Globe Valve vs Gate Valve: Need to know Critical Facts – Lambda Geeks

10 Aug.,2022

 

how does a globe valve work

Globe valves and gate valves are used for different applications. This article discusses about the topic globe valve vs gate valve in detail.

Globe valves are used for regulating the flow whereas the gate valve is used to completely shut off the flow. Lets see more differences in detail in further sections of this article.

What is a globe valve?

A globe valve is a type of control valve that is used for regulating or controlling the flow in a pipeline.

It is different from a ball valve. It consists of movable plug and a stationary ring seat fitted generally inside a spherical body.

Image: Globe valve

Image credits: Wikipedia

What is a ball valve?

A ball valve is also a type of control valve that is used to regulate or control the flow in pipeline.

It is different from a globe valve. It has a hollow or perforated ball which is used for controlling the flow of fluid in the pipeline.

Where is a globe valve used?

Globe valve finds its applications in more areas than a gate valve does as it can be used for regulating flow and pressure as well.

Globe valves are most commonly used in plant piping. They can be used as a pressure relief valve or a check valve and they are also suitable for manual and automatic operations.

Which is better gate valve or ball valve and why?

A gate valve may be cheaper but it has many disadvantages over ball valve. So application wise, ball valve is superior than a gate valve. Although in high pressure applications, gate valve is desired more. Lets see why.

  • Gate valves are susceptible to corrosion, whereas ball valves are less likely to undergo such process.
  • Ball valves provide a tighter seal and prevents leakage.
  • A gate valve is superior in high pressure applications because ball valve has short opening and closing time which results in water hammer.

How do I know if my globe valve is open or closed?

A globe valve consists of a stem, bonnet and plug. The relative positions of these can determine whether the globe valve is open or not.

If the stem is completely inside bonnet, then the plug will rest on body where a hole is given for the water to flow. This means the globe valve is closed. If the stem rises from the bonnet then it is in open condition.

To open or close, one has to rotate the handle as done with screws.

Can globe valve be used for isolation?

First we need to understand what is isolation valve, it is simply a valve that can stop the fluid flow process to given location.

A typical globe valve can be used for lowering the pressure as well as isolation purposes. But globe valves show higher pressure drop than straight through valves (I.e ball valve, gate valve etc). So, a globe valve can be used for isolation when pressure drop is not a controlling factor of the flow.

Can a gate valve fail?

Absolutely yes. Every mechanical component has a life expectancy and so does a gate valve. Following are the cases where it can fail-

  • Most commonly it fails due to wear and corrosion.
  • Jamming of a gate valve takes place if not used for quite some time.
  • Freezing of bonnet can break the valve resulting in massive flooding.
  • Some amount of liquid can leak through the seats so that leakage factor has to be kept in mind.

When would you use a gate valve?

Normally gate valves are used when the liquids need to be shut off rather than being regulated.

Gate valves can be used in following scenarios-

  • When liquid needs to shut off.
  • When minor leakage of liquid is not an issue (eg. Heater circuits and sewer pipes etc.)
  • Low pressure applications where friction won’t be significant.

Can a gate valve reduce pressure?

Yes, a gate valve can reduce pressure if a bypass controller is attached to it.

The gate valves with larger diameters are fitted with a bypass controller. This way the pressure is reduced by a significant value before even reaching the valve itself. Pressure is reduced because in high pressure, the friction becomes a significant problem.

How can you tell if a gate valve is open or closed?

There is no visual indicator that indicates whether the gate valve is open or closed. However, the position of knob can be used to determine whether the valve is open or closed.

A gate valve consists of a knob which when rotated counter clockwise, opens the valve and closes when turned clockwise. As it opens the valve, knob rises up indicating that the valve is open and closed when the knob is resting on the bonnet.

Is globe valve a control valve?

A globe valve can be called as a control valve.

Globe valve can be used to regulate or completely stop the flow making it a control flow valve.

Is globe valve unidirectional?

Yes, a globe valve is unidirectional. Unidirectional means that it allows flow in only one direction, it cannot change the direction of the flow completely.

When compared to other valves, only gate valve is bi directional whereas globe and check valves are uni directional.

