never throttle- keeping it slightly open causes wire draw and erosion
Adv:
good shutoff
minimizes pressure drop
Bidirectional shutoff
Useful in slurries or heavy viscosity- knife edge can cut through
Disadv:
threaded type is usually slow to open and to close in emergencies
Needs considerable clearance
Not recommended for shock load
Difficuly to repair
Cannot be throttled
Types of discs (valve plug)
Solid wedge
most common
Position between tapered seats to seal
Steam, hot and cold water, air or gas service
Ideal for turbulent flow- full port and has no parts to vibrate loose
Issue: when severe conditions, valve body may contract more when cooled than disk and might get seized. To overcome this, the flexible wedge exists
Flexible wedge
hollow edges and solid center
Disc has some flexibility to prevent disc from being pinched when body cools
Split Wedge
2 pieces sit between matching tapered seats in the body. Mechanism spreads discs apart to form seal.
Suitable for laminar flow with no vibration. Vibrations will damage the internal mechanism
Double Disc
disc and seat parallel to eachother and not tapered. Mechanism spreads discs against seal
Quick opening
has lever mechanism for quick opening
Gate valve install:
flow either direction but ensure with mfg. flow arrow is cast on body
Usually stem vertical but can be rotated if no clearance. Ensure mfg confirms this is allowed.
Ensure valve can fully open and fully close after install
Installed in vertical lines it will act as drip pocket when closed, usually has drain plugs built in body.
seat is parallel to line of flow- fluid makes 4× 90deg turns to get through the valve so it induces a pressure drop.
Has specific flow direction! Must follow flow patter, enters cavity from bottom and rises into face of globe disc
Adv:
good shutoff
Good throttling but do not exceed 20% pressure drop
Shorter stroke needed to operate than a sliding stem gate
Straight, Y (keeps press loss to a minimum, minimizes sediment), or angled (90 deg flow change, slightly less flow drop)
Disadv:
higher pressure drop
More force required to hold pressure
Seat and Disc:
Plug Disc: wide surface contact so allows for finer throttling.
Conventional disc: small seat contact, not great for close throttling, cut through solids, used where debris exists.
Composition Disc: soft material- can have solids build up and maintain sealing capability,
Needle valve: high pressure and small line sizes, allows very fine throttling. Try cocks are needles valves used on boilers to check for water level if sight glass damaged.
Globe valve install
valve stem vertical
Specific flow direction- inlet pushes up on seat
Prevent backflow
Styles:
Lift check:
common on systems using globe valves since both valves have common flow characteristics.
Beveled bronze disc and seat ring- both are regrindable
Beveled disc and seat- the seat is not renewable
Composition disc - air and gas where metal seat may not give tight shutoff
Ball lift check valve- extensively used on sewage effluent
Swing check:
Common on systems using gate valves as they both have low pressure drop.
Install vertical or horizontal, but gravity may close disc.
You can differentiate it via the hinge pin on valve body
Tilting disc type exists to operate a low velocity
Non-slam check valves(aka folding disc):
Larger pipes, spring loaded flaps inside.
Seat is usually soft material
Open on differential pressure of ¼ to ½ psi. Will close with no flow.
Designed to help prevent liquid reversal in a line.
Check valve install:
Rule of thumb: swing checkif gate valves, lift check if globe valves.
Ensure velocity of flow is adequate for check valve. Swing check needs alot of velocity. May need to be reduced in size to increase velocity through body.
Swing check : horizontal or 45 degree slope
Lift check: horizontal, often used where pressure loss not important, suited to high flow velocities
most commonly used- laminar flow and easy operation. Only needs ¼ turn.
Seats usually teflon, ball is carbon or stainless steel
Adv:
bubble tight
Quick to open
Smaller in size than gate valves
Lighter in weight
Minimal resistance to flow (full port)
Clean or slurry fluids
Less force needed to actuate
Disadv:
not for throttling
Sharp matter can settle and create leakage
Adv:
Compact and min space req
Light
¼ turn
1 ½ to 200” NPS
Low pressure drop
Can be made bubble tight
Can be 100% shutoff (i personally don’t believe this though)
Designed for throttling and little to no resistance wide open
Disadv:
throttling is limited - operating range about 30 to 80 degree effectiveness.
