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Plant Maintenance - Chapter 50: Introduction To Valves
Terms in this set (151)
How can Valves be opened?
Valves can be manually operated or have an actuator to change and control the valve opening
How may the actuator be operated?
The actuator may be operated:
What consideration must be given when selecting a valve?
Working Pressure and Temperature
Type of Fluid (Corrosive or Erosive
Rate OF Flow
Valve characteristics desired (Percentage valve travel to rate of flow
Cost of Installation and maintenance
What are 7 common valves found in a power plant?
Describe the operation of a Gate Valve
Gate Valves consist of a gate-like disk, which is actuated by a threaded stem and handwheel, moving the disk up and down at right angles to the flow path. In the closed position, the disk seats between two faces to shut the flow off
What are two designs of gate valves?
Explain The operation of a Rising Stem Gate Valve
In this design the stem is attached to the gate; the top portion of the stem has screw-like threads, which mesh with threads in the valve wheel. As the valve wheel turns, the stem and disk rise up or down, but the wheel does not
Explain The operation of a Non-Rising Stem Gate Valve
In this design the stem has threads on the bottom half, which mesh with threads in the disk. When the valve wheel turns, the disk rises up or down on the stem, while the valve wheel does not move up or down
What Are Gate Valves NOT suitable for?
Gate Valves Are NOT suitable for throttling flow because excessive wear (Erosion) of the gate and seats may occur due to high velocity (Called Wire Drawing)
What are Gate Valves Suitable for?
They are suitable for Stop (Or Isolating) Valves, where conditions require either full flow or no flow
What is an Advantage of a gate Valve
When fully opened, the resistance to flow is low with a minimum pressure drop since the fluid flows in a straight line
Moving on to globe valve mothaaa ƒuuuuuugga
What does the construction of the globe valve force the fluid flow to do?
The globe valve is constructed in such a way that the fluid flow passing through it must Change Direction Twice
What position is the Globe-Shaped Disk and Seat in apposed to the main flow path?
How is the disk moved toward or away from the seat?
The globe-shaped disk and seat are parallel to the main flow path; the disk is moved toward, or away from the seat by means of a threaded stem.
When the valve is open, what happens inside?
When the valve is open, the disk is raised off the seat and the flow enters below the disk, passes up through the seat, and then goes to the outlet
Can the glove valve be a rising steam?
Yes, but unlike the rising steam gate valve the whole steam + Handle raises, or lowers opposed to just the steam
What is A Globe Valve Ideal For?
With a minimum of what two things?
The Globe Valve Is ideal for throttling or regulating flow with a minimum of wire drawing and seat errosion
What is a disadvantage of a Globe Valve?
A disadvantage of a globe valve is that, due to the change in flow direction, it offers more resistance to flow than the gate valve does
What is The Unbalanced, single Disk Globe Valve Used in sizes larger then??
Due to what?
The Unbalanced, single disk globe valve is seldom used in sizes larger then 305mm, due to the difficulty with opening and closing against high fluid pressure
Just moving right along.
And think.... This is only 20 Slides in
What are needle valves designed to allow?
Needle Valves are designed to allow precise flow control
Where does The "Needle Valves" name come from?
Their name is delivered from the sharp pointed disk and matching seat
Where are Needle Valves Extensively Used?
They are extensively used for continuous blowoff or chemical feed control services
Why are the stem threads finer then usual in a Needle Valve?
The stem threads are finer than usual so that considerable movement of the hand wheel is required to increase or decrease the opening through the seat
What do Needle Valve's "Reduced Seat Diameter" Have a relation with?
Usually, these valves have a reduced seat diameter in relation to the pipe size
Hang in there
What, and where is a Butterfly valve often used as/in?
The Butterfly Valve is often used as a Final Control Element in Air, Or in
Large water piping systems
What sizes (mm) In diameter do Butterfly Valves come in?
It comes in sizes from 25 to 3800mm in diameter
What Pressures are Butterfly valves designed up to?
Butterfly Valves are designed for pressures up to 13800 kpa
What Temperatures are Butterfly Valves designed up to?
Butterfly Valves are designed for Temperatures up to 1100°C
What are Butterfly valves often lined with?
Butterfly valves are often lined with a resilient material so the rotating disk seats tightly when closed
What type of seal do Butterfly Valves Provide?
High or low Operating Torque?
When the disk is open, what position is it to the flow?
