table:
JIS10K Cast Iron Flange End Gate Valve
Before determining the selection of a ball valve or gate valve, you may consider the following criteria:
Ports: A standard gate valve comes with 2 ports and a ball valve has the option of more than 2 ports.
Flow capacity: Gate valve has a larger flow capacity due to the larger diameter size compares to a ball valve.
Opening and closing speed: Ball valve is suitable for application which requires a faster open and close speed. The gate valve requires more than a 360-degree turn to operate and it is slower than the ball valve.
Sealing: Compare to a gate valve, a ball valve provides a tight sealing and it has a complete shut-off characteristic. The ball valve is a better option for applications such as natural gas where proper sealing is important.
Working Pressure: Both gate valves and ball valves are suitable to apply in low-pressure applications.
Connection: The valve connection type is critical to ensure the high performance of system installation. Ball valve has variety connection options in difference valve design which compare to gate valve.
HOW TO INSTALL A GATE VALVE
The gate valve has a long life in terms of application. The storage condition is important in order to ensure the valve performs inconsistent manner. To protect the seals and seat before gate valve installation, do not unpack the valves before installation in order to protect the valve from dust and debris which may cause the seat leakage.
*** Please ensure the valve is stored in a cool well-ventilated space.
Verify the material, size, and connection before installation, Ensure there are no defects on the gate valve components.
Complete the welding works before valve installation. Ensure the flange connector has cooled to ambient temperature before inserting a gasket in the installation.
Align the gate valve flange with another piece of the pipe flange. This is the most common problem where misalignment caused the leakage. Support the gate valve was necessary to reduce the load on the assembly process.
Install the spacing hex bolts and adjust the face to face of the two flanges.
Once the pipes are centered, place the hex bolts through the bolt holes. The bottom of the valve is prevented from falling through.
Tighten the hex bolt and hex nut by hand once at a time. Torque the hex bolts gradually in diagonal sequence and a seal is formed between the valve and flange.
Operate the valve several times once the installation is completed.