Christian P. Koop
I also believe it is worth much more than the sum of its parts because without it, firefighters could not put out fires, save lives, and protect property. That is why I believe it should be held in venerable status and be kept in tip-top shape.
This article will cover basic fire pump types in use today, pump maintenance, common problems, key components, and testing required by National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus, which establishes that pumps must be able to flow rated capacities.
|1 Shown are sample anodes removed during pump maintenance requiring replacement. (Photos by author.)|
Pumps are rated by gallons per minute (gpm) or liters per minute. The pumps are to be tested at 150 pounds per square inch (psi) at 100 percent of rated capacity, 200 psi at 70 percent of rated capacity, and 250 psi at 50 percent of rated capacity. Additionally, there is another test required by NFPA 1901 that is called the Pumping Engine Overload Test for 750-gpm or larger pumps that consists of pumping at 165 psi for rated capacity at net pump pressure for at least five minutes. Basically, if your rig’s engine, drive train, and fire pump pass this rigorous test, then the pump is in great condition. This test should be performed right after the 150-psi 100 percent of rated capacity test. These tests should also be performed annually, which is required by NFPA 1911, Standard for the Inspection, Maintenance, Testing, and Retirement of In-Service Automotive Fire Apparatus.
There are several different types of pumps in the fire service today with various drive configurations that depend on the output ratings of the pumps and the type of firefighting they are specified for. Regardless of the type of pumps you have on your rigs, they require proper care, maintenance, and testing to ensure long and trouble-free lives.
The most common type of fire pump used by the United States fire service today is the centrifugal pump, which is available in both single-stage and multistage versions. Both are nonpositive displacement pumps with main components consisting of an impeller mounted on a shaft housed inside a casing.
The centrifugal pump is a nonpositive displacement pump because unlike a piston-type pump, it does not pump a specific amount or volume of water with each revolution. It works on the basic principle that as water enters the center of the impeller (eye) as it rotates, the water is flung outward by velocity, and the faster it rotates the greater the pressure it creates. Which type is better when considering single-stage vs. multistage is still debated to this day. However, multistage pumps can develop higher pressures than the single-stage or single-impeller pumps, and they allow the pump operator to select either volume or pressure modes depending on firefighting needs. Selecting pump type and size basically boils down to preference and a department’s needs based on the structures it protects.
The pump operator or driver is the most important person tasked to ensure the fire pump is properly maintained. I consider this person to be the first line of defense in keeping the pump in top condition. He should operate and test the pump on a daily basis and follow the pump manufacturer’s published maintenance checklist. He should exercise all valves and pump controls and keep the valve operation shafts and linkages clean and lubricated. Not doing this in a timely manner as required in the manufacturer’s recommendations will jeopardize optimal service life and reliability. This usually translates into wasted dollars, which we all know are in short supply these days. Various other factors, such as water quality in the region, will also dictate how frequently maintenance items must be checked. It could actually be more frequent than the manufacturers’ recommendations.
Years ago my fire department had many two-stage pumps in service. However, the department phased these out over time, and single-stage pumps are the norm now. I believe this has happened partly because the single-stage pump is simpler to operate and therefore much easier to train operators to use. Because there are fewer parts and components that can fail, there is less maintenance required for these pumps. When I first started working on pumps, my department had a number of high-pressure-fog pumps in service (positive-displacement, piston-type manufactured by John Beam). These also have gone the way of the dinosaur-at least in my neck of the woods-although I understand there are some fire departments in the United States specifying high-pressure pumps as part of the main fire pump.
Regardless of whether you have a single-stage or multistage pump, sand, dirt, and debris that get beyond the pump intake screens are big enemies of the pump impeller and wear rings and can gradually reduce the pump’s rated capacity. If your department performs pump tests on an annual basis, you will be able see this by comparing test results from previous years. This is one of the reasons it is so important to flush hydrants prior to connecting to your pump. Understand that fine particles-even when taking all proper precautions-will eventually wear the pump to where it won’t meet rated capacity and will require repair or derating.
A key indicator that a pump is wearing and losing efficiency is if operators have to increase engine rpm year over year to achieve the same gpm and pressure as when the truck was new. This is why flushing and back flushing the pump on a weekly basis by the driver are very important. Getting out sand, dirt or sediment, and rust that accumulates in the pump will protect and extend its life. For those with two-stage pumps, it is very important to keep the pump clean because transfer valves, used by the operator to place pump in volume (parallel) or pressure (series) modes, can get stuck or jammed with sand and sediment. When this happens and it won’t break loose, a technician will need to remove it for cleaning, repair, or complete replacement. This won’t be cheap. Also keep in mind that the main reason behind pump testing is to be reasonably sure that the pump will function and pump properly at the fire scene. The fire scene is not the place to find out that your pump will not perform, not to mention the potential liabilities involved.
