Centrifugal pumps are the most common pumps used in firefighting applications, which Compliance BD Ltd. as a one of countries reputed Company generally deals with various kind of firefighting system solutions and frequently uses and in this article stated the basic differences between most common types of centrifugal pumps, “End Suction” & “Horizontal Split Case”, discussion on the design, construction of each type and comparison between capacities range, initial cost, maintenance, and space requirements for each type.
End suction pump
A single suction pump having its suction nozzle on the opposite side of the casing from the stuffing box and having the face of the suction nozzle perpendicular to the longitudinal axis of the shaft. usually of “overhung hung impeller” type in which the impeller is mounted on the end of a shaft which is “overhung” from its bearing supports. End suction pumps are available as close coupled in which the impeller is mounted directly on the motor shaft or separately coupled in which the impeller is mounted on a separate pump shaft supported by its own bearings.
Horizontal split-case pump
A centrifugal pump characterized by a housing that is split parallel to the shaft. usually of “Impeller Between Bearing” type in which the impeller is mounted on a shaft with the bearings at both ends. Horizontal split case pumps are available as separately coupled single stage or multistage type.
The durability of the horizontal split case pumps design allows the pump to be used for very large water flows in excess of 5000 gpm as the pump casings are often heavier and designed to handle higher working pressures, moreover, the design of “Impeller between bearing” and since the water enters the two sides of the impeller (double suction), these pumps can withstand the large amount of vibration and thrust forces often caused by water turbulence in the suction piping.
For end suction pumps and since water is entering one side of the impeller, and due to the design of “Impeller overhung”, these pumps cannot be used for large water flow applications and usually not exceeding 1500 gpm of flow.
Due to the large flanges required for the split casing sealing joint, larger impeller, and overall large size, horizontal split case pumps are normally heavier and cost more than comparable end suction pumps which has lower initial cost.
However, requiring long operating life, the cost of maintenance of end suction pumps and down time may far exceed any initial cost savings.
Horizontal split case pumps are easy for maintenance as the top half of the casing can be removed, so the internal components (Bearing, shaft, impeller, and etc.) are exposed without disturbing the suction or discharge piping, or moving the motor.
On the other hand, maintenance of end suction pump is more difficult due to their compact design, for example, the removal of the impeller requires removal of the motor to provide a space for pulling the impeller back out of the casing.
Fire department connection according to NFPA 13
FDC stands for Fire Department Connection. This is a connection on the exterior of a commercial building where a responding fire department can attach a fire hose and pump water into the building’s stand pipe system supplementing the water pressure to the building’s sprinkler system.
The traditional FDC connection consists of a brass fitting in the shape of a Y protruding from an outside wall of the building. This is known as a Siamese valve as it usually has two 2.5″ female fittings that allow water to flow into one 4″ pipe on the interior of the wall.
The two 2.5″ fittings are typically female and swivel. The firefighters will hook the female end of their hose to their pumper truck, run the hose to the FDC and attach the male end of their hose to the female swivel connections on the FDC.
The threads on these swivels are almost always 2.5″ NH aka NST. There are exceptions such as San Francisco which typically uses 3″ NH plugs and New York City which has its own thread. City specific threads are known as “local” threads. You can check with your local fire department to find out what thread size and type are used in your area.
There are two common parts that need to be replaced on the typical FDC unit, the plugs or covers and the swivels themselves
Purpose of FDC
To supplement the water supply but not necessarily provide the entire sprinkler system demand, Fire department connections are not intended to deliver a specific volume of water
When FDC is required?
FDC is required for all building except the followings:
- Buildings in remote areas inaccessible for fire department.
- Large-capacity deluge systems exceeding fire department pumping capacity.
- Single-story buildings not exceeding 185 m2 in area.
Location of FDC
At nearest point of fire department apparatus accessibility, or at a location approved by the AHJ. Installation height of FDC
Not less than 500 mm and not more than 1200 mm above grade.
Valves on FDC piping
* Shutoff valves shall not be permitted in fire department connection piping.
* A listed check valve shall be installed in each fire department connection and shall be located in an accessible location with automatic drain valve where subject to freezing.
Sizing of fire department connection
The size of the pipe for the fire department connection shall be in accordance with one of the following:
* Pipe size shall be a minimum of 4 in. (100 mm) for fire engine connections.
* Pipe size shall be a minimum of 6 in. (150 mm) for fire boat connections.
* For hydraulically calculated systems, the pipe size shall be permitted to be less than 4 in. (100 mm), but not less than the largest riser.
No. of 2½” Inlets:
* For riser 3” or smaller: Single 2.5” outlet
* For riser larger than 3”: Two 2.5” outlets