There are Two Type of Gate Valve
The Rising Stem Gate Valve
Cast Iron Gate Valve is designed with straight through bore type with rising stem, outside screw & yoke, bolted bonnet and stainless steel trim. The open and closed position of the valve is easily distinguished by the stem position. The Wedge is replaceable without needing to remove the valve from the pipelines.
Cast Iron Gate Valve allows for two-way flow direction and used for closing or opening the medium flow. This valve can be installed in horizontal and vertical positions in the piping systems. It is widely used in process industries such as Palm Oil and Refinery Plant, Food Industries, Petrochemical, Fire Protection System, Power Plant and Cooling System.
Non-rising Stem Gate Valve
Used in fire protection systems for on/off operation, Tyco Resilient Seated Gate Valves incorporate high strength stainless steel stems, dezincification resistant copper alloy components, high-grade elastomers and quality coating systems. The lightweight ductile iron body weighs less than conventional cast iron valves, which allows for easier handling on site and reduces shipping costs. A fully encapsulated EPDM ductile iron wedge is intended to achieve bubble-tight sealing. Components that are not designed to be inherently corrosion resistant are coated with a thermally applied fusion-bonded epoxy.
The gate sealing design combines wedge and compression mechanisms to achieve low torque, drop tight sealing. The stem seal arrangement incorporates five separate O-rings designed to provide a lifetime seal. Available end connections include flange-by-flange, flange-bygroove and groove-by-groove configurations.
There are Two Type of Gate Valve Body
Body acts as an enclosure to stem and disc assembly and flow passage for the fluid to flow. in most of the gate valve body construction ,the upper portion is extended to enclose the disc when the valve is at fully open condition. This provision can also give in bonnet by changing the bonnet design ,if a short body is prefered.
Casted valve bodies are mainly used for large sized valve where other fabrication process not feasible.
Forged body can use for smaller sized high pressure application of gate valves.
There are Two Type of Gate/Disc
For a parallel gate both the faces of the gate is parallel
Knife gate is a parallel gate having sharp bottom edge used in slurry handling pipelines to separate the slurry by slicing the flow.
Through Conduit Gate
A through hole is drilled in the gate.to achieve full port see more details about full port double expanding through conduit gate valve.
The gate design is in the form of a wedge having two flat inclined surfaces.Two are inclined but might have a slight angular mismatch. Sealing will be in tight contact with the wedge by wedge action. Due to the inclined contact between the wedge and the seat, an immediate disengagement without any sliding action between the wedge and the sealing ,when the gate starts to travel upward during valve opening. This reduces the wear due rubbing action and increases the life of sealing and gate compared to parallel gates.
Single Solid Wedge Gate
This is the most common and stronger wedge design. Due to the simple construction of the wedge, the fabrication cost is much less compared to other wedge designs.Solid wedge design can be assembled and operated in any orientation and can used in any fluid application even for a turbulent flow.
Solid wedge working in high temperature applications like steam pipelines may undergo slight expansion due to the temperature gradient and will induce more compression forces during tight shut off condition and undergoes deflection as shown in figure. This may cause seating mismatch and leads to leakage.This can be solved using split or double plate wedge design by inducing wedge flexing.
Split Flexible Wedge gate
The solid wedge is stilted all round the perimeter.This makes the single piece wedge into two piece which can flex to correct any angular miss match between the wedge and seating and more tight seating as shown in figure without loosing much strength of the wedge.
Double plate Wedge Design
Double plate design having two plates assembled using ball and socket to adjust any mismatch/alignment problems or any solid entrapment like dirt between the wedge and seating. This types of wedges mainly used for non condensing gas and liquid applications.