A–B–C–D–E–F–G–H–I–J–K–L–M–N–O–P–Q–R–S–T–U–V–W–X–Y
Abrasive Wear
Chemical which speeds the vulcanization of an elastomer, so that it takes place in a shorter time or at a lower temperature. Picking up where an activator leaves off, an accelerator is often used in conjunction with a catalyst, hardener or curing agent.
AC (Alternating Current)
Unit of measurement Hz (cycles per second)
Accelerated Life Test
A test method designed to force products to fail more quickly than they would under normal use conditions. Accelerated life testing involves acceleration of failures with the single purpose of quantification of the life characteristics of a product at normal use conditions.
Accelerator
Chemical which speeds the vulcanization of an elastomer, so that it takes place in a shorter time or at a lower temperature. Picking up where an activator leaves off, an accelerator is often used in conjunction with a catalyst, hardener or curing agent.
Accumulator
A vessel in which a gas is enclosed and compressed by the liquid in a hydraulic system, thus storing energy to supply liquid under pressure to the system when needed. Types available are bladder, piston and diaphragm.
ACME Thread
Screw thread profile used in translational applications such as those involving large loads transmission. It was developed as a compromise to offer better strength than a 60 degree V-form thread while overcoming the problems with manufacturability of the square thread form. It uses a 29 degree thread angle with flat apex and valley.
Actuator
A device attached to a valve to provide the operation. Motion energy can be pneumatic, hydraulic, electric or manual or a combination. Types include:
- Spring Return – Pneumatic or hydraulic
- Double Acting – Pneumatic or hydraulic
- Direct Gas – Double-acting or spring-return
- Gas/Hydraulic – Double-acting or spring-return
- Positioning/Modulating – Double-acting or spring-return
All the above can be fitted to quarter-turn or linear acting valves.
Adapter Spool
An extension which is added to a short end-to-end valve to conform to either standard or customized end-to-end dimensions. Also termed Spool Piece.
Adaption
A term used to describe the interface between the valve and the valve actuator when the actuator device cannot be directly bolted to the valve top-work flange. Can be a simple plate or a fabricated pedestal.
Additive
A substance added in small amounts to an elastomeric compound to improve, strengthen or alter its properties. For example, a reinforcing agent to improve strength or a plasticizer to aid flexibility and processability.
AED (Anti Explosive Decompression)
Phenomenon occurring in rubber seals after exposure to high pressure gas. This gas permeates into the elastomer through flaw sites present in all molded rubber products. During an equilibrium shift (rapidly lowered pressure), the gas expands within the seal causing internal ruptures in high shear modulus (hard) materials and surface blisters in low shear modulus (soft) materials.
AGA (American Gas Association)
A trade association which represents local energy utility companies that deliver natural gas throughout the United States. www.aga.org
Aging
Change in rubber characteristics over time brought about by environmental factors such as heat and light. Accelerated aging of plastic materials is covered by ISO 188 and by ASTM D573.
Air Receiver
A container (vessel) in which gas is stored under pressure as a source of pneumatic fluid power.
AISI (American Iron & Steel Institute)
An association of steel producers which sets standards for the chemical and physical properties of steel and iron in various shapes and forms – pipe, tubing, sheet, strip and wire. www.steel.org
Ambient Temperature
The prevailing temperature of the environment immediately surrounding a system.
Amine
An organic compound that contains nitrogen as the key atom. Amines are basic compounds with strong odour. They are used as curing agent for fluoroelastomers; also a film-forming inhibitor used to prevent corrosion in oil-field tubular goods.
Analogue
Representation by means of a continuously variable physical quantity. Typical analogue control or measured variable signal is 4 to 20mA.
Anchor Pin
A pin fitted onto the body of quarter turn valves. This pin aligns the adapter plate and restrains the plate and gear operator from moving while the valve is being operated. Also termed Dowel Pin.
Angle Valve
A variation of the globe valve, in which the end connections are at right angles to each other rather than being in line.
ANSI (American National Standards Institute)
The principal standards writing organization in the United States which oversees the creation, promulgation and use of norms and guidelines that directly impact businesses in nearly every sector. www.ansi.org
ANSI Rating Class
Numerical pressure design class defined in ASME B16.5 – 1988 and used for reference purposes. The ANSI rating class is designated by the word “Class” followed by a number. For valve operating temperatures in the range of -20° to +100°F, the maximum allowable non-shock operating pressures for the various ANSI pressure classes are:
| ANSI Pressure Class | Max Operating Pressure (psig) |
| 150 | 285 |
| 300 | 740 |
| 400 | 990 |
| 600 | 1480 |
| 900 | 2220 |
| 1500 | 3705 |
| 2500 | 6170 |
Anti Extrusion Ring
Relatively hard, high modulus ring (or similar device) placed in the gland between the seal and the groove side walls to prevent extrusion of the seal into the clearance gap. Also termed Back-up Ring.
API (American Petroleum Institute)
The main United States oil and natural gas industry trade association. Among the other programs, it has some standards and recommendation practices writing development functions for the petroleum and petrochemical industry. www.api.org
API 6D / ISO 14313
An API/ISO specification dealing with pipeline valves. Most pipeline valves are manufactured to this specification and can be identified with the API 6D monogram. Over the years, many standards have been incorporated into the state and federal regulations; more recently mutual adoption of a number of standards occurred with the International Organization for Standardization (ISO).
API 6FA / ISO 10497
A fire test for valves in accordance to the American Petroleum Institute’s (API) test specification.
ASME (American Society of Mechanical Engineers)
A not-for-profit professional organization focused on technical, educational and research issues of the engineering and technology community. It publishes many technical books, papers, codes and standards. Of principal interest is the ASME Boiler and Pressure Vessel Code, which is referred for many aspects of valve design and fabrication, although not for the valves themselves. http://www.asme.org/
ASTM International
A voluntary standards development organization, originally known as American Society for Testing and Materials. It is a not-for-profit organization that provides a forum for the development and publication of consensus standards for materials, products, systems and services. Valves of most manufacturers are made of materials which comply with ASTM standards. www.astm.org
ATEX
The name given to the framework for controlling explosive atmospheres and the standards of equipment and protective systems used in them. It is based on the requirements of European Directives 99/92/EC and 94/9/EC.
Atmospheric Pressure
The force per unit area exerted against a surface by the weight of the air above that surface. At seal level the weight of the air corresponds to 14.7 psia, i.e. 1.013 bara.
AWS (American Welding Society)
A non-profit organization, which sets guidelines and standards for welding and related joining technologies. http://www.aws.org/
Axial Seal
A seal that seals on a plane perpendicular to its axis instead of on its outside diameter (OD) or inside diameter ( ID). Also termed Face Seal.