Valves Flashcards
What are the most common valve designs
- Gate
- Plug
- Ball
- Globe
- Diaphragm
- Butterfly
Name the different parts of a typical valve
- Stem
- Actuator
- Packing
- Bonnet
- Seat
- Disc
- Body
Describe the body of the valve
The large part of the valve through which the fluid flows
Describe the seat of the valve
The part of the valve that stays motionless
Describe the disc of the valve
The part that moves to the seat to stop flow and if raised completely the valve is fully open
Describe the stem and actuator of the valve
Used to lower or raise the disc
Describe the bonnet of the valve
The space that the disc moves into if the valve is opened
Describe the packing of the valve
Surrounds the stem and keeps the fluid from leaking out
Sketch a typical valve
Pg 104
Give the function, operation and applications of a gate valve
Gate valves are designed to be fully open or closed and are mainly used as shut off valves. They are often used to isolate equipment and are typically found in the auction and discharge pipelines of pumps. The disc is wedge shaped and is lowered and raised like a gate.
Give the function, operation and applications of a globe valve
Globe valves can be used half open without any problems and can bused with confidence in throttling. The disc is rounded and most globe valves contain a back seat which protects the packing from the wear that is caused by fluid flow and pressure.
Give the function, operation and applications of a needle valve
A needle valve is used when good control of flow is needed in small diameter piping. The disc is cone-shaped and only a small movement of the stem is needed to give a small and gradual change in the flow
Give the function, operation and applications of a plug valve
Plug valves are used mostly for on/off control and where tight shutoff is required - for example in a gas line. A handle is fitted and instead of packing there is a plastic deal with metal reinforcement
Give the function, operation and applications of a three way plug valve
A multiport valve may reduce the number of valves. It is often used in a filter system where if the handle is turned a quarter the fluid passes through outlet 2 and the filter is back washed
Give the function, operation and applications of a four way plug valve
A four way multi-valve is often used in heat exchangers. In position 2 the flow of fluid is sent in the reverse direction through the heat exchanger - usually to prevent build up of scale or to break up fouling
Give the function, operation and applications of a ball valve
Ball valves are used mainly for on/off control and handles slurries extremely well. As the ball is turned, the edges in the hole of the ball cut away any accumulation of fibers or small particles between the ball and the seat.
Give the function, operation and applications of a butterfly valve
The body of the butterfly vale is thin and takes up very little space. The disc rotates as the handle is turned and when fully opened the pressure drop is very low as the disc gives little resistance to flow
Give the function, operation and applications of a diaphragm valve
A diaphragm valve is recognized by its bell-shaped bonnet. It does not have a disc, but it uses a flexible diaphragm that presses against the seat to control or stop the fluid. It is used as an on/off valve as well as for controlling flow. The fluid does not come in contact with the operating parts of the valve and a diaphragm valve is therefore used when process fluids are corrosive or contains
Name the classes of valves and their primary function
- Shut off valves (block valves) - purpose is to close off flow
- Control/throttling valves (manual and automatic) - purpose is to regulate flow
- Check valves (one way valves) - purpose is to let flow only in one direction
- Relief valves (safety valves) - purpose is to relieve excess pressure to protect equipment and people
Give the function, operation and applications of a pinch valve
Pinch valves are used to control the flow of sludges and slurries. It does not use a disc, but instead uses a flexible cylinder or tube. When the hand wheel is tightened, the tube is pinched between two bars and thus the flow of the fluid is stopped.
List the different types of check valves
- Swing check
- Lift check
- Ball check
What are check valves
Valves that make sure the fluid only flows in one direction and does not flow back. It does not contain stems, handwheels or handles. If the fluid is flowing, the valve is open but once the flow stops the valve closes automatically
What are relief valves
Relief valves are designed to release the build up of pressure in a vessel or pipeline and are mainly used in liquid systems. The disc is kept in place on the seat by a spring when the system is at operating pressure. The disc will rise and open the valve if the pressure in the system reaches a pressure that is higher than the predetermined pressure of the relief valve.
What are safety valves
Safety valves are similar to relief valves, except they are usually used on gas or steam lines. When the gas pressure is decreased this volume increases and thus a larger diameter is needed at the outlet of the safety valve to accommodate the extra volume of gas
Identify the different symbols for valves
Pg 126
How is a normally open/closed valve symbol shown
NO - unshaded symbol
NC - shades symbol
What is a specification sheet
It specifies the valve type, materials of construction, minimum and maximum flow rate, operating temp, etc. It helps the engineer choose the correct valve for a particular application
