Pumping from the hydrant is an operation that has been done for many years. It involves placing the pumper at the hydrant, making hookups with short supply hose and pumping through its discharge lines to either another pumper, water delivery appliances, or handlines. The latter is most common when the hydrant is close to the fire.
The main reason, at least hydraulically, the engine pumps from the hydrant is to create enough pressure to move the water to the discharge delivery point when the hose layout from the hydrant to the discharge point is so pressure restrictive that it is not able to produce the required streams. The restrictions can be the diameter of the hose, length of the lay, low hydrant residual pressure and/or the volume of water, all of which cause pressure loss. In the olden days before Large Diameter Hose (LDH) 2-1/2″ and 3″ were the norm for supply line evolutions. Depending on the capacity of the hydrant system being used, pumpers on the hydrant were quite common even in low flow house fire scenarios. When the water requirements were high, it was also common to see multiple supply lines being pumped from the hydrant.
A 3″ supply line supporting a house fire
With the coming of LDH, fire departments realized its low friction loss capabilities and hydrant pump operations faded away to the point where most hose evolutions did not include it. Basically we got spoiled. In fact on large flow fires it is very common to just lay LDH supply lines from not only the close hydrants initially used from the first alarm, but even the farther ones brought in from hundreds of feet away.
This 600′ 5″ supply line is powered from hydrant pressure. It would have performed better being pumped from the hydrant.
Well guess what, even LDH, as good as it is, has friction loss that has to be overcome from a positive pressure source. Hydrant systems, even the hot ones, are limited in their pressure capabilities. In fact, when a supply line supplied directly from a hydrant is pushed to the max and can’t provide any more water it’s usually not because it ran out of water, instead it’s because it runs out of system pressure. An important point to remember is that a hydrant pressure starts at static which is the water in the system not flowing. The static pressure is often thought of as the pressure that moves the water and this is incorrect. Once the water starts flowing the pressure turns to residual and starts dropping. The more you flow, the lower the pressure gets. This happens until you can’t get any more water because the pressure will not deliver it through the supply line. As an example a hydrant has a 100 psi static pressure but after flowing 1000 GPM the residual pressure is 40 psi. The friction loss in 5″ hose is 5 psi per 100′. After leaving 20 psi for an intake pressure the 40 psi will only move the 1000 GPM 400′. The moral of this story is that in a lot of situations we can move more water by creating more pressure by putting a pump at the hydrant.
Let’s take a look at some things that can be done to improve hydrant pumping capabilities.
When making the hydrant hookup, it is important to get as much water as possible to support the units on the fireground. Many departments that have LDH only make the connection with a single line. In fact there are departments that only have the capability on their engines to use one line choosing to leave one of the main pump intake ports capped off. Why settle for less when you have the capability to get more. The worst thing that could happen is that you won’t need the extra water. It’s better to be safe than sorry.
Very common It does have its place
These hookups made with a single LDH lines are not getting the full capacity of the hydrant.
The most common hydrants in use today have three discharge ports. One is large, usually 4″, and the other two are 2-1/2″. Many departments make their multiple hookups with hose matching the outlets. The large outlet gets the large line and the 2-1/2″ outlet gets a 2-1/2″ or 3″ line because their 2-1/2″ couplings match the outlet. At first this sounds sensible but the true fact is that water follows through the path of least resistance. With this combination of hose, the path of least resistance is the large outlet with the large hose. The smaller outlet with the small diameter hose will not get its full potential. A simple flow test was done using a 500 GPM flow to illustrate this concept. A flow meter was placed on a 3″ line 30′ long from the 2-1/2″ hydrant port while the large port had a 5″ line 50′ long. 500 GPM was discharged from the engine and only 60 GPM came through the 3″ line. Next the 3″ line was used by itself to get the same 500 GPM and was able to provide it with a little water left over. Always use LDH on every port , even the small one.
This hook up is made with a 5″ and 3″ line restricting the flow
I recommend using at least two lines for a hookup. In most cases this will get the hydrant capacity. However, if the hydrant is known to be exceptionally good, use a third line. You might be surprised as to what this can do for you.
Multiple hydrant line hookups
Even a 2-1/2″ intake will get you some additional water.
Spotting the hydrant has always been one of the true tests for the pump operator’s skills with the objective of being able to have a kink free line after it is charged. Back in the day soft suction lines were short for reasons I do not know. It was common to have lines as short as 12′ to 15′. This did take a lot of skill to use. I am all for having well trained operators but the shortie’s just mentioned do not help in this type of operation. The use of 25′ and 50′ sections makes a lot more sense. The extra length does not affect the flow but more importantly it allows the unit placement to be simple. Basically all that is needed is to pull up in the area of the hydrant, of course within reason, and the lines will connect with no kink issues. If there are some initial kinks when the line is charged they will most likely straighten out on their own or with a little assistance.
Finally, let’s talk about actually deploying the lines that will make the hydrant hook up. One negative about large diameter hose is that it is heavy, especially if you are using the 25 and 50 footers. You don’t want to be carrying this stuff if at all possible. Single rolls of LDH require the firefighter to unroll it like throwing a bowling ball. This does not work well with the 50′ sections. Rolling the hose in a double donut roll allows the firefighter to drag instead of carrying or doing the bowling ball throw allowing the hose to deploy safely and easily.