Relief Valves for Centrifugal Pumps According to NFPA 20
Muhammad Mosad May 14, 2020 firefighting, NFPA 20
Relief Valves for Centrifugal Pumps According to NFPA 20
Relief Valves for Centrifugal Pumps According to NFPA 20
What is relief valve?
A device that allows the diversion of liquid to limit excess pressure in a system.
Where shall we install relief valve?
relief valve shall be installed for centrifugal pumps in only two cases:
1. For diesel engine fire pump: Where a total of 121% of the net rated shutoff (churn)
pressure plus the maximum static suction pressure, adjusted for elevation, exceeds the
pressure for which the system components are rated.
2. For electric variable speed pump or a diesel pressure limiting driver: Where the
maximum total discharge head adjusted for elevation with the pump operating at shutoff
and rated speed exceeds the pressure rating of the system components.
Sizing of relief valve:
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The relief valve size & its discharge pipe shall not be less than that given in table below,
or sized hydraulically to discharge sufficient water to prevent the pump discharge
pressure, adjusted for elevation, from exceeding the pressure rating of the system
components.
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If the discharge pipe employs more than one elbow, the next larger pipe size shall be
used.
Relief Valve sizing According to NFPA 20
Location of relief valve:
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Relief valve shall be located between the pump and the pump discharge check valve.
Types of relief valve:
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Listed spring-loaded
Pilot-operated diaphragm type.
Discharge of relief valve:
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The relief valve shall discharge into an open pipe or into a cone or funnel secured to the
outlet of the valve, Water discharge from the relief valve shall be readily visible.
Notes on installation of relief valve:
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A shutoff valve shall not be installed in the relief valve supply or discharge piping.
Relief valve discharge piping returning water back to the supply source, such as an
above-ground storage tank, shall not be combined with the discharge from other relief
valves.
Relief valve discharge piping from a single fire pump returning water back to the supply
source shall be permitted to be combined with fire pump test piping downstream of any
control valve.
The discharge piping from multiple relief valves shall not be combined with fire pump test
piping.
Isolation of the test header piping from the pressure relief valve discharge shall be
possible.
where a pressure relief valve has been piped back to suction, a circulation relief valve
discharges to atmosphere shall be provided downstream of the pressure relief valve,
and shall actuate below the opening set point of the pressure relief valve to ensure
cooling of the pump during churn operation.
Where the supply of water to the pump is taken from a suction reservoir of limited
capacity, the drain pipe shall discharge into the reservoir at a point as far from the pump
suction to prevent the pump from drafting air introduced by the drain pipe discharge.
Jockey Pump Requirements & Sizing - NFPA 20
Muhammad Mosad October 13, 2018 firefighting, NFPA 20
Jockey Pump Requirements & Sizing - NFPA 20
Jockey Pump Requirements & Sizing - NFPA 20
What is jockey pump?!
A pump designed to maintain the pressure on the fire protection system between preset limits
when the system is not flowing water.
General requirements of Jockey Pump:
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Jockey pump is preferred to be of centrifugal type pumps
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Jockey pump shall be approved but shall not be required to be listed
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The controller for a jockey pump shall be listed but shall not be required to be listed for
fire pump service.
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The jockey pump shall not be required to have alternate or standby power.
Valves of Jockey Pump:
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An isolation valve shall be installed on the suction side of the jockey pump to isolate the
pump for repair.
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A check valve and isolation valve shall be installed in the discharge pipe of the jockey
pump.
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Valves and components for the jockey pump shall not be required to be listed.
The isolation valves serving the jockey pump shall not be required to be supervised.
Sensing line:
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Jockey pump shall have its own individual pressure sensing line (15 mm) nominal size
made between its discharge check & isolation valve.
For more information about sensing line, click here.
Jockey Pump Sizing:
The jockey pump shall be sized to replenish the fire protection system pressure due to allowable
leakage and normal drops in pressure and shall have discharge pressure sufficient to maintain the
desired fire protection system pressure as followings:
1- For situations where the jockey pump serves only above ground piping for fire sprinkler and
standpipe systems:
The jockey pump should be sized to provide a flow less than a single fire sprinkler. The main fire
pump should start and run (providing a pump running signal) for any water flow situation where
a sprinkler has opened, which will not happen if the pressure maintenance pump is too large.
2- For situations where the jockey pump serves underground mains:
NFPA 24 permits the underground mains to have some leakage, one guideline that has been
successfully used to size pressure maintenance pumps is to select a pump that will make up the
allowable leakage rate in 10 minutes or 1 gpm, whichever is larger.
