Slide Gate Valve – Definitive Guide

Slide gate valve is mainly suitable for oil, gas pipelines, petrochemical oil depots and other process pipelines, as an ideal valve for the transmission and interception of media flow. It can also be installed at the outlet of the oil pump to regulate and control the flow. It can be operated by hand wheel, gear or electric actuator. The valve is compact in structure, small opening and closing torque, good sealing performance, small flow resistance coefficient, long service life. It is an ideal supporting product for oil and gas and other media pipelines.

Structure and performance characteristics of slide gate valve:

1. Slide gate valve classified by structure
According to its structural characteristics, it can be divided into standard slide gate valve and light slide gate valve. Standard slide gate valve can be divided into slide gate valve without diversion hole and slide gate valve with diversion hole.

2. According to the seal structure, it can be divided into soft and hard dual sealing slide gate valve and metal hard seal slide gate valve.

3. The valve seat is treated by a special process and the RPTFE embedded on the valve seat allows for a soft and hard double seal. The valve seat and seal are equipped with a grease injection valve. When the sealing failure, it can be injected with sealing grease to achieve on-line emergency auxiliary sealing. With (soft, hard, grease injection) triple seal protection, the seal is more reliable and truly zero leakage and longer service life. At the moment of gate opening, the sealing surface can remove the dirt on the gate.

4. The bonnet gland box adopts the sealing sleeve O-ring seal of the piston principle or the gland sealing structure of the V-shaped RPTFE or flexible graphite. The sealing performance is reliable. The opening and closing torque is small. And the opening and closing torque is only 1/3-1/2 of other industrial valve.

5. Reliable fire safety design, the sealing surface of the valve seat has a soft and hard double sealing function, the seal between the valve body and the bonnet is a flexible graphite gasket, and the stem seal is sealed with a 0-ring and flexible graphite packing, when the non-metallic soft sealing is failure In case of high temperature or fire, the metal can be used to achieve fire protection for metal hard seal and the flexible graphite seal, and the fire resistance meets the requirements of API 6FA standards.

6. Anti-static function, static electricity generated during operation of the gate and valve seat sealing pair can be transmitted to the pipeline to the ground, through the stem nut, bearing, bracket, bonnet, bolt, valve body and other metal parts connected to the stem to reach the ground Static requirements.

7. Anti-blow stem design
The valve stem and bonnet are connected by a T-shaped connection. The contact part with the bonnet is designed with a 90° chamfered upper seal structure, which can effectively prevent the stem from blow out of the bonnet and ensure the safety of use.

8. The edge of the gate has chamfers
It can prevent damage to the seal during the opening and closing process.

9. Drain and venting systems
The bottom of the valve body of the slide gate valve and the upper part of the bonnet are equipped with drain valve and vent plugs respectively, which can be used to drain or vent when necessary.

10. Stem protection
The bracket and stem protection cover of the os&y slide gate valve are designed to be fully enclosed, and can effectively protect the stem thread and surface from corrosion from the external environment.

Each side of the valve can withstand a full pressure difference. Replaceable dual valve seat structure with function of double block and bleed (DBB). The floating valve seat can realise automatic pressure relief when the middle cavity is over pressured. When the middle cavity pressure is greater than the channel pressure, the middle cavity pressure will drain the pressure to the channel. When the upstream pressure of the channel is higher than the downstream pressure (the valve is closed), the middle cavity pressure will be released to the upstream channel. When the upstream pressure of the channel is equal to the downstream pressure (the valve is fully open), the middle cavity pressure can be discharged by the two-sided channel, and the valve seat is automatically reset after the pressure relief.

1. When the pressure inside the valve (middle cavity, inlet and outlet) is equivalent or no pressure, the gate is closed, and the RPTFE sealing ring on the surface of the seat forms the initial seal. Each time the valve is opened or closed, the valve seat ring can automatically clean the sealing surface on both sides of the gate.

2. When applying media pressure to the valve, the pressure acts on the entrance side of the gate, forcing the gate to move to the PTFE ring on the outlet seat. The gate is pressed against the sealing surface of the metal seat, thus forming a soft and hard double seal. The PTFE seal the metal is in first sealing, then the metal seal the metal. the outlet valve seat is also pushed to the end face of the seat hole of the valve body, where the O-ring ensures the sealing of the outer circle of the valve seat and the valve body.

3. After the pressure in the cavity of the valve body is released, an inlet seal is formed and the medium pressure acts on the inlet valve seat move it to the gate. This is the inlet valve seat forms the RPTFE seals metal and metal seals metal, forming a soft and hard double seal. At the same time, the O-ring ensures the sealing of the outer circle of the valve seat and the valve body.

4. Automatic valve pressure relief function. When the pressure in the cavity of the valve body is greater than the pressure of the pipeline, due to the effect of pressure difference, the inlet valve seat is pushed to the end surface of the upstream valve seat hole under the effect of the pressure difference in the cavity. The excess pressure in the valve body in between the upstream seat and the sealing surface of gate is released into the upstream pipeline.

The advantages and disadvantages of slide gate valve

Advantages
The flow resistance is small. The slide gate valve with the diversion hole is installed on the pipe and can be cleaned directly by the pipe-clearing machine. Since the gate slides on the two valve seats, the slide gate valve is suitable for media with suspended particles. The sealing surface of the slide gate valve is actually positioned automatically. The sealing surface of the seat is not damaged by thermal deformation of the valve body. And even if the valve is closed in cold conditions, the heat elongation of the stem will not overload the sealing surface. When the valve is closed, the slide gate valve without a diversion hole does not require a high precision for the closing position of the gate, so the electric slide valve can use the stroke to control the opening and closing position.

Disadvantages
When the media pressure is low, the sealing force of the metal sealing surface is not sufficient to achieve a satisfactory seal. Conversely, when the media pressure is high, if the sealing surface is not lubricated with the system medium or foreign media, frequent opening and closing may cause the sealing surface to wear too much. Another drawback is that, when a circular gate that moves horizontally on a circular runner is only at 50% of the valve closing position, the valve is sensitive to flow control. Moreover, when the gate intercepts high-speed and high-density media flow, it produces severe vibrations. It can also be used as a throttle if the seat is made into a V-shaped port and is guided closely to the gate.

The selection guide
1. For oil and gas pipelines, single gate or double gate flat gate valves are used. If need to clean the pipeline, use a single gate or double gate os&y slide gate valve with diversion hole.
2. The delivery line and storage equipment of refined oil products, single gate or double gate slide gate valves without diversion holes are used.
3. The wellhead devices for oil and natural gas mining, use single gate or double gate slide gate valves with concealed rod seats and diversion holes. Most of them are API16A standards, and the pressure levels are API2000, API3000, API5000, API10000, API15000 and API20000.
4. Pipelines with suspended particle media, use knife type slide gate valve.
5. For urban gas transmission pipeline, single gate or double gate soft seal os&y slide gate valve is used.
6. For urban water supply projects, single gate or double gate open stem slide gate valves without diversion holes are used.