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The globe valve is designed with a stem that moves up and down to allow the medium flow one-way movement and make the sealing surface of the valve disc and seat tightly fit to prevent medium flow. It’s characterized saving elbow and operate conveniently and can be installed in the bent part of the pipeline system. There are various types of globe valve and designs, each with their own pros and cons. In this blog, we will introduce the classification of globe valves in details.

 

The flow direction of globe valve

1. Tee shape/Split body globe valve
   The design making inlet and outlet channels of the valve are 180° in the same direction and has the lowest coefficient of flow and highest pressure drop. Tee/Split type globe valve can be used in severe throttling services such as in bypass line around a control valve.
2. Y pattern globe valve
   Its disk and seat or the seat sealing an inlet/outlet passage present a certain angle, usually 45 or 90 degrees to the pipe axis. Its fluid hardly changes flow direction and has the least flow resistance in the globe valve types, suitable for coke and solid particles pipeline.

3. Angle pattern globe valves

Its flow inlet and outlet are not in the same direction with a 90° angle, which produces certain pressure drop. The angle globe valve is characterized by its convenience and without the use of an elbow and one extra weld.

 

Stem and disc of globe valves

1. Outside screw stem stop valve
   The stem thread is outside of the body without connection with the medium to avoid the corrosion, easy to lubricate and operate.
2. Inside screw stem stop valve
   The inner valve stem thread contact directly with the medium, easy to be corrosion and cannot be lubricated, usually used in the pipeline with the small nominal diameter and the medium working temperature is not high.
3. Plug disc globe valve

Plug valve is also known as the plunger globe valve. With a radial sealing structure design, by the polished plunger on the two elastic sealing ring through the body and bonnet connection bolt applied on the bonnet load around the elastic sealing ring to achieve the sealing of the valve.

4. Needle globe valve

Needle globe valve is a kind of small diameter instrument valve, which plays the role of opening and closing and flows control in instrument measuring pipeline system.

5. Bellows globe valve

Formed stainless steel bellows design offers reliable sealing performance, suitable for flammable, explosive, toxic and harmful media occasions, can effectively prevent leakage.

 

Applications of globe valves

1. PTFE-Lined globe valve
   PTFE Lining globe valve is the valve that molding(or inset) Polytetrafluoroethylene resin in the inner wall of the metal valve pressure piece (the same method applies to all kinds of pressure vessels and pipe accessories lining) or the outer surface of the valve inner piece to resist the strong corrosive medium of the valve. PTFE lined globe valve is applicable to Aqua regia, sulfuric acid, hydrochloric acid and various organic acids, strong acids, strong oxidants at various concentrations of -50 ~ 150℃, as well as strong alkali organic solvent and other corrosive gases and liquid medium in the pipeline.
2. Cryogenic globe valve
   Cryogenic globe valves usually refer to valves operating below -110℃. It is widely used in liquefied natural gas, petroleum and other low-temperature industries. At present, the globe valve with an applicable temperature of -196℃ can be manufactured, which uses liquid nitrogen for low-temperature pretreatment to completely avoid sealing deformation and leakage.

PERFECT manufacture and supply globe valves according to ANSI and API standards, the valve disc and seat sealing surface are made of stellite cobalt carbide surfacing that offering various advantages like reliable sealing, high hardness, wear resistance, high-temperature resistance, corrosion resistance, abrasion resistance and long service life. We design each valve according to the flow parameters presented. Contact our sales representative for details.

Valve actuators refer to devices that provide linear or rotary movement of the valve, which using liquid, gas, electricity or other energy sources and converted it by motors, cylinders or other devices.

Pneumatic actuator uses air pressure to realize the valve drive open and close or regulation with one piece implementation and regulation mechanism, can be divided into the membrane, piston and rack and pinion pneumatic actuator. The pneumatic valve structure is simple, easy to operate and check, can also easily achieve the positive reaction of the exchange, more economical than electric and hydraulic. It is widely used in power plant, chemical industry, oil refining and other production processes with high safety requirements.

Electric actuator has a large torque, simple structure and easy to maintenance, can be used to control air, water, steam and corrosive media like mud, oil, liquid metal, radioactive media and other types of fluid flow. It also has good stability, constant thrust and good anti-deviation ability. Its control accuracy is higher than the pneumatic actuator and can well overcome the imbalance of medium, mainly used in power plants or nuclear power plants.

When selecting a valve actuator, it is necessary to know the type of valve, torque size and other issues. Generally in the term of the structure, reliability, cost, output torque and other terms to consider. Once the actuator type and the drive torque required for the valve are determined, the actuator manufacturer’s data sheet or software can be used for selection. Sometimes the speed and frequency of valve operation should be considered. Here we collect some tips or suggestion for the actuators  choices:

Cost
The pneumatic actuator must be used together with valve positioner and air source, and its cost is almost the same as the electric valve. In water and sewage treatment, most valve actuators are operated in on/off mode or manually. The monitoring functions of electric actuators, such as overtemperature monitoring, torque monitoring, conversion frequency and maintenance cycle, must be designed in the control and test system, which leads to a large number of line input and output. In addition to terminal position sensing and air source handling, pneumatic actuators do not require any monitoring and control functions.