Prone to cavitation or choked flow when throttling
Turbulence affects disc movement
quarter turn but has a non tapered plug running vertically through the valve body.
Adv:
simple, can be serviced in place
Quick open/close
Minimal flow resistance (has a reduced port compared to ball valve though)
Leak tight- used often on gas appliances
Disadv:
greater forced req to turn, if >4” it needs actuator (gear reductors)
Port size is smaller than a ball valve
Styles:
lockable service
Insulated service (luboseal) :
most commonly used gas valve on outside installs.
Has insulated union to provide barrier between underground and building pipe, as well as joining 2 piping systems together.
Gas valve/cock
Fitting valve or appliance valve
Pilot gas valve
Main or corportation stop valve (service connecting to water main or water service. Inlet is a AWWA thread and outlet is flared for copper water tube)
Curb or cock stop valve- private property boundary line on water heater service. Both ends are flared unions or compression sleeves
Square headed steam cock- key handle is parallel when on and 90deg to pipe when off- this should not be used on gas because its backwards!
Gauge cock - used to isolate gauges
Pet cock- used for rubber hose connections because the one end has a barb.
these are all considered full port
Butterfly and ball valves are usually recommended to be installed with ball valves with stem horizontally.
If seat retainer exists, recommended to be downstream of valve.
ideal for fluid on/off because:
simple length of pipe with elastomeric material and mechanical system for squeezing
can be engineered for bubble tight shutoff
true full bore
no mechanical parts in contact
Is a configuration of the pinch valve but the diaphragm valve has 2 features that make it desireable:
diaphragm can be changed without removing the valve from the line
bonnet is totally isolated from fluid.
O-Ring can be placed on valve stem to isolate bonnet from environment completely.
No stuffing box.
A.K.A Packless valve.
Globe valve only, cannot be gate.
Weir design is meant to reduce the amount of distance the diaphragm has to travel.
Application:
tough corrosive, abrasive, radiactive, viscous process
food processing, pharma
applications where atmospheric contamination is to be avoided.
Adv:
Throttling or on/off
chemical resistance
no stem leakage, no packing needing service
bubble tight shutoff
can be used in flow direction changes
Disadv:
weir design may prevent full drainage
limited service temp of -76 to 232c, pressure up to 300psi
diaphragm erosion if severe service throttling
Valves designed to allow full flow of fluids are used for on/off capability and have little to no restriction built into body.
Valve Body
directs fluid flow through valve and provides mountings for valve trim.
Cast, forged, or fabricated
Valve Bonnet
mounted on top of valve body and completes pressure casing - usually the valve stem passes through it (gate, globe, stop check, diaphragm valves).
May contain stuffing box for valve packing to prevent fluid from leaking out
Styles:
Screwed in Bonnet - can be difficult to disassemble
Screwed union bonnet - for valves that need frequent service
Bolted bonnet - most common on larger high pressure vessels. Usually found on larger valves that need frequent service.
U Bolted version is a variation where the liquid flowing through the valves cause constant problems
Welded lip seal bonnet
Pressure seal bonnet
Valve Disc
controls flow through valve body, when closed - it is considered part of the pressure casing as it is subject to the same line pressure as the valve body and bonnet.
Terms:
Rectangular Port: area of the rectangular port can be equal to 100% of standard pipe, or can be restricted
100% area or full port: area through valve is equal to or greater than standard pipe
standard opening: area through valve is less than the standard pipe area
round port: full round opening of same size as standard pipe
diamond port: diamond shaped port, less than standard pipe area
non-lubricated plug valves: tapered plug, mechanism plug unseats before turned to reduce operating torque required, or rubber sleeve with low friction.
perform function while in contact with fluid
Valve Seats
valves may have more than 1
Globe and check : single seat thats seals to disc
Gate : 2 seating surfaces, upstream and downstream.
Ball : may have more than 1 depending on port configuration
Lubricated: small ports in tapered plug allow sealant to pour in.