They provide a bubble tight seal with low operating torque and operate by the wing-like action of the disk; when open, the disk is parallel to the flow
What ° Can the disk be rotated through from a wide open to the fully closed position?
The flat disk can be rotated through 90° from wide open to the fully closed position
What two ways do Butterfly valves fit into piping?
Butterfly valves fit into the piping in two ways:
The Two-Flange (Or Double Ported Type)
The Wafer Type
What is required to position the disk for bigger sizes?
A power actuator is required to position the disk for bigger sizes because large pressure differentials can exist across the disk
What 4 places can a butterfly valve be used in?
Thermal and Hydroelectric power stations
Oil & Gas Processing Industries
Oil and Gas Transmission
Water and Sewage Plants
What are 3 Advantages of Butterfly Valves?
Relatively Light Weight
Ease of Operation and Self Cleaning
Negligible pressure drop across the valve when it is fully open
What does a Ball Valve Consist of?
What does it allow The Fluid to do?
The ball valve consists of a spherical plug with a passage bored through it witch controls the fluid flow through the valve body
How Many turns does the Basic Ball Valve Require to move from fully open to the fully closed position
The basic type of ball valve requires a quarter turn (90Degrees) to move from fully open to the fully closed position
How else can a Ball Valve Be operated?
(2 Other Ways)
The valve can also be operated by means of a leaver which also serves an open or shut indicator, or
By using an automatic Actuator
What Type of control does the Spherical Plug allow?
The Spherical Plug Allows Precise control of flow through the valve
What does the The Spherical Plug Give when in a closed position?
The Spherical Plug gives a Tight shut-off when in the closed position
Is lubrication required in a Ball Valve?
Lubrication is NOT required
True or False
The Ball and Stem From a Ball Valve Are Machined from One Piece
The Ball and stem are machined from one piece
For larger sizes and higher pressure ratings, What is the ball is constructed with?
What s it supported by?
What does this construction require for one end and the opposite end?
For larger sizes and higher pressure ratings, the ball is constructed with a double stem and is supported by bearings.
This construction requires a seal for one end and packing box for the opposite end
What sizes are Ball Valves Manufactured in?
Ball valves are manufactured in sizes from 2 to 1000mm
What pressures are Ball Valves Designed up to?
Pressures up to 69000 kPa
What Temperatures are Ball valves Designed up to?
-185°C to 550°C
What are Ball valves are suitable for?
What type of industries or plants have ball valves found a wide application for?
(1 Industry, 2 Plants)
Ball valves are suitable for handling slurries and fluids with a high solid content and, for this reason have found wide application in the paper industry, chemical plants, and sewage treatment plants
How many Turns is a Ball Valve?
How many Turns is a Plug Valve?
¼ Turn Valve
What does The Plug Valve Consist of?
Consists of a tapered or straight cylinder containing a hole inserted into the cavity of the valve body.
What does the hole in the plug in The Plug Valve Line up with?
The hole in the plug lines up with the axis and opening in the valve body
What prevents leakage in the steam of a Plug Valve?
A packing box, with packing held in place by the gland. This prevents leakage along the stem
What Shitttty Thing does The tapered plug have the tendency to do?
What does this cause if Forced?
How can this issue be resolved?
The tapered plug has the tendency to jam in the tapered seat and can cause scoring if forced to turn.
Most Plug Valves are Lubricated to prevent the issue
Where is Lubrication Supplied through In a Plug Valve?
The Lubricant is suppled through the centre of the stem and is distributed through channels to the seating surfaces
What can Other Plug Valves be equipped with to eliminate the need for lubrication?
Other Valves are equipped with a flexible, smooth liner which eliminated the need for lubrication
Is the Pressure drop across the Plug Valve High Or Low, In its wide open position?
The pressure drop across the Plug Valve when it is wide open is very low
How is A plug Valve Cleaned?
The Plug Valve is Self-Cleaning
Plug Valves are used as Quick Opening valves in the Following 4 Places:
(2 Lines, 2 Plants)
Gas Supply Lines
Low Pressure Steam Lines
Water Treatment Plants
Pulp And Paper and Chemical Plantst
What does the Check Valve Prevent?
The Check Valve Prevents reversal of flow in piping
What keeps the Check Valve Upen?
What causes the valve to close?
The flow of the fluid keeps the check valve open while gravity and reversal of flow cause the valve to close
Two basic Types of Check Valves are?
Swing Check Valve
Lift Check Valve
What does the Swing Check Valve Consist of?
