Valves A

Obj 1 identify types of valves

Gate Valve

• 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.

Globe Valves

• 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

Check Valves

• 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

Ball Valves:

• 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

Butterfly Valves:

• 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

Plug Valves/Cocks

• 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.

Ball, butterfly, plug valve install

• 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.

Pinch 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

Diaphragm

• 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

Fluid Flow Pattern through valves

• Valves designed to allow full flow of fluids are used for on/off capability and have little to no restriction built into body.

Obj 2 - fundamental design variations and their applications

Valve Parts

• 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.

Valve Trim

• 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

• 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)