To help maintain a pump in good working order and extend its service life, a driver can keep pressure out of the pump when not in use, keep it cool during pumping operations and prevent debris from entering it. I tell my driver engineers that centrifugal pumps do not like heat, debris and air.

At a recent breakout session at the Fire Department Instructors Conference, presenter Chad Szeklinski from the Milwaukee Fire Department addressed how to relieve pump pressure. His method was to briefly open the tank-to-pump valve while the truck was out of pump gear.

The method I would use, as taught to me by one of the “old-timers” was once out of pump gear, I would remove a discharge cap from one of the two-and-a-half discharges at the pump panel and "crack" it open using a discharge gate.

You would immediately hear that "hiss," which was the pressure being released. You don’t want to leave it open too long because you could lose your prime on the pump. (However, losing your prime is obviously not an issue if your fire department keeps the pump drained for colder environments.) The importance of doing this was to relieve the excess pressure to prevent affecting the pump packing.

Subsequently, a common problem over time when excess pressure is kept in the pump is undesirable constant water dropping. Due to the leaking pump issue, my former department had a policy in place stating "no fire department pumping apparatus will be stored in the station with pressure on the pump."

For those unfamiliar with pump packing, check out this document, published by the Minnesota Public Safety State Fire Marshal titled, "Quick Response Fire Pump Packing."

"The area where the shaft penetrates the outer casing of a fire pump needs to be sealed so water will not leak out of the pump. The seal at the point of penetration of the casing is known as the packing.

Usually the packing is a ring(s) of resilient rubberized material which is wrapped around the shaft. This material is intended to be kept moist thus cooling the packing while providing lubrication between the packing and the shaft. Water from the discharge side of the pump is utilized to provide this lubrication. As such, on some pumps the packing only gets lubricated while the fire pump is running. Some pumps are designed so that constant positive pressure in the pump casing allows water to constantly be delivered to the packing. These pumps have continuous dripping from the packing gland even when the pump is not running.

More water is brought to the packing than can be absorbed. During normal operation of the fire pump the excess water will drip from the pump. The amount of leakage is controlled by the packing gland. The packing gland, which is adjustable, should not be over tightened. Adjusted too tight, the packing dries out, heats up and usually causes a scored shaft, which then produces a rapid rate of packing wear."

Cavitation is a term most pump operators have heard time and time again. Colder climates may not experience as much of this as we do in warmer climates; however, it can still be present if water is not moving and just "churning" in the pump.

In Miami, there were times that even with water moving or flowing, we would experience some cavitation during pumping operations due to the surrounding temperature and water temperature. It would typically sound like "gravel" inside the pump.

This was caused by the water becoming heated and turning to steam (vapor) which is basically air. As a result, there would be a loss of pressure and the RPM going up, due to no resistance of pushing the water.

Tank-to-Pump vs. Tank Fill/Recirculating Valves

The tank-to-pump valve functions differently than the tank fill/recirculating valve.

The tank-to-pump valve controls the flow between the water tank and pump inlet. With this valve open, water from the tank floods the pump intake manifold and slowly primes the pump.

The tank fill/recirculating valve opens the connection from the discharge side of the pump to the water tank. Open the tank fill valve to refill the water tank from a water source that is connected to an intake fitting.

Many feel that keeping the tank fill/recirculating valve open or cracked constantly at fires resolves overheating problems. While true, the process above also allows sand or grit and small debris that make it past your strainer screen via the gated intake valve/piston intake valve from your water source to enter the pump then back into the tank.

Next time the water tank is pulled from a truck for repair or replacement, look at the bottom of the tank. I guarantee you will be surprised at what you find. Remember what comes from the tank goes back into the pump.

Over time, the small particles that get into the pump begin to cut grooves into the wear rings located in the pump housing next to the impellers. Eventually, your pump will need higher and higher RPM to attain the desired pressure than it did when it was first delivered, and will eventually result in failing the Underwriters Laboratory (UL) Pump Test.

I instructed my drivers that once you had your water supply established, close your tank-to-pump valve, and only open your tank fill/recirculating valve when needed to cool your pump or to immediately fill your tank.

Leaving it open also can heat the tank water if the pump water coming from the discharge side is hot; therefore, becoming ineffective at cooling the pump when needed. Keeping it closed also keeps unwanted debris from entering the tank and pump. Remember, opening the "tank fill" is like opening another discharge on the pump and may rob some pressure from the discharges/hose lines already flowing.

I used to see drivers pull up to an active fire and, many times, in the heat of battle after putting the truck into pump gear, they would rush to start raising the throttle and realize there was no pressure. They would immediately start pulling the "primer." My tip to them: pull their tank-to-pump valve first so they would get a prime, then if no pressure is shown on the pressure gauge, reach for the primer!

Expensive Lessons

I had a collection of the different types of materials that were found by our shop that had made their way into the tank and even into the bronze impeller, causing significant and very expensive damage. It is imperative to check for strainers on all pump intakes.

This includes your spud intakes and main pump intake. If they have become damaged or have pieces missing that would allow larger objects to pass through them, they need to be immediately replaced.

Since Miami is surrounded by the ocean, there were times that we would have to draft with sea water. The policy we had at the City of Miami Fire Department was to flush the pump after drafting from salt water — through the "intakes" and out the "discharges," not "back-flush" through discharges and out the intakes.

Before this policy was adopted, we would "back-flush." I had noticed that for some time the pump was not functioning correctly and could not figure out the reason.

Then, one day I was performing a back-flush procedure, and a piece of fiberglass mesh approximately 12-by-12 inches came out of the pump intake. We believe it had come from the tank itself, because it would have been caught by the strainers if coming from a water source. That truck manufacturer is no longer in business, and we now only use polypropylene tanks.

In conclusion, you never know what you may find in your tank or pump. You can do your part to extend the life of the pump and prevent from damaging it. It will help save money in the long run and keep you in your front line apparatus and out of a spare!