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Globe Valve

» Globe Valve

Globe Valve

 The Globe valve is used to cut off the flow of the medium and is suitable for occasions that need to be throttled frequently. The most commonly used is in chemical production.

The valve disc and the valve seat is the sealing parts of the globe valve. In order to close the valve tightly, the matching surface of the valve disc and the valve seat should be grinding, and the corrosion-resistant and wear-resistant materials such as Stellite 6 and stainless steel can also be welded on the sealing surface. The valve disc and the valve stem of the globe valve are designed flexible connection to facilitate the valve disc and the valve stem fitting.

 
Table of Content

1. Globe Valve Types

2. Construction of a Globe valve and Working Principles

3. Performance and Application of Globe Valve

4. Installation and use of globe valve

5. Selection guide of globe valve

6. Common problems and maintenance of globe valve

7. Conclusion

 
1. Globe Valve Types

A. Based on bore pattern

tee type globe valve

Straight through flange globe valve

            ※ Straight Through/TEE Pattern/Z-Body Globe Valve

The medium inlet and outlet flow path of the T Pattern Globe valve are 180° in the same direction. This design has low coefficient of flow and pressure drop. It relies on the valve stem to navigate the valve disc towards the sealing surface of the valve seat, fully shut off the flow. During the open/close process, the friction between the sealing surfaces is small, minimizing wear and tear. The degree of throttling height is minimum and the process performance is optimum. Compared to gate valve, the structure of the globe valve is straight forward, and it is easier to maintain. It is the most commonly used valve in the industry.

y type globe valve

Y type globe valve

         
           ※ Y Type Globe Valve

The valve stem and the flow path of the Y type globe valve form a certain angle, and the sealing surface of the valve seat and the inlet and outlet flow path also have a certain angle. The valve body can be made integral or split body. The split body type Y globe valve uses two valve bodies to sandwich the valve seat between them, which is convenient for maintenance. Y type globe valve will not change the direction of flow. It is the smallest flow resistance among globe valve. The sealing surface of the valve seat and disc can be welded with hard alloy for erosion and corrosion resistance. It is very suitable for alumina production pipelines, and is also suitable for pipelines with slurry medium.

angular globe valve

Angular globe valve

           ※ Angle Globe Valve

The biggest advantage of the angle globe valve is that the valve can be installed at the right angle of the pipeline system, which saves 90° elbows and is easy to operate. Therefore, this type of valve is most suitable for use in synthetic ammonia production systems and refrigeration systems in chemical fertilizer plants.

     B. Other Globe Valve Types

bellow globe valve

Bellow globe valve

           ※ Bellow globe valve

Bellow globe valve is also called bellow seal globe valve. It is designed by automatic roll welding to form a metal barrier between the fluid medium and the atmosphere to ensure zero leakage of the valve stem. The bellows globe valve uses a bellows structure, and the lower end of the stainless-steel bellows is welded to the valve stem to prevent the process fluid from corroding the valve stem. The other end of bellow is installed between the valve body and bonnet to form a static seal. Double seal design is adopted. If the bellows fails, the stem packing will act as secondary seal. The bellows are welded to the stem to maintain stable operation performance, to avoid stem vibration caused by valve plug vibration. It is suitable for media which require vacuum circumstance such as steam, flammable, explosive, thermal oil, high purity, toxic and atc

plunger valve

Plunger Valve

           ※ Plunger Globe Valve

This type of plunger valve is a radial seal, which is realized by two spring loaded sealing rings sleeved on the polished plunger. The two spring loaded seal rings are separated by a collar, and the load applied to the bonnet through the connecting bolts of the valve body and the bonnet presses the spring-loaded seal ring around the plunger firmly to ensure the tight sealing. The valve material combination is carbon steel for the body, Cr13 stainless steel for the plunger, and flexible graphite for the sealing ring, which can be used for water, steam, oil pipelines; if the body and the plunger is made of stainless acid-resistant steel, with PTFE seal ring, it is suitable for acid and alkali corrosive medium.

