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Gate Valve vs Butterfly Valve

At first glance, it is not simple to decide between a gate valve and a butterfly valve for an application. Therefore, it is important to understand the differences between these two valve types to avoid unnecessary setbacks in an operation. This article lays out the fundamental similarities and differences between a gate valve and a butterfly valve, which can be seen in Figure 1, and looks at their application suitability, advantages, and disadvantages.

Gate and butterfly valves are both used to turn on and off the flow, but butterfly valves can also regulate flow via partial disc closure. Butterfly valves are part of the quarter-turn family of valves and can be shut off much faster than gate valves, which are multi-turn valves. Gate valves are preferable for high-pressure systems whereas butterfly valves are preferable for larger port sizes.

Gate valves

How does a gate valve work?

A gate valve is named after its disc, which behaves like a gate by either stopping or allowing media flow. It has a simple operation compared to other control valves, which makes it one of the most commonly used valves. Because a gate valve is a full-port valve, which means that the valve’s ports are the same size as the inner diameter of the connecting pipes, there is very little resistance to liquid or gas media that flows directly through it. Therefore, the pressure drop through the valve is quite low. For a more extensive understanding, read our article on gate valves.

Operating a gate valve

Gate valves are multi-turn valves, meaning the handwheel must turn more than 360° to fully open or close the valve. Turning the handwheel in one direction or the other moves the gate up or down via the stem. When the gate is completely up, the passageway is unobstructed, and media can flow. When the gate is down, media is blocked and cannot flow. Gate valves cannot modulate or throttle flow because there is a nonlinear relationship between the gate’s travel and flow rate. If the gate is partially open, the flow will crash into it while traveling through the valve, causing the flow to move at a higher velocity and create turbulence, both of which lead to increased wear on the disc and seats.

The three common means for actuating a gate valve are manually, pneumatically, or electrically. The manual method requires an on-site user to spin the handwheel to open or close the valve. This method is the most cost-effective since gate valves are not typically opened or closed often. The pneumatic and electric solutions allow for remote operation of a gate valve. Pneumatic actuation requires a pneumatic system on-site and electrical actuation requires electrical power on-site.

Gate valve types

As mentioned above, there exist different styles of gate valves. Three factors typically determine a gate valve’s style: the gate type, the bonnet type, and the stem type.

Gate type refers to the disc that blocks the flow when the valve is closed, for example:

  • Wedge disc: The gate is shaped like a wedge and it sits on two inclined seats. This provides a high wedging force which assists with sealing.
  • Knife disc: The gate is a piece of metal with a beveled edge like a knife. It can be used to cut through thick fluids and dry solids.
  • Double disc: The gate is two discs which sit on two seats. The discs expand away from each other to provide a tight seal.

Bonnet type refers to how the bonnet is attached to the valve body. It can be:

  • Screwed: This is the simplest type of bonnet construction and is normally used in small size valves.
  • Bolted: These bonnets are used in larger valves and high-pressure applications.
  • Welded: The bonnet is threaded in and the body-bonnet joint is welded. This offers extra protection against leaking.
  • Pressure sealed: The body-bonnet joint seal enhances as pressure within the valve increases. Used typically for high-pressure applications above 100 bar.

Stem type refers to the position and action of the stem

  • Rising vs non-rising: Rising stem gate valves require more space above the valve than non-rising.
  • Remains within the valve vs rises out of the valve upon opening: Rising out of the valve makes the stem easier to lubricate.

Materials

The correct material depends on the application’s fluid service and temperature. Common materials used for a gate valve are:

  • Body and bonnet: cast steel, stainless stell, cast iron, gunmetal, bronze, brass, and PVC
  • Disc: stainless steel, polypropylene, Teflon, rubber lined (e.g., wedge disc)
  • Seal: EPDM, NBR, Teflon
  • Butterfly valves

    How does a butterfly valve work?