|2 Anodes can be resurfaced, if sufficient material remains, at considerable savings. This can be done very efficiently on a machinist’s lathe or can also be done using a belt sander.|
Pump anodes are very important items that protect the fire pump. These components are vital to protecting the pump and cast iron housing from galvanic erosion. Many years ago, they were located in the top covers of steel booster tanks to protect the tanks but also afforded the pumps some protection. With the advent of plastic or fiberglass tanks, they were no longer needed and now are threaded in the pumps if equipped. These sometimes overlooked items during pump maintenance are often referred to as zincs because of the material they are made from but are also made of aluminum and magnesium alloys.
|3 This is an example of heavily corroded sacrificial anodes removed for replacement or resurfacing. These anodes are mounted as a pair on one mounting bolt.|
These anodes provide cathodic protection and are sacrificial. They protect against galvanic erosion/corrosion, which occurs when there are dissimilar metals that are immersed in water. This is not to be confused with electrolysis, which is a similar process; however, it occurs when electricity is part of the circuit because of a loose or missing ground. Galvanic erosion/corrosion is created because of a current that flows between these metals via the water, and it removes tiny amounts of metal, generally from the cast iron. It is essentially a battery, and by installing this other metal (the anode) into the circuit, the anode now becomes the sacrificed metal that wears away in the process rather than other vital and costly components, such as the cast-iron pump housing and related parts.
|4 Although some pitting is still present after resurfacing, these anodes are still good for continued use and will offer plenty of protection against galvanic erosion for considerable time at a savings to the organization.|
The process is continuous and can even accelerate if the water becomes acidic. Most manufacturers recommend checking the anodes and replacing if necessary every six months or every 100 pump hours. If they are heavily corroded and covered with white- to tan-colored deposits, they cannot protect the pump. I recently heard of a department where the water was so acidic that galvanic erosion was eating away the anodes in a matter of a few weeks.
Microbiologically Influenced Corrosion
Another phenomenon to be aware of is microbiologically influenced corrosion (MIC), which can affect fire protection systems. It is caused by specific bacteria in the water and it is another form of corrosion that can affect any metallic component in the system and cause pinholes. The rate of corrosion with fire sprinkler systems is expected to be very slow; however, MIC has been found to be concentrated in certain areas and can also be abnormally accelerated. This could be an issue for departments that keep water in fire pumps for unusually long periods of time without periodic flushing.
Protect the Pump
Corroding bits of metal can also damage the pump, discharge valves, intake relief valves, discharge relief valves, and thermal relief valves of a pump not properly protected. Older pumps that don’t have electronic pressure governors and are equipped with pilot-operated manual-style relief valves are even more prone to pilot control clogging because of the very small orifices in the valve. Discharge valve gauges also have small lines and orifices that can clog with rust flakes caused by corrosion and galvanic erosion. Other important components that work in concert with anodes are zinc intake screens. The pump operator should check these once a week to keep them clean.
The most common fire truck pump arrangement is the midship-mounted type. The truck transmission is connected by a short driveline to the pump transmission, or transfer case, and drives the pump. Rope-style packing or mechanical seals seal the pump shaft. The rope style requires periodic adjustment if leakage under pressure while pumping exceeds approximately 12 to 15 drops of water per minute. This leakage rate is important because keeping the shaft cool requires water. If the packing is too tight and water does not drip, the packing can overheat and score the pump shaft. If this happens, it will need to be removed to be repaired. Excessive leakage here can also cause air to be drawn in the low or suction side of the pump and cause cavitation. Pump cavitation can also cause damage to the impeller assembly. If not corrected in time, this can severely damage it. Cavitation can sometimes sound like marbles rattling around inside the pump and sometimes operators can feel it by placing their hand on the steamer cap. Excessive water leakage in this area can also cause pump water to leak past the pump transmission oil seal that is adjacent to the pump packing and contaminate the oil. This will damage the transmission bearings and drive gears if not caught in time, requiring replacement. Mechanical seals do not require adjustment. However, they too can be damaged by sand, sediment, and rust.
The driver or pump operator is the key person tasked with keeping the fire pump in optimal condition. Following the pump manufacturer’s basic preventive maintenance checklist and testing it as the NFPA recommends will go a long way toward ensuring the venerable fire pump will perform as designed and give its users many years of trouble-free service life.
CHRISTIAN P. KOOP is the fleet manager for the Miami-Dade (FL) Fire Department. He has been involved in the repair and maintenance of autos, heavy equipment, and emergency response vehicles for the past 35 years. He has an associate degree from Central Texas College and a bachelor’s degree in public administration from Barry University and has taken course work in basic and digital electronics. He is an ASE-certified master auto/heavy truck technician and master EVT apparatus and ambulance technician. He is a member of the board of directors of EVTCC and FAEVT and a technical committee member for NFPA 1071, Standard for Emergency Vehicle Technician Professional Qualifications.