ABS: American Bureau of Shipping. Inspects and certifies pressure vessels manufactured for use on ships built under their auspices. (www.eagle.org)

AIR DRYER: Usually a pair of vertical pressure vessels piped together and filled with desiccant. Moisture is removed from the compressed air supply to protect equipment. To allow for continuous service, one tank is active as the other is being dried out.

AIR RECEIVER: A vessel designed to specific rules to store air under pressure. Often called an AIR TANK.

ANODES: Rods of magnesium alloy installed in Glass Lined Hot water Storage tanks. They erode first, thus protecting the steel tank. They must be changed as necessary. They are sometimes installed in Cement lined tanks, but never with Epoxy.

ANSI: American National Standards Institute. Oversees the creation and use of guidelines for US Industry. ANSI rated flanges are an example related to pressure vessels. (www.ansi.org)

ASME: American Society of Mechanical Engineers. The Group that oversees boiler and pressure vessel construction and safety rules in the USA. (www.asme.org)

ATMOSPHERE: One atmosphere is approximately 14.7 psi at sea level.

BAG TANK: See BLADDER TANK.

BACK-UP BAR (or RING): A strip of steel at the head to shell (girth) weld that remains in the tank after welding.

BLADDER TANK: A type of Hydropneumatic tank that separates the air and water with a rubber bag. Usually less than 500 gallon capacity.

BOILER: A closed tank (pressure vessel) in which water is heated to make steam or hot water for industrial or domestic use. Usually fueled by natural gas.

BUFFER TANK: A Vessel that adds volume to a system to stabilize water temperatures. Can be used in both hot and chilled water systems. Will reduce cycling of the boiler in a domestic hot water system or the chiller in an air conditioning unit.

CATHODIC: Relating to the Cathode side or pole of the generation of electrolysis. The anode is the opposite side.

CEMENT LINING: A Blend of Portland Cement specially formulated as a tank lining. It is usually applied over a galvanized steel mesh to a thickness of .75". Rated at 210^o F

COLLECTOR: In a solar hot water system, a flat panel unit that contains fluid heated by the sun's rays.

CONTACT TANK: Used in a well water system to increase chlorine contact time to required amount.

CORROSION ALLOWANCE: An optional increase in a tank's metal thickness over ASME minimum. Usually 1/16th or 1/8th of an inch.

CORROSIVE SERVICE: If the tank contents include any material that can corrode carbon steel, the tank must be designed accordingly. The most common example is compressed air, which contains water vapor. Inspection openings or a manway is required in pressure vessels designed for corrosive service.

CRN: Canadian Registration Number. On approval of a pressure vessel design for a fee, each Province allocates a number to appear on the tank drawing, data sheet and name plate. Required for most US built pressure vessels for use in Canada.

DEAERATOR: A vertical vessel in a water line that allows air bubbles to rise to the top. This protects pumps and other vulnerable equipment from damage trapped air causes.

DIELECTRIC CONNECTION: A Union between a hot water tank and its piping that isolates it electrically from the building. In functioning condition will reduce the likelihood of damage to the tank due to electrolysis.

DEMAND: The amount and temperature rise of hot water required from a hot water generator. For example: "500 GPH, 40-140^o F".

DFT: Dry Film Thickness. Normally used to describe paint thickness after drying.

ELECTROLYSIS: The action of stray electrical currents that causes rapid erosion of a steel hot water tank when it is not electrically isolated from the piping by dielectric unions.

EPOXY LINING: Two part epoxy polyamide coating applied on a sand blasted surface to a 10-12 mil dry film thickness. (DFT) Correctly cured, some are NSF approved for potable water service up to 180^o F.

EXPANSION TANK: A vessel that holds the extra volume of hot water in a system due to thermal expansion and allows it back into the system when it cools down.

FILTER TANK: A tank that contains a filter medium that traps contaminants in the water circulated through it. Often mounted in pairs.

FRACKING: Releases natural gas from underground rock formations by injecting high pressure fluid.

GALVANIZED: Describes a fabricated vessel that has been coated in and out by immersion in molten Zinc. Known as Hot Dip Galvanizing, it is rated at 400^o F in service.

GLASS LINING: Porcelain enamel coating. Material is sprayed on a sandblasted surface and fired at 1500^o F. Hanson Glass lined tanks are supplied with magnesium ANODES and are rated at 210^o F.

HEAT CURE: Controlled drying and curing of an epoxy tank lining by hot air blowers.

HEAT EXCHANGER: A coil or tube bundle installed in a water tank that heats up the water by passing steam or boiler water through the tubes. (www.tema.org)

HEAT PUMP: In HVAC systems, a vapor-compression device optimized for transfer of thermal energy in two directions. Heating at night and cooling during the day. Systems include a thermal storage tank insulated to R16 value or more.

HLW: A section of the ASME Boiler and Pressure Vessel Code for Lined Hot Water Tanks only. Limited to 160# psig design working pressure and 210^o Fahrenheit.

