Fireground hose evolutions can take many forms, from the very basic LDH supply line with 1-3/4″ attack lines to the extremely complex multi apparatus combination master stream and handline operation. No matter what type of evolution is going to be in operation the goal should be to provide the required flow as safely and efficiently as possible.
There are various types of appliances and adapters that are used to put together these evolutions. One appliance in particular that is very useful is the large gated manifold. The large gated manifold is an appliance that distributes water from one LDH supply line on the inlet side to multiple gated outlets on the discharge side.
Let’s talk about the design of the manifold. Most manifolds are equipped with a pressure dump valve (PDV). Its main purpose is to guard against pressure surges in the system. The PDV valve is connected to the manifold body and expells excess pressure that may be created from a shutdown of a line or overpressurization from the pump. Another function of the PDV allows it to be preset to the potential pressure setting of the discharge lines which in turn helps to come up with an accurate pump discharge pressure(PDP). The PDV is adjusted by actually pumping the required pressure to the PDV/manifold and turning the adjusting bolt on it either clockwise or counter clockwise until just a trickle of water is discharging from the PDV port.
There are three basic types of large manifolds.One type has an LDH inlet and wyes off to multiple 2-1/2″ gated discharge ports with the most common being three ports. This manifold is used at the end of the feeder line and supplies multiple discharge lines. The second type of manifold also has an LDH inlet but also has an LDH gated outlet which allows the manifold to be placed inline in an LDH system which in turn allows water to be distributed through its discharge outlets and then sent down the line to another delivery system such as another manifold or engine. It can also be used as a wye and dead ended. The most common manifold of this type has four 2-1/2″ gated outlets. Finally the third type has a large diameter intake and two large diameter gated discharge ports.
Gated Wye Operation
The key to a sucessful gated wye operation with the manifold is two fold. First, it is important not to commit more discharge lines to the manifold than the water supply will allow. For the most part this is not an issue if small attack lines are used. However when you start getting into the higher flows that a 2-1/2″ attack line or other high demanding lines might create, just make sure that the water supply will support it. Because of the multiple outlets on manifolds there is a tendancy to over extend the discharge capabilities. It’s really simple, water in equals water out.
Developing The Correct Pump Discharge Pressure
Now let’s talk about a really important issue with the manifold , that is developing the correct PDP for the discharge lines connected to it. When discharge lines are extended from an engine, it is easy to control the pressure on the lines because of the individual valves and gauges that are able to be used. However when these lines are extended hundreds of feet from the engine and supplied from one discharge through one supply line there is only one gauge that can be monitored. This can present a real problem when multiple lines are placed in service. Because of this issue, dialing in multiple lines is more difficult and cannot be expected to be as accurate as it would be if directly connected to an engine. The goal should be to provide as close to the required flow as possible and in a safe manner.
The first thing that needs to be done to establish the PDP is to come up with the dimensions of the line that the PDP will be calculated from. This can obviously be different from incident to incident. Establish a common line that will most likely be used a high percentage of the time for the purpose of creating a starting point for the pump operator to get water flowing. I like to use a 200′ line simply because in most cases it will be long enough to reach the fire. The next step is to preset the PDV on the manifold to the pressure. Since there is the chance of having 1-3/4″ and 2-1/2″ handlines from one manifold as well as other types of discharge lines, the goal is to come up with one pressure that will safely flow all types of lines. More than likely the individual lines will not be 100% accurate. We are looking for ballpark flows that will provide a required flow safely.