The swing check valve consists of a flap or disk of the same diameter as the pipe bore which hangs down the flow path.
What happens to the disk with the flow in the forward direction in a swing check valve?
With flow in the forward direction, the pressure of the fluid forces the disk to hinge upwards, allowing flow through the valve
With flow in the opposite direction in a swing check valve?
A Reversal in flow causes The disk to shut against the seat and stop the fluid from going back down the pipe
What Do swing check valve produce?
due to what?
Swing check valves produce relatively high resistance to flow in the open position, due to the weight of the disk.
What kind of pressure drop does the swing check valve have?
Larger pressure drop across the valve then other types
What can happen with abrupt changes in flow to the Swing Check Valve?
How can this problem be resolved?
With abrupt changes in flow, the disk can slam against the valve seat which cam cause significant wear to the seat, and generate water hammer in the pipe system
This problem can be resolved by fitting a damping mechanism to the disk and by using metal seats to limit the amount of seat wear
What happens to the flow In a LIFT CHECK VALVE?
The flow through a LIFT CHECK VALVE undergoes two changes in direction as it passes through a horizontal section upon which the disk seats
How does the disk move to allow fluid to pass through?
How does the Disk Move to close if the flow tries to reverse?
(IN A LIFT CHECK VALVE)
The disk moves upward to allow the fluid to pass through and moves downward to close if the flow tries to reverse.
IN Larger Lift Check Valves What is used to cushion the action of the disk?
In larger check valves of the Lift Type, a Dashpot (Dampening Cylinder) Is often used to cushion the action of the disk.
What other type of Valve are Lift Check Valves Similar in Configuration to?
Lift check valves are similar in configuration to Globe Valves except that the disk (Or Plug) is automatically operated
What is a Lift Check Valve Only suitable for if a Metal Seat is Used?
If a metal seat is used, the lift check valve is only suitable for applications where a small amount of leakage under reverse flow conditions is acceptable.
What Is the Life Check Valved Limited for its use?
(What type of applications)
What is the Lift Check Valves purpose?
For what Type of Equipment?
Since the lift check valve generally limits its use to water applications, it is used to prevent reverse flow of condensate in steam traps
What is the main advantage of a Lift Check valve?
The main advantage of the lift check valve is its simplicity.
What is the only Moving part?
Since The ____ is the only moving part, what does this make the Lift Check Valve?
Does it require a lot of maintenance?
Since the plug is the only moving part, the valve is robust and requires minimal maintenance.
What does the Use of a Metal Seat In A Lift Check Valve Limit?
The use of a metal seat limits the amount of seat Wear.
Where is The Lift Check Valve Only Designed for installation in?
The Lift Check Valve is designed only for installation in Horizontal Pipelines
END OF THE TYPES OF VALVES
BOILER VALVE TYPES
Each Boiler Discharge Outlet (Except safety valve connections) Must be fitted with What?
Each Boiler Discharge Outlet (Except safety valve connections) Must be fitted with a stop valve
Located as close as is convenient and practical to the boiler
What are two types of valves commonly used on the steam outlet of a boiler?
The two types of valves commonly used on the steam outlet of a boiler are the GATE VALVE and The GOBE VALVE
What Valve is most likely to be used out of the two on the steam outlet of a boiler?
Why is This?
The Gate Valve since it offers the least resistance to flow and because it will be wide open during operation
(Not Throttling Involved)
What kind of stop valves are recommended?
Using stop valves of the outside screw-and-yoke type with rising spindles are reccomended
What is the Advantage of The outside screw-and-yoke Type Stop Valve?
The advantage of this type is that the operator can see even from a distance, whether the valve is open or closed
What are Two advantages of the threads on a Outside Screw-And-Yoke Stop Valve?
(Since the threads are Located outside of valve body)
Since the threaded part of the spindle is located outside of the valve body, it is not exposed to the corrosive action of water and steam, the threads can also be easily lubricated
What is the difference in spindles between the Gate Stop Valve and the Globe Stop Valves?
The Gate Stop Valve features an outside-screw-and-yoke with rising spindle. The handwheel is carried on the toke and does not rise with the spindle
The Glove Stop Valve Has a rising spindle with internal threads. In this case, the handwheel is attached directly to the spindle and rises with it
Non-Return Stop Valve
What is The Non-Return Stop Valve also Referred to as?
The Non-Return Stop valve, is also referred to as a "Stop-and-Check" Valve
Where is the The Non-Return Stop Valve Installed?