The advantages of plunger globe valve are reliable sealing, long life span and easy maintenance. The disadvantage is the slow open/close speed. This type of valve is widely used in urban construction systems, water and steam pipelines in urban heating system.

needle valve

Needle valve

            ※ Needle Globe Valve

The needle type globe valve is used for precise flow control. The valve disc and stem are usually integrated. It has a high precision needle-shaped probe matched with valve seat. Moreover, the thread pitch of the stem thread of the needle-type globe valve is smaller than that of the stem thread of the general globe valve. Under normal circumstances, the needle globe valve’s seat hole size is smaller than the pipe size. Therefore, it is usually limited to use in pipelines with a small nominal diameter, mainly used as sampling valves.

3 way globe valve

3 way globe valve

           ※ Three Way Globe Valve

The three-way globe valve body has three flow paths, also can be designed to four-way; the three-way globe valve can replace the three-way joint and three ordinary globe valves in the pipeline to divert, bypass or combining flow. The three way globe valve has high performance sealing which will prolong life span and prevent leakage. Hence it can reduce the maintenance cost.

 
2. Construction of a Globe valve and Working Principles

The globe valve is constructed of valve body, valve disc/plug, bonnet, stem, etc. The opening and closing parts of the globe valve are plug-shaped disc, the sealing surface is either flat or tapered, and the disc move linearly along the center line of the fluid. The stem operation type includes lift type (the valve stem is turned up and down by hand wheel with handwheel remained at its location), and the rotating and lifting stem type (the hand wheel and the valve rod rotate and move up/down together, the lock nut is positioned on the valve body)

The globe valve is only suitable for fully open and fully closed operation, and it is not suitable for regulating and throttling. The globe valve is a force-sealed valve, when the valve is closed, pressure must be applied to the disc/plug to established tight sealing. When the medium enters the valve from below the valve disc, the resistance that the operating force needs to overcome is the friction of the valve stem and packing and the force generated by the pressure of the medium. When the force to close the valve is greater than the force to open the valve, the diameter of the stem should be increased to avoid stem from distort and bend.

With the introduction of pressure seal globe valve, the medium flow direction of the globe valve is changed to the valve cavity from above the valve disc. Under this circumstance, the pressure of the medium will be caused force of closing the valve to decrease, and the force of opening the valve is increase, thus can reduce the stem diameter accordingly.. At the same time, under the action of the medium, this type of valve is relatively tight sealed.

 
3. Performance and Application of Globe Valve

      A. Advantages of Globe Valve
  1. Shorter stroke (compared to a gate valve).
  2. Good shutoff capability, Less friction between sealing surfaces and longer life span.
  3. Moderate to good throttling capability.
  4. Available in T type, Y type, and angle patterns, each offering unique capabilities.
  5. Valve can be used as a stop-check valve when disc does not attached to the stem.
     B. Disadvantages of Globe Valve
  1. Longer in size and Higher pressure drop (compared to a gate valve)
  2. The structure of the globe valve is complex, and it is difficult to manufacture and maintain
  3. Requires greater force or a larger actuator to open/close the valve (with pressure under the seat)
  4. Globe valves are generally not suitable for media with particles, high viscosity, and easy coking.
     Globe valve application

Globe valves are often used in pipelines that need to be fully opened and closed, and steam pipelines are more commonly used. The connection between the globe valve and the pipeline can be weld type or flange type

 
4. Installation and use of globe valve

  1. Handwheel operated globe valves can be installed at any position in the pipeline.
  2. Handwheel and actuated mechanism are not allowed for lifting.
  3. The flow direction of the medium should be in line with the direction of the arrow shown in the valve body.

 
5. Selection guide of globe valve

  1. Globe valves should be used on pipelines or devices with high-temperature and high-pressure medium. Such as thermal power plants, nuclear power plants, high temperature and high pressure pipelines in petrochemical systems.
  2. On pipelines where the flow resistance and pressure loss is not a concern.
  3. Small size globe valves is suitable to replace Needle valves, instrument valves, sampling valves, pressure gauge valves, etc.
  4. Suitable if the regulating precision requirement is not a concern and the nominal diameter is less than 50mm
  5. For small chemical fertilizers and large chemical fertilizers in synthetic industry, high-pressure angle globe valves or high-pressure angle throttle valves with a nominal pressure of 1500LB or 2500LB should be used
  6. In the desiliconization workshop produced by alumina Bayer method and the pipeline easy to coking, the T type globe valve or T type throttle valve with spilt body with welded hard alloy seat can be used.
  7. In the water supply and heating system in urban construction, the nominal passage through the smaller pipelines can be selected as the globe valve, balance valve or plunger globe valve, if the nominal passage through the pipeline is less than 150mm

