Showing posts with label loop. Show all posts
Showing posts with label loop. Show all posts

Sunday, September 10, 2017

8 Critical Control Valve Selection Criteria

Control Valve (Valtek)
Control Valve (Valtek)
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
    Control Valve Specialized Kammer
    Control Valve
    Specialized for Food/Bev
    Pharmaceutical (Kammer)
    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.

Tuesday, September 5, 2017

Consider Flangeless Wafer Style Control Valves for Excellent Flow Control

Mark 75 Flangeless Wafer Style Control Valve
Jordan Mark 75 Flangeless
Wafer Style Control Valve
Valves are essential to industries which constitute the backbone of the modern world. The prevalence of valves in engineering, mechanics, and science demands that each individual valve performs to a certain standard.

One category of valves are "control valves". These can be linearly operated, or rotary operated. There are many types of control valves, such as gate, globe, ball, butterfly, and plug. All of these valve types have some sort of ball, plug, gate, or disc that throttles the flow as the valve opens and closes. Some valve designs are better suited to uniformly control flow, such as gate valves or valves with specially machined disks. This post is about the Jordan Mark 75, a valve that uses a unique sliding gate design.

According to Wikipedia, "A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level."

The Mark 75 Series control valve is a industrial process control valve manufactured by Jordan Valve. It's design benefits include the sliding gate seat design, low weight, and compact wafer style body. The Mark 75 offers an incredible pricing advantage in the market place due to its wafer style body.

The stroke length of the Mark 75 is a slightly longer stroke than standard sliding gate valves. This longer stroke enables better turndown. Combined with the capacity of the Mark 75, the increased turndown makes for a great control valve.

Please watch the video below, and see the specification sheet at the bottom for further details. For more information about this valve, or any Jordan Valve product, contact Swanson Flo at 800-288-7926 or visit http://www.swansonflo.com.