Fire Protection Systems Chapter 15 PDF

p> Chapter 15 • Fire Protection Systems OBJECTIVE 6 Describe the construction and operation of a typical fire hydrant TYPES OF FIRE HYDRANTS There are two general types of fire hydrants. The most common is the base valve (dry barrel), shown in Figure 23, in which the valve controlling the water i...

p> Chapter 15 • Fire Protection Systems OBJECTIVE 6 Describe the construction and operation of a typical fire hydrant TYPES OF FIRE HYDRANTS There are two general types of fire hydrants. The most common is the base valve (dry barrel), shown in Figure 23, in which the valve controlling the water is located below the frost line between the foot piece and the barrel of the hydrant. Figure 23 - Dry Barrel or Frost Proof Hydrant Operating nut Oil hole screw Housing joint gasket Body cap cover Housing cap screw Body cap Housing Hose nozzle Body cap'0'ring Hose nozzle cap Pumper cap gasket Pumper nozzle cap Pumper nozzle Hose cap gasket Hose and pumper nozzle pin Housing stem '0' rings Upper operating stem with bronze sleeve Body 16 .Intermediate section bolts and nuts Safety flange Intersection flange •Retaining ring Gasket Safety coupling Safety coupling Intermediate section Main valve seat Seat casing Seat upper '0' ring nuts and bolts Operating stem Holding clamp Drip valve facing Drip valve Seat lower '0' ring Drain hole lining Seat casing '0'ring Main valve disc Main valve washer Elbow Main valve '0' ring •Main valve locknut Cotter pin (Courtesy of the National Fire Protection Association) 804 3rd Class Edition 3 • Part A2 Fire Protection Systems • Chapter 15 Fire Pump Testing Fire pumps must be tested after manufacture and (as a minimum) annually after installation. The testing is required by insurance companies, which rely on the standards set by the Underwriters Laboratories of Canada (ULC). Pump manufacturers must be approved by the ULC. A new fire pump, after successful inspection and testing, has a ULC label attached. The manufacturer is required to conduct an operation test and a hydrostatic pressure test on each fire pump. The operation test determines the pump speed, horsepower input, and suction and discharge pressure at rated capacity and at 150% of rated capacity. The hydrostatic pressure test of the pump casing requires that twice the maximum design working pressure (but in no case less than 1724 kPa) be maintained, without leakage, for at least 5 minutes. Annual testing of the pump involves using the test line (see Figure 22) on the pump discharge, which directs the flow through an orifice, through a flow meter, and back to the storage tank. The pump speed or the valves are manipulated to achieve a pressure that is 65% of design pressure. At this pressure, the pump must deliver 150% of the design flow. For example, if the design flow is 15 000 L/m at a pressure of 600 kPa, the test must achieve 22 500 L/m at 390 kPa. Annual testing is also covered in NFPA 25 Requirements for Fire Pump Tests. While annual capacity testing is considered the minimum, normal practice is to also test run the fire pumps (not a capacity test) for a short time on a regular schedule (usually weekly) to always ensure they are ready and able to start in an emergency. 3rd Class Edition 3 ' Part A2 803 Fire Protection Systems • Chapter 15 The barrel of this hydrant is normally dry; water is admitted only when there is a need. A drain valve at the base of the barrel is open when the main valve is closed, which allows residual water in the barrel to drain out. This design is used whenever there is a chance the temperature will drop below freezing, since the valve and water supply are installed below the frost line. The other type ofhydrant is the wet barrel (California) type, shown in Figure 24, which is used where temperatures remain above freezing. These hydrants usually have a compression valve at each outlet, but they may have another valve in the bonnet that controls the water flow to all outlets. Figure 24 - Wet Barrel (California Type) Hydrant Seat washer retainer Stem "0" ring -Seat ring retaining pin Stem thread cleaning slots Slotted nut Seat ring Cap gasket Stem Stuffing box Cap Cotter pin Cap Stuffing box "0" ring Barrel "0" ring Chain Upper barrel Valve carrier Seat ring "0" ring Seat washer (Courtesy ofMueller Co.) Hydrant Maintenance Well-designed and properly installed hydrants require minimal maintenance. The dry barrel hydrant, for example, has a small drain near the base of the barrel to permit water to drain out when the main valve is shut. When the main valve is opened several turns, this drain is closed. If the drain is working properly and the main valve is tight, the problem of water freezing in the barrel is avoided. Occasionally, ground drainage is unsatisfactory or ground water may stand at dangerous levels. In these cases, drains may be closed entirely and hydrant barrels pumped out periodically. The use of salt or salt solutions to prevent freezing is not recommended because of their corrosive effect and limited usefulness. If antifreeze is used in hydrant barrels, its use must be confined to hydrants that are not part of a system supplying water for domestic consumption. Ethylene glycol is extremely toxic and should not be used as an antifreeze in hydrants. Propylene glycol is not as toxic and may be used to prevent freezing with proper precautions and in accordance with local health regulations. 3rd Class Edition 3 - Part A2 805 ?& Chapter 15 • Fire Protection Systems Suggestions for detecting freezing in hydrants include: • Sounding, by striking the hand over an open outlet. Water or ice in the hydrant raises the pitch of the sound. • Turning the hydrant stem. If solidly frozen, the stem will not turn. If only slightly bound by ice, place your pipe wrench on the nut and strike it with enough force to release the stem. Blows should be moderate to prevent breaking the valve rod. • Lowering a weight on a stout string into the hydrant. It may strike ice or come up wet, indicating water in the barrel. Likely the most satisfactory method of thawing a hydrant is with a steam hose. A thawing device in which steam may be rapidly produced should be standard equipment for fire departments in cold climates. The steam hose is introduced into the hydrant through an outlet and pushed downwards, thawing as it goes. 806 3rd Class Edition 3 • Part A2