Page 97 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

PIPING

PIPING 2.47

VALVES

GENERAL

Valve functions can be defined as ON/OFF service, throttling service (flow control), pre-
vention of reverse flow (or back flow), pressure control, regulation, and pressure relief.
Valves can be classified as either linear (gate valve) or rotary (ball valve) based on the
action of the closure member. They are also classified by the shape of their closure member
such as gate, globe, butterfly, ball, plug, diaphragm, pinch, and check.
Their primary function, however, is to control the flow of liquids and gases, including
plain water, corrosive fluids, steam, toxic gases, or any number of fluids with widely varying
characteristics. Valves must also be able to withstand the pressure and temperature varia-
tions of the systems in which they are used. Some valves on combined water service mains,
and those handling flammable material, may be required to be fire safe or approved for fire
protection use.
Pressure regulating valves for water service are discussed in Chap. 9, “Plumbing Systems,”
in the section entitled Water. Pressure-regulating valves are discussed in their respective
chapters. Pressure relief valves are outside the scope of this handbook.

CODES AND STANDARDS

The following standards apply to valve construction:
1. AWWA C 500: gate valves for water and sewage systems
2. AWWA C 504: rubber seated ball valves
3. MSS SP 67: butterfly valves
4. MSS SP 80: bronze gate, globe, angle, and check valves

VALVE COMPONENTS

The following are the primary components of a valve.
1. A valve body is the housing for all the internal working components of a valve, and it
contains the method of joining the valve to the piping system.
2. The closure element, known as the disk or plug, is a valve component that, when
moved, opens or closes to allow the passage of fluid through the valve. The mating
surface of the disk bears against the seat.
3. The actuator is a movable component that, when operated, causes the closure element
to open or close.
4. The stem is a movable component that connects the actuator to the closure element.
5. The bonnet is a valve component that provides a leakproof closure for the body through
which the stem passes and is sealed.
6. The seat is a component that provides a surface capable of sealing against the flow of
fluids in a valve when contacted by a mating surface on the disk. The seat is attached
to the valve body.
7. The stuffing box is the interior area of the valve between the stem and the bonnet that
contains the packing.

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