    The essential operation of a butterfly valve is achieved by turning its handle 90° or using a pneumatic or electric actuator. This turns the valve’s stem, which rotates the disc. In the fully closed position, the disc is perpendicular to the flow, and in the fully open position, the disc is parallel to the flow. Partial opening or closing of the disc can achieve proportional or throttled flow rates. In cases of a large butterfly valve or a valve used in a liquid application for which fast closure could produce water hammer, a butterfly valve can be gear operated via a gearbox (Figure 2, right). The gearbox’s handwheel must be turned more than 90°, though, which eliminates the butterfly valve’s relatively fast closing speed. For a more comprehensive understanding, read our article on butterfly valves.

    A zero offset butterfly valve with a lever handle on the left and an eccentric butterfly valve with a hand wheel on the rightFigure 2: A zero offset butterfly valve with a lever handle on the left and an eccentric butterfly valve with a hand wheel on the right

    Butterfly valve types

    There are two key topics when discussing types of butterfly valves: body and stem offset. Body refers to how the valve’s body connects with piping, and stem offset refers to whether the stem passes through the center of the disc or is offset.

    The butterfly valve body types are:

    • Double-flanged: This design is typically used for larger butterfly valves.
    • Wafer: Most cost-effective design; sandwiched between two pipe flanges.
    • Single flange: This design uses bolts and nuts passed through the valve’s holes to connect to both sides of the piping.
    • Lug type: This design has threaded inserts, and bolts are used to connect pipe flanges to each side. Suitable for removing piping from one side without affecting the other.
    • Flangeless: Like the wafer style, this design is sandwiched between two pipe flanges.
    • Butt-welding ends: Prepared for welding directly to piping.
    • U-section: Also clamped between pipe flanges and suitable for end-of-line service.

    The stem can pass through the centerline of the disc (concentric) or be offset behind the centerline (eccentric). Offset, which can be single-, double-, or triple-offset, is used to reduce how much the disc rubs against the seating while closing. The higher the offset, the more the disc moves towards fully closed before contacting the seal. Any rubbing against the seal can reduce the service life of the valve. High-performance butterfly valves are specifically designed to withstand more demanding applications in terms of pressure and temperature.

    The following compares a high-performance butterfly valve with a standard butterfly valve:

    • Maximum shutoff pressure: Approximately 50 bar (725 psi) vs approximately 14 bar (203 psi)
    • Tight shutoff: Below 260°C (500°F ) vs below 120°C (248°F)
    • Shutoff with allowable seat leakage: Below 538°C (1000°F) vs below 425°C (797°F)

    Read our article on butterfly valve design differences article for more details on the features of each design type.

    Materials

    The valve’s body and seat materials should be chosen carefully based on the needs of the application. Common body materials are iron, stainless steel, carbon steel, nickel alloy, titanium alloy, and nickel aluminum bronze. These materials vary in weight and resistance to corrosion and extreme temperatures.

    Common seat materials are EPDM, EPDM white, FKM, XNBR, and NBR. Depending on the seat material, a butterfly valve can be used in temperatures ranging from -10°C to 180°C. Resilient and metal seated butterfly valves are also available, using the same materials listed here, and are designed to operate under more extreme temperatures and pressures.

    Gate valves vs butterfly valves

    There are many factors to consider when deciding whether a gate or butterfly valve is correct for a given application. Below are some of the most important:

    • Cost: A butterfly valve is typically less expensive than a gate valve, especially at larger port diameters.
    • Installation space: A butterfly valve takes up less installation space than a gate valve.
    • Weight: A butterfly valve weighs less than a gate valve; the latter may need support structures at larger port diameters.
    • Maintenance: While a butterfly valve is relatively easy to maintain, repair, or install due to its small size and low weight, its center disc makes it not suitable for systems that use pigging and swabbing for cleaning purposes. On the other hand, a gate valve is ideal for such maintenance.
    • Operation: A butterfly valve can close faster than a similar port diameter gate valve. However, this fact means that butterfly valves are more susceptible to water hammer.
    • Flow regulation: A butterfly valve can modulate or throttle flow, whereas a gate valve can only be on/off.
    • Flow resistance: A gate valve offers less flow resistance and, therefore, less pressure drop than a butterfly valve.
    • Pressure: Gate valves can handle higher pressures than butterfly valves.

