When to use gate valves and when to use ball valves

When to use gate valves and when to use ball valves

Ball valves and gate valves both belong to the same family: shut-off valves. When inside a hydraulic system, these mechanical devices interrupt or regulate the flow, depending on whether the valves are fully open or closed, or if they are used in intermediate positions.

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It is important to specify that ball valves, given their fast opening and closing mechanism, are not used to regulate the flow but only to stop or interrupt it.

Gate valves, instead, can be partially open during use, even if it should be remembered that in this case the liquid can become disturbed and friction losses can occur.

Gate valves: flow stopping and choking

Gate valves are used to isolate specific areas of the water supply network: during maintenance, in order to do maintenance, with new installations, or for deviating the flow through the conduit. A completely free passage and minimum pressure drop are the strong points of gate valves. If used in an intermediate position, these valves choke the flow in the conduits.

Gate valves get their name from the shape of their closing disc, which can be straight, like a guillotine, or inclined (wedge). The first solution is preferable above all for high delivery capacities, but in both cases it is always the closing disc that determines valve closing or opening according to whether it is raised or lowered. The valve is opened and closed by the rotary movement of a threaded stem connected to the closing disc. To move from closed to open and vice versa, the handwheel needs to be turned a few times. It is therefore a slow operation, which has the advantage of avoiding dangerous hydraulic shocks.

Ball valves: speed and versatility

Commonly used in civil and industrial applications, ball valves get their name from their round closing disc; the disc has a bore that is coaxial to the flow.  When the valve is open, the hollow ball becomes a part of the conduit and allows the fluid to flow; when it is closed, the flow is completely blocked. To open or close a ball valve, just give it a quarter turn, making the ball rotate along the same axis as the fluid flow, and as such the piping. Even though this quick movement can be made manually (think about taps in a home), it can just as easily be automated, for example using a pneumatic actuator, in the case of industrial systems.

(read also Motorised valves with pre-assembled pneumatica actuator: the advantages of a perfect combination)

As anticipated, the quick movement can cause hydraulic shock; the wave generated by the movement of the fluid when stopped quickly can damage the piping, a problem that is solvable by installing check valves along the piping.

(read also How to prevent water hammer consequences and avoid damages)

Which are better: gate valves or ball valves?

In conclusion, here is an outline of the strong points, and differences between, these two types of valve:

when fully open, gate valves and ball valves both have scarce pressure loss and, as such, an optimal hydraulic yield;

ball valves cannot be used to regulate the flow, while gate valves can, even when at the intermediate position;

ball valves are easy to move: just turn the handwheel 90° to open or close the valve. This fast movement, however, favours hydraulic shock;

gate valves are slow to open and close, and this is why they tend to avoid overpressure waves;

to avoid clogging, ball valves should be used with clean water and fluids that do not contain suspended particles;

gate valves can be used with denser, more dirty liquids, for example wastewater and sludge.

How It Works: Gate Valves

Stem

Gate valves can have a rising or nonrising stem design. Rising stems are attached directly to the gate and provide a visual indicator of the valve position. Nonrising stems are generally threaded into the upper part of the gate and have a pointer threaded onto the top to indicate position. Nonrising stem designs are ideally suited for applications where vertical space is limited, in well applications, and where scraping or pigging is not required.

Gate valves are designed with a sealing unit to provide a tight seal around the stem. Our patented single loaded-spring (SLS) stem seal design, used in Saf-T-Seal Slab Gate valves and WKM Pow-R-Seal double expanding gate valves, provides superior leak protection and a self-adjusting seal designed to reduce maintenance.

Bonnets

Gate valves generally have one of four types of bonnets, which provide closure to prevent fluids from leaking out of the valve. Screw-in bonnets are simple, durable sealing units that use pressure to seal. Union bonnets provide easy access to the valve body for applications that may require frequent maintenance or inspection. Bolted bonnets are generally used for larger valves in higher-pressure applications. Pressure seal bonnets are designed for services with pressure in excess of 2,250 psi [15 MPa].

Applications

Because of the diversity of construction materials, trim offerings, and design combinations available with gate valves, they are appropriate for a wide variety of applications. From high-temperature coking units to food and pharmaceutical services, gate valves can be trusted to reliably perform.

The protected seat-face design of double expanding and slab gate valves eliminates degradation of the seat face caused by debris in the process fluid, which makes them ideal for liquid service. When additional protection is needed at points in pipeline applications where operational integrity is vital and the consequences of environmental exposure are higher, such as near waterways and municipalities, double expanding gate valves are a particularly wise choice.

Our smaller 2- to 4-in nonrising stem version of the Pow-R-Seal API 6A Expanding Gate Valve is commonly used in wellhead manifold systems because of its reliable mechanical seal and high pressure capability.

Drilling manifold systems can also be easily designed to use certain gate valves, such as the Cameron DEMCO valve DM series, with space-saving and versatile mounting designs.

In the power industry, NEWCO gate, globe, and check valves and DOUGLAS CHERO forged-steel gate, globe, and check valves are ideal for standard and critical applications, such as steam distribution in power plants. By replacing the body and bonnet flanges with a welded connection, the design of this valve eliminates a leak path, reduces weight, and simplifies the application of exterior insulation. This, in concert with the forged steel body, provides the highest integrity sealing available.

