Gate valves are used to shut off the flow of liquids rather than for flow regulation, which is frequently done with a globe valve. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low flow resistance.[1] The size of the open flow path generally varies in a nonlinear manner as the gate is moved. This means that the flow rate does not change evenly with stem travel. Depending on the construction, a partially open gate can vibrate from the fluid flow.[1]
Gate valves are mostly used with larger pipe diameters (from 2″ to the largest pipelines) since they are less complex to construct than other types of valves in large sizes.
At high pressures, friction can become a problem. As the gate is pushed against its guiding rail by the pressure of the medium, it becomes harder to operate the valve. Large gate valves are sometimes fitted with a bypass controlled by a smaller valve to be able to reduce the pressure before operating the gate valve itself.
Gate valves without an extra sealing ring on the gate or the seat are used in applications where minor leaking of the valve is not an issue, such as heating circuits or sewer pipes
Common gate valves are actuated by a threaded stem that connects the actuator (e.g. hand wheel or motor) to the gate. They are characterized as having either a rising or a non rising stem, depending on which end of the stem is threaded. Rising stems are fixed to the gate and rise and lower together as the valve is operated, providing a visual indication of valve position. The actuator is attached to a nut that is rotated around the threaded stem to move it. Non rising stem valves are fixed to, and rotate with, the actuator, and are threaded into the gate. They may have a pointer threaded onto the stem to indicate valve position, since the gate’s motion is concealed inside the valve. Nonrising stems are used where vertical space is limited.
Gate valves are typically constructed from cast iron, cast carbon steel, ductile iron, gunmetal, stainless steel, alloy steels, and forged steels.
All-metal gate valves are used in ultra-high vacuum chambers to isolate regions of the chamber
Bonnet
Bonnets provide leakproof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. A screw-in bonnet is the simplest, offering a durable, pressure-tight seal. A union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. A bolted bonnet is used for larger valves and higher pressure applications.[3]
Pressure seal bonnet
Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 2250 psi (15 MPa). The unique feature of the pressure seal bonnet is that the bonnet ends in a downward-facing cup that fits inside the body of the valve. As the internal pressure in the valve increases, the sides of the cup are forced outward. improving the body-bonnet seal. Other constructions where the seal is provided by external clamping pressure tend to create leaks in the body-bonnet joint.
Knife gate valve
For plastic solids and high-viscosity slurries such as paper pulp, a specialty valve known as a knife gate valve is used to cut through the material to stop the flow. A knife gate valve is usually not wedge shaped and has a tapered knife-like edge on its lower surface
Gate valve is for use in fixed firefighting applications such as riser and hydrant system. It features threaded body ends with hand wheel or lock shield handle.
anding valves are something that is used for fighting fires and is provided on risers in buildings. These are usually located in staircase landings, allowing easy access to firefighters. A fire hydrant system is comprised of water supply pipework and valves, which can be connected to the hose of fire brigades for firefighting purposes. Hose reel drum and hose pipe are also effective in fighting fires inside a building. Both the hydrant valve and landing valve have similar designs, irrespective of the place installed. Flow Control Valve is a device that is used to control the flow of water by varying the size of the flow directed by a signal from a controller.
Difference between Hydrant Valves & Landing Valves:
Landing Valve
Landing valves are permanently charged with water using a pressurized supply. In simple words, they are globe valves, installed on hydrants. Also, a hose and a branch are connected to a coupling on it. Landing valves are installed in all the floors of a building where installation of hydrant valve is not possible and is then used by fire fighting department to extinguish the fire. The normal pressure of a landing valve is around 65 psi. In order to keep the nominal working pressure at the inlet of the hose reel, a pressure reducing valve is used in hose reel system.
Hydrant Valves
Fire Hydrant Valves are efficient in fighting large fires. They allow firefighters to extinguish the fire from a distance. Pumping facility is the most important part of the fire hydrant system. The main use of the pump is to pull the water from the reservoir and supply the same pressure to the hydrant points enabling firefighters to extinguish the fire effectively. In order to connect and operate fire fighting equipment from a hydrant valve, the pressure rating must be 100 psi (7 kg/cm2). But, it varies depending on the size of the building. The pressure of hydrant valves in large industrial complexes might range around 10-11 kg/cm2 while in small buildings it might range around 4-5 kg/cm2.
Fire sprinklers and flexible hoses can be effective in fighting small fires. Fire sprinklers discharge water when the effect of fire or extensive heat is detected and is effective in the early stage of fire. Flexible hoses act as a connection between the pump to the system. The standard length of a flexible hose is around 100 ft.