Valves

Question 1

What are the most common valve designs

Answer 1

• Gate
• Plug
• Ball
• Globe
• Diaphragm
• Butterfly

Question 2

Name the different parts of a typical valve

Answer 2

• Stem
• Actuator
• Packing
• Bonnet
• Seat
• Disc
• Body

Question 3

Describe the body of the valve

Answer 3

The large part of the valve through which the fluid flows

Question 4

Describe the seat of the valve

Answer 4

The part of the valve that stays motionless

Question 5

Describe the disc of the valve

Answer 5

The part that moves to the seat to stop flow and if raised completely the valve is fully open

Question 6

Describe the stem and actuator of the valve

Answer 6

Used to lower or raise the disc

Question 7

Describe the bonnet of the valve

Answer 7

The space that the disc moves into if the valve is opened

Question 8

Describe the packing of the valve

Answer 8

Surrounds the stem and keeps the fluid from leaking out

Question 9

Sketch a typical valve

Answer 9

Pg 104

Question 10

Give the function, operation and applications of a gate valve

Answer 10

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.

Question 11

Give the function, operation and applications of a globe valve

Answer 11

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.

Question 12

Give the function, operation and applications of a needle valve

Answer 12

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

Question 13

Give the function, operation and applications of a plug valve

Answer 13

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

Question 14

Give the function, operation and applications of a three way plug valve

Answer 14

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

Question 15

Give the function, operation and applications of a four way plug valve

Answer 15

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

Question 16

Give the function, operation and applications of a ball valve

Answer 16

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.

Question 17

Give the function, operation and applications of a butterfly valve

Answer 17

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

Question 18

Give the function, operation and applications of a diaphragm valve

Answer 18

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

Question 19

Name the classes of valves and their primary function

Answer 19

1. Shut off valves (block valves) - purpose is to close off flow
2. Control/throttling valves (manual and automatic) - purpose is to regulate flow
3. Check valves (one way valves) - purpose is to let flow only in one direction
4. Relief valves (safety valves) - purpose is to relieve excess pressure to protect equipment and people

Question 20

Give the function, operation and applications of a pinch valve

Answer 20

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.

Question 21

List the different types of check valves

Answer 21

• Swing check
• Lift check
• Ball check

Question 22

What are check valves

Answer 22

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

Question 23

What are relief valves

Answer 23

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.

Question 24

What are safety valves

Answer 24

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

Question 25

Identify the different symbols for valves

Answer 25

Pg 126

Question 26

How is a normally open/closed valve symbol shown

Answer 26

NO - unshaded symbol

NC - shades symbol

Question 27

What is a specification sheet

Answer 27

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