3.3 Valve types, parts, accessories and application,

Gate valve
Application: on/off. Usually use for complete isolation.
Typical serviceable parts: Stem, seat, wedge
Types: Solid wedge, flexible wedge, split wedge.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, packing.

Image Source: profmaster.blogspot.com

Globe valve
Application: throttling. Usually used for throttling liquid flow. Large pressure drop across due to significant change in direction in design.
Typical serviceable parts: Stem, disc, seat, packing.
Types: Angle, Y-type, straight type.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, packing.

Image Source: www.globalspec.com  /  Mcgraw-hill Publishing

Needle valve
Application: throttling. This valve is exactly like globe valve, except with a tapered seat. For more info, see globe valve above.
Typical serviceable parts: Stem, disc, seat, packing.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem.


Diaphragm valve
Application: on/off. Usually used for very corrosive chemicals to protect valve trim.
Typical serviceable parts: Stem, disc, diaphragm.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, diaphragm

Image Source: www.globalspec.com

Ball valve
Application: throttling or on/off. Usually use for quick opening with less torque requirement.
Typical serviceable parts: stem, handle, ball, seat.
Types: straight, angle, L-port, T-port
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, body connection type, L/T port arrangement, design/material of the body, ball, seat, stem.

Image Source: www.kitz.co.jp

Plug valve
Application: See ball valve, except that a turnable plug with a bore is used instead of a ball.


Butterfly
Application: throttling or on/off. Not suitable when opposite sides of fluid have large differential pressure, makes the valve hard to open, not tight sealing.
Typical serviceable parts: Stem, disc, seat, packing.
Types: wafer type, lug type.
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, design/material of the body, disc, seat, stem, packing.

Image Source: www.kitz.co.jp

Check valve
Application: Non-return flow.
Typical serviceable parts: Disc/ball, seat
Types: Swing Disc, lifting disc, butterfly, ball,
What to specify when buying: Pressure rating, temperature, flow rates, process medium, end connection type, bonnet connection type, swing/lift/flap arrangement, design/material of the body, disc, seat.

Swing type check valve

Image source: www.kitz.co.jp

Lift Type Check Valve (Similar to globe, but w/o a stem)

Image source: www.jdvalves.com

Safety valve 
Note: Usually referred to many as PSV (Pressure Safety valve for gas systems, opens when overpressure detected) or PRV (Pressure relief valve for liquid systems, opens based on proportion of overpressure)
Application: Pressure relief or thermal relief application. Selection based on pressure and flowrates usually sized according to API 520 PSV Sizing. ASME Section I & Section VIII also denotes their required settings for allowable tolerance on set pressures and blow down(closing back pressure)
Typical serviceable parts: Lever, spring, adjusting ring, disc, seat, bellows.
Types: Conventional, Balanced pressure, Pilot operated, Power operated,
What to specify when buying: ASME Section I (w/ Lever, open bonnet, 2 adjustment ring configuration with U stamped for boilers), ASME Section VIII (Any configuration with UV Stamped for general process), Other design (with or without lever, open or closed bonnet, with or without bellows(back pressure compensation).) , Pressure rating, temperature, flow rates, process medium, end connection type, design/material of the body, disc, seat, stem,

Typical ASME Type I PSV.

Image source: Consolidated Catalogue Type 1900.

Image Source: spiraxsarco.com

Detail of PSV with Bellow/diapgragm

Image Source: spiraxsarco.com

Pneumatic Actuator - variable control

Pneumatic Actuator - on/off control
Air being a more powerful actuating media suitable for explosive environment, is also used for on off control of a valve by an piston actuator.
It comes with a solenoid valve which allows air into itself, the electrical component(solenoid valve) is smaller and less costly to own, as compared to having a huge electrical component with hazardous area protection which could cost significantly more.

Solenoid Actuator - Usually used for on/off control, for where quick opening and closing of the valve is required. Used on small systems, or when used for saving cost on pipelines which requires explosion proof set up(see Pneumatic Actuator above).

Motorized actuator - Usually used for on/off control, for where more torque is required to actuate the valve, motor can be powered by electrical power, hydraulic power or pneumatic.

Handwheel, handle, disc, seat, bonnet - See above photos on valve description for a clearer picture.
The bonnet-body of these valves could be integral or separable. Advantage to be separable if the valve is costly to purchase as replacement. ie. Exotic material or CTE/BAM tested are very costly to purchase, disadvantage is that the leak sealing will not be as robust.

Spoke wheel pulley - Used where valves are installed in high location, where access is inconvenient.

Extended spindle - Used on cryogenic systems, where high humidity leads to icing which eventually ices up the entire handwheel, as such denying user from operating the valve. A long handle alleviates this problem.

Pressure rating - American systems, 150#, 300#, 600#.... sometimes it may denote 600WOG instead which is equivalent. WOG stands for water, oil gas. Read the post on Piping Specs for details on how pressure rating come about.


Valve Sizing for pressure loss (liquid)
dP = SG * (41720Q/Cv)^2

dP = Pressure loss (kPa)
SG =  Specific gravity (dimensionless)
Q = flowrates (m^3/s)
Cv = Coefficient of flow (check valve specification from manufacturer)

For gas/steam, use its specific formula for Cv.


What to specify when buying
The above will help you the understand a valve. With regards on how to specify a purchase to the procurement or vendor when sourcing for valves, refer to the short write up on this section:
3.2 Valve Spec & Purchase

For each of these valves, the essential details to be knowledgeable to select the right valve for the right application. If in doubt, consult manufacturer's application engineer for advice.