How many lines can you supply off a hydrant?

[PanekJ]

Fellow Firefighters,

I know that there is a formula that you can use to determine how many more hoselines you can utilize at a certain pressure... I have the formula written down (at work), but could someone please explain it to me?


Thanks,

James

[MG3610]

Calculating Additional Water from a Hydrant

When a pumper is connected to a hydrant and is not discharging water, the pressure shown on the intake gauge is the static pressure. When the pumper is discharging water, the pressure shown on the intake side is the residual pressure. The difference between the two pressures is used to determine how much water is available, and consequently the number of additional lines of the same size, that can be added and supplied with efficient water. To use this method, the pump operator has to convert this drop in pressure to a percentage. Use the following formula to determine the percentage.

Percent drop = (Static - Residual)(100)
Static

EXAMPLE:
A pumper is supplying one line with 250 gpm flowing. The static pressure was 70 psi and the residual pressure reading is 63 psi. Determine how many additional lines may be added.

Percent drop = (Static - Residual)(100)
Static
Percent drop = 70 - 63 (100)
70
Percent drop = 10 %

WATER AVAILABLE TABLE

Percent Decrease Water Available
0 - 10 % 3 times amount being delivered
11 - 15% 2 times amount being delivered
16 - 25% same as being delivered
Over 25% less than is being delivered

Three times the amount of water already being delivered is available for additional lines. It is possible to add any combination of hand lines or master streams as long as they do not exceed 750 GPM. (250 x 3 = 750).

Note: By connecting all three outlets of the hydrant to the pumper with large diameter hose, the maximum capability of the hydrant will be available for use.

From Houston FD http://www.houstontx.gov/fire/firefi...e/June00CE.htm

[PanekJ]

Fantastic... Thanks for all your help!

[johnny46]

You stole my reply!

[2Chief]

You do not have to utilize all three outlets for full capacity on a hydrant. LDH can take full capacity on a 2.5" outlet on a typical hydrant. 4.5" steamer will supply most any flow unless its a very high flow hydrant.

[NVdualrole]

Lets say you already have your first line going ie 1 3/4 to start fire attack and you establish your hydrant after that. Your not using your true static in your problem. In that case you would use...

Residual 1 - residual 2 divided by 2 + Residual 1

that will give you an estimated true residual.

[clifton36]

You do not have to utilize all three outlets for full capacity on a hydrant. LDH can take full capacity on a 2.5" outlet on a typical hydrant. 4.5" steamer will supply most any flow unless its a very high flow hydrant.

We recently conducted some simple flow tests to test this very theory. For years we were teaching how to maximize the hydrant using hard suction hose. Yeah, it works great but takes the entire crew to make the hookup, and it's still not easy.

Two sections of 5" LDH (one from the steamer and one from a 2.5) will maximize hydant flowas well as as one 6" hard suction, and can be handled by the engineer alone. This procedure is now in our pump operations manual.

[xxxshiftxxx]

Lets say you already have your first line going ie 1 3/4 to start fire attack and you establish your hydrant after that. Your not using your true static in your problem. In that case you would use...

Residual 1 - residual 2 divided by 2 + Residual 1

that will give you an estimated true residual.

can u give an example, thanks!!

[kfactor]

Percent Decrease Water Available
0 - 10 % 3 times amount being delivered
11 - 15% 2 times amount being delivered
16 - 25% same as being delivered
Over 25% less than is being delivered

Good rule of thumb, a little conservative on the low end though. 5% drop actually gets you about 4 times delivered and 2-3% about 5 times. 11 through 25% plus is about right on the money. This approach pretty much assumes a minimum residual of 20 psi. More volume will be available if you drop at all below 20 psi.

[kuh shise]

First, for those who live in hilly terrain. Lets say that you are working on a hydrant that is in a dip between two low hills. The hill to your left has the reservoir at its summit. When you check the static pressure the compound gauge shows 86 psi. You know that the water level in the reservoir is almost exactly 200 feet above your engine in elevation. (1 ft of water = 0.435 psi)

If the hill to your right is 100 ft. high, then the pressure supplying a house on this hill will be 43 psi. What happens if you pull the hydrant pressure down to 40 psi in the dip? (the house on the right will loose all water pressure)
If you continue to draw the hydrant down (maximize the flow) it is likely that you will create a vacuum on the inside of the pipes and hot water tank in that house. cylindrical shapes can handle internal pressures very well, but fail catastrophically under vacuum. Result - city pays resident for new water tank.

If you use 25 ft 3" x 2 1/2 couplings the friction loss in 100 ft of this hose at 600 gpm is 36 psi, but we only have 25 feet, so we get a 9 psi drop from the hydrant to the engine. Using dual 3" lines from the hydrant to the engine we can supply 1200 gpm and still provide some degree of protection to the home owner. You must be careful when attaching to the engine, as most people will want to use the 2 1/2" gated pony suctions. There may be as many as 4 - 90 degree elbows behind the pump panel. Each 90 can cause as much as 5 lbs loss or more depending upon the flow rate. Use a siamese or a reducer to go directly into the main suction for best results. At 1600 gpm (800 gpm per line) friction loss will be only 16 psi.

You are correct to use a 5" soft sleeve, at 2000 gpm the friction loss in the hose is about 6 psi., and the engineer should not take the compound below 20 psi. There is a second problem with "maximizing" flow by taking the intake to zero. By creating a vacuum on a part of the system it is possible to draw in contaminants from aywhere the pressure drops below atmospheric. If the home owner on thr right was applying fertilizer or bug killer with a garden hose the chemicals might end up in the water and poison a whole group of residents.

We must try to be aware of the entire system and not just what we are doing ourselves.