It is installed at the boiler outlet in cases where the boiler outlet discharges into a common header with other boilers
Read This.. It is the operation of a The Non-Return Stop Valve on the steam outlet of a boiler.
It acts as a stop valve when the valve wheel is in the closed position, pushing down on the valve stem and forcing the valve disc onto the seat. However, the valve wheel is not directly attached to the calve stem. When the valve wheel is raised to the full open position (or Partially open position) It does not apply direct force to the stem and does not directly lift the disc off the seat. It simply releases its downward force on the stem, thus allowing the stem and disc the freedom to move upward if steam pressures allow
Now, if the steam pressure below the disc is greater than the steam pressure above the dic, the disc will rise and allow steam to flow out of the boiler. However, if and when the pressure above the disc becomes greater than the pressure below the disc, the disc will be forced down onto the seat, thus closing the valve in the same manner as a check valve. This prevents the reversal of flow back through the valve
This action of the Non-Return Valve is important in 3 Situations:
1.) When the boiler is being started and brought online with other boilers, the disc will remain closed until the boiler pressure exceeds the pressure in the common steam header. This prevents the higher steam header pressure from flowing back into the boiler
2.) If the boiler trips during normal operation, the pressure in the boiler will quickly drop below the pressure in the common header. The non-Return Valve will close, again preventing flow reversal into the boiler
3.) If a boiler tube were to rupture, the pressure in the boiler would drop and the non-return valve would automatically close, thus preventing the other boilers from keeping the damaged boiler pressurized.
Pressure Reducing Station:
What is the purpose of a Pressure Reducing Station?
The purpose of a pressure reducing station is to receive a process fluid (Such as Steam) at a higher pressure, and reduce it to a controlled lower pressure for use downstream, lower pressure system or Equipment.
What is the "heart" of the Pressure Reducing Station?
The Pressure Regulator
What can is a Pressure Regulator also called?
(PRV) Pressure Reducing Valve
What does a sensing line feed to the pressure regulator?
What does this adjust?
To do what?
A sensing line feeds lower (Controlled) Pressure to the regulator, which then adjusts the position to control that presure
Where is a strainer located in a Pressure reducing station?
A strainer is located upstream of the regulator which prevents foreign particles from entering the PRV
What are installed on either side of the Regulator and strainer for isolation for maintenance?
Block valves on either side allow the regulator and strainer to be isolated for maintnance
What Two things are used to manually provide downstream pressure when the regulator or strainer are being maintained?
A Bypass line and valve are used to manually provide downstream pressure when the regulator or strainer are being maintained.
Where are pressure gauges installed?
Pressure gauges are installed on the low and high side of the station, allowing the operator to monitor the regulator operation
Where is a Pressure RELIEF Valve Required?
(NOT PRESSURE REDUCING VALVE)
What will this protect the system from if 'something' Fails? Or During _______ Operation.
A Pressure Relief Valve is required on the Low pressure side to protect the system if the regulator fails and/or during bypass operation
What is a steam system Common to have (2 Things) To remove free water before the Pressure Regulator?
For a steam system it is common to have a steam separator, with a steam trap, to remove free water before the regulator
Pressure Reducing Valves:
What are 2 common Pressure Reducing Valves?
Spring-Operated Reducing Valve (Internal Diaphragm)
Spring-Operated Reducing Valve (External Diaphragm)
Spring-Operated Reducing Valve (Internal Diaphragm)
Spring-Operated Reducing Valve (External Diaphragm)
Read Pan Global A2
Chapter 50, Page 15
Too Lazy To Type all this Bulllshiiit Out
Materials Of Construction
FOR VALVES BITTTTTCH
What Are 3 Main Things that can determine the Material of the Valve Body?
Materials of the construction for valve bodies will be determined mainly by:
3.) Type of Fluid
What are 6 Materials That can be used for Construction?
Special Alloy Steels
What is Cast Iron Material used for in terms of Valve Bodies?
Used for Low Pressure and Temperature applications
What is Bronze Material used for in terms of Valve Bodies?
Used Fro Moderate Pressures and Temperatures up to 280°C
What is Carbon Steel Material used for in terms of Valve Bodies?
Used for services up to 425°C
What is Alloy Steel Material used for in terms of Valve Bodies?
Used for high pressure applications and temperatres up to 650°C
What is Special Alloy Steel Material used for in terms of Valve Bodies?
