Globe Control Valves

Globe valves are typically used in process control applications to regulate the flow of steam or other gases. The valve consists of a cylindrical body with a plug or disc inside that can be rotated to control the flow of fluid through the valve. The disc is connected to a stem, which extends out of the top of the valve and is connected to a handwheel or other actuator.

When the handwheel is turned, the stem moves up or down, which in turn moves the disc in the valve body. As the disc moves towards the valve seat, it reduces the size of the opening through which the fluid can flow, which reduces the flow rate. Conversely, as the disc moves away from the valve seat, it increases the size of the opening and the flow rate increases.

The design of the globe valves allows for a large range of flow control and precise control of flow rate. It also has the capability of both modulating and on-off control depending on the requirement of the process. 

There are several types of actuators that can be used to automate globe control valves, including:

• Pneumatic actuators: Pneumatic actuators use compressed air to move the valve stem and adjust the position of the valve disc. They are popular because they are relatively inexpensive, easy to install, and require minimal maintenance.
• Electric actuators: Electric actuators use an electric motor to drive a mechanical linkage that moves the valve stem and adjusts the position of the valve disc. They are typically more precise than pneumatic actuators, and can be controlled by a variety of electronic devices such as process controllers, programmable logic controllers (PLCs), and distributed control systems (DCS).
• Hydraulic actuators: Hydraulic actuators use a fluid under pressure to move the valve stem and adjust the position of the valve disc. They are typically used in large valves or high-pressure applications where high force is required.
• Electro-Hydraulic actuators: This type of actuator is a combination of electric and hydraulic actuator. The electric motor operates a pump that generates the hydraulic pressure which is then used to move the valve stem and adjust the position of the valve disc.
• Smart actuators: Some modern actuators have the capability of communicating and self-diagnostics which is important for advanced control systems, These smart actuators are typically interfaced with digital control system which enables to monitor, control, and adjust the performance of the valve.

It's worth to note that choosing the actuator is depends on the requirement of the process, in term of flow rate, the process conditions, cost, and maintenance.

In summary, globe control valves are used to regulate the flow of steam or other gases in process control applications by adjusting the position of the plug or disc inside the valve body, which in turn controls the flow rate of the fluid through the valve.

For more information, contact M.S. Jacobs by calling 800-348-0089 or visit https://msjacobs.com.

New Manufacturer Partner - ARCA Valves

M.S. Jacobs & Associates, Inc. is happy to announce its appointment as an official ARCA Valves distributor. ARCA Valves has garnered global renown for its innovative technology and established quality since its foundation over a century ago. ARCA's pneumatically and electrically operated control valves provide high value for many industrial applications. They meet the rigors of many challenging applications in various industries, including power plants, chemical plants, pharmaceutical and food processing, and steel mills. 

Thanks to its excellent vertical integration, ARCA's manufacturing process is versatile and has a high supply capacity. ARCA manufactures and supplies valves with nominal diameters up to 48" and pressure ratings of over 5,000 PSIG for high-pressure applications. 

ARCA's technological leadership is built on 90 years of expertise and ongoing innovation, evidenced by several patents. The factory's output, which is of the highest technical quality and certified to appropriate quality standards, ensures a high level of dependability.

For more information, contact M.S. Jacobs by calling 800-348-0089 or visit https://msjacobs.com.

SVF Flow Controls Explains Surface Roughness for Valves Intended for Special Applications

Vales utillized in industrial processes
can require special materials or finishes.

Fluid control operations can sometimes require special materials of construction or finishes for piping and specialties, like valves. A segment of the industrial valve manufacturing sector specializes in providing fluid control valves with coatings, surface finish, and materials of construction suitable for the requirements of applications not well serviced by more common constructions.

One manufacturer, SVF Flow Controls, has published a short article explaining some of the basics about surface finish. The article defines surface finish and goes on to describe some of the methods employed to achieve various levels of surface roughness and texture. The article, included below in its entirety, is short and informative.

Share your specialty valve applications with product experts. The combination of your process expertise and their product knowledge will produce the most effective solutions.

Surface Roughness in Metal Finishing from MSJacobs-Cali

Control Valve Selection - 8 Things to Remember

Cashco Control Valve

Choosing an improperly applied sized or improperly sized control valve can have serious consequences on operation, productivity and most important, safety. Here is a quick checklist of basics that need to be considered:

1. Control valves are not intended to be a an isolation valve and should not be used for isolating a process. 
2. Always carefully select the correct materials of construction. Take into consideration the parts of the valve that comes in to contact with the process media such as the valve body, the seat and any other "wetted" parts. Consider the operating pressure and operating temperature the control valve will see. Finally, also consider the ambient atmosphere and any corrosives that can occur and effect the exterior of the valve. 
3. Put your flow sensor upstream of the control valve. Locating the flow sensor downstream of the control valve exposes it to an unstable flow stream which is caused by turbulent flow in the valve cavity.
4. Factor in the degree of control you need and make sure your valve is mechanically capable. Too much dead-band leads to hunting and poor control. Dead-band is roughly defined as the amount of control signal required to affect a change in valve position. It is caused by worn, or loosely fitted mechanical linkages, or as a function of the controller setting. It can also be effected by the tolerances from mechanical sensors, friction inherent in the the valve stems and seats, or from an undersized actuator. 
5. Consider stiction. The tendency for valves that have had very limited travel, or that haven't moved at all, to "stick" is referred to as stiction. It typically is caused by the valves packing glands, seats or the pressure exerted against the disk. To overcome stiction, additional force needs to be applied by the actuator, which can lead to overshoot and poor control.
6. Tune your loop controller properly. A poorly tuned controller causes overshoot, undershoot and hunting. Make sure your proportional, integral, and derivative values are set).  This is quite easy today using controllers with advanced, precise auto-tuning features that replaced the old fashioned trial and error loop tuning method.
7. Don't over-size your control valve. Control valves are frequently sized larger than needed for the flow loop they control. If the control valve is too large, only a small percentage of travel is used (because a small change in valve position has a large effect on flow), which in turn makes the valve hunt. This causes excessive wear. Try to always size a control valve at about 70%-90% of travel.
8. Think about the type of control valve you are using and its inherent flow characteristic. Different types of valve, and their disks, have very different flow characteristics (or profiles). The flow characteristic can be generally thought of as the change in rate of flow in relationship to a change in valve position. Globe control valves have linear characteristics which are preferred, while butterfly and gate valves have very non-linear flow characteristics, which can cause control problems.  In order to create a linear flow characteristic through a non-linear control valve, manufacturers add specially designed disks or flow orifices which create a desired flow profile.

These are just a few of the more significant criteria to consider when electing a control valve. You should always discuss your application with an experienced application expert before making your final selection.