 
6. Common problems and maintenance of globe valve

A. The valve is passing.
  1. Check if there is solid particles such as debris or steam scale in the medium have worn the valve disc or valve seat,
  2. The solid particles are cushioned between the valve disc or valve seat,
  3. The valve stem and the valve disc are not well connected, so that the valve disc has no tight contact with valve seat deflection,
  4. corrosion of stem or stem nut, etc.
B. The valve is not functioning/ cannot be opened or closed.
  1. Check if there is debris between the valve stem and the valve stem nut or the contact is not good.
  2. The valve stem and the valve disc are detached
  3. The valve stem and the valve stem nut are corroded.
  4. The valve disc is subjected to excessive reverse pressure, and Packing too tight and so on.
 C.Partial leakage of packing.

It is mainly caused by the loss of filler of packing or damage to the structure of the filler foil. Therefore, you should pay attention to the following issues during operation:

  1. Globe valves should not be used in liquid pipelines where deposits or crystals are easily formed. Even if it is used in steam, compressed air, vacuum pipelines or liquid pipelines that need to regulate the flow, a filter must be installed in front of the valve to ensure that the medium is clean when flow into the valve.
  2. When closing the valve, if the valve disc is found to be plugged, it should not be closed violently to prevent the valve disc from deflecting or the debris from damaging the seal: rapid opening and closing several times to flush out the debris. If the measures taken are ineffective, they should be dismantled and overhauled
  3. Frequently lubricate the stem and stem nut and clean debris (especially water and steam valves), to prevent rust or debris that causing the valve to fail.
  4. If found that the valve seal, joint surface or packing is loose, the gasket or packing should be replaced in time to avoid damage to the valve disc, valve seat or various joint surfaces under high-speed medium (such as steam or compressed air).
  5. In view of the above reasons, the dehydration valve of the steam pipeline must be closed. Do not use steam to prevent the valve from freezing and cracking. The short connection between the valve and the pipeline should be as short as possible.
  6. The globe valve changes the clearance of the flow path by the lifting and lowering of the disc. The flow path in the valve are not at the same horizontal center. During installation, pay attention to the direction of the arrow on the valve body (the flow direction is low in and high out). Otherwise, the flows in from above the valve disc, which causes the valve disc to withstand the reverse pressure. Resulting the valve hard to open. When it is forced to open, the valve will be damaged due to excessive force. However, on low-pressure, small-diameter, and short-distance pipelines, some require two consecutive globe valves, one of which is installed in the front and the other in reverse. The advantage of this configuration will make it easy to replace the valve packing
  7. When replacing the valve packing, pressure shall be released via the outlet. Loosening the gland flange may caused severe injury if the valve is still under pressure.
  8. For the non rising globe valves, when the valves are full open, the handwheel should be left half a turn to avoid accidental opening and closing during the next operation, and excessive force may damage the valve.
  9. The operation is the same as other valves, it cannot be opened and closed quickly to avoid the phenomenon of “water hammer” in the pipeline

 
7. Summary

The globe valve is mainly used to cut off the pipeline flows. Compared to gate valve, globe valve regulating performance is better, opening height is small, closing time is short, manufacturing and maintenance are easy. The sealing surface is not easy to wear and scratch, sealing performance is good, and the service life span is long. The valve body structure design of the globe valve is more complicated, therefore, the flow resistance is large and the energy consumption is large; it is suitable for media such as steam and oil products, and it is not suitable for media with large viscosity, particles, coking and precipitation. Medium and high pressure globe valves and large-diameter globe valves can be used as a balanced structure. The extended product of the globe valve is choke valve, by controlling the pressure and flow of the medium with changing the of the flow path. Except the opening and closing parts is streamlined cone type, the rest are same as globe valve.

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