5 Must-Have Features in a globe valve in ship

What is Globe Valve used in Ship？

Globe valves, commonly found in marine applications, are linear motion valves that are designed to start, stop, and regulate flow. In some cases, specialized globe valves are also used for isolating and throttling functions. These valves exhibit higher pressure drops when compared to straight-through valves like ball and gate valves.

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A globe valve used in ship will not vary much from a standard globe valve. This valve has a bulbous body shape and consists of two main parts – the valve seat and a disc. A globe valve is constructed in such a way that its valve seat and disc are perpendicular to the axle of the valve. To set the valve in the open position, the axle is turned to move the disc away from the valve seat.

The Main Function of a Marine Globe Valve

A globe valve can be used for three main purposes – to start the flow, to shut off flow completely, and to regulate media flow. By rotating the axle of a globe valve, a user can control media flow. This is why a globe valve is a good option for throttling function. In some cases, certain types of globe valve are also used as check or pressure relief valves. 

The primary function of marine globe valves is to prevent leakage and manage excess seawater onboard ships. The basic use of globe valve in ship is not to start or stop flow but to regulate fluid flow.

Globe valves can be of three types based on their construction – Z-body type valve, Y-body type, and Angle valve. Among these, the Z-body type globe valves are the most commonly used – these are preferred for applications that involve water flow. Y-body type valves are employed in situations where pressure resistance is a problem. Angle globe valves are more or less structured like Z-body valves but the diaphragm is a flat plate.

Common Applications of Onboard Globe Valves

Globe valves find several applications on board ships. Primarily, these valves are used to regulate seawater in bilge systems – these valves are installed in pipelines that connect to the emergency bilge suction lines. This is because these valves are responsible for pumping out excess seawater from ships. 

Also, the reason why global valves are used in bilge suction is that they work well where variable pressure is required.

A globe valve used on ships can also be used for many other applications:

Globe valves can serve as a non-return valve to prevent back flooding.

Some variants of globe valves are used in sewage and waste treatment onboard.

A globe valve used in ship prevents excess seawater from entering the ship.

Features of a Marine Globe Valve

Marine globe valves are similar to standard globe valves in many ways, but there are a few defining features that make the former a suitable choice for onboard applications. For instance, a globe valve used in ship is manufactured from materials that keep them durable even when the valves are in constant exposure to seawater. 

Here are a few defining characteristics of globe valves used in marine applications:

They come in 3 different variants, each of them offering special advantages.

Globe valves have excellent shut-off capability.

Compared to ball valves, the throttling capacity of a globe valve is better.

They are easy to manufacture, install, and maintain.

These valves have a short open-close time, making them suitable for emergency situations.

The sealing properties of globe valves are excellent.

Maintenance

While globe valves require comparatively lesser maintenance, there are still a few things that every engineer should make sure to inspect. When it comes to maintenance of marine globe valves, here are some important things to keep in mind:

The gland area of the globe valve is prone to wear and tear with continual usage, so it is necessary to replace the parts to ensure optimal sealing.

When the valve is not operated often, the valve can be cycled temporarily.

If the valve is opened and closed frequently, the valve seat will be damaged – this must be taken into attention.

If the marine globe valve is not made of the right material, then it will be prone to corrosion.

Over-tightening the bolts in the gland of the globe will cause damage.

Conclusion

Globe valves serve a special function on ships – while ensuring that wastewater does not leak into the ship, these valves also prevent back flooding. Also, marine globe valves regulate the amount of seawater that enters a ship through a bilge system. The installation and maintenance of the valves need a close inspection – this ensures that no leakage or flooding occurs.

Angle Seat Valve Working Principle

Angle seat valves, also known as angle body piston valves or pneumatic angle seat valves, are 2/2-way pneumatically actuated piston valves. The piston actuator provides a linear motion to lift the seal off its seat. Because the seat is positioned under an angle, the flow is minimally impeded in the open position, resulting in an excellent flow rate and a low pressure loss. They are used to regulate the flow of liquids, gases, steam, vacuum, and even aggressive fluids. They can also operate with high temperatures and high viscosity media, even under zero differential pressures.

The robust design makes angle seat valves a popular choice for harsh applications, and they have very high cycle lives. Therefore, they are excellent long-life alternatives to ball valves. These valves are also suitable alternatives for solenoid valves, especially with contaminated, viscous media where typical solenoid valves would fail. They may be operated using a single-acting or double-acting configuration, which has an influence on its pressure rating. They can also be designed as manually operated or electrically operated, but in this article, we will focus on the pneumatic angle valve.

Construction and design

Angle seat valves have a robust construction similar to globe valves but use a piston-operated angle type valve with a closure spring. The body is normally cast or die-forged in one piece. A plug is connected to the end of the piston which is seated on PTFE seats. The piston is designed to retract further from the seat, thereby providing maximum flow rate. They may be Normally Closed (NC), Normally Open (NO), or Double Acting. The piston actuator comes with threaded ports or with NAMUR ports which allows for direct mounting of NAMUR style solenoid valves.