Here is an example of three types of discharge lines that could be on one manifold. First, a 150 GPM combination nozzle and 15/16″ smooth bore tip combined into a break apart nozzle with a nozzle pressure of 50 psi and a friction loss of 35 psi per 100′ of 1-3/4″ hose. Second, a 250 GPM combination nozzle with a nozzle pressure of 50 psi and a 1-1/8″ smooth bore tip both used on 2-1/2″ hose with a nozzle pressure of 50 psi with a friction loss of 15 psi per 100′ of hose. Finally, a Mercury portable master stream flowing 500 GPM using 3″ hose with a 1-1/2″ tip at 55 psi nozzle pressure with a friction loss of 20 per 100′ of 3″ hose. In this case the target pressure on the PDV should be set at 120 psi. Here’s the reasoning behind this pressure. The 1-3/4″ hose at 200′ actually calculates out to 120 psi. This is probably the most important line to keep to the flow and pressure requirements. With the 2-1/2″ handline calculating out to 80 psi and the Mercury master stream calculating out to 90 psi based on the 120 psi pressure setting ,they will be over pumped creating a higher flow and nozzle pressure. Flow tests can evaluate whether or not this is an issue but in this particular situation I think you will find that it will not be a problem. It’s one pressure does all.
The purpose for setting it at the required pressure for the handlines is to be an indicator to the firefighters from its activation that the correct pressure at the manifold has been obtained.
With the PDV being preset, the pump operator simply throttles up to the set pressure on the manifold and through communication with the firefighters at the valve slowly continue increasing the pressure until the PDV starts to activate.
Now let’s say that the lines attached to the manifold are going to be longer than 200′. A simple friction loss chart can indicate what the new PDV setting should be allowing the PDP and PDV to be readjusted accordingly.
Supplying multiple handlines
When the manifold is used in an inline operation to support discharge lines as well as sending the remaining water on through the hose evolution, the PDV concept of calculating the PDP will not work.The reason for this is that the PDP has to be able to provide the required flow for the entire operation which could include a number of different operations through multiple manifolds and/or engines being used. There is only one accurate way to establish the PDP for the discharge lines. An inline pressure gauge can be placed between the discharge port of the manifold and the discharge line to read the required pressure for the line. This will allow the valve controlling the line to be gated down accordingly. This requires adding additional gauges to the manifold since they are not provided from the manufacturer. The other option is to gate the line down by the feel of the nozzle reaction on the handline itself. An experienced firefighter should have a feel of what a particular line should feel like at the required flow.This would be able to create a safe operating situation and although it might not be 100% accurate it should be close enough.
Used in an inline operation
A common water supply problem that can develop happens when a large flow multi company operation is created. What usually happens is the first few units placed in service grab the closest hydrants for their water supply.
There is a real good chance that some if not all of these hydrants could be on the same main thus drawing down the available water from each other. Oftentimes these units are in place to attack the fire and have the available hose, appliances, and personnel to get the job done. The initial attack gets started but eventually gets stifled due to a dwindling water supply.These units are already flowing water and in most cases only need a little bit more to accomplish their goal. This is where a relay pump operation comes into play.
A traditional relay pump operation only delivers water to one pumper. There is a good possibility that the receiving pumper will have water left over from the relay, especially if it already has its own supply line,.and will not be able to share it. This is when a relay/manifold operation can be put into place to supplement units on scene. The manifold allows for multiple supply lines to be connected supplementing units hopefully with the balance of water that they need.
Don’t be fooled by the 2-1/2″ outlets on the manifold thinking that it will restrict the water delivery capabilities. Yes, the 2-1/2″ is more restrictive than a larger 5″ outlet but it is possible to move enough water through the 2-1/2″port to make it work. The key to this operation is to use the same diameter hose to supply the engines. The reason for this is that water follows the path of least resistance. So if you have a large diameter hose and a small diameter hose, more water is going to move through the larger making for an unbalanced delivery.
When the pumper suppling the relay makes its hookup at the hydrant a minimum of two LDH lines should be used to get maximum flow. The pumper should plan on throttling up to the maximum allowed pressure if possible.
After the relay/manifold operation is set up the PDV can be readjusted to the proper setting which is indicated when just a trickle of water is coming from the PDV port.
Suppling water to multiple engines using the same diameter supply lines
The large manifold is a tool that will probably not be used that much. However, if the situation should arise, and it will at some point, the manifold will prove itself as a water distribution appliance worth its weight in gold.