Testing and Maintenance of Fire Pumps
By Thomas Gray, P.E.
To minimize the possibility of disaster, fire pumps must be kept at the peak of effectiveness at all times.
Fire pumps are perhaps the most critical single piece of fire protection equipment installed at a site. Just like people, fire pumps come in all shapes and sizes. Fire pumps are needed at sites where public water supply pressure is too low for sprinkler effectiveness or where there is no public water supply at all. In the former case, a booster fire pump is installed to boost public water pressure to increase sprinkler effectiveness. In the latter case, a fire pump is connected to a private water supply (storage tank, reservoir, lake, river, or other) to create water pressure needed for sprinkler effectiveness and fire-fighting efforts.
Most fire pumps are either diesel engine driven or electric motor driven; however, some of those manufactured before 1974 are gasoline engine powered or even steam engine driven (though this is very rare). Booster fire pumps are usually electric pumps, whereas diesel fire pumps are more common on private water supplies. The pumps range in size from 25 gpm to 5,000 gpm (or more) at pressures from 50 psi to 125 psi (or more). Some are vertical shaft turbine-type pumps, while others are centrifugal pumps. For reference, “NFPA 20, Stationary Pumps for Fire Protection” (1999 edition) gives the latest requirements and other information on fire pumps. Appendices A and B (not part of the NFPA 20 standard) give valuable tips on fire pump design, installation, testing and maintenance, including troubleshooting.
This article will primarily focus on the testing and maintenance needed to ensure the fire pumps will perform as expected in a fire. Fire pump failure could spell disaster for a site, but basic testing and maintenance will minimize the risks.
Basics on Fire Pumps
Let’s take a minute to cover a few basic facts about fire pumps. They can be expected to produce 120-140% of rated pressure at zero flow (or churn, as it is commonly known) conditions. The rated point of the pump yields 100% of its rated flow and pressure. The maximum flow expected from a fire pump is 150% of rated flow at only 65% of rated pressure. These three points help define the characteristic fire pump curves for a particular fire pump.
What size fire pump is the right one? Well, there are probably as many answers to that question as there are letters in the alphabet, but most experts would say that a fire pump needs to be large enough to provide an adequate water supply (flow and pressure) for the maximum flow expected from any single sprinkler or deluge system, plus an extra (hose) allowance for fire-fighting needs. For example, if maximum sprinkler demand is 1,000 gpm at 60 psi, and fire-fighting (hose) allowance is 500 gpm, then at least 1,500 gpm at 60 psi is needed from the combination of the fire pump and public or private water supply. Some insurers and Authorities Having Jurisdiction (AHJ) would prefer that the maximum demand point not exceed the rated point (100% of flow and pressure) of the fire pump. Others would accept something between the rated point and the maximum flow point, but few would go all the way to the latter point.
It is not uncommon to install one extra fire pump at very large sites so that, even if one pump fails or is out of service for repair, there will still be a more than adequate water supply for the site. An electric fire pump is considered reliable but is dependent upon the ready availability of a reliable electric power supply. Diesel fire pumps are also reliable but have their own power supply (diesel fuel). At some larger sites, a common and more reliable method is to have one electric and one diesel fire pump. There is no “one size fits all” answer when it comes to fire pumps.
Regular Testing Required
One thing is certain–fire pumps (all types and sizes) must be tested regularly, preferably by automatic start (most of the time), but also by manual start (occasionally). How often? Some say weekly no matter what, as in NFPA 20. Others say weekly for diesel fire pumps and monthly for electric fire pumps. These tests are startup and run tests (with no water flow), similar to starting your car on a frigid winter morning. How long should these tests run? Again, everybody has different advice, but I say 30 minutes for diesel pumps (at rated speed and normal operating temperature) and 10-15 minutes for electric fire pumps (again under normal running conditions). “NFPA 25, Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems” (1998 edition) contains a full range of recommended tests and frequencies in Chapter 5. All of the specifics are included in that document. NFPA 25 is adopted into state law in some areas and certainly a requirement in that case, but gives excellent guidance in any case.
Water Flow Testing
What about water flow tests? Fire pumps (all types) need to be full flow-tested at least annually and measured against the pump characteristic curves of churn, rated point and maximum output. Pump performance can gradually deteriorate over time or be affected by temporary impairments to water supplies. The annual flow test results can pinpoint these problems and help solve them before the fire pump is really needed in a fire emergency. Many sites now use independent contractors who specialize in fire pump testing, and I think that is a great idea. They have the expertise, spare parts and training to perform these tests in a professional manner and achieve good results.
Very large fire pumps typically have flow meter devices installed to facilitate flow testing without flowing thousands of gallons per minute (gpm) of water. The flow meter is used to measure the amount of water flow in a recirculating system. Fire pumps rated larger than 2,500 gpm usually have flow meters for testing, although smaller pumps might need flow meters as well. Sometimes conditions don’t permit full water flow on site.
Full Unit Inspections
Fire pumps (again, all types) should be inspected (and started) at least weekly to check the general condition of the pump, driver and controller. The inspections should include the pump itself, bearings, stuffing boxes, water supply suction and discharge, strainers, pump running and power off alarms, and fuel/power supplies. Diesel or gasoline fire pump inspections should also include batteries, oil level, cooling system, belts and hoses, and general mechanical condition of the engine. Just like your car or truck, the diesel engine driver for a fire pump needs an annual tune-up and other maintenance specified by the manufacturer. An expert diesel mechanic should do this work.
All functions of the fire pump controller should also be tested at least annually. The controller manufacturer can recommend a local expert to assist with these tests. After the tests are completed, you should get a test report describing which tests were conducted and settings of all time delay devices. The report should include test results for operation of the pump, driver and controller. A trending comparison of year-by-year results can show early indication of problems before they are really serious.
What about a newly installed fire pump? I think (and most insurers and Authorities Having Jurisdiction agree) that a special fire pump acceptance test is needed for every new fire pump installation. NFPA 20 requires acceptance tests of new fire pump installations and gives specific criteria in Chapter 11 (of the 1999 edition). The typical “three-point test” of the pump characteristic curve is a basic minimum flow test requirement, and I recommend as many as five test points be taken on acceptance tests.
The fire pump controller unit is also put through its paces on an acceptance test. NFPA 20 calls for six manual starts and six automatic starts, and a minimum run time of 5 minutes for the pump driver. Electric fire pumps must also be tested by measuring the voltages and electrical currents under various flow conditions. NFPA 20 now requires the use of voltmeters and ammeters on fire pump controllers to allow these tests to be conducted safely. Diesel pumps must be started on both sets of batteries. The fire pump must operate for not less than 60 minutes (total) during all of these tests.
Fire pump experts, including the manufacturers and installer, typically do acceptance tests. Insurers and Authorities Having Jurisdiction are typically present as well. If the pump impeller was mistakenly installed backwards or there is an obstruction in the suction line, the acceptance test is a good time to find out.
Fire pumps can be somewhat expensive ($50,000 to $100,000 for booster pumps, and $200,000 or more for fire pump and suction tank), but they are invaluable when it comes to fire protection at sites that need improved water pressure or don’t have a public water supply. That kind of investment deserves special care. Properly installed and maintained fire pumps will be on duty, ready to go at a moment’s notice, for many, many years. Take a few steps to make sure your site fire pump fits that description to a tee!