Fire Fighting Pumps

Fire Fighting Pumps

Fire pump Characteristics :

• Pumps are selected to supply the system demands (sprinkler and standpipes ) on the basis of three key points relative to their rated flow and rated pressure .
• Fire pumps are sized to exceed its duty point requirement .
• NFPA 20 ( Specifies that each horizontal fire pump must meet these characteristics, and the approval laboratories ensure these points are met :
• Fire pumps shall be UL listed and FM Approved .

Pump Performance Curve 

Fire Fighting Pumps Types

• Centrifugal pump .A pump in which the pressure is developed principally by the action of centrifugal force .
• End suction pump . A single suction pump having its suction nozzle on the opposite side of the casing form the stuffing box and having the face of the suction nozzle perpendicular to the longitudinal axis of the shaft.
• Gear pump . A positive displacement pump characterized by the use of gear teeth and casing to displace liquid .
• Horizontal pump . A pump with the shaft normally in a horizontal position .
• Horizontal split Case pump .A centrifugal pump characterized by a housing that is split parallel to the shaft .
• In Line Pump . A centrifugal pump whose drive unit is supported by the pump having its suction and discharge flanges on approximately the same center line .
• Piston Plunger Pump . A positive displacement pump characterized by the use of a piston or plunger and cylinder to displace liquid .
• Positive Displacement pump . A pump that is characterized by method of producing flow by capturing a specific volume of fluid per pump revolution and reducing the fluid void by a mechanical means to displace the pumping fluid .
• Rotary Lobe Pump . A positive displacement pump characterized by the use of a rotor lobe to carry fluid between the lobe void and the pump casing from the inlet to the outlet .
• Rotary Vane Pump . A positive displacement pump characterized by the use of a single rotor with vanes that move with pump rotation to create a void and displace liquid .

Vertical Inline Pumps

Advantages:

• Compact
• Cost effective

Disadvantages :

• Available only up to 1500 gpm .
• Electric driven only .

End Suction Fire Pump

Advantages :

• Electric and diesel driven .
• Moderate required space .

Disadvantages :

• Available only up to 1500 gpm .
• Low head .

Vertical Pump

Used when the source of water is too below ground level .

Advantages :

• Electric and diesel driven .
• Wide range of capacities and heads .

Disadvantages :

• Very costly .
• Very hard to maintain .

Fire Fighting Pump Horizontal Split case

• The primary fire fighting pump is preferred to be horizontal split case type .
• Horizontal split case pump characteristics (single - multi suction ) :

1. High flow rate and head
2. Electric or Diesel driven
3. Expensive
4. Huge space

Fire Fighting Pump

A continuous water and pumping station supply should always be available and ready to fight fire the following three pumps should be connected to a suction header (from water tank) and discharged to a discharge header ( to fire fighting network ).

Pumping stations should include : 

1. Electrical fire fighting pump
2. Stand - by  Diesel Fire Fighting Pump ( No need If an extra electric pump is connected to an electric generator ). 
3. Jokey Pump. 

Electrical Fire Fighting Pump Horizontal Split Case

Diesel Fire Fighting Pump Stand - By Pump

Diesel pump should be provided to the pumping station if no extra electric pump is connected to an electric generator.

Diesel pump works If :

1. The electrical pump is out of service or if there was lack of electricity . 
2. The electrical pump is working but can't satisfy system water requirements .

Jockey Pump Pressure Maintenance Pump

• Jockey pump is a multi stage vertical pump (low capacity and high pressure )works to make up the system pressure in case of leakage or during the first seconds of fire .
• Without jockey pump the primary pump would be damaged due to the fast frequent operation and shut down .( primary pump should not operating for minor leaks ) .
• Jockey pump capacity should be( 10% to 15% of the rated primary pump capacity ) .
• Its  pressure should be about (10 ft higher than primary pump rated pressure ) .

Sequence of operation

Pressure sensing lines connected between pressure gauges at control panel and the point after discharge line check valve .

If the system pressure is 10 bar .

• Jockey pump works on 9.5 bar .
• Electric pump works on 9 bar .
• Diesel pump works on 8 bar .

Pressure Sensing Line

The pressure sensing line connection for each pump , including jockey pumps shall be made between that pumps discharge check valve and discharge control valve , as follows :

• This line shall be brass , copper, or series 300 stainless pipe or tube and the fitting shall be of 15 mm (.50 in) nominal size .
• Check valves or ground face unions shall be installed as follows :

1- There shall be two check valves installed in the pressure -sensing line at least 1.52 m apart with a nominal 2.4 m hole drilled in  the clapper to serve as damping .

2- where the water is clean ground face unions with noncorrosive diaphragms drilled with a nominal 2.4 mm orifice shall be permitted in place of the check valves .

Speed of fire fighting pump

While selecting a fire fighting pump its preferred to select the high speed one . 

Advantages :

Less expensive - smaller size .

Disadvantages :

1- less life time -noisy 

2- Noise isn't a big issue since it won't work for along time , it works inside the mechanical room ( no noise for the surroundings )

Pumps Accessories

 Suction pipe - Vortex plate- Puddle flange - OS&Y gate valve with tamper switch -pressure relief valve - Automatic Air vent -Check valve -Flexible connection - pressure gauges -Test line - Eccentric  Reducer - Control panel Diesel tank muffler - Fuel Tank -ATS -Pipes - pump room accessories.

Suction Pipe

Where located in the suction pipe of the pump check valves and back flow prevention devices or assemblies shall be located a minimum of 10 pipe diameters from the pump suction flange .

Vortex Plate

For pump(s) taking suction from a stored water supply a vortex plate shall be installed at the entrance to the suction pipe 

Puddle flange

Puddle flange is used to prevent water leakage from suction or discharge ports at the water tank or any line connected between water tank and pump room ( ductile iron-HDPE)

OS&Y Gate Valve with Tamper switch

Installed at the suction and discharge lines for each pump to isolate the pump during maintenance.

Check valve

Should be installed at the discharge line of each pump to prevent back flow from one pump to another or from the system when the pump stops

Flexible coupling(Strain relief )

Should be Installed at the suction line only but its preferred also to be installed at the discharge lines for decreasing the effect of vibrations on pumps and avoid excessive forces on pipes .

Diesel Tank Muffler

Diesel Pump Fuel Tank

Capacity for diesel fuel tank

Fuel tank capacity 

• fuel supply tank shall have a capacity at least equal to 5.07 L per kw ( 1 gal per hp) plus 5 percent volume for pump 
• larger capacity tanks could be require and shall be determined by prevailing conditions such as refill cycle and fuel heating due to recirculation and shall be subject to special conditions in each case .
• The fuel supply tank and fuel shall be reserved exclusively for the fire pump diesel engine .

Eccentric Reducer

Without the eccentric reducer air pockets would be generated which may lead to pump cavitation

Test Line

• For testing pump, OS&y gate valve is installed at a test line which is connected to the discharge line and drain back into the water tank.
• Flow meter should be installed to measure pump flow rate .

Pressure gauges

Installed at the suction and discharge line of each pump.

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