How do you free up a gate valve?

A gate valve can be jammed if not used over several years. It has to be tested after certain period of time else it will be damaged and we would not even know.

To open up a jammed valve, we can simply try moving the knob back and forth slowly with a plier. This way the jamming will open up gradually. Remember not to do it very fast else it might get damaged.

Can you adjust a gate valve?

It is very easy to adjust a gate valve or rebuild it again after dismantiling it. First we check the position till where the knob goes inside.

If the knob goes completely inside then the valve need not be fixed. If it goes upto only a certain length, then we will have to flush it out. Flushing means getting rid of excessive or unwanted materials lying inside the valve. This can be done by loosening one of the screws in the body.

What are the advantages and disadvantages of gate valve?

Each and every mechanical component has its own advantages and disadvantages.

The advantages of gate valves are-

  • They have very less fluid resistance–  The shape of this valve allows the fluid to flow with minimal fluid resistance.
  • They have a leak proof seal- The opening and closing mechanism of this valve are superior than shut off valves.
  • They have wide range of applications- Gate valves can be used for oils, steam or even granular solids like Alumina. They can be fond in a wide range of applications.
  • Gate valves are bidirectional- Unike globe valves, as discussed above, gate valves are bi-directional meaning they allow dual fluid flow directions.

The disadvantages of gate valves are-

  • The closing and opening speed of these valves is very slow– This particular disadvantage makes this valve undesirable for applications requiring rapid actions.
  • These valves can get scratches easily- Scratches may seem normal but eventually they grow and affect sealing capability of the valve.

How many turns does it take to open a gate valve?

Number of turns required for closing or opening a gate valve can be found out using the AWWA formula.

Number of turns is equal to three times the nominal valve size plus two or three turns of the operating nut.

For example 5 x 3= 15 plus 2 or 3= 17 or 18 turns.

Function of globe valve and gate valve

The function of globe valve and gate valve are given in the table as shown below-Globe valveGate valveRegulates, starts and stops the flow of fluid.Used for completely shutting off flow of fluids rather than regulating.Can be used as ON/OFF valve.Used in heating circuits and sewer piping.Can be used for throttling purposes.They are used with large pipe diameters because they are easy to construct.Table: Functions of globe valve and gate valve

Globe valve types

The term globe doesnt necessarily mean that the valve will have a round shape. In addition to that, it comes in various types. They are-

  • Tee-This is the most common type of globe valve. They are used in throttling purposes. The horizontal design of the seat allows the stem as well as disk to travel perpendicular to the horizontal plane.
  • Angle-The name suggests that there is an angular turn inside this valve which is true. The ends of this valve are at ninety degrees allowing the flow to flow in a perpendicular direction to handle the slugging effect.
  • Wye-This valve is an alternative for high pressure drop found in globe valves. The angle between seat and stem are forty five degrees which provides a better flow path with lesser resistance to flow.

Globe valve vs butterfly valve

The differences between a globe valve and butterfly valve are given below-Globe valveButterfly valveThe disc of the globe moves in a straight line.Butterfly valve has a plate shaped disc that rotates around its own axis.Main parts are bonnet, stem, body and handwheel.Main parts are valve body, stem, butterfly plate and sealing ring.Can be used for cutting off or regulating the flow of fluid.It is used for flow regulation mostly for throttling purposes.Table: Difference between globe valve vs butterfly valve

How does a gate valve work?

These valves work by inserting a gate (mostly rectangular) or wedge between the path of flow. This plate is actuated by threaded stem which itself is actuated by hand or electric motor.

How does a directional valve perform in three functions?

A directional valve is designed to work only in three functions.

The three functions in which the directional valves work are- stop the fluid flow, start the fluid flow or change the direction of fluid flow.

How do you lubricate a ball valve?

Lubrication is necessary else the ball inside the ball valve will jam and the valve will be rendered useless.

We can lubricate the ball valve by spraying penetrating lubricant around the ball valve handle precisely between the coloured handle and the pipe portion of the ball valve. After applying lubricant, turn the knob back and forth so that the lubricant can pass through the tight crack and enter the body of the valve.

This way the lubricant can penetrate inside and lubricate internal components of the valve too.