Every sprinkler, hydrant and hose reel line in a building eventually leads back to one room. If the pump room is wrong, the hydraulic calculations upstream lose their meaning. In our experience a good share of site problems come not from the pipework but from the layout of this room and its auxiliary details.
This article collects the points we check on projects designed to TS EN 12845 and NFPA 20. The two standards agree on much but differ in detail, so the governing standard should be fixed at the start of the project.
Pump arrangement
A typical fire pump set has three pumps:
- Duty electric pump: delivers the system design flow and pressure.
- Standby diesel pump: takes over during a power failure, with the same rating as the duty pump.
- Jockey pump: makes up minor leakage and keeps the system pressurised so the main pumps do not start unnecessarily.
The jockey pump is not a fire pump, and its capacity should stay small. If jockey flow approaches the flow of a single sprinkler head, the pressure will not drop when a real head opens and the main pump starts late. Start pressures are staggered: jockey first, then electric, then diesel. Without enough pressure difference between the steps, the pumps end up triggering each other.
Some high hazard sites and insurer specifications call for two diesel pumps or two independent water supplies. That decision has to be made early, since it drives the room dimensions.
Suction conditions
Pump performance is very often decided on the suction side. Wherever possible, pumps should be installed with positive suction, meaning the tank water level sits above the pump centreline. TS EN 12845 only accepts suction lift under specific conditions and then requires extra measures such as a separate suction pipe, priming tank and foot valve for each pump.
Details we pay attention to on the suction line:
- Enough straight pipe ahead of the pump suction flange. An elbow right at the flange gives the impeller an uneven flow.
- Eccentric reducers with the flat side on top, so no air pocket forms.
- Valve types that do not disturb the flow when fully open, rather than butterfly valves on suction.
- NPSH checked at the lowest effective tank level and at the 150 percent flow operating point.
- A vortex plate at the tank outlet.
The suction pipe is usually one or two sizes larger than the discharge. If velocity limits are ignored, the pump cavitates and will not deliver its catalogue curve on site.
Test header and flow meter
The annual flow test requires running the pump at 100 and 150 percent of rated flow. The pump room therefore needs a test line with a flow meter.
Two methods are common. In the first, the test line returns water to the tank and flow is read from an in-line meter. No water is wasted and the test is easy to repeat every year. In the second, water is discharged outside through a test header and flow is measured with a pitot. A closed-loop arrangement needs a check on tank volume and water temperature rise.
The meter manufacturer’s straight-run requirements must be respected. Squeezing a flow meter in right after an elbow in a cramped room produces test results that mean nothing.
Discharge side
Each pump discharge has a check valve and a supervised isolating valve. Diesel pumps may need a pressure relief valve so that overspeed or a closed valve cannot push pressure above system limits. Its outlet should be visible and discharge to a safe point.
A small circulation relief is also provided to stop the pump overheating while running against a closed valve. Suction and discharge gauges should be mounted at a readable height.
Controllers
Each pump needs its own controller, listed or approved for fire pump service. The electric pump controller should be fed by a dedicated supply taken ahead of the building’s main switch, so that isolating the building does not isolate the pump. Overload protection is not set up to stop the pump as it would be on an ordinary motor. In a fire, risking the motor is preferable to losing the pump.
The diesel controller manages two separate battery banks and attempts a start from the second bank if the first fails. Pump running, fault and power failure signals should be relayed to the fire alarm panel and to a permanently staffed location.
Room conditions for diesel pumps
A diesel engine puts a significant heat load into the room and needs combustion air. That means:
- Louvres sized for combustion and cooling air, opening directly to outside. Radiator-cooled engines need ducted hot air discharge.
- An insulated exhaust run that leaves the building by the shortest practical route and cannot re-enter it.
- Minimum winter room temperatures. The standards set roughly 4 °C for electric pump rooms and, depending on the engine manufacturer, 10 °C or higher for diesel rooms.
- A fuel tank sized for full-load running over the period the standard specifies for the hazard class (typically several hours), with a bund and a level gauge.
Room layout
The pump room should be a fire-separated compartment with easy access for the fire brigade. Plan for floor drainage, maintenance clearance around each pump and lifting provision for engine removal. And the room should never be used for storage, which is the situation we run into most often.
Final note
The pump room is the space most likely to be squeezed into whatever is left once the rest of the building is laid out. Reserving the right space at the architectural stage saves a lot in both cost and operation. ESFA carries out performance tests and compliance reviews on existing pump rooms and designs pump rooms for new projects. If your project is at that stage, we would be glad to talk.