Edwina Dorsey Valves April 14th, 2019 - 12:30:53
The formula for the theoretical length of tubing, TL, needed to lower a set number of half steps, x, for an instrument of length, L, is TL = L (16/15) ^ x. Example: 100" instrument lowering 3 half steps: TL = 100(16/15)^3. TL = 21.36.
A valve is a device which controls the flow rate, pressure or the direction. The controlled fluid can be the liquid, gas, the mixture of gas and liquid or the mixture of solid and liquid. The valve usually is composed of body, seat, bonnet, parts for opening or closing, actuating device, sealing element and so on. The controlling function of the valve depends on the actuating device or the movement of the fluid which drives the sliding, rotating or turning of the parts for opening or closing to change the area of the flow passage.
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.
There are many different types of valves that are used in various ways. The butterfly valve is a commonly used valve. This valve is especially made for use in broad pipes. It is a disk revolving on a perpendicular axis inside the pipe and also functions as a damper or a control valve. This valve is an apparatus that regulates movement especially used in controlling a particular liquid that would run through a specific part of the pipe.
The fourth one is the disk valve which is also known as swing check valve. It operates in the same manner as ball and cone valves, but the plug that settles over the opening is a disk. Disk and cone valves tend to wear down more because they have more moving parts and because they get bumped around on top of the flow of water when it is turned on.
There are three kinds of this valve. There is a valve that is high in performance, which is reliable in functioning under higher pressure that can withstand as high as 725 PSI and temperature applications. Next is the resilient valve, it has an elastic rubber seat and could work up to the pressure of 232 PSI. Lastly, the tricentric valve that is commonly adorned with a seating made of metal and it can function up to the pressure of 1450 PSI.