Date: August 6, 2013
DON’T LET YOUR PUMP GET YOU HEATED – OVERHEAT PROTECTION
When it comes to fighting fire, one of the most important tools is the fire pump. Sure you could find other ways to put out a fire, but centrifugal fire pumps make the job a lot easier. As an apparatus operator, your tasks are numerous, and as in any other operation on the fireground, your first priority must be the safety of the firefighters on your rig. But safety doesn’t stop with the ability to transport the team safely to and from the scene. Operators also need to constantly be cognizant of changing conditions while transferring water from the source to the fire itself.
No need to start fresh from Basic Pump 101, but the fire apparatus of today prefer the use of a centrifugal pump when it comes to that transfer of water, whether it is from the on-board water tank, or an outside source such as a hydrant, portable tank, or even the tank of another engine via relay pumping operations. As with most moving parts, especially in enclosed places, lubrication is required to maintain moderate temperatures. Inside a fire pump, the most logical lubricant is water. As long as water is flowing through the pump, it will remain cool during normal operations.
During pump operations, it is imperative that cooler temperatures are maintained inside the pump. Question No. 1: What happens to metals like brass when the temperatures increase? Answer: It begins to expand or warp. Most tolerances inside of a centrifugal pump are only thousandths of an inch, so any type of expansion or warping could be potentially devastating for that pump. If the internal components begin to rub across each other, the friction then increases the heat significantly. There have been instances where the impeller shafts have seized because the parts have virtually melted together. This type of repair could easily run upwards of ten thousand dollars, not to mention the down time of the apparatus.
How does a pump overheat? Testing indicates that when a pump is “dead-headed” (not flowing water) at 150psi, a midship pump will increase roughly 10 degrees per minute. If the pump is running higher pressures, it will increase faster (testing has indicated up to 15-35 degrees per minute at 200psi. An important factor of pump operations is the circulation of water in order to keep the temperatures cool. This cannot be stressed enough.
While the pump is “dead-heading”, the water continues to increase in temperature. Eventually, the water will get to its maximum temperature (212 degrees F or 100 C at sea level) before it will change physical states. Water goes from a liquid into a gas form, which we all know as steam, and centrifugal pumps are not designed to pump gaseous products, in addition to other potential hazards as causing hoses or pipes to rupture. But even prior to cavitation affecting a pump, this superheated water will flow through the hose line to the nozzles, and once the nozzles are opened, crews who are not suspecting any type of dangerous situation may get injured by the superheated water from the hose. This is a situation that needs to be avoided. There have been injuries throughout the fire industry caused by overheated pumps – and improper operations.
When the centrifugal pump is in operation, a fresh supply of water needs to enter, and leave the pump. Whether this is coming in from the fire hydrant, and leaving through a hose, or entering from the on board tank and leaving the pump through the pump cooler lines (which send that water back to the on board tank, typically). But sometimes internal circulation is not enough. If the suppression crews have not communicated to the apparatus operator that they have completed their suppression role and started with overhaul, the operator may keep the pump running at the higher pump pressures when they are not needed. This creates a dead-head situation, which generates unnecessary heat.
Question No. 2: How does the pump operator know if the pump is overheating? Answer: Cast iron is a great conductor of heat. If the operator were to simply feel the intake fitting as it extends from the pump panel, and it were warm to the touch, there is roughly 30-40 degrees of additional heat towards the center section of the pump, meaning the effects of heat are already affecting the pump, and potentially the crews at the end of the hoselines. If an operator cannot keep his hand on the intake because it is too hot, there may be significant damage occurring inside the pump. It is imperative to bring in an additional water supply to cool the pump, or to slow the pump down so that it is not turning as fast, thus not building as much heat. An Overheat Protection Management System is a pre-emptive indication system that should be able to alert the operator to circulate water prior to the temperatures reaching increasingly dangerous levels.
The OPM system will either visually and/or audibly, alarm when the centrifugal pump reaches a certain temperature. Some of these systems will also begin to move water, either to the ground or back to the on board tank so that there is some kind of circulation going on BEFORE detrimental damage occurs inside of the pump. These systems are a great protection policy so that the department is not spending thousands on what should be an unnecessary repair bill. But operators also must keep in mind that the OPM system will not stop a pump from overheating, but does provide the initial awareness of overheating. An operator still must begin to circulate water or add an additional source of water to cool the pump.
Most of these types of systems are options, so if a department hasn’t specified an overheat protection system on the pump; it will probably not be there. However, several of these systems are also able to be retrofitted onto a pump. So regardless if it is a two-year old front line apparatus or a 30-year old reserve unit, the overheat protection management systems can be made to work.
The key is to minimize the potential hazards of overheating – not only to the equipment, but to our firefighters on the nozzle as well.
The Waterous Overheat Protection Manager system, for example, consists of a thermal switch, a dump valve, and a panel assembly. If mounted on the pump when the pump is new, the valve will begin to dump water (typically to the atmosphere) when the water temperature reaches 140 degrees F. this alone should alert an operator that something is wrong when the sudden release of water hits the ground, but in the event nothing is done to mitigate the overheating, the thermal switch will send a signal (either audibly or visibly) when the water temperature reaches 180 degrees F. This way there is some kind of water movement BEFORE detrimental damage occurs inside of the pump. These systems are a great protection policy so that the department is not spending thousands on what should be an unnecessary repair bill. But operators also must keep in mind that the OPM system will not stop a pump from overheating, but does provide the initial awareness of overheating. An operator still must begin to circulate water or add an additional source of water to cool the pump.
Waterous also has an option to retro fit this system to an older unit (previous to 2000). It consists of the same components, mounted to a 4-bolt flange that will mount to any available discharge port. But because it is not directly in contact to the center of the pump, the valve is set to move water when the temperature reaches 120 degrees F. The thermal switch will still trigger the audible and visible indicator when the water temperature reaches 180 degrees F. So regardless if it is a two-year old front line apparatus or a 30-year old reserve unit, the overheat protection management systems can be made to work.
STEVE MORELAN, Service Manager, has been with Waterous for 32 years. He has spent all of this time learning the pump trade in the Service Department at Waterous, conducting Mechanic Seminars, mobile demonstrations and leading the way to make Waterous Service the best in the industry.