Obtaining a water supply on the fireground is one of those “gotta haves” for a successful outcome in combating a fire. For the simple low flow fireground operation this task is fairly easy. When fire hydrants are available usually a single line from the hydrant will do the trick. Well what about the more complex large flow fires that require large volumes of water to support master streams and big handlines to get the job done? This is where water supply operations can get quite difficult. There are a lot of things that can dictate how well a water supply operation works. Issues such as fire hydrant performance, fire hydrant availability, supply hose, available units, topography of the fireground, and management of water supply, just to name a few.
In this article in going to discuss three different types of supplemental water supply operations for large flow water delivery involving multiple units. A supplemental water supply is defined by IFSTA as a method of operation for bringing in additional water to a pumper that is already connected to a water supply and needing more water.
A relay pump operation is used when there is not enough pressure at the water source to move the water through the supply hose to the pumping apparatus on the fireground. It involves placing a pumper at the water source to increase the pressure in the supply hose. A relay pump operation is the back bone of big water operations simply because the additional water needed to support the fire ground operations will more than likely be coming from distant hydrants. The longer the supply line is the more pressure loss will be because of the friction loss in the hose.
It’s been an accepted practice to allow the shorter LDH supply lines to be supplied solely from hydrant pressure. Remember the old saying “laying an LDH supply line is like taking the hydrant to the fire, or like laying and above the ground water main.” In other words, LDH laid from a hydrant, especially on the shorter lays, is going to bring in maximum flow. It is this type of thinking that can get us in trouble. LDH is great, but can still have its restrictions. LDH must be used in conjunction with everything else on the fireground to its best capability in order to reap its benefits.
Looped Supply Line Operation
The first supplemental water supply operation we will be discussing is what I like to call a looped supply line operation. A looped supply line operation is a combination of supply line hose evolutions set up to work as one. Large flow operations most always require multiple supply lines from various locations all working towards the goal of providing an overall water supply for the incident. These operations can be quite complex and taxing because the overall goal is to provide the required flow to multiple units without interruption. Notice I said goal. It can be extremely hard to implement a water supply operation and accomplish it without issues.
The looped supply line operation is designed to deliver a supplemental water supply to as many pumpers as possible based on the placement of the apparatus on the fire. Think of this as a fire hydrant water main system. A single supply line connected to a pumper is like a fire hydrant connected to a dead end main only getting water from one supply, the main that is feeding it. The hydrant that is connected in the looped grid system is actually receiving additional water from another point in the grid system itself thus the term supplemental. Well if it works with underground water mains it should work above ground with supply hose as well.
The technique or operation that is a key factor in building a looped supply line operation is a pump operation called dual pumping. Dual pumping is a water sharing evolution designed to share water between pumpers. This has actually been done throughout the years by one pumper discharge pumping into another. This works and can usually move slightly more water than a dual pump operation. So why don’t we just use this operation? When you discharge the pump through a hose line the water only goes in one direction, from discharge to intake. This can hinder a true looped operation. Dual pumping, believe it or not, is an operation that connects two or more pumpers together through the unused intakes of the pumps involved to share the water. Yes I said intake to intake. Because there is no actual discharge pumping in the dual pump operation the water can flow in either direction. The water will flow in the direction of the pumper that has the lowest residual pressure. Here’s how it works. Let’s say a pumper lays in a 5 inch supply line and goes to work. The supply line has the capability of moving 1500 GPM and the pumper that laid the line is going to flow 500 GPM. After flowing 500 GPM the intake gauge of the pumper reads 60 psi. The 60 psi is a residual pressure of the water supply left over after the 500 GPM is flowing. The 60 psi represents water under pressure from the hydrant that is available within the supply line and the intake side of the pump. Now let’s say this first in pumper wants to share some of its water with another pumper. A line is connected from its unused intake to the intake of the pumper it is going share water with. When the command is given to share the water the first pumper opens its intake valve that is connected to the dual pump line and the water will start to move through the supply hose to the next pumper under the 60 psi residual pressure. You can really just think of this as being connected to a hydrant because the 60 psi residual pressure is actually coming from the hydrant. It’s before the impeller of the first pumpers pump therefore does not have anything to do with the pumping capabilities of the first pumper. When the water is received by the second pumper the pump operator simply opens up the intake valve and gets the shared water from the first pumper. One of the unique things about this operation is that the pumper that is sharing the water with the next pumper can never be robbed of water it is discharging. Due to the pumps design all available water that comes into the initial pumper will always be available for that unit. Let’s go back to the initial part of this example. After the first pumper is flowing 500 GPM and sharing water through a dual pump operation to the next pumper the first pumper has to increase its flow by another 500 GPM. The only thing the pump operator will have to do is open the proper discharge lines and throttle up to the proper pressure to flow that extra 500 GPM. The water will basically be taken back from the dual pump operation to the next pumper. Again the initial pumper receiving water from the water supply will always have priority.