For challenging subsea environments, where pressures are extremely high, temperatures are low, and operation is difficult, subsea manifolds that integrate valves and interface panels are used for critical isolation. The simple design of the Cameron RING-O subsea valve is ideally suited for integration into these systems and can be actuated manually, via ROV, or hydraulically for ease of operation.

Gate Valve Actuator

What is a gate valve?

Gate valves are linear valves where the closing membrane is a wedged disc or gate which moves perpendicular to the flow, allowing more flow as it moves away from the seat. These valves usually have metal seats and are bi-directional, the gate is wedged into the seat for which reason they are thrust seated valves. Gate valves are designed to be used as isolation or on/off valves therefore, are usually in a fully open or fully closed position. Normally in industry, they are flanged but also are offered in other connections such as threaded or welded.

Gate Valve Applications

They are often found at the end of pipelines where they serve as a final barrier against leaks before connecting into other pipelines or tanks, also very commonly used as isolation valves to do maintenance on other piping equipment such as pumps or control valves. Because of their seat design, they are used in extreme temperature applications and this makes the gate valve very useful in applications in chemical plants, oil refineries, mining processing, etc.

Gate Valve Advantages

Gate valves contain very low friction loss because they do not obstruct the passage of fluid when fully open. This helps to save energy and reduce operating costs.

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Are available in large sizes

Easy to maintain and disassemble and are relatively inexpensive

Can be used with slurries and viscous liquids

Bidirectional

Most wedge gate valves are metal seated which allows them to be used in high-temperature applications.

Gate Valve Disadvantage

They have slow open and close times due to their linear opening characteristic.

Gate valves are difficult to repair since the valve seating surfaces are complex

In systems where high-temperature changes rapidly, due to the load in the pipe at the valve end, leakages in gate valves occur.

They have a large design, so they are heavy valves and need good mechanical support in the pipeline.

Higher costs compared to valves of a more compact design.

Most gate valves are metal seated, which affects the ability to provide tight shutoff

Gate Valve Actuators

The gate valve has a long history and the first valve patent ever issued was for a gate valve in . In those times, steam was used to control the actuation movement. This long history makes for a technology that has not seen much change but has an extremely important function for industrial process control.

Gate valves, like any other type of valve, need an energy source to be operated. The energy required depends mainly on the design and the pressure differential across the valve. Gate valve actuators can be selected depending on the source of power (hydraulic, pneumatic, electric, etc.) to the actuator.

When pneumatic pressure is available, gate valve actuators can be:  

 Double-Acting Valve Actuator, for double-acting actuation

Spring-Return Valve Actuator, for single-acting actuation

When hydraulic pressure is available, gate valve actuators can be: 

Double-Acting Hydraulic Actuator, for double-acting actuation

Spring-Return Valve Actuator, for single-acting actuation

When electric power is available: 

Electro-hydraulic Linear Actuator, for double and single acting actuation

Gate valves, also called sluice valves, are more likely to be found in older houses. Their mechanism usually involves a knob that, when turned, lowers or raises an internal gate or wedge to control the water flow rate. The familiar outdoor spigot for a garden hose is a good example of a gate valve.

Gate valves allow you to control the rate of the flow of water, from a slow trickle to a full flow, but don’t provide an immediate stop. They are usually controlled by a manual handwheel that requires more than a 360-degree turn to change the gate’s position.

Tip: Some areas require the use of gate valves placed before and after the water meter in certain systems. This makes it easier for your water department to swap out the meter if needed.

Ball valves, also called shut-off valves, tend to be found in newer homes. Ball valves use a handle to control the placement of a hollow, perforated sphere in the mechanism. When the handle is turned, the hole immediately opens or closes the water flow. This mechanism is a lot quicker than a gate valve because a ball valve needs only a 90-degree turn to go from open to completely closed.

Tip: You can tell by the handle placement whether the ball valve is opened or closed. When open, the handle lies flat, in alignment with the flow. When the ball valve is closed, the handle sits at a 90-degree angle to the flow.

Now that you know the differences between the two mechanisms, we can compare other factors between ball valves and gate valves.

• Cost: Gate valves tend to be more wallet-friendly than ball valves
• Reliability: Gate valves are more susceptible to corrosion. Over time, the internal stem that connects the knob to the gate becomes more likely to fail.
• Frequency of use: Since gate valves wear out quicker, they are often found in applications where they don’t need to be adjusted very often. Ball valves are recommended for applications that require frequent, quick control over the flow of liquid.
• Space: Ball valves are smaller than gate valves, but the size of their levers means that they require more space for proper operation
• Number of ports: If your application calls for a multi-port flow pattern, then a ball valve will likely be your choice because they are much more widely available in multi-port configurations
• Water hammer: Because ball valves can open and close immediately, they are more likely than gate valves to cause water hammer. When a valve is quickly closed on water moving at high pressure through pipes, it can cause shock waves through the plumbing that create a hammering sound. Under high enough pressure, a water hammer can cause a pipe to weaken and break. For that reason, users are advised to turn the ball valve lever slowly to avoid water hammer.

Since gate valves and ball valves have different strengths, you can find each commonly used in different industries. Gate valves often turn up in large water supply lines, mining and power plants. You’ll see ball valves being used in places like the automotive industry, manufacturing facilities and in food and beverage equipment.

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