Fire Pump Pressure Settings

Code Update Amongst the myriad of changes to NFPA20 in 2003, pump rooms with a diesel driven fire pump are now required to be sprinklered in accordance with NFPA13 (2002). The text in section 5.12 (section 2-7 of NFPA20 1999) has also been improved to further clarify fire resistance and sprinkler requirements for pump rooms. INDUSTRY NEWS A fire claiming six lives in a hotel in Greenville South Carolina once again calls in to question "grandfather" legislation permitting existing hotels and motels to operate without automatic sprinklers. Statistics clearly indicate that automatic sprinklers save lives. In 1999, no fire related deaths occurred in sprinklered hotels and motels. PRESSURE CONTROL SENSING LINES: THE LIFE-LINE OF A FIRE PUMP SYSTEM The following article was contributed by Bill Harvey of Harvey and Associates and Matt Roy of Armstrong Pumps. One of the most critical parts of a fire pump installation is the pressure control sensing line, and the most common installation mistake found in new fire pump installations. The pressure control sensing line is the lifeline for the entire fire protection system. The fire pump is often used as the sole source of water for the fire sprinkler system, and in other cases is used to enhance a marginal water supply as in the case of a booster pump. The control sensing line provides the input for each fire pump controller to start the pump. Improper installation occurs frequently resulting in the possibility of equipment failure, or worse, failure to start under emergency conditions. Independent pressure control sensing lines for each pump including jockey pumps should be installed in strict conformance to NFPA-20 (2003) sections 10.5.2.1.6 and 12.5.2.1.6. The pressure sensing line for each pump, including jockey pumps, should be made between that pump's discharge check valve and discharge butterfly (or OS&Y) valve. The line should be installed using 1/2 inch corrosion resistant (stainless steel or copper) tubing. Two check valves should be installed at least 5 feet apart in the pressure-sensing line with a 3/32-in. (2.4-mm) hole drilled in the clapper to prevent hammering of the pressure switch on pump starting. Further clarification is given in the appendix section A.10-5.2.1 and A.12.5.2.1 figures (a) and (b). Also of note, the jockey pump and individual fire pumps must be equipped with individual sensing lines to allow service of each pump without taking the entire system off line. When dealing with multiple pumps, it is important to set the pressure switch set points such that the jockey pump maintains pressure without starting the main or standby fire pumps. Appendix A of NFPA20 gives an example of set points for a multiple pump installation in section A.14.2.7 (4) (f) as follows: "Examples of fire pump settings follow (for SI units, 1psi = 0.0689 bar): 1. 2. 3. 4. 5. 6. 7.

Pump: 1000gpm, 100psi pump with churn pressure of 115psi Suction supply: 50psi from city to minimum static; 60psi from city to maximum static Jockey pump stop = 115psi + 50psi = 165psi Jockey pump start = 165psi to 10psi = 155psi Fire pump stop = 115psi + 50psi = 165psi Fire pump start = 155psi to 5psi = 155psi Fire pump maximum churn = 115psi + 60psi = 175psi"

Standby fire pumps should be set 10psi below the set points of the primary pump. It is recommended to install a sequence start timer in multiple pump installations to ensure both pumps don't start at the same time creating a strain on the electrical supply. FIRE PUMP TIPS

QUESTION: Why is the direction of rotation important for horizontal split-case pumps? ANSWER: Horizontal split-case pumps can be built for "left hand" and "right hand" rotation. The reason for this is that the motor is located to the side of the pump (perpendicular to the piping). The location of the motor constrains the design of the mechanical room piping and wall locations. If a pump is supplied with the wrong rotation, the pump needs to be rebuilt to correct the problem. For electric pumps, this is less of a problem, and a field rebuild can be performed. This is about a day's work for two service mechanics. For diesel pumps, this becomes a big difficulty as there are no UL/FM listed "left hand rotation" diesel engines available on the market. In the past this was not the case as 3 and 6 cylinder Detroit Diesel engines could be supplied with either rotation. These engines no longer meet North American emissions standards, and have been discontinued by the manufacturer. Vertical in-line and end suction pumps eliminate the problem of rotation since the driver is mounted in line with the piping. NEW FROM ARMSTRONG Check out Armstrong's industry leading range of End Suction Fire Pumps. Available up to 1500gpm ratings, the end suction pump reduces cost, saves space, and allows design flexibility for the pump room.