Pump Operators Glossary

Appliance loss is the pressure water gives up turning and splitting inside a device such as a gated wye, manifold, or monitor. Budget about 25 psi for an appliance in the lay.

Back pressure is pressure working against the pump, most often from lifting water to a higher elevation. It adds to the pump discharge pressure the operator must produce.

Elevation pressure is the pressure the pump must add or can subtract because the nozzle sits above or below the pump. Figure about 5 psi for each floor of rise, added on top of nozzle pressure and friction loss.

Flow rate is how much water is moving through a line per unit of time, usually measured in gallons per minute. It is the quantity that drives friction loss, tank duration, and stream effectiveness.

Friction loss is the pressure water gives up rubbing against the inside of the hose as it flows. It depends far more on the flow than on the hose, and it grows with the square of the flow — double the flow and the loss roughly quadruples.

Net pump discharge pressure is the pressure the pump itself actually adds — the discharge pressure minus whatever the intake is already supplying. It separates the pump's own work from the help a pressurized hydrant is giving.

Nozzle pressure is the pressure of the water as it reaches the nozzle, and it sets both how much water flows and how good the stream looks. Each nozzle type is designed around a specific tip pressure.

Nozzle reaction is the backward push a flowing nozzle exerts on the crew, the equal-and-opposite force to the water leaving the tip. It rises with both the flow and the nozzle pressure.

Pump discharge pressure is the total pressure the pump must produce so the nozzle gets what it needs after the hose, appliances, and elevation take their share. It is the sum of nozzle pressure plus every loss between the pump and the tip.

Residual pressure is the pressure that remains in a supply while water is actually flowing. The gap between static and residual is what tells you how much more the source can give.

Static pressure is the pressure a water source shows when no water is moving. On a hydrant it is the reading before you flow a line — the system at rest.

Water hammer is the pressure surge that travels back through a line when moving water is stopped or started too suddenly. Closing a valve fast turns the water's momentum into a damaging spike.

An automatic nozzle is a fog nozzle that holds a roughly constant tip pressure across a range of flows by moving an internal baffle. Pump it to its target tip pressure — about 100 psi — plus the line's friction loss.

A discharge is an outlet where a line leaves the pump, each with its own valve and pressure gauge. Opening a discharge sends pump water into that attack line.

A fire department connection is the inlet on a building where an engine pumps water into the standpipe or sprinkler system. It lets the pump boost a building's fixed fire-protection piping.

A fog nozzle breaks water into a cone of droplets and is built around a higher tip pressure than a smooth bore — a standard fog wants about 100 psi. The droplet pattern gives reach, absorbs heat, and can be adjusted from straight stream to wide fog.

A gated wye is an appliance that splits one incoming line into two outgoing lines, each with its own valve. It lets one supply feed two attack lines while controlling them independently.

The intake is where water enters the pump — from the booster tank, a hydrant, or a drafting source. What feeds the intake determines how much water the pump has to work with.

Large diameter hose is wide supply hose used to move big volumes of water with very little friction loss. Its size is what lets an engine pull a strong supply over a long distance.

A master stream is a high-flow stream from a deck gun, monitor, or portable appliance — far more water than a handline, aimed by hardware rather than held by hand. Master-stream fog devices are built around about 80 psi at the tip.

A preconnect is an attack line already connected to a discharge and loaded at a fixed length, ready to pull and stretch. Its known length and hose make its pump pressure predictable enough to memorize.

A pressure governor is the control that manages engine speed to hold a set discharge pressure as demand changes. It keeps the pump pressure steady when lines open or close instead of letting it spike or sag.

A siamese is an appliance that combines two or more incoming lines into a single outgoing line — the mirror image of a wye. It is used to feed one demanding line or system from multiple supply hoses.

A smooth-bore nozzle is a plain tapered tip that produces a solid stream and forms it at a lower tip pressure than a fog nozzle — about 50 psi on a handline. Its flow depends on the tip diameter and the pressure behind it.

Cavitation is what happens when the pump tries to discharge more water than the intake can supply, forming vapor pockets that collapse violently inside the pump. The discharge pressure becomes erratic and the pump can damage itself.

Churn pressure is the pressure a pump produces when it is running against closed discharges, moving no water. It is the top of the pump curve — maximum pressure at zero flow.

Drafting is drawing water from a static source like a pond or tank that sits below the pump, using the pump to create a partial vacuum so atmospheric pressure pushes water up into it. It is how an engine pulls supply where there is no hydrant.