Used for temperatures in excess of 650°C
What is Stainless Steel Material used for in terms of Valve Bodies?
Used for corrosive surfaces
What are three ways the valve body can be attached to the piping system?
The body can have screwed or flanged ends or be welded to the piping system
Valve trim consisting of a disc, seat ring, and valve stem and guide bushings, if acceptable are manufactured from what 4 Materials?
Valve Packaging, depending on the service is made of combinations of what 4 things?
Teflon Coated High strength Yarns and Vegetable Fibres
IDENTIFICATION OF VALVES
Valves must be identified to eliminate accidents from this type of equipment.
All Valves not properly or clearly identified should be:
All Markings shall be legible and must indicate at least what 3 things?
Manufactures Name or Trademark
Service Designation i.e., Pressure-Temperature for which the fitting is designed
Material Designation i.e., Steel or Cast Iron, ASTM Number, etc.
What is 2 Good things to do for valves in regards to maintenance?
Frequently do a visual inspection of all valves and repair small leaks immediately
Valve Leak is often Remedied ______ and _________.
Failure to stop a leak early in a valve may result in what?
A Valve Leak is often remedied easily and quickly. Failure to stop a leak early may result in damage to the bonnet and the flange surfaces, which may then require costly and time consuming repairs
What are 2 places Valve Leaks usually occur?
Bonnet and Flange
How can a stem leak normally be fixed?
Steam Leaks can normally be fixed by slightly tightening the packing nut, or gland
If insufficient packing is left to stop leakage, renew the packing.
Why shouldn't a Packing nut, or Gland be overtightened?
Never tighten more then necessary to stop leakage since over tightneing causes extra friction resulting in wear, and added effort when opening and closing the valve
What is wear on the stem packing mainly due to?
What can increase the life span of the packing?
Wear on the stem packing is mainly due to the rising and turning motion of the valve stem.
A few drops of oil applied Occasionally to the Valve stem will reduce friction and extend the life of the packing
What can cause Bonnet and Flange Leaks?
These leaks can be cause by insufficient tightening of the bolts or by bolts loosing under service strain
If tightening of the bolts do not stop a Bonnet and Flange Leak, what should be replaced as soon as possible?
If tightening of the bolts do not stop the leak, replace the gasket as soon as possible.
What will Neglecting to repair flange leaks result in?
Neglecting to repair flange leaks will result in "wire-drawing" on the faces of the fanges
What is Wiredrawing?
Wiredrawing is the forming of deep grooves, running from the centre of the flange to the outside, caused by the scouring action of the scouring fluid
Most Valves are designed to permit internal inspection without removing the body from the line
What is the Best Preventative Maintenance for valves?
Periodic Inspection of the valve disk and seat is the best preventative maintenance
If inspection of the Valve disk (Or the Wedge) and seat shows damage, such as ___________, and _________________ What should be done to the seating surfaces?
If inspection of the Valve disk (Or the Wedge) and seat shows damage, such as grooving, and wire-drawing, the seating surfaces should be refaced
When should a Globe valves equipped with a composition disk have its disk replaced?
What will this prevent?
Globe valves equipped with a composition disk should have the disk replaced as soon as a seat leak is discovered
Early replacement will prevent damage to the seat.
To repair damaged disks and seats of globe valves, what are 3 procedures that can be used?
Next Slides Will Explain...
1.) How can Slightly damaged surfaces be refaced?
Slightly damaged surfaces can be refaced by grinding the valve disk in on the valve seat in combination with a grinding compound
2.) If Damage is more Extensive What should be done to the seat and disk?
If damage is more extensive, the seat should be refaced with a reseating tool. The valve disk should be refaced either by carefully filing down the damaged seating surface or by taking a slight cut off on the lathe or grinding machine. Then the disk and dat should be ground in together to obtain matching seating surfaces
3.) When the valve is equipped with a renewable seat and the disk and seat are extensively damaged, what will be easiest to do?
When the valve is equipped with a renewable seat and the disk and seat are extensively damaged, it will be easier to replace both rather to repair
What type of valves are harder to reface then globe valves?
The seating surface of gate valves are such harder to reface than those of globe valves. Special equipment is required to do a satisfactory job
END OF THIS LONG ASS CHAPTER 50
Fuuuck that sucked
It comes in sizes from 25 to 3800mm in diameter
The Unbalanced, single disk globe valve us seldom used in sizes larger then 305mm, due to the difficulty with opening and closing against high fluid pressure