Figure 2: Section view of an of angle seat valve.

Often, the actuator head can be rotated 360° to allow the optimum position of air and electric lines in tight locations. The valve body is generally made of brass or stainless steel. Connection types include threaded, clamped, or welded. Typically, a visual indicator on the top of the piston shows whether the valve is open or closed.

Working principle

Angle seat valves are operated pneumatically such that air pressure is used to control the piston actuator, which lifts the valve plug off its seat. Normally Closed (NC) valves usually have the valve closed in unpressurized conditions and use a spring to return the valve to the rest state. Normally Open (NO) valves have the valve opening always open unless air pressure acts to close it. A NO valve can be obtained if the spring is placed on the opposite side of the piston actuator. Double Acting valves can be used to handle flow in both directions. These valves have no spring and depend on the supply air to determine the valve position.

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Flow up and under the valve (causing the valve to open) will reduce the water hammer effect but reduces the maximum working pressure of the valve by typically 50%. However, fitting a strong return spring will help increase the working pressure, but a larger actuator will be required to overcome this increased spring strength. With flow over the seat (causing the valve to close), full working pressure is achieved, and water hammer can be reduced by restricting the compressed air supply flow.

Controlling the angle seat valve with a solenoid valve

Normally, a three-way solenoid valve is used to operate NC or NO angle seat valves. These angle seat valves have one connection port to the piston chamber. The solenoid valve controls whether the chamber is pressurized or vented. Double-acting angle body valves have two connection ports and cannot be controlled with a single three-way valve. They can be controlled by a five-way solenoid valve that can pressurize one port while venting the other, and vice versa.

Application

These valves can be used to deliver millions of cycles of operation in demanding applications such as steam, water, and aggressive media. They are ideally suited for vacuum applications and can be used in fast-acting applications up to cycles per hour with an expected life of over 10 million cycles. They are used in many industries, including food & beverage, chemical, oil and gas, water and sewage, etc.

Angle seat valve selection

End connections and line size

Angle seat valves come in various sizes and end connections, ranging from 1/2 to 3 BSP or NPT threads, with some manufacturers offering flange options. The nominal diameter (DN) of the valve seat and the Kv-value, which indicates the flow rate of water at a pressure drop of 1 bar, are essential for selecting the right size. Use our valve sizing calculator to determine the minimum required Kv-value for your application, ensuring high and efficient flow with minimal wear and leakage.

Operating temperature, pressure and material properties

The maximum working pressure typically ranges from 5 to 20 bar. Consider both the media pressure and the compressed air circuit pressure range. Angle seat valves can handle temperatures up to 200 °C with PTFE (Teflon) sealing, while other materials like NBR, FKM, and EPDM have lower temperature ratings. The choice of housing material, such as bronze, stainless steel, brass, plastic, or gunmetal, affects the temperature and pressure rating, with stainless steel providing excellent corrosion resistance and material strength. For high-pressure or high-temperature applications, opt for a stainless-steel housing with PTFE seals.

Valve installation and maintenance

Proper angle valve installation is critical for performance and safety. Ensure that the valve is installed according to the manufacturer's specifications. Regular maintenance checks are necessary to prevent leaks and ensure the valve operates efficiently.

Globe valves are operated with a handwheel and modulate water flow. But they also cause higher pressure loss.

Picking the right valve is important, as different types have different features and uses. Some of them only have two states: open or closed. Others allow fluid flow and pressure to be modulated. Distinct valves also cause different amounts of pressure loss. Depending on the situation, specific features are needed.

One of the most common types of valves is the globe valve. In this article, we explain how globe valves work, including their advantages and disadvantages. Then, we look at the different shapes of globe valves and compare them to other types of devices, like gate valves and ball valves.

QRFS stocks a wide range of valves, including globe valves. Shop T-shaped globed valves and angle valves now.

What is a globe valve, and how does it work?

To decide if a globe valve is right for your application, consider its three core features. First, they are lateral movement valves, which means they open or close based on the up-and-down movement of a stem. Second, they allow, stop, or throttle fluid flow. Some valves have only open and closed states, but globe valves can throttle flow without totally stopping it. Third, they cause significant head losses compared to other valves, a tradeoff for the throttling services.

How globe valves work

From the outside, globe valves have three parts, a handwheel, a bonnet, and a body. The bonnet houses a stem, and when the handwheel is turned, the stem screws up and down in the bonnet. The end of the stem has a small component called a disk or plug, which can be metallic or non-metallic and may come in different shapes, depending on the need.

The globe-shaped body for which the valve is named houses a seat. The seat is a metal frame that divides the body into two chambers and has a hole to allow fluid to pass. When the valve is open, fluid flows up through the opening in the seat. To close it, the stem is screwed down until the disk blocks the seat’s opening.

One of the main advantages of globe valves is their ability to throttle or modulate flow. Besides being closed or open, they can also be partially open. This allows you to adjust flow without totally stopping it.

