Knowledge of globe valves
The globe valve is the valve whose valve discs (valve clacks) are driven by valve stems, moving linearly along the axis of the valve seat (sealing surfaces) up and down. The globe valve is generally composed of the drive member (the handwheel), valve stem, valve body, valve bonnet, valve clack (the closing member) and packing device. The hand wheel is connected with the valve stem and the valve stem is used to drive the valve clack so that the valve clack can move along the direction of the axis of the valve seat up and down. In that way, the pipeline can be turned on or off.
The globe valve is widely used and is mainly used in high pressure and small diameter occasions. Generally, the biggest diameter of the globe valve is DN400 (NPS16). The globe valve with a larger diameter is only applied to special pipelines. For example, a large oxygen pipeline uses stainless steel globe valves with large diameters, because other valves are easily on fire caused by friction.
Benefits of using globe valve
Globe Valve is an equipment that has been widely used in the plumbing industry because it effectively controls fluid flow in both opening and closing mechanism and in throttling service. The movement of the fluid through the valve changes from time to time and this is the reason why the pressure drop on the valve increases during the course of use. More often than not, such type of valve contains a stem that is vertically positioned towards the body and the higher pressure fluid stream linked to its pipe provides a tight seal in situations where the valve is fully closed. During the early years, valves are typically designed with metal disks and seats but due to the recent developments with the technology, a number of manufacturers produced valves that have elastomeric disk seal and this innovation have generated valves that are inexpensive and easy to repair.
Going further, in order for this equipment to become fully functional, the parts of Globe Valves should always be in a superb working condition and all of it should be properly installed and connected to one another. This equipment indeed demands money and effort and it is just essential that its operator will be able to use it to the fullest. The information below shows the benefits of using this valve.
- One distinctive feature of this valve would be its close regulation. Close regulation is achieved through the proportional relation of the size of the seat opening towards the number of turns executed in the hand wheel. Through this, the operator can manipulate the frequency of flow based on the number of turns made to the hand wheel.
- This type of valve requires fewer turns and this benefit allows the operator to save time, work, and wear. In cases wherein wear happens as an outcome of a severe operation, this simply indicates that the operator needs to still maintain the valve only that it requires easy repairs or renovation.
- The seat and disk can be repaired with ease because there is no need to remove the valve from the pipeline.
Generally, this type of valve can be assembled to ensure that the disk closes against or in the similar direction of the fluid circulation. Once the disc closes against the direction of the flow, the kinetic energy of the fluid delays the closing mechanism but aids in opening the valve. On the other hand, if the disk closes in the same direction of the flow, the kinetic energy generated from the fluid will assist in executing the closing mechanism and will block the opening. This procedure is ideal most especially for operators who are looking for a device that contains a quick acting stop valves. Given that this valve contains a lot advantages, some pitfalls are still present and it includes large openings for disk assembly, its plank mounting of the disk towards the stem, and it is heavier than other valves that contains similar flow rating.
Overall, the uses of Globe Valves prove to be beneficial in monitoring fluid movement that passes through the pipelines. Ensure that you are able to examine the performance of the valve on a regular basis in order to address concerns about its entire functioning.
There is nothing to deny that proper care and safeguarding your Globe Valve can certainly keep it in an outstanding working condition. Such valve indeed is a piece of investment and it is just essential to know the ways on how to maintain it to secure that it provides a consistent performance; making use of valve selection guides can give details that specify important measures that you need to see in this equipment. More often than not, most of the problems that this equipment acquires would be coming from leakages present in seat, disk, stuffing box, sticking valve stems and loose valve disks. If these problems will not be addressed the earliest time possible, its functions can for sure fluctuate and the possibilities of wasting a substantial amount of air, steam, or fuel will definitely occur during the course of use thus, money is likewise wasted.
Gaining awareness regarding valves and the methods of its preservation can give you a head start on how you can avoid further problems from happening in the future. Making a habit of checking proper valve operation can initially tell if something is wrong with your equipment; leakages greatly affects the direction flow of pressure in the valve and this should be addressed right away. Deeming that there are a variety of reasons regarding leakages in the Globe Valve, the information below explains some of its causes and remedies that can aid in fixing the difficulties present in your equipment.
Problem 1: If the equipment is loaded with scales, dirt, or heavy grease, this can already prevent the disk from being properly positioned.
Solution: In instances where the obstructing material cannot be blown through, it is best to open the valve and clean it thoroughly.
Problem 2: Erosion can potentially cause scraping of the valve seat or disk.
