backflow prevention Cross-Connection Control Handbook
A Brief History of Cross-Connection Control Contents Page Backflow — What is it?................................................................ 1 Case Histories......................................................................... 2 - 3 Typical Cross-Connections.................................................... 4 - 5 Backflow Prevention Devices ..................................................... 6 How Backflow Prevention Devices Work .................................. 7 Device Selection ............
Backflow… What is it? Backflow? You may have heard of it, and you may understand some of what it involves. This booklet will help you to understand it better; exactly what it is, and how to prevent it. Backflow is the undesirable reversal of the flow of water or mixtures of water and other undesirable substances from any source (such as used water, industrial fluids, gasses, or any substance other than the intended potable water) into the distribution pipes of the potable water system.
Case Histories “All of this is very interesting, but does it REALLY happen?” you may ask. The answer to that is an emphatic YES! Below are listed some typical cases of backflow that actually occurred. Case No. 1 The year was 1933. People from all over the world were crowding into one of America’s largest cities to see the “World’s Fair.” An epidemic of Amoebic Dysentery broke out and official records show that 98 people died and 1,409 others became seriously ill.
Case Histories Case No. 6 In August, 1969, 83 football team members and coaching staff were stricken with infectious hepatitis due to subsurface hose bibs and a nearby fire. The fire trucks in fighting the fire reduced the main pressure enough to cause backsiphonage from the hose bibs. City Main Case No. 7 In the summer of 1970 in New Jersey, a soft drink vending machine in the Caddy house of a golf club was connected to the building heating system in which hexavalent chromium had been added.
Typical Cross-Connections Spray Hose in Sink This type of cross-connection is commonly found in the food industry and in janitor’s sinks. A hose has been connected to the faucet on the sink. When the faucet is left running, a loss in pressure of the supply main can siphon this used water back into the potable water system. Submerged Inlets In many industrial installations that use chemically treated baths, the make-up water line runs directly into the tank.
Typical Cross-Connections Lawn Sprinklers On a large number of lawn sprinkler installations, the sprinkler head is below the ground level. Water which may have been in contact with fertilizers and weed killers can then be backsiphoned through a leaky valve into the potable water system. Irrigation Pumping Systems On many farms water is pumped from irrigation water channels into the sprinkler system.
Backflow Prevention Devices There are several different types of mechanical backflow prevention device. An alternative to a mechanical device, is a physical separation, or air gap. The air gap is a physical break in the system. The different types, of mechanical device, are used in different situations (if there is backpressure or backsiphonage) and for different degrees of hazard. The degree of hazard is based on the fluid (or other substance) that may backflow into the supply piping system.
How Backflow Prevention Devices Work This figure shows an RP device during a backsiphonage condition. If you will notice, both checks are closed tight and the pressure differential relief valve is discharging to atmosphere. This is due to the fact that the relief valve is designed to maintain a lower pressure in the zone between the two check valves than the supply pressure. In this figure of an RP device, there is a backpressure condition.
Device Selection Installation The selection of the proper type of device is important. Depending upon the fluid that can backflow, whether it is toxic or non-toxic; and whether there can be backpressure or backsiphonage; it will govern the type of device selected. The following chart will help you to decide what type of device to use. Having a device on the connection is not enough, the device MUST be installed correctly.
Installation Testing Side View Protective Enclosure Water Meter Double Check Valve In these figures, the double check assembly is shown on the service connection, it can also be used for internal protection as well. The minimum and the maximum distances are the same as they are for the RP device. 30" Max 12" Min Top View Water Meter 12" Min 24" Min Dual Check The dual check is usually installed immediately downstream of the water meter in residential installations (not shown).
A Watts Water Technologies Company F-F-CCCH 1209 USA: Tel: (559) 441-5300 • Fax: (559) 441-5301 • www.FEBCOonline.com Canada: Tel: (905) 332-4090 • Fax: (905) 332-7068 • www.FEBCOonline.
