Proper valve selection is critical for ideal operation of any system. Improper valve selection can cause system underperformance or failure. The greatest problem when selecting valves is incorrect information.
Often, we may only have access to incomplete or dated information regarding valve applications. Do we know enough about the system the valve will be used in or the main purpose of its use? This “bad information” can create a situation where the theoretical situation does not match reality.
Good Information is Key
“Bad information” comes in many forms. Original design specs might be difficult to obtain, and having those specs does not guarantee success. Occasionally, specs aren’t properly updated. Information that was good at first can fail to incorporate changes in process conditions. If the actual pressure, temperature, flow-rates or the media is different than that which was used to select the valve, it may fail or fail to work properly.
When choosing a gate, globe, ball or check valve, we always want the valve to be operating in the full open or closed position. Control valve selection, however, targets 40% to 60% open for normal flows. When most control valves operate below 20% open or over 80% open, they can lose their ability to control properly.
What information is required to properly size a valve? Fluid type, operating pressures and temperatures upstream and downstream of the valve, and the flow rates associated with these conditions are required information to have.
Knowing What is the Right Valve for the Application
There are many different types of valves available. They do not all work the same way or for the same purposes. Each valve type has its advantages and disadvantages.
For proper control valve selection, it is important to understand how the valve is used to control system flow. For example: is the system tuned for a constant set point, or is it set to modulate a variable flow over time? The layout of the piping system and locations of reducers and elbows also impact valve performance.
Often, choosing what seems to be the most efficient valve might not be the best valve for application. Replacing a valve “in kind” with an upgraded version of an older valve might actually do more harm than good.
Poor Performance – Get Good Information
Unfortunately, the blame for poor performance often lands on the installed valve when it is actually bad information that caused its failure. Simply repeating the bad information to select a different valve is doomed to have the same results. When DFT Inc. is asked to troubleshoot an installation, we start by collecting all of the available information and check for “bad information” concerning flow conditions and application mismatches with respect to the installed valves.
Take the time to get good information. Fortunately, the information is more readily available today than it has been in the past through trending information. If you can provide actual system operational information, your chance for success increases significantly.