Solution: Examine if the damage is minimal and if it is, the valve can still be restored and it can go back to its proper working order. Nevertheless, if the damage is substantially massive, the valve should be repaired and re-seated so that it can function again.
Problem 3: Fitting the guides way too tight and bending the spindle guide and valve stem can result in disk distortion. If you are making use of a valve disk that is too weak, it can potentially cause damage.
Solution: If the conditions mentioned above become present in your equipment, it is time to replace the valve.
Problem 4: Occurrence of packing gland leakage; this problem can persist if the valve stem is scored o bent.
Solution: The remedy for this can be done by tightening the gland or by means of repacking it. If repacking the gland would be necessary, it is just essential to know if it is the string type or the ring type; the string packing is commonly used for small valves with low pressure systems and ring packing is utilized mainly for huge valves for high pressure systems. Remember to get the right tools for the replacement to ensure that it will fit the pressure and temperature that it will be exposed.
Overall, Globe Valve maintenance is a task that demands time and effort. A regular tune up can make a difference and it can further improve the performance of the equipment.
Globe valve selection guide
A Globe Valve is commonly known as a form of mechanism that is mainly used to regulate or impede the flow of liquid or gas within a pipe. Its seat is structured in the middle and parallel towards the pipe and the opening is enclosed with the use of a disc. In this type of valve, the plug is connected to a stem that works by means of screw action in manual valves. This type of valve indeed assists in obtaining good control regulating the flow of liquid; water pipes fit together in this valve so that its operator would be aided in monitoring the water flow when the valve is opened either partially or all the way.
Going further, this type of valve is made out of metallic alloys but there are some products that are formed with the use of synthetic materials; such materials have been utilized according to pressure, temperature and controlled media properties. The life of this valve can last for a long time once it goes through a process of corrosive and erosive steams that typically requires a careful selection of materials or body coatings; given that this valve is made of high grade materials, there is a guarantee that it can last for years and it can give consistent results at all times. Furthermore, this valve has two forms known as the threaded valve and the flanged valve; the threaded valve contains a brass body coat and it has metal to metal seats, stainless steel stems, and interchangeable spring-loaded packing while a flanged valve may come in two-way or three way forms and it has cast iron body coat, a steam and water pressure inlet. In order to know the ideal valve that you can use, here is a Globe Valve selection guide that you may want to look at:
- Look for direct coupled linear actuators that have passed quality control specifications. This guarantees that the manufacturers of the valves were able to meet quality requirements and demands.
- The coupled actuators should be structured for easy mounting. This mounting process should be done without needing adjustments, linkages, brackets or adapters.
- Check the models that will suit your need and select between water and steam control.
- The valves should be built based on the flow characteristics percentage towards water, and linear flow characteristics together with steam applications.
- Verify the valve’s accurate positioning to secure that it will provide the right amount of temperature control when in use.
- Search for models that contains pressure balance for it aids in obtaining high close.
- Auxiliary switches may be utilized if necessary.
Now that you know the factors that need to be considered in searching for the ideal Globe Valve that you can use, ensure that you will be purchasing them from reputable manufacturers to guarantee that you will be able to obtain a product that is of superb condition. Proper installation of the valve definitely matters so that you maximize it to the fullest and avoid any inconveniences on the course of use.
Parts of a globe valve
Globe Valve is mostly utilized for the purpose of regulating the flow of liquid in a pipeline; it can be programmed to stop the flow of liquid entirely, slow down the stream or set the fluid to move freely. This type of valve is named after its globe-shaped body that is being separated by an internal baffle; the baffle is the device that is being used to control the fluid flow and it contains two parts – the flat plug and the ring shaped seat. Once the plug is properly positioned in the seat, the movement of the fluid is totally constrained nevertheless, the baffle can be manipulated by either opening it or closing it depending on the amount of fluid flow that you want to have.
Understanding the functions of this valve is very fascinating. All of its parts work as one so that it can follow through the directions that its operator executes. This valve can serve a lot of uses and it can last for many years if the owner knows the proper method of how to maintain a Globe Valve. Moreover, knowing the parts of such valve can aid in learning how the flow of liquid moves and circulates around the equipment; its parts are enumerated and explained in the information below.
This part of the valve is noted to contain the main pressure structure and it aids in forming the mass of the valve. The body surrounds the valve’s entire internal parts that will come in contact with the movement of the substance that is being regulated. The bonnet is linked to the body and it stipulates the containment of fluid, gas, or slurry that is being regulated.
