Exploring The Basics Of Butterfly And Gate Valves

The structural design:

As mentioned earlier, the gate valve has a rectangular or round-shaped wedge, and the butterfly valve has a circular flap-like disc. However, increased demand for both valves has been the driving force behind manufacturers coming up with various structural designs for both valves.

Also Read : What Are Butterfly Valves?

The structural designs in gate valves include:

• Bolted bonnets.
• Screwed bonnets.
• Welded bonnets.
• Pressure sealed bonnets.
• Wedge gate valve.
• Double disc gate valve.
• Parallel slide or conduit valve.

Butterfly valves are available in the following structural designs:

• Lug type.
• Flanged type.
• Wafer type.
• Butt-welded type.
• Concentric or zero offset valve.
• Triple eccentric or triple offset valve.
• Double eccentric or double offset valve.

How they operate:

Butterfly valve:

The butterfly valve has a handle or an actuator that is used to turn on and turn off the valve. When in operation, the handle is turned manually, electrically or pneumatically to a quarter turn. The stem that bridges the handle and the disc turns the disc to a position parallel to the centreline. When the handle is closed, the disc is perpendicular to the centreline and fuses with the seat inside the valve's body to effectively seal off the flow.

The butterfly valve's thickness creates a natural resistance that obstructs the medium flow and causes a drop in the valve pressure even when the disc is fully opened.

Gate Valve:

The gate valve operates by opening and closing a movable door or gate, which is controlled by a threaded screw. Unlike the butterfly valve, the door in a gate valve opens and closes completely, thus providing an unobstructed flow of media. But the mechanism is slower than that of the butterfly valve due to its high opening height.
Applications:

Butterfly valves:

Butterfly valves are some of the most widely used and preferred valves. Their industrial applications include:

• Refineries and fuel industries.
• Food and beverage industries.
• Wastewater treatment facilities.

Gate Valves:

Gate valves are built to withstand high pressures, but they cannot regulate or throttle the flow of media. They are commonly used in applications that require unrestricted flow, such as:

• Domestic water use.
• Commercial water use.
• Wastewater plants.
• Fire protection services.
• Oil and gas industries.

Pros and Cons:

Butterfly valve: The pros

• They can throttle and control the fluid flow very effectively.
• Extremely lightweight.
• Can be fixed in compact or limited spaces.
• Very suitable for applications where the media is at an ambient temperature and pressure.
• Quick turn-on and turn-off mechanism.
• Can isolate particles in the media.
• Affordable pricing even in large sizes.

The cons:

• They leave residual materials in the pipeline.
• The valve's thickness causes a pressure drop even if it is fully opened.
• The movement of the disc is affected by the flow of the turbulence.
• The disc is always on the path of the flow, thus affecting the movement of thick materials.
• Water hammers is a possibility.

The Gate valve: The Pros:

• No loss of pressure as there is an unobstructed flow of media.
• Leaves no residue inside the pipelines.
• They are bi-directional and allow a uniform linear flow.
• They can withstand high pressures.
• Fewer possibilities of water hammer.

The cons:

• No control or adjustments can be made as the valve can only close or open completely.
• Slow mechanism does not allow emergency shutoffs.
• Gate valves are expensive.
• When kept in a partially open state, the valve can erode or get damaged.