Lined plug: polymer lining modeled to form seating surfacee
Butterfly: 2 options
elastometer lined bore
Offset disc from axis of rotation to use line pressure (eccentric disc)
Valve Stems:
passes through and plugs bonnet opening
Check valves do not have these.
Not pressure retaining, part of valve top works
Connecting component between actuator and valve disc
Mechanism that causes calve to move in a valve is referred to as the operator.
Styles:
rising stem with outside screw and yoke.
non rising hand wheel; screw mechanism (operator)
Threads are above the valve packing
Threads of stem never exposed to process fluid
Valve stem travels in linear motion without rotation- reduces torsion in valve packing
Disc face designed for backseating, used to ensure valve is fully open. Once fully open, the valve is turned back in so the backseat is nit engaged. This allows packing to do it’s job. If packing is leaking, backseat it and it may help stop the leaking until repairs can be made. → backseating is only a temporary measure and not meant to replace the function of packing.
Meets ASME and API sections that indicate a valve must clearly indicate full open or full closed. Can also have plastic indicators.
Stem protectors may be needed to prevent dirt on threads
Rising stem with rising hand wheel
Stem rotates as hand wheel is turned causing it to rise or drop
Threaded stem portion is in contact with process fluid
Non rising stem with inside screw
valve stem rotates with hand wheel but has no linear travel
Threads are under the packing
Threaded portion is exposed to process fluid, so can only be used with specific fluids
Disc is drilled through, the threads raise or drop the disk via those threads.
Inside screw rising stem globe valve
handle and stem both rise,
threads exposed to process fluid
Stuffing box milled or formed into top of bonnet ti seal against stem leakage.
Collar on end of valve stem allows stem to rotate without the disc rotating.
Stuffing Box Designs:
gate and globe valves
smaller valves use just a packing nut, larger valves use a packing gland
Lantern ring: small ring built into stuffing box that allows lubrication to be applied to larger valves.
Stop Check Valve Stem:
Similar to a globe valve but main difference is that there is no connection between valve stem end and disc.
Valve stem acts as a push rod to hold the disc closed.
Hand wheel rises with stem (as with most globe valves)
Disc is a steel cylinder (or piston) that uses line pressure to push it up.
Sliding Valve Stem
used on pneumatic and hydraulic control valves.
Same as an outside screw rising stem but no threaded section, instead it is a coupling that attaches to the actuator.
Same stem as used in a hand-lever operated quick opening valve
Rotary Valve Stem
Ball, plug and butterfly valves.
90 deg rotation
Valve stem usually not directly connected to the ball.
Tapered Plug Valve Stems
stem machined as a integral portion of the plug.
Upper and lowe portions of plug are machined outside sealing area to act as shaft for rotating the plug.
Butterfly Valve Stems
Uses O rings to prevent stem leakage instead of packing
Top and bottom have bushings to keep disc centered, disc secured in center with taper pins.
Actuators operate valves. Can be manual or powered.
Types:
Sprocket and Chain:
remote operation of gate or globe valves that are not accessible.
Bevel and Spur Gear:
gear arrangement with mechanical advantage. Operating handle is usually 90 degrees to the usual position.
Power Actuators:
automatic devices for opening, closing, modulating valve position for throttling.
May be motorized (electric/hydraulic) or pneumatic.
Bonnet Relief:
Prevents “Pressure Locking” - when flexible wedge or double disc gate valves have pressure inside the bonnet and the actuator cannot overcome it.
A small manual hand valve mounted connecting the bonnet to the inlet pressure side of the valve - this valve gets opened before attempting to open the valve (actuator pushes the pressure back into the inlet).
A 3 way valve may be used to position the line to bypass to equalize the disc pressure prior to opening (when closed - the bonnet is vented back to the inlet, when open - this is closed off).
Bypass Valve:
Prevents Thermal Binding - common on wedge gate valves that are closed when the system is hot, if the system cools with the valve still closed then it creates the binding. Solid wedge gate valves are most susceptible to this.
Some valves come pre-tapped for this. The valve is opened to warm up the line slowly before opening the valve.
Required on high pressure steam block gate valves to warm up prior to opening the main block valve (ASME code requirement)