This part supplies a leak proof closure towards the body of the valve; the threaded portion of the stem passes through a hole that contains matching threads in the bonnet. The valves may have screw-in, union, or bolted bonnet. The screw-in bonnet gives a durable and pressure tight seal; the union bonnet is ideal for application that demands inspection or cleaning on a regular basis; bolted bonnets can be utilized for larger and higher applications.
Plug or Disk
This part is considered as the closure member of the valve and it is linked to the stem which is screwed up or down to adjust the control. Plugs or disks are categorized in two forms such as the balance and unbalanced type. The balanced type contains holes towards the plugs; it aids in easier shut off mechanism and it can overcome static force. The unbalanced type is solid and it can be maximized for smaller valves that require low pressure drops.
The stem connects the actuator inside the valve and it helps in transmitting the actuation force. It is necessary that the stem is able to withstand a large compression force and it should acquire a substantial amount of strength during valve opening.
The seat offers a stable, consistent and replaceable shut off surface. This part may be installed and screwed in the same area of the body.
This is used for the manual regulation of the valve
Keep in mind that in order to ensure that Globe Valve executes an outstanding performance all the time, all of its parts should be properly installed and it should always be in its proper working order.
HOW DO THEY FUNCTION?
Globe valves get their name from their body shape, which was once consistently spherical. As technology has changed, so has the body’s exterior shape. Globe valves now come in a number of different looks, not all globe-like.
The internal shape and function, however, is much the same as it has always been.
You can picture a typical straight line, or “Tee” pattern, globe valve’s interior – like the ones that we sell – as a kind of flattened “S” shape. The letter’s center point is the valve seat and the stem descend vertically through it to that point.
The fluid or gas enters through the lower end of the letter and then travels up until it meets the midsection.
If the plug is in place, the flow stops at the midpoint. If not, it continues through at a rate determined by the plug. The globe valve’s ability to throttle a substance’s flow makes it useful as a control valve.
HOW ARE THEY USED?
Globe valves are used in operations which require frequent changes in flow rate.
In normal operation, the direction of flow comes from under the plug. In high temperature operations, the direction of flow may be changed so that flow comes from the opposite direction. Doing so keeps the stem at a constant higher temperature, which decreases the chance that it will contract and lift the plug off of the valve seat.
One drawback of globe valves is greater flow restriction. The twists and turns of the valve along with a narrowed channel through the valve seat opening conspire to increase flow resistance. That makes pressure drop a factor in some applications.
The working principle of globe valves
Generally, the valve stem of the globe valve rotates and moves up and down. The hand wheel is fixed on the top of the stem. When the handwheel is rotated clockwise, the stem thread rotates downwards. The sealing surface of the valve clack is in close contact with the sealing surface of the valve seat, and the glove valve will be closed. When the handwheel is rotated counterclockwise, the stem thread rotates upward. The sealing surface of the valve clack and the sealing surface of the valve seat will be separated from each other. The globe valve will be opened.
Advantages and disadvantages of globe valves
Advantages of globe valves
a. Compared with the gate valve, the globe valve has a simple structure. Usually, the globe valve only has one sealing surface on the valve body and valve clack. The globe valve has small sealing area and can save precious materials, resulting in low costs. Therefore, the manufacturing process of the globe valve is relatively good and the maintenance is easy.
b. The sealing surface of the globe valve is worn and scratched lightly, and the globe valve has good sealing performance. When the valve is opened or closed, there is no relative sliding between the valve clack and the sealing surface of the valve body (except for the conical sealing surface). Therefore, wear and scratches of the globe valve are not serious, which makes the globe valve have good sealing surface and long service life.
c. The opening height of the globe valve is small, and it is generally only 1/4 of the diameter of the valve seat channel. The globe valve has compact structure, which saves installation space.
Disadvantages of globe valves
a. The globe valve has longer structure.
b. The globe valve has large opening and closing torque. When the globe valve is closed, the force of the medium must be overcome, because the direction of movement of the valve clack is opposite to the direction of the medium pressure.
c. The globe valve has large flow resistance. The medium channel in the valve body is relatively tortuous, resulting in large flow resistance and power consumption. The pressure loss of the globe valve is particularly obvious, especially in the hydraulic device. The flow resistance of the globe valve is the largest among the various types of cut-off valves.
d. The direction of media flow is limited.
When the medium flows through the globe valve, it can only flow from bottom to top or from top to bottom at the seat channel. Therefore, the medium can only flow in a single direction and the flow direction can not be changed.
e. When the globe valve is closed, solid particles in the fluid medium may be trapped between the sealing surfaces.
f. The globe valve is not easily installed.
Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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