THE VOLUNTEERS CORNER

THE VOLUNTEERS CORNER

DEPARTMENTS

THE WAY the first pumper is hooked up to a hydrant may mean the difference between getting all the water you need from that hydrant and having to send a second engine to another plug. This can mean costly delay in getting enough water on the blaze and can invite confusion when hydrants are far apart. Manpower needed on hose lines may have to be diverted to hooking up an engine that never should have been used at a hydrant.

When the order to take a hydrant is given, an engine company officer should make sure that the flow of water is limited only by the potential of the hydrant or the pumping capacity of the piece. Under no circumstances should the supply lines between the hydrant and the pump be too meager in size or number so that the water flow is unnecessarily limited.

Whenever a steamer outlet is available, the suction hose should be attached to that outlet—which may be 4, 4 1/2 or even 5 inches in diameter. Then, if it looks like a 50-gpm lb-inch line attack turns out to be a worker, the pumper is ready to handle a heavy volume of water.

If only a 2b-inch supply line was put on the hydrant, then that line would be the limiting factor in getting more water for the pump. It might be necessary to shut down the plug and then hook up big. The tragedy is that fires have a habit of surging into new fury whenever an attack is suspended.

Figure 1

There’s no excuse for not hooking up big when a 4b-inch or larger soft suction line is carried on the pumper. One man can handle a length of large soft suction, whereas it takes two men to handle a length of 4-inch or larger hard suction. And the added bonus is that you get just as much water from a hydrant through soft suction as you do through hard suction.

We’re not going to get into the old debate of soft vs. hard suction except to recall that the New York Fire Department some years ago made exhaustive tests that showed no practical water-flow advantage for hard suction.

For added speed in hooking up, the soft suction may be carried preconnected to the pump. This is usually done through a front suction inlet—although a rear inlet could be used. The advantage of having the preconnected suction in front is in positioning the piece at the hydrant. The driver can see everything in front of him— particularly with the cab-forward models.

Before you preconnect soft suction, however, there is one thing to remember. There must he a valve in the line so that the preconnect inlet can be closed off to permit using the booster tank or drafting without having to take off the soft suction and cap the inlet. This can be accomplished by putting an inline valve in the suction pipe or by putting a gate valve on the suction inlet before attaching the soft suction.

In most cases, a large soft suction line will deliver all the water a pump requires. However, when you hit a hydrant with low residual pressure and a moderate potential volume, the use of an added 2 1/2-inch supply line may make a noticeable difference.

Figure 2

That is why some departments require one 214-inch hydrant outlet to be gated when a large suction line is used. When he has a chance, the pump operator can then connect a 214-inch supply line from the hydrant to the pump. This adds 4.9 more square inches to the total waterway and may make it possible, in a critical water supply situation, to provide flow for another 114-inch line using 50 or 75 gpm.

When a hydrant has only two 212inch outlets—no steamer outlet—then one outlet should be gated when the first supply line is attached to the other outlet. This permits the pump operator to start supplying his first line at once. Then he can run the second 214-inch supply line from the hydrant gate to a gated pumper inlet as soon as he has an opportunity. This doubles the 4.9 square inches of waterway of a single 214-inch line to a total of 9.8 square inches of waterway.

Figure 3

However, a comparison with the table below shows that, at best, parallel 2⅜inch lines are no match for the square inches of waterway provided by a steamer connection and big suction lines.

When parallel 2 1/2-inch supply lines are used, they shouldn’t be greater than four or five lengths because the friction loss becomes excessive after that point.

Some idea of the effect of pumper hookup on the potential water flow can be had from an experiment we recently conducted. A hydrant with a 50-psi static pressure on a 6-inch main was used.

A 750-gpm pumper was employed to supply two 2 1/2 lines using 200 gpm each. Thus the total gallonage supplied was 400 gpm. The engine pressure was maintained at 75 psi throughout the test. The following table shows the range of the residual hydrant pressure:

This leaves no doubt that as we increased the total square inches of waterway, the potential water flow increased.

There is a rule of thumb for estimating what the difference between the static (no water flowing) and the residual (water flowing) pressures on a pumper’s compound gage indicates. If the residual pressure drop is less than 10 percent of the static pressure when one 2 1/2-inch line is charged, then the hydrant will probably supply three more lines requiring the same gpm. If the difference is not over 15 percent, two more lines of the same gpm can probably be supplied. If the difference is up to 25 percent, you may not be able to handle one more line requiring the same gallonage.

However, there is nothing like experience. The next time you hold a hydrant hookup drill, try different supply methods and note the various flows obtained. It will help you to determine your standard procedures in harmony with your hydrant flow characteristics.

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