Claire Christian Valves April 14th, 2019 - 12:31:56
Valve response time is another important factor for us to consider. For optimum control of many processes, it is important that the valve reach a specific position quickly. A quick response to small signal changes is one of the most important factors in providing optimum process control. Valve response time includes both the valve assembly dead time, which is a static time, and the dynamic time of the valve assembly. It is important to keep the dead time as small as possible. Dead band, whether it comes from friction in the valve body and actuator or from the positioner, can significantly affect the dead time of the valve assembly.
Now you're probably wondering how instrument makers know how much tubing to add so that the pitch is lowered by half step. And if you're not, I'm still going to explain it! Because of acoustical theory, to lower the pitch by a half step, the working length of the instrument must increase by about 1/15, or 6.67% of the working length. For explanation purposes I will be using an instrument which is 100 inches in length (which is actually close to length of a euphonium). This means the second valve should have a length of 100/15 or 6.67" in order to lower the pitch by one half step. Now, to lower it a half step past that you must add 106.67/15 or 7.11" so the first valve must have a length of 6.67"+7.11" or 13.77 inches. Now let me explain that last statement as it may have thrown some of you off. The reason the first valve would not be simply 2(6.67) is that in order to lower the pitch by a whole step, there must be enough tubing to lower the pitch by a half step (6.67") and then enough tubing to lower that pitch a half step (7.11"). This same theory goes for the third valve, and yields a length of 21.36 inches.
In fact, the water faucet in your home is a popular example of this valve. The water faucets in houses have a handle that is used to regulate the flow inside it. This valve is designed with a gate and an actuator. The actuator can either be a hand wheel, a lever or an electric motor. Every one of these is anticipated to regulate the performance making it more useful with the anticipated condition. This gate is usually referred to as a piece of metal that is rectangular or circular whose up or down will determine the passing or non-passing of the flow.
We have come across pipelines all around that efficiently transport vast amounts of liquids and gases (collectively called as fluids). But they need a regulating body to decide the amount of the flow and to start and stop the flow for their efficient working. Here, valves come into picture and are the regulating body that control the flow rate and act as a switch to start and stop the flow.
This is a valve that plays a major role in many areas of industry, including instrumentation and flow control processes. The operational environments will, on occasions, be offshore in extreme, adverse conditions such as oil and gas exploration and extraction processes. The quality and reliability of a manual pinch valve is something that can make a significant difference to an application of this nature.
Thus, it is also very necessary to learn something about the dead band. It is a major contributor to excess process variability, and control valve assemblies can be a primary source of dead band in an instrumentation loop due to a variety of causes such as friction, backlash, shaft windup, relay or spool valve dead zone, etc. It is a general phenomenon where a range or band of controller output values fails to produce a change in the measured process variable when the input signal reverses direction.