Last week, I addressed handlines. This week, I'll take a look at supply lines. Which really is better? The 2.5-inch, 3-inch, 4-inch or 5-inch line? I know for a lot of us, the 2.5-inch line for supply is practically taboo, but the fact is, some departments use it, and it serves them fine. The 3-inch is generally the minimum, and many of us use the 4- and 5-inch. So if you're in the market for supply line, here's the skinny on friction loss per 100 feet of hose at some common gpm's.

500 gpm
2.5 inch: 50 psi
3 inch: 20 psi
4 inch: 5 psi
5 inch: 2 psi

750 gpm
2.5 inch: 113 psi
3 inch: 45 psi
4 inch: 11 psi
5 inch: 5 psi

1,000 gpm
2.5 inch: 200 psi
3 inch: 80 psi
4 inch: 20 psi
5 inch: 8 psi

Obviously, the 2.5-inch hose is a realistic option if your needed flows are significantly less than 500 gpm and/or less than a 100-foot stretch, or you use multiple stretches of the hose.

The 3-inch hose puts you in the same boat above 500 gpm. The 4-inch hose does well for long stretches at flows to 1,000 gpm. At 150 psi, you can flow 1,000 gpm right at 1,200 feet. With 200 psi, you can flow 1,000 gpm a little over 1,500 feet.

For flows greater than 1,000 gpm, the 5-inch hose is the way to go. At 150 psi, you can flow 1,000 gpm more than 3,000 feet. With 200 psi, you can flow 1,000 gpm beyond 4,000 feet. (Note: 300 psi 4- and 5-inch hose is also available.)

Also, the 3-inch hose has 2.1 more square inches of area than a 2.5-inch hose; consequently, the 3-inch flows almost 1.5 times more water than the 2.5-inch hose. The 4-inch hose has 5.5 more square inches of area than a 3-inch hose. The 4-inch flows 1.75 times as much water as the 3-inch and 2.5 times as much water as the 2.5-inch hose. The 5-inch hose has 7.1 more square inches of area than a 4-inch hose. The 5-inch flows 1.5 times as much as the 4-inch, 2.8 as much as the 3-inch hose and 4 times as much as the 2.5-inch hose.

Finally, for a 500-foot stretch at 25 psi: The 2.5-inch hose will flow 140 gpm; the 3-inch hose at 222 gpm; the 4-inch hose at 651 gpm; and the 5-inch hose at 1,108gpm (Source: Paul Shapiro "Layin' the Big Lines," 2001 edition).

So, there you have it. I'm not trying to tell you what size hose to buy, but take the information given, combine it with the flows and distances your response district will need in the next five years, and buy for that.

And if you'd like more information on large diameter hose, get in touch with Paul Shapiro at www.fireflowtechnology.com.