A rule of thumb for sizing jockey pump supplying underground piping is to use 1% of the fire
pump rated capacity.
For example:
A fire pump with rated capacity of 1500 gpm.
Then the jockey pump flow rate is 1500 gpm * 1% = 15 gpm.
Jockey Pump Head:
Pressure of jockey pump shall be greater than the pressure of main fire pump by minimum of 10
psi to avoid false starting of main fire pump.
Fire Pump Setting
Fire Pump Setting
The fire pump system, when started by pressure drop, should be arranged as
follows:
(a) The jockey pump stop point should equal the pump churn pressure plus the minimum static supply
pressure.
(b) The jockey pump start point should be at least 10 psi (0.68 bar) less than the jockey pump stop point.
(c) The fire pump start point should be 5 psi (0.34 bar) less than the jockey pump start point. Use 10 psi
(0.68 bar) increments for each additional pump.
(d) Where minimum run times are provided, the pump will continue to operate after attaining these
pressures.
The final pressures should not exceed the pressure rating of the system.
(e) Where the operating differential of pressure switches does not permit these settings, the settings
should be as close as equipment will permit. The settings should be established by pressures observed
on test gauges.
Examples of fire pump settings:
i. Pump: 1000 gpm, 100 psi pump with churn pressure of 115 psi
ii. Suction supply: 50 psi from city — minimum static; 60 psi from city — maximum static
iii. Jockey pump stop = 115 psi + 50 psi = 165 psi
iv. Jockey pump start = 165 psi - 10 psi = 155 psi
v. Fire pump stop = 115 psi + 50 psi = 165 psi
vi. Fire pump start = 155 psi - 5 psi = 150 psi
vii. Fire pump maximum churn = 115 psi + 60 psi = 175 psi
General requirements of Circulation Relief
Valve
Circulation Relief Valve
Circulation Relief Valve
Definition:
A valve used to cool a pump by discharging a small quantity of water. This valve is separate
from and independent of the main relief valve.
General Requirements:
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Where an electric variable speed pump is installed, the automatic circulation relief valve
shall open at the minimum speed.
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Each pump shall have an automatic relief valve listed for the fire pump service installed
and set below the shutoff pressure at minimum expected suction pressure.
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The valve shall be installed on the discharge side of the pump before the discharge check
valve.
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For multistage multiport pumps, the automatic circulation relief valve shall be installed
before the discharge check valve for the last port and set below the churn pressure of the
first port.
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The valve shall provide sufficient water flow to prevent the pump from overheating when
operating with no discharge.
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Provisions shall be made for discharge to a drain.
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Circulation relief valves shall not be tied in with the packing box or drip rim drains.
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The automatic relief valve shall have a nominal size of 0.75 in. (19 mm) for pumps with a
rated capacity not exceeding 2500 gpm (9462 L/min) and have a nominal size of 1 in. (25
mm) for pumps with a rated capacity of 3000 gpm to 5000 gpm (11,355 L/min to 18,925
L/min).
Sprinkler positioning in angled & irregular-shaped rooms
Muhammad Mosad October 24, 2018 firefighting, NFPA 13
Sprinkler Positioning in Angled & Irregular-Shaped Rooms
Sprinkler Positioning in Angled & Irregular-Shaped Rooms
According to NFPA 13, For standard & extended coverage pendant & upright spray
sprinklers, where walls are angled or irregular, the maximum horizontal distance
between a sprinkler and any point of floor area protected by that sprinkler shall not
exceed 0.75 times the allowable distance permitted between sprinklers, provided that
the maximum perpendicular distance is not exceeded.
Spacing of standard spray pendant and upright sprinklers:
NFPA 13 classifies the occupancies according to hazard degree, therefor the sprinkler
spacing shall be different form hazard degree to another one, below we will clarify the
sprinkler spacing according to hazard degree
For light hazard occupancy:
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Maximum distance between sprinklers is 4.6m
Minimum distance between sprinklers is 1.8m
Maximum distance from sprinklers to walls is 2.3m
Minimum distance from sprinklers to walls is 100mm
For ordinary hazard occupancy:
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Maximum distance between sprinklers is 4.6m
Minimum distance between sprinklers is 1.8m
Maximum distance from sprinklers to walls is 2.3m
Minimum distance from sprinklers to walls is 100mm.
