Parallel Slide API 600 Gate Valve Bolted Bonnet 1/2 inch - 36 Inch
Bolted Bonnet Parallel Slide Gate Valve
This type of on-off valve is an alternative to the traditional wedge type gate valves. The disc is in two halves, spring loaded, that seat on parallel seat rings. The disc “slides” in contact with the seats, hence the name. The advantages of this product versus the traditional wedge type product are:
- the disc never blocks in closed position (phenomenon that may occur with a wedge type that is closed with the line in temperature and opened when the line is cold).
- The opening/closing torque is much lower than a corresponding wedge type valve, resulting in less expensive actuation systems.
- The “sliding” feature keeps dirt away from the seating surface.
The double spring loaded disc has the tendency to trap working fluid in the body cavity when the valve is closed. This is avoided, when unidirectional functioning is allowed, by applying an equalizing hole on the upstream part of the disc.
Design codes and overall configuration, including stem-to-disc connection are the same than the wedge type gate valves. Materials range from carbon steel to low alloy steel, to austenitic stainless steel, to nickel alloys.
Materials are either to ASTM/ ASME standards or to EN standards, either harmonized or calculated to design conditions. Pressure classes (per ANSI standard) are normally ranging from 150# to 300# to 600#. Size range depends on pressure class requirements.
1. The parallel slide gate valve closes with a sliding action instead of the usual compression, so there is no tendency, notch or indent on the sealing surfaces. This result of this action can bring a better tightness to the disc on the seat-ring, and a longer lifetime of the discs and seat sealing surfaces.
2. parallel-slide gate valve has a cleaning function with intimate contact on the seats during the closing action. So if any impurities appear or tendency on the seats and discs, they are eliminated and the sealing contact is free from undesirable particles. It also reduces seat bearing stress and guarantees long life. The wide flat seating can minimize the effect of minor damages on the surface as sealing occurs over the entire surface.
3. No additional power and final surge of torque are required to make the seating leak-tight because sealing is obtained by sliding, not by compression. Furthermore, the valve operates with low energy because there is no need of high energy when opening the valves.
4. Actuator size of the parallel slide gate valve can be much smaller than the wedge type. Hammering or impacting hand-wheels are not usually necessary on this valve.
5. The low torque operation brings less stress and fatigue on the trim. This gives longer lifetime and greater leak-tight reliability.
6. When the valve is closed, the exact position of stem dose not play a great role. As a result, there is no problem with the differences in the thermal expansion coefficient of the materials. Also, the actuators can be stopped with general position switches.
7. The possible jam found in wedge gate valves as result of body contraction will never occur in parallel slide gate valves.
8. In wedge gate valves, the wedge must have positioning guides on its slides to keep it inline while closing under full flow condition. These guides are not usually made of any hard materials, and tend to wear, and eventually may cause jamming.
The problems of solid wedge gate valves:
1. Malfunction of disc opening due to Thermal Binding
In wedge type valves, thermal binding is caused by dimensional interference between wedge and seat, due to temp-erature differences and thermal expansion. Valves are commonly used at high.
2. Leakage problems due to thermal deformation
Since the sealing of the valve is obtained by compression, enough surface pressure between discs and seats is necessary. The bodies should be designed to be thick and strong in order to stand agains.
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