Rotary Valves; Packing Flashcards
What is a rotary valve body?
A rotary valve body is one where the rotation of a shaft actuates the trim.
What type of valve is this?
it is a ball valve.
description:
In the ball valve design, a spherical ball with a passageway cut through the center rotates to allow fluid more or less access to the passageway. When the passageway is parallel to the direction of fluid motion, the valve is wide open; when the passageway is aligned perpendicular to the direction of fluid motion, the valve is fully shut (closed)
how does a characterized or segmented ball valve differ from a normal ball valve
Provides more precise flow control
What type of valve is this?
butterfly valve
description: : the “butterfly” element is a disk that rotates perpendicular to the path of fluid flow. When parallel to the axis of flow, the disk presents minimal obstruction; when perpendicular to the axis, the disk completely blocks any flow.
What is difficult to obtain in the classic butterfly design?
Fluid-tight shutoff is difficult to obtain in the classic butterfly design unless the seating area is lined with a soft (elastic) material.
What type of valve is this?
disk valve
description:
The disk’s center is offset from the shaft centerline, causing it to approach the seat with a “cam” action that results in high seating pressure. Thus, tight shut-off of flow is possible even when using metal seats and disks.
Disk valves are also known as?
eccentric disk valves, or high performance butterfly valves
Dampers (otherwise known as a louvre) are?
multi element flow control devices used to throttle large flows of air pressure at low pressure
Dampers (otherwise known as a louvre) find common application in?
Dampers find common application in furnace and boiler draft control, and in HVAC (Heating, Ventilation, and Air Conditioning) systems.
Whats the purpose of valve packing?
.
It prevents leaks between the moving stem and the body of the valve.
explanation of packing rings ( warning: super long text) oops
The packing material takes the form of several concentric rings, stacked on the valve stem like washers on a bolt. These packing rings are forced down from above by the packing flange to apply a compressive force around the circumference of the valve stem. This compressive force is necessary to generate mechanical stress in the packing material to make it seal tightly against the stem of the valve and the interior wall of the bonnet.
Two nuts threaded onto studs maintain proper force on the packing rings. Care must be taken not to over-tighten these nuts and over-compress the packing material, or else the packing will create excessive friction on the valve stem. Not only will this friction impede precise valve stem motion, but it will also create undue wear on the stem and packing, increasing the likelihood of future packing leakage. Insufficient packing flange force will lead to poor sealing, with process fluid potentially leaking past the packing and out of the valve.
What type of valve packing is this called?
stationary packing
what must be done when the stationary packing begins to wear out and fatigue?
the packing follower must be re-compressed by carefully tightening the packing nuts.
What is the purpose of these springs located in the packing assembly?
the elasticity of the spring helps to maintain an appropriate amount of packing stress as the packing material wears and ages.
What type of valve stem packing is this called?
Live-loaded valve stem packing
What are the two most common materials used for packing?
Teflon (PTFE) and graphite.
in regard to fluid sealing, stem friction and stem wear. What material is better for packing valves?
TEFLON!!!!
The main reason why graphite would be used as a valve packing material as a opposed to Teflon (PTFE)
Graphite has a far greater temprature range than Teflon. From cryogenic tempratures to 1200 fahrenheit. As opposed to Teflon having a range between -40F and 450F
What is this called?
(kinda impossible not gonna lie sorry guys)
Bellow seal
What is a bellow seal?
a way to valve pack.
an accordion-like metal tube fastened to the valve stem and to the bonnet, forming a leak-proof seal with negligible friction. CANT DEVELOP LEAKS BECAUSE IT IS A UNITERRUPTTED METAL TUBE
description in the answer card
In some process applications, it is important that the control valve be able to completely stop fluid flow when placed in the “closed” position. Although this may seem to be a fundamental requirement of any valve, it is not necessarily so. Many control valves spend most of their operating lives in a partially-open state, rarely opening or closing fully. Additionally, some control valve designs are notorious for the inability to completely shut off (e.g. double-ported globe valves). Given the common installation of manual “block” valves upstream and downstream of a control valve, there is usually a way to secure zero flow through a pipe even if a control valve is incapable of tight shut-off. For some applications, however, tight control valve shut-off is mandatory.