Security
Electric valves are an electric power source, circuit board or motor failure prone to spark, generally used in the environmental requirements are not high occasions. Pneumatic actuators can be used for potentially explosive occasions, and it is worth noting that the valve or valve island should be installed outside the explosion area, the pneumatic actuators used in the explosion area should be driven by trachea.

The service life
The electric actuators are suitable for intermittent operation, but not for continuous closed-loop operation. Pneumatic actuators have excellent overload resistance and are maintenance-free, requiring no oil change or other lubrication, with a standard service life of up to one million switching cycles, which is longer than other valve actuators. In addition, pneumatic components with high vibration resistance, corrosion resistant, strong and durable, even not damage at a high temperature. Electric actuators consist of a large number of components and are relatively easy to damage.

Response speed
Electric actuators run slowly than pneumatic and hydraulic actuators, it takes a long time from the regulator output signal to response and movement to the corresponding position. There is a great loss of energy when the supplied energy is converted into motion. Firstly, the electric motor converts most of the energy into heat, and then it uses gears with a complex structure. Frequent regulation will easily cause the motor to overheat and generate thermal protection.

Essentially, the main difference between electric and pneumatic valves is the use of actuators and has nothing to do with the valve itself. Choose which actuator to use that depends on the operating conditions, such as a chemical application or explosion protection or wet environment where need pneumatic valve and an electric valve is ideal for large diameter piping system.

Plug valve with one piece top -entry design has a lot of similarities with a one piece top – entry ball valve. Strictly speaking, ball valve and plug valve are the same types of valve due to their similar function and characteristics and both of them have a very wide range of applications. Today we will introduce the difference of plug valve and ball valve.

Plug valve also known as cock valve, rotating plug valve, is a kind of oldline valve. The valve “plug” (mostly conical or cylinder) combined and the body of the conical hole surface of the sealing, to move depending on the plug body around the center line of the valve to achieve open and close. It is mainly used for cutting, distribution and change the flow of media. The plug valve is simple in structure and small in size. It can be opened and closed by only 90% rotation. It is widely used in a low pressure, small diameter and medium or low-temperature occasions. Plug valve sealing surface is easy to wear, also easy to get stuck in the occasion of high temperature or high pressure, not suitable for flow regulating.

The ball valve is evolved from the plug valve with a ball as its closing parts, it around the center of the valve to achieve the opening and closure, mainly used to cut off, distribution and change the flow direction of the medium. Ball valves can close tightly just 90 degrees of rotation or a small torque. Full horizontal of the valve body cavity provides little resistance, through the flow path for the medium. The main characteristics of the ball valve are compact structure, easy to operate and maintenance, suitable for water, solvent, acid and natural gas and other general media, also suitable for working conditions of harsh media, such as oxygen, hydrogen peroxide, methane and ethylene. The ball valve body can be one piece, can also be combined. It is generally considered that ball valves are most suitable for opening and closing directly, but recent developments have designed them for throttling and flow control.

 

Plug valve VS ball valve

Different principle

The ball valve is evolved from the plug valve. They have the same 90-degree rotation operation, but depends on the “plug” is a plug or a ball with a circular through hole or channel passing through its axis. The ball and the ports should look like this: when the sphere rotates by 90 degrees, it will appear as a sphere at the inlet and outlet to cut off the flow. For the plug valve, the conical plug and the body surface formed by the conical pressure, the upper parts are sealed with packing between the plug and the gap between the body. Plug valve is simple and often economical because it usually does not have bonnets, but the handle exposed outside at the end instead.

Different application

Plug valves offer better performance in the term of cutting than ball valves, but that doesn’t show obviously. The sealing surface of the plug valve is much larger than the ball valve and supplies a better sealing effect, but a greater torque and small diameter. The ball valve is ideal for switching pipeline medium, not as a throttle valve to avoid the valve long time by medium erosion and loss of tightness. Now the sealing effect of the ball valve has been greatly improved with the progress of the sealing technology, so we can say that the plug valve is used for the sealing requirements are strict but the diameter is not large, and the ball valve is used for the sealing effect is not too strict and the diameter is large.

Plug valve is lower cost

For the plug valve, the “plug” is completely covered by the bushing, making the valve body and plug free from wear. Replacement of the bushing and top seal can complete the repair and update of the valve, which can meet the long-term service requirements of 300℃. This has considerable competitive advantages over other hard-sealed metal ball valves in this temperature range. In addition, the plug valve processing area only is the top face and flange, other parts all one-step casting molding and the internal body need no processing. Compared with the ball valve, it offers low processing allowance, when making the INCONEL, MONEL, HAST alloy and other special materials as its materials, plug valve has an obvious price advantage.