There are a couple things that need to be monitored during a dual pump operation by both pump operators. Once the initial pumper shares the remaining water supply it will lose some residual pressure because the residual pressure is being used to move the water to the next pumper. So the pump operator on the initial pumper might have to apply more throttle to increase the pressure back to whatever is required pressure was. If the pump is equipped with an electronic governor it will automatically adjust the RPMs to the new residual pressure. Again the initial pumper is not losing any water only residual pressure. If the initial pumper needs to take back some water, the pump operator should communicate with the pumper that is receiving the extra water that he will be taking water back which will in turn drop the intake pressure of the receiving pumper. The pump operator on the second pumper should try to maintain the engine pressure that was required for its flow and may have to throttle up because of a drop in intake pressure. Below is an illustration of a basic dual pump operation.
Summary of Dual Pump Operations
- Dual pumping moves water from one pumper to another with supply hose connected intake to intake.
- The water is moved by the residual pressure of the first pump.
- Dual pumping works real good for low flow operations such as handlines when the water source to the initial pumper is coming directly from a hydrant with hydrant pressure only.
- If a dual pump operation is going to be used to share big water, the water source to the initial pump needs to be boosted from the hydrant with a relay pump operation.
- The distance a dual pump operation is based on the flow requirements and the available residual pressure.
- The opening of the intake valves should be done slowly until the line is charged to avoid cavitation.
- 7. Since dual pumping shares residual pressure, pump operators need to monitor the pump discharge pressures in case there is a drop in residual pressure.
Most firefighters have never heard of dual pumping before so what I would like to suggest is before integrating it into a looped supply line multi-company operation, go out and train with it to get comfortable with its operations to see what it can really do for you.
The next illustration I’d like to show you is the beginning of a multi-company large flow operation. The illustration shows three pumpers connected to their initial water sources.
This is basically the first alarm assignment. These units are in the big water mode so they are really starting to tax the main that is connected to the three hydrants. Grabbing the closest hydrants by first in companies is a realistic scenario and there is the possibility of some if not all hydrants being on the same main. Now is when these first-in units start running low on water. Just running low on water in itself isn’t the risk as long as the engines will not be trying to deliver more water than their current discharge evolutions. However, often times especially with the first alarm assignment, the units are usually in a good spot to deploy multiple streams. With this being the case there is a good chance the first alarm assignment will need more water.
The next illustration will show supplemental pumping by use of the looped supply line operation which involves relay pump operations and looping or connecting the receiving pumpers together to share a common water supply. Remember these units already have water coming into them from their initial supply lines, they just need to freshen up their water supplies. In some cases they won’t need that much more water while in others they may need to double their current flow. As mentioned earlier when units are connected in a dual pump operation the water will automatically flow in the direction of the pump that has the lowest residual pressure.
I’m a big fan of preparing for worst-case scenarios. In regards to this operation it’s best if the pumpers are equipped with at least three large intakes, the two steamers coming off the pump and either a front or rear suction. There are manufacturers that actually make valves that can be connected to the main steamer that will allow two supply lines to be connected. The illustration shows two dual pump operations using pumpers with two intakes and pumpers with three intakes. Both will work however the pumper with three intakes allows for more options.
The second method for supplementing a water supply at a large flow operation is to use large diameter hose manifolds in conjunction with a relay pump operation. Remember in a supplemental operation we are giving additional water to units that already have their own supply lines but are running low on water and need more. There are two types of large diameter hose manifolds that are available. One has a large diameter hose inlet and outlet as well as multiple 2 ½ inch outlets. This style is designed more for handline operations supported by a large diameter hose line. In our situation where we are attempting to move large volumes of water only, the 2 ½ inch discharge ports on the manifold will be very restricting and therefore should not be used for this type of operation.
The other manifold that I do recommend has a large diameter hose inlet and two large diameter hose outlets. The body of these manifolds is large and have unrestricted waterways and are very efficient for moving big water. These manifolds work best in conjunction with a relay pump operation. The manifold should be placed on the fireground close to the units that it will be supplying and can be fed by a single large diameter hose relay line.
Although this is an efficient operation it’s important to remember that the water is being discharged through the entire hose evolution and therefore will only flow the water in one direction. Therefore it cannot be used in a looped system.
2-1/2” outlets on the large diameter hose manifold are for 2-1/2” or smaller hose. This would be very restrictive for supplying large volumes of water.
Large diameter hose can be connected to the 2-1/2” ports on the manifold however the
2 ½ inch waterway is very restrictive.
Large diameter hose manifold with large diameter inlet and outlet’s is very efficient.
A Pumper Supplying Multiple Large Diameter Supply Lines
The third method for supplying a supplemental water supply to units on the fireground is by simply pumping multiple large diameter hose discharge lines to the individual units. This can be done either from the hydrant or at the end of a relay on the fireground. Most units only have one large diameter discharge however the 2-1/2” discharge adapted to a large diameter hose line can move 1000 GPM fairly efficiently.
This pumper is at the receiving end of a relay on the fire ground supporting two 5 inch supply lines to units on the fireground. One 4” discharge and one 2 ½ inch discharge are being used.
This pumper is set up at the hydrant discharging two 5 inch supply lines in a relay directly to units on fire ground.
There are several ways to support units with an adequate water supply on the fireground. This article has talked about three different evolutions. The key to a successful operation such as this is to be proactive with the water supply and develop an evolution that works best for your agency based primarily on safety and efficiency.