    Applications

    • Gate valves have a higher sealing tightness, and therefore are more suitable for applications that require zero leakage.
    • Butterfly valves are more suitable for applications that require flow modulation or throttling.
    • If a slurry flow does not need to be modulated, gate valves are preferable to butterfly valves.
    • Gate valves are more suitable for systems that require bi-directional, uninterrupted flow.

    FAQs

    Which is better, a gate valve or a butterfly valve?

    A gate valve has a stronger seal and is more suitable for high-pressure applications. A butterfly valve is less expensive and available in very large sizes.

    Can a butterfly valve be used instead of a gate valve?

    A butterfly valve can be used instead of a gate valve in low-pressure systems for which some leakage is not a major concern.

What-is-a-Gate-Valve-and-How-does-they-work

Gate Valve – How They Work


Figure 1: Gate valve

A gate valve controls the medias flow by lifting the gate (open) and lowering the gate (closed). A gate valves distinct feature is the straight-through unobstructed passageway, which induces minimal pressure loss over the valve. The unobstructed bore of a gate valve also allows for a pigs passage in cleaning pipe procedures, unlike butterfly valves. Gate valves are available in many options, including various sizes, materials, temperature and pressure ratings, and gate and bonnet designs.

Gate valves tend to be slightly cheaper than ball valves of the same size and quality. They are slower in actuation than quarter-turn valves and are for applications where valve operation is infrequent, such as isolating valves. Gate valves should be used either fully open or fully closed, not to regulate flow. Automated gate valves exist with either an electric or pneumatic actuator, but a manual gate valve is cost-effective since they have infrequent usage.

Table of Contents

Functioning principle

Gate Valve ComponentsFigure 2: Gate valve components

A gate valves main components as seen in figure 2 are the handwheel (A), spindle (B), gasket (C), bonnet (D), valve body (E), flange (F), and gate (G). The primary operation mechanism is straightforward. Turning the handwheel rotates the stem, which moves the gate up or down via the threads. They require more than one 360° turn to fully open/close the valve. Lifting the gate from the path of the flow, the valve opens. Lowering the gate to its closed position seals the bore resulting in a full closure of the valve.

For a gate valve, the relationship between the gates vertical travel and the flow rate is nonlinear, with the highest changes occurring near shutoff. When used to regulate flow, the relatively high velocity of the flow at partial opening results in gate and seat wear, which along with possible vibrations of the gate, shortens the valves service life.

Gate valve design & types

Gate valves come in a wide variety of designs, each of which uses different technologies to meet various application requirements.

Bonnets

Bolted bonnet gate valveFigure 3: Bolted bonnet gate valve

A bonnet protects the internal parts of a gate valve (Figure 2). It is screwed in or bolted to the valve body, creating a leak-proof seal. Therefore, it is removable for repair or maintenance purposes. Depending on applications, gate valves can have screw-in, union, bolted, or pressure seal bonnets.

Screw-in Bonnets

Screw-in bonnets are the simplest in construction. They are common in small size valves and provide a durable leak-proof seal.

Union Bonnets

Union bonnets are held in place by a union nut. The union nut sits on the lower edge of the bonnet and screws into the valve bodys threads. This type of design ensures that the leak-proof seal created by the nut does not deteriorate by frequent removal of the bonnet. Therefore, union bonnets are common for applications that require regular inspection or maintenance.

Bolted Bonnets

Bolted bonnets provide sealing in larger valves and higher pressure applications. In this type, the bonnet and valve body are flanged and bolted together. Figure 3 shows a gate valve with a bolted bonnet.

Pressure Seal Bonnets

Pressure seal gate valves are ideal for high-pressure applications (more than 15 MPa). This type of construction uses internal pressure to create a better seal. Pressure seal bonnets have a downward-facing cup inserted into the valve body. When internal fluid pressure increases, the cups forced outward, improving the seal.