Hydrant changeover is the transition from running on tank water to running on a hydrant supply without interrupting the attack line. Done smoothly, the line never notices the source has changed underneath it.

Overdraw is demanding more water from a source than it can deliver, whether a weak hydrant or a draft. Push past the supply's limit and the line does not just sag — it can lose its water entirely as the pump starves and cavitates.

Priming is removing air from the pump and suction hose so water can be drawn in, the essential first step of a draft. A primer pump evacuates the air and lets atmospheric pressure push water up to the pump.

The pump curve is the relationship between how much water a pump moves and how much pressure it can make at the same time — more flow means less available pressure. It explains why pressure drops when you open another line.

Recirculation is routing some pump water back to the tank to keep water moving through a pump that is turning but not discharging much. In the training model it gives the pump a cooling path so it does not overheat at idle against closed lines.

Relay pumping is moving water over a long distance by chaining engines, each one boosting the pressure for the next. It overcomes the friction loss that would otherwise bleed a single long supply line dry.

Tandem pumping is using two engines together to feed a high-pressure or high-volume demand a single pump cannot meet alone. It is a way to stack capacity when one apparatus runs out of pump.

Tank to pump is the valve that opens the path from the apparatus's booster tank into the pump. Opening it gives the pump its first water source so the first line can flow immediately, before any external supply is established.

Available fire flow is an estimate of how much more water a hydrant can still deliver, based on how far its pressure dropped between static and residual. A small drop means a lot left; a large drop means little.

The booster tank is the water carried on the apparatus itself, used to flow the first line before an external supply is set. It is a countdown, not a supply — a working line empties it in a couple of minutes.

A drop tank is a portable open container set up near the fire that tankers dump into and the attack engine drafts from. It is the hub of a tanker shuttle, decoupling the haulers from the pumper.

A hydrant is a pressurized connection to the water main, the most common engine supply. Its real strength shows not in its static reading but in how far the pressure drops once you flow water.

Lift is the vertical distance a pump must raise water from a static source up to its intake when drafting. Atmospheric pressure sets the ceiling on how high water can be lifted, and that ceiling drops with altitude.

A standpipe is a building's built-in vertical water pipe with outlets on each floor, so crews can connect attack lines inside instead of stretching hose up stairwells. The engine supplies it through the fire department connection.

A static water source is unpressurized water — a pond, lake, pool, or portable tank — that an engine must draft from. Because it has no pressure of its own, the pump has to lift the water to itself.

A tanker shuttle is a rotation of water-hauling apparatus that carries water from a distant fill site to the fire, sustaining a supply where there are no hydrants. The shuttle's sustained flow depends on the cycle time and the number of tankers.

The coefficient of friction is the number in the friction loss formula that captures a hose's diameter and roughness. Larger hose has a much smaller coefficient, which is why bigger lines lose so little pressure.

A fire flow formula estimates how much water a building needs to control a fire, from its size and the area involved. Pre-planning methods like the national-academy and Iowa approaches give a target flow before crews arrive.

The friction loss formula multiplies a hose's coefficient by the flow squared by the length to estimate the pressure a lay consumes. Because the flow term is squared, friction loss is driven mostly by how much water is moving.

The pump discharge pressure formula adds nozzle pressure, friction loss, appliance loss, and elevation pressure into the target the operator pumps to. It is the recipe that turns a tip-pressure goal into a panel setting.

The smooth-bore flow formula estimates a solid-stream nozzle's flow from its tip diameter and nozzle pressure. Bigger tips and higher pressures both raise the flow — and the reaction force the crew must hold.

AHJ stands for authority having jurisdiction — the office or official whose rules, procedures, and approvals govern operations in a given area. Real fireground decisions follow the AHJ's requirements, not a training estimate.

GPM stands for gallons per minute, the unit of flow used throughout pump operations. It measures how much water a line is moving, which drives friction loss, tank duration, and fire-knockdown power.

PSI stands for pounds per square inch, the unit of pressure on every pump gauge. Nozzle pressure, friction loss, elevation, and pump discharge pressure are all expressed in psi.

RPM stands for revolutions per minute, a measure of engine speed. On the pump it sets how fast the impeller turns, which determines the pressure and flow the pump can produce.

SOP and SOG stand for standard operating procedure and standard operating guideline — a department's written rules for how to carry out operations. They define the specific pressures, flows, and methods a crew is expected to use.