Head lift at 0 flow is the maximum pressure a pump can generate when its discharge is completely closed and no water is moving through the system. It represents the highest point on a pump’s performance curve, sometimes called “shut-off head” or “dead head pressure.” This number tells you the absolute ceiling of pressure the pump is capable of producing.
Why This Number Appears on Pump Curves
Every centrifugal pump comes with a performance curve, a graph that plots flow rate along the bottom axis against head (pressure) on the vertical axis. As flow increases, head decreases. The curve starts at the far left where flow is zero, and that starting point is the head lift at 0 flow. It’s the pump’s maximum pressure potential with nowhere for the water to go.
Think of it like pressing your thumb over the end of a garden hose. The water stops flowing, but you can feel the pressure build behind your thumb. A centrifugal pump behaves the same way: close the discharge valve entirely, and the impeller keeps spinning, converting all its energy into pressure rather than movement. The head value at that point is what the manufacturer lists as the 0 flow (or shut-off) head.
What “Head” Actually Means in Practical Terms
Head is measured in feet (or meters) and represents the height a pump could theoretically push a column of water straight up. A pump with 100 feet of head at 0 flow could, in principle, push water 100 feet vertically against gravity if no friction losses existed. This unit is used instead of PSI because it stays constant regardless of the fluid’s density, making it easier to compare pumps across different applications.
To convert feet of head into PSI, multiply by 0.433. So 100 feet of head equals about 43.3 PSI. One foot of head is equivalent to 0.433 PSI, the pressure you’d feel at the bottom of a one-foot-deep column of water.
How Engineers Use This Value
The 0 flow head tells you whether a pump can overcome the static height of a system before any water starts moving. If you need to push water up to a tank 80 feet above the pump, the shut-off head must be higher than 80 feet, or the pump will never get water to the top. In practice, the shut-off head needs to exceed the static height by a comfortable margin because friction in the pipes eats into available pressure once flow begins.
This value also helps when selecting between pumps. Two pumps might deliver the same flow at your design point, but different shut-off heads. A higher shut-off head gives you more flexibility if system conditions change, like partially closed valves or clogged filters adding unexpected resistance.
The Dead Head Test
Field technicians use a procedure called a “dead head test” (or pump shut-off head pressure test) to verify a pump’s actual condition. The idea is simple: close the discharge valve, measure the pressure, and compare it to the manufacturer’s curve. If the measured shut-off head falls significantly below the published value, the impeller is likely worn, damaged, or undersized.
The procedure works like this:
- Prepare the system. The piping must be completely filled with fluid and purged of air. Pressure test ports are needed on both the suction (inlet) and discharge (outlet) sides of the pump.
- Connect gauges. A pressure gauge or hydro-manometer connects to both test ports to read suction and discharge pressure separately.
- Close the discharge valve. With the pump running, slowly close the valve on the outlet side. Leave the suction side fully open.
- Read the pressures. Record the discharge pressure and the suction pressure in PSI.
- Calculate dead head pressure. Subtract suction pressure from discharge pressure. For example, if discharge reads 31.4 PSI and suction reads 18.3 PSI, the dead head pressure is 13.1 PSI.
That PSI value gets converted to feet of head (divide by 0.433) and plotted on the manufacturer’s curve at the 0 flow point. This confirms the pump’s flow potential and verifies the impeller size. Without this test, the actual pump capacity is essentially unknown.
Why You Should Never Run a Pump at 0 Flow
While the dead head test is a brief, controlled procedure, operating a pump at or near zero flow for extended periods causes serious problems. When water isn’t flowing, the energy from the spinning impeller has nowhere to go except into heat. The trapped water inside the pump casing heats up rapidly, which can damage seals, warp internal components, and cause the pump to flash (turn liquid into steam), potentially leading to a run-dry condition that destroys the pump entirely.
Excessive vibration is another risk. Centrifugal pumps are designed to operate within a specific flow range, and running far below that range creates unbalanced hydraulic forces called radial thrust. These forces push the shaft sideways, accelerating bearing and seal wear.
How Systems Prevent Zero-Flow Conditions
Because demand in real systems fluctuates, engineers build in safeguards to keep pumps above their minimum flow even when downstream valves close. The most common approaches fall into three categories.
A continuous bypass line is the simplest option. A small pipe routes water from the pump’s discharge back to the suction side or a reservoir, ensuring some flow always circulates even when the main system demand drops to zero. For low-head pumps, this can be just a piped connection with no extra hardware.
Controlled bypass systems use a flow sensor to monitor how much water is moving through the main line. When flow drops below the pump’s specified minimum, a control valve opens a bypass path automatically, diverting enough water to keep the pump in a safe operating range.
An automatic recirculation control valve combines sensing and bypass into a single device. It uses a flow-activated check disc linked mechanically to a bypass valve. When process flow drops to zero and the check disc closes, the bypass valve opens fully. As the check disc opens with increasing flow, the bypass gradually closes. No external controllers or sensors are needed.