Theoretical lift. At sea level atmospheric pressure is 14.7 psi, and one psi supports 2.31 feet of water, so in a perfect vacuum a column of water rises 14.7 ÷ 0.434 = 33.9 feet. No fire department primer makes a perfect vacuum, so that figure is unreachable. Atmospheric pressure falls by roughly 0.5 psi per 1,000 feet of elevation, which costs about 1.1 feet of theoretical lift per 1,000 feet of altitude.

Maximum lift. The greatest height to which any amount of water can be raised through a hard suction — about 25 feet in most circumstances, and it depends on how much vacuum the primer can produce and on the prevailing atmospheric pressure. It says nothing about flow: a trickle counts. You can read it off the compound gauge while priming with L = 1.13 × inches of mercury.

Dependable lift. The height a column of water can be lifted in sufficient quantity to provide a reliable fire flow. Every fire pump that is working properly should have a dependable lift of at least 14.7 feet, allowing for atmospheric pressure and friction loss in the intake hose. This is the number to plan around, and the one that will get you in trouble if you plan around one of the others.

The pressure correction. PC = (lift + total intake hose friction loss) ÷ 2.3. The lift goes in as feet and the intake friction loss as psi — the division by 2.3 converts the sum back into psi of work the pump is doing on the suction side. Net pump discharge pressure when drafting = PDP + PC, so the pump is always doing more work than the discharge gauge shows. Worked example: a 1,000 gpm pumper showing 142 psi on the discharge gauge, 10 feet of lift, 9.5 psi intake friction loss. PC = (10 + 9.5) ÷ 2.3 = 8.5 psi, so NPDP = 150.5 psi.

What lift does to your capacity. NFPA 1901 rates every pump drafting from 10 feet of lift through 20 feet of intake hose — a "1,500 gpm" pump is 1,500 gpm at 10 feet. Pumps rated 2,000 gpm and above are rated at a 6-foot lift. Go to 15 feet and expect about 70 % of rated capacity; 20 feet, about 60 %; 25 feet, under half — and with a rising risk of cavitation and vacuum leaks, because the deeper the lift the harder the primer has to work. Pump service tests are run at a lift of not more than 10 feet for exactly this reason.

What this cannot tell you. The intake friction loss figure belongs on your department's table (IFSTA Table 11.2), because it includes the strainer, the couplings and the hard suction itself — the estimate this tool shows is a coefficient-method cross-check and deliberately omits those. Neither figure knows about debris on the strainer, a collapsing soft suction, a barrel strainer too close to the bottom drawing silt, water cold enough to cavitate, or a source that is being drawn down faster than it refills. And the priming standards — 30 seconds for pumps rated 1,250 gpm or less, 45 seconds for 1,500 gpm and above, maximum vacuum of at least 22 in. Hg holding to within 10 in. Hg over five minutes — are pass/fail on your apparatus, not on a formula.

Disclaimer. A training and drill aid. Pump operation from draft must follow NFPA 1901, your apparatus manufacturer's instructions and your department's SOPs, and be confirmed on the pump panel gauges. Sources: IFSTA Pumping and Aerial Apparatus Driver/Operator Handbook, ch. 11 · NFPA 1901 · National Fire Academy driver/operator materials. Last reviewed: 2026-09-21.