Backflow preventer

Water. Water mains should be connected to plant fire mains at two or more poiats, so that a sufficient water supply can be deHvered ia case of emergency. The plant loop and its branches should be adequately valved so that a break can be isolated without affecting a principal part of the system. If there is any question of maintaining adequate pressure, suitable booster pumps should be iastaHed. Any connection made to potable water for process water or cooling water must be made ia such a manner that there can be no backflow of possibly contaminated water check valves alone are not sufficient. The municipal supply should faH freely iato a tank from which the water is pumped for process purposes, or commercially available and approved backflow preventers should be used. 

Various features may be included in a pilot-operated valve, such as backflow preventers, field testing connections, pilot line filters, manual or remote opening for depressuring purposes, etc. Details may be obtained from manufacturers literature. 

Check backflow preventers on the system as well as on the city mains supply to the building. 

A reciprocating piston pump is a pump that utilizes a piston in a cylinder to pull and push the liquid mobile phase from the mobile phase reservoir through the HPLC system. Two check valves (backflow preventers) are in-line to help force the liquid in only one direction. See Figure 13.4. 

Many of these enclosures are designed to meet certain standards. For example, the American Society of Sanitary Engineers (ASSE) has developed Standard 1060, Performance Requirements for Outdoor Enclosures for Backflow Prevention Assemblies. If an enclosure will be used to house a backflow preventer, this standard specifies the acceptable construction materials for the enclosure, as well as the performance requirements that the enclosure should meet, including specifications for freeze protection, drainage, air inlets, access for maintenance, and hinge requirements. ASSE 1060 also states that the enclosure should be lockable to enhance security. 

To prevent backflow, various types of backflow preventers are appropriate for use. The primary types of backflow preventers are ... 

Install direct to the system piping or pump suction using water from a high-pressure source to sweep the treatment into the closed-loop system. Caution Install appropriate backflow preventer devices to... 

The pilot exhaust is normally vented to the main valve oudet. Set pressure and operability are unaffected by backpressure up to 70% of set pressure, provided that a backflow preventer is used whenever backpressure is expected to exceed inlet pressure during operation (consult the manufacturer for backpressures greater than 70% of set pressure). The capacity is affected, however, when flow is subcritical (ratio of absolute backpressure to absolute relieving pressure exceeds 55%). In this case, the flow correction factor Kb (see Appendix B) must be applied. If the ratio of absolute backpressure to absolute relieving pressure is less than 55%, no correction factor is required, Kb = 1. 

This company s approach was somewhat different than the approach described in the previous incident. The polymer plant implemented a procedure to require force-loaded check valves for backflow prevention on any temporary connection to piping that contained flammables. The check valve had to be rated for the highest design process pressure of either fluid. [8]... 

In reduced-pressure backflow preventers (Fig. 7), a zone is provided between the check valves, in which a relief valve continually and automatically maintains pressure at a level lower than supply pressure. Because fluids w ill not flow from a low-pressure zone to a higher-pressure zone, these devices are able to provide excel-... 

Codes in most states require that backflow preventers be tested and certified on an annual basis. Certified testing personnel provide this service. Generally, because of the critical nature of backflow prevention and the need to maintain devices in proper working order, reduced-pressure backflow preventers should be designed for ser icing w ithout removal from the line. 

Upflow saturators use a bed of undissolved sodium fluoride as a bed in which water is forced through upward. Water under pressure is distributed through a spider-type distributor head located at the bottom of the tank. This head contains hundreds of tiny slits in which water is forced under pressure through these slits and flows upward through the sodium fluoride bed at a controlled rate to ensure the desired 18,000 ppm of fluoride solution. An upflow saturator requires water pressure at a minimum of 20 psi to a maximum of 100 psi, and the flow into the saturator is regulated at 2 gpm. Because the introduction of water to the bottom of the saturator constitutes a definite cross-connection, a certified backflow preventer must be installed on the water supply line to the saturator along with anti-siphon valve on the solution feed pump (2). 

There are two types of process equipment to feed hypochlorite solution (a) basic system and (b) complex systems. Both basic and complex systems are electrically and hydraulically activated. The basic liquid hypochlorination systems include two metering pumps (one serving as a standby), a solution tank, diffuser, and appropriate quantities of tubing. The more complex system adds a diffuser corporation cock, antisiphon backflow preventer, a safety housing enclosure, a flow pacing system, and a flow meter and signal. 

Deininger (2000) also described potential attack points to our water-supply system upstream of the water intake or treatment plant (which would require large amounts of contaminant) the water intake or treatment plant a service reservoir and a point in the distribution system such as a fire hydrant. Individual houses and buildings, not isolated by backflow prevention devices, could also become attack points to the distribution system. He also concluded that there would be greater chances of success if contamination occurred after the treatment plant. There are many and varied agents that could be introduced into water-supply systems, and any one of the contaminants, or even the threat of contamination of the water supply, could cause panic, societal and political dismption. 

Secure plastic or rubber hose connections. If proper clamps are not used, hoses can slip off fittings, causing serious floods and water damage. Backflow preventers often require periodic testing to comply with local building codes. Locking quick-disconnects are available for locations where lines often need to he disconnected. 

Create a backflow prevention plan to prevent possible reversal of water flow and resultant water contamination that can occur from unwanted pressure changes. 

Some plants also produce their own potable water by treating a well or groundwater supply. This is not a common situation, and it is a specialized subject that will not be covered here. Most plants receive potable water from a local supplier or municipality. This water is used for drinking and sanitary use and usually in safety shower/eye wash systems. In some cases, the municipal potable water supply also serves as a general plant utility. Drinking water systems must always be kept separate from plant service systems. The method of separation is often prescribed by local regulations. Backflow preventers are a standard, but dedicated tanks that provide physical breaks are more positive and in many locations are required. These are discussed in Section 12.7.2. 

Shot capacity n. The maximum weight of plastic that can be delivered to an injection mold by one stroke of the ram or screw. In the case of screw-injection molding machines that are not equipped with backflow-preventing valves at the end of the screw, slippage of material may occur in the screw flights and may not be reckoned with in calculations of shot capacity that are based on cubic displacement. 

Most systems found in schools are wet pipe systems, meaning all the piping of the system contains water at all times. Starting from the outside, a connection is made to a source of water with adequate pressure and flow, rated in gallons per minute, called the water main. As part of the plumbing code, the water main is equipped with a backflow preventer, which prevents the nonsanitary water found in the sprinkler systems from returning into the potable water supply. Next, a main control valve is placed in the line to allow for the system to be turned on and off. This connection must be electronically monitored or locked in the open position. 

The procedures must also cover the source of the gas. If a compressor is used to boost tire gas to filling pressure, its startup, operation, and shutdown must be covered. Backflow prevention must be designed into the system, along with protection against overpressure at the source or tire cylinder. 

Determine the need for check valves or backflow preventers. Make sure that they are correctly oriented and that proper documentation is available to verify this. 

Reference (NRC95) UWNR OTM, Reactor Water Systems III, Demineralizer - Backflow prevented ... 

Riickflusssperre/ Riicklaufsperre/ Riickstauventil backflow prevention, backstop (valve)... 

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