Gates

The gate comes in a variety of designs and technologies to produce effective sealing for differing applications.

Wedge Gates

In most gate valves, the gate has a wedge form and sits on two inclined seats (Figure 4). In addition to the primary force created by fluid pressure, a high wedging force on the seats created by the stems tightening assists with the sealing. The wedge-shaped gate does not stick to the seat in case of high fluid differential pressure and has an increased service life due to less “rubbing” on the seats.

Wedge gate valve vs parallel gate valveFigure 4: Wedge gate valve vs parallel gate valve

Parallel Slide Gates

Gate valves can also come in a parallel form where the gate is flat, and the seats are parallel. Parallel gate valves use line pressure and positioning to make a tight seal. Flat gates consist of two pieces and have a spring in the middle. The spring pushes the pieces towards the seats for enhanced sealing. Due to their inherent design, parallel gate valves have a safety advantage in higher temperature applications. In wedge-shaped gate valves, an additional compression load on the seats may result in thermal binding and restricted opening of the valve due to expansion. Furthermore, since there is no wedging action in parallel gates, closing torques are comparatively smaller, resulting in smaller, less expensive actuators or less manual effort. Due to their sliding into position, parallel gates keep dirt away from the seating surfaces.

Slab Gates

Slab Gate ValveFigure 5: Slab gate valve

Slab gates, also called through-conduit gate valves, are one-unit gates that include a bore size hole (Figure 5). In the open state, the bore is in line with the two seat rings. This alignment creates a smooth flow with minimal turbulence. This unique design allows for minimal pressure loss on the system and is perfect for the transportation of crude oil and natural gas liquids (NGLs). The valve seats remain clean. However, the disc cavity can capture foreign material. Therefore, the cavity typically has a built-in plug for maintenance purposes of draining the accumulated foreign material.

Parallel Expanding Gates

Expanding gate valves have two slab gates matched together that provide sealing through the mechanical expansion of the gate (Figure 6). When lifted, both of the slab gates cavity allows the media to flow. The upward force on one slab and the stoppage of the second slab, by a step in the valve body, allows for outward mechanical expansion for a proper seal. When closed, the slab gates block the media flow, and the downward force (stem) on one slab and upward force (step in valve body) allows for outward mechanical expansion for a proper seal.

These valves provide an effective seal simultaneously for both upstream and downstream seats. This seal makes them ideal for applications like isolation valves in power plants, block valves in process systems, and high-temperature valves in refineries.

Expanding gate functioningFigure 6: Expanding gate functioning

Knife Gates

Knife gate valves are for thick fluids and dry bulk solids. The gate is only one piece of metal, which is typically pointed. These valves are self-cleaning as they pass the seat rings every time they open and close.

Stem design

The gate is raised and lowered by the spinning of a threaded stem. A manual wheel or actuator spins the stem. Depending on the design, the stem is either considered rising or non-rising. So, as you spin the stem it either raises or stays in place with the spin as seen in Figure 7.

Outside Screw and Yoke (OS&Y), also referred to as rising stems, are fixed to the gate. Therefore, the threads are on the actuation side. So, as the gates raised or lowered, the stem moves with it up and down. Consequently, they have built-in visual indicators of the state of the valve and are easily lubricated. Since they have moving components, they cannot be used with bevel gears or actuators. Therefore, rising gate valves are suitable for manual actuation.

On the other hand, a non-rising stem is fixed to the actuator and threaded into the gate. An indicator is often threaded onto the stem to show the open or closed state of the valve. Non-rising gate valves are common in underground installations and applications with limited vertical space.

Mechanism of rising stem gate valves vs non-rising stem gate valvesFigure 7: Mechanism of rising stem gate valves vs non-rising stem gate valves

FAQ

What is a gate valve?

A gate valve controls the medias flow by lifting the gate (open) and lowering the gate (closed).

How does a gate valve work?

By rotating the manual handle, the threaded stem moves the gate up and down. As the gate goes up it opens and down it closes the media flow.

What is a gate valve used for?

A gate valve is for on and off flow control.