HOLIDAY TEST: A test to confirm that a tank lining or paint system has achieved complete coverage. This requires that all sharp edges are ground smooth after welding.

HOT WATER GENERATOR: A hot water tank that has a heat exchanger installed.

HOT WATER TANK: A storage tank in a hot water system. Usually lined to inhibit internal corrosion and built for storage at City water pressure.

HYDRAULIC FRACTURING: Releases natural gas from underground rock formations by injecting high pressure fluid.

HYDROPNEUMATIC TANK: A tank that contains both air and water under pressure. Larger sizes cushion water hammer caused by large valves opening and closing.

INORGANIC ZINC PRIMER: Zinc-rich primer applied over a sand blasted surface. The zinc adds some cathodic protection against external corrosion. It is a highly recommended option in humid or moist environments.

ION EXCHANGE VESSEL: A water tank that contains a special resin medium that interacts with pollutants for purification purposes.

ISO: International Organization for Standardization. Publishes procedures designed to improve efficiency in manufacturing and other industries worldwide. (www.iso.org)

JOGGLED HEAD: An end cap that has had a lip added that fits inside the tank shell for welding.

LINING: Several types are available, usually for hot water tanks. The most common are: EPOXY, GLASS, GALVANIZING & CEMENT.

METRIC SYSTEM: A system of measurement based mainly on units of ten. Used almost exclusively throughout the world except for the civilian USA market.

MIL: .01" (Often used as a measurement for paint and linings) eg: "15 mils DFT"

NATIONAL BOARD: An inspection, safety, educational and record keeping association of pressure vessel inspectors. Publishers of the National Board Inspection Code. (www.nationalboard.org)

NEMA: Association of Electrical and Medical Imaging Equipment Mfrs. A Trade Association that represents the interests of Electrical manufacturers. Publishes safety and technical information including standardized mounting designs for electric motors used with air compressors. (www.nema.org)

NON CODE: A tank that is not built to ASME rules. Usually not for internal pressure.

NON CORROSIVE SERVICE: Tanks that are designed for contents that have no moisture or other corrosive material in them. For example, propane tanks can be built without a manway or inspection openings in most cases.

NSF: National Sanitary Foundation. Provider of public health and safety-based risk management solutions. Publishes tank lining standards. (www.nsf.org)

NURSE TANK: A cargo tank on a trailer operated by a private carrier used for the transportation of bulk anhydrous ammonia used exclusively for agricultural purposes.

PASSIVATE: Usually a mild acid washing of an unlined tank interior to clean and neutralize it. Often used in stainless steel tanks to restore anti corrosion characteristics.

PRESSURE VESSEL: Usually a welded steel cylindrical tank designed and built to store its contents under pressure. Different rules apply according to the contents.

PSIA. Pounds per square inch atmospheric. A pressure measurement that includes atmospheric pressure. (approximately 14.7# psi at sea level)

PSIG. Pounds per square inch gage. A measurement that does not include the normal atmospheric pressure of approximately 14.7# psi at sea level.

SOLAR PANEL: (Liquid) Flat plate solar thermal collectors that use the sun’s rays to heat water for domestic or industrial purposes. Usually roof mounted, systems include an insulated hot water storage tank.

SOLAR TANK: A pressure vessel that stores water heated directly or indirectly by the sun.

SHELL: The cylindrical section of a vessel, not including the heads.

SRCC: Solar Rating and Certification Corporation. Administers certification, rating, and labeling programs for solar collectors (OG-100) and solar water heating systems. (OG-300)

SSPC: The Society for Protective Coatings. (Formally the Steel Structures Painting Council.) Publishes information on surface preparation, coating selection, coating application, environmental regulations, and health and safety issues. (www.sspc.org)

STRESS CRACKING (I): Ammonia (NH3) can cause this problem in carbon steel pressure vessels unless they have been stress relieved. As cold formed heads are more at risk that the tank shell, often the heads only are stress relieved before tank fabrication.

STRESS CRACKING (II): This can occur in 300 series stainless steel vessels that have had any contact with chlorides. More likely at higher temperatures and higher concentrations of chlorides. Much less likely with 316 grade than 304.

STRESS RELIEVING: Heat treating a fabricated tank in a furnace. This relaxes the stresses caused by metal forming and welding during manufacture.

SURGE TANK: A vessel that adds volume to a system to reduce the effect of surges.

USCG: United States Coast Guard. Approves designs for pressure vessels used on ships under their jurisdiction. (www.uscg.mil)

VACUUM TANK: A vessel designed to withstand external pressure. A full vacuum at sea level is one atmosphere, approximately 15 psi. ASME construction is optional.

WATER HAMMER: Closing a valve in a large water pipe can cause damage due to the shock of water stopping abruptly. It is prevented by including a pressure vessel that contains an air cushion in the system.