The main disadvantage of globe valves is the comparatively significant head loss they create. Head loss, also called pressure loss, refers to the amount of resistance a liquid encounters as it flows through pipes. The more resistance, the more pressure that is lost. Gravity, friction (of the fluid against the walls of the pipe), and turbulence all cause this loss. Valves and fittings cause pressure loss mainly through turbulence.

Globe valves force fluid to change directions as it passes through, creating loss and turbulence. The exact amount of loss depends on factors like fluid velocity and friction factor. However, it’s still possible to review the pressure losses from different valves using a metric called the L/D coefficient.

A valve’s L/D coefficient lets us compare it to a straight section of pipe with the same friction factor. L and D stand for length and diameter, respectively. A valve with L/D=5 creates the same friction loss (all else being equal) as a section of pipe with a length-to-diameter ratio of 5. The larger L/D is for a component, the higher the head loss it creates.

A standard globe valve has an L/D=340, compared to an L/D=30 for a 90-degree pipe elbow.

Globe valve shapes

Globe valves come in three shapes—t-pattern/z-pattern, y-pattern, and angle pattern. Each form stops or throttles fluid flow in the same way, but the path of flow—and thus the head loss—differs.

Most globe valves are t-shaped globe or z-shaped. They are called “t-pattern” for the profile of the valve—the inlet and outlet of these valves are in a straight line. “Z-shaped” is arguably more descriptive, however, because it refers to the path of the water as it flows through the valve rather than the device’s external shape. In the standard z-shaped globe valve, the water changes direction twice in a pattern that resembles the letter Z. As mentioned, standard Z-shaped valves cause the most significant head loss, with an L/D=340.

Y-pattern globe valves are modifications of z-pattern valves. The inlet and outlet are still in a straight line, but the bonnet and stem are placed at an angle to the body (as opposed to perpendicular), forming a y-shaped profile. This provides a straighter path for the water than the z-shape, reducing head loss. For y-pattern globe valves, L/D=55.

The inlet and outlet of angle valves are oriented at 90 degrees from one another, and these devices serve both as elbows and valves. Because they only make fluid change direction once, they create less head loss than z-shaped valves, with L/D=150.

When to use globe valves

Globe valves are ideal whenever you need to modulate flow, but you don’t have to worry about the amount of pressure loss. Some applications include:

• Cooling water systems
• Fuel oil systems
• Feedwater and chemical feed systems
• Turbine lubricating oil systems
• Drain and trim applications in fire sprinkler or other water-based fire protection systems

Globe valves aren’t the best choice for control valve applications in fire sprinkler systems, where pressure is at a premium. Instead, butterfly valves are commonly used.

Globe valve vs. gate valve

There are several alternatives to the globe valve, and understanding the different options can help you pick the right valve for the job. Two major alternatives to the globe valve are the gate valve and the ball valve. First, let’s consider the differences between globe and gate valves.

Gate valves, like globe valves, are linear-motion valves. They are opened and closed by turning a handwheel that screws a stem in and out of the bonnet. When a gate valve is closed, an obstruction is pushed down by the stem perpendicular to the path of the fluid.

Unlike globe valves, gate valves don’t require fluid to change directions—the flow path is straight. As such, gate valves cause very little head loss (L/D=8). However, they do not throttle as well as globe valves—fluid flow rate in a gate valve is not proportional to how open the valve is at any moment.

Globe valve vs. ball valve

Unlike globe valves and gate valves, ball valves are rotary-motion valves. This means that ball valves open and close when the obstacle rotates rather than opening and closing with the lateral movement of an obstruction. Specifically, a ball-shaped component with a hole through it spins in its housing, either stopping the fluid or letting it pass.

Instead of turning a handwheel, a ball valve is typically opened or closed with a wrench handle. Only a quarter-turn (90 degrees) is needed to open or close it—much faster than turning a handwheel multiple times. Quick closing can actually be a problem because of water hammer. When fluid flowing through a pipe is suddenly stopped, its momentum has nowhere to go because water is non-compressible. Water hammer occurs when a pressure wave propagates back through the pipe, potentially causing damage.

Since ball valves don’t force water to change direction, they create very little head loss (L/D=3). As with gate valves, this low pressure loss comes with the tradeoff of little throttling capability. Ball valves are either open or closed, with little in-between.

Globe valves adjust flow, but be careful of the pressure application

When building a piping system, it’s important to choose the right components for the job, which is especially true with valves. Because globe valves force water to change directions even when fully open, they create comparatively large pressure losses. One of the core advantages of globe valves, however, is their ability to modulate water flow. They can be open, partially open, or closed.

Gate valves and ball valves, two alternatives to globe valves, cause minimal pressure losses. However, they don’t provide throttling services like globe valves. For applications where pressure is at a premium, gate or ball valves are better choices than globe valves.

Shop our inventory of standard (z-pattern) globe valves and angle valves. For other options, shop our full selection of valves, including ball valves.  If you don’t see the item you need, contact us, and our customer service team will help you out.