For extra hazard occupancy:
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Maximum distance between sprinklers is 3.7m (for density ≥ 0.25gpm/ft2) or
4.6m (for water density <0.25 gpm/ft2)
Minimum distance between sprinklers is 1.8m
Maximum distance from sprinklers to walls is 1.85m or 2.3m according to density
Minimum distance from sprinklers to walls is 100mm
Examples for standard spray sprinklers distribution in angled rooms:
The following figures include examples for distribution of standard pendant and upright
sprinklers in different hazard occupancies:
Sprinkler Positioning in Light Hazard Angled Room
Sprinkler Positioning in Ordinary Hazard Angled Room
Sprinkler Positioning in Extra Hazard Angled Room
Spacing of extended coverage pendant and upright sprinklers:
The rule of angled or irregular shaped rooms can also be applied to extended coverage
sprinklers, so the distance of an extended coverage sprinkler and a point in a floor area
is permitted to be 0.75 of the maximum allowable distance between sprinklers provided
that the perpendicular distance to the wall doesn't exceed half of the maximum
allowable distance between two sprinklers.
Maximum protection area per sprinkler and maximum spacing between sprinklers for
extended coverage sprinklers shall be as the following table.
Extended Coverage Sprinklers Spacing & Protection Area
Sprinklers in electrical rooms according to NFPA 13
Muhammad Mosad September 02, 2019 firefighting, NFPA 13
Sprinklers in Electrical Rooms
Sprinklers in electrical rooms according to NFPA 13
This article is not about high value equipment rooms like server rooms which shall be protected
by a system other than sprinkler systems, this is about basic electrical rooms like (switchboards,
panelboards, switchgear, or motor control centers) 1000 volts nominal or less.
Are sprinklers or sprinkler piping permitted to be installed in electrical rooms?
According to NFPA 13 – 2019 edition, Sprinklers and sprinkler piping is permitted in and is
permitted to pass through an electrical room as long as the piping is not within the “dedicated
electrical space”.
Sprinkler systems had been successfully installed in rooms containing electrical equipment for
100 years, with no documented instances of a problem, this measure was always controversial,
based on the following concerns for fire fighters:
1- Risk safety for responding firefighters in or near electrical rooms where sprinklers might be
discharging over live equipment.
2- Water would cause additional damage to the electrical equipment.
Considering above concerns, NFPA has permitted to omit sprinklers of electrical room in
specific cases which will be discussed later in this article.
What is dedicated electrical space?
According to NFPA 70 – 2017 edition, a dedicated electrical space is defined as the space equal
to the width and the depth of the equipment extending from the floor to a height of 1.8 m above
the equipment or the structural ceiling, whichever is lower.
Can we install sprinklers in the dedicated electrical space?
Systems or equipment foreign to the electrical installation such as (Plumbing, heating,
ventilation, and air conditioning piping, ducts, and equipment) are not allowed in dedicated
electrical space and must be installed outside this space. So, as long as the sprinkler piping does
not run through this space, it can go in and out of the electric room without any issue, while
busways, conduits, raceways, and cables are permitted to enter equipment through this zone.
Foreign systems installed directly above the dedicated space reserved for electrical equipment
are required to include protective equipment that ensures that occurrences such as leaks,
condensation, and even breaks do not damage the electrical equipment located below.
Can we install sprinkler piping above the dedicated electrical space?
Foreign systems are allowed in the area above the dedicated electrical space as long as the
electrical equipment is properly protected against leaks or breaks in the foreign system. So the
sprinkler piping can run above the dedicated electrical space 1.8 m above equipment as long as
the equipment below is protected from leaks.
Can we protect dedicated electrical space by sprinkler system?
Sprinkler protection is permitted for the dedicated space if complying with above mentioned
constraints.
Note that: Leak protection could include drip pans which may create an obstruction to sprinkler
system discharge. So, it is always best to avoid locating sprinklers and sprinkler piping directly
above electrical equipment, additionally, sprinklers and sprinkler piping are not permitted to be
located directly within the working space for the equipment as shown in the figures below.
Sprinklers in electrical rooms according to NFPA 13
Sprinklers in electrical rooms according to NFPA 13
To know how to determine the working space of electrical equipment, please visit the link
below:Working Space & Dedicated Electrical Space
When can we omit Sprinklers in electrical equipment rooms?
Where all of the following conditions are met, sprinklers shall not be required in electrical
rooms:
(1) The room is dedicated to electrical equipment only.
(2) Only dry-type or liquid-type with listed K-class fluid electrical equipment is used.
(3) Equipment is installed in a 2-hour fire-rated enclosure including protection for penetrations.
(4) Storage is not permitted in the room.
References of this article:
1- NFPA 13 - 2019 edition (Standard for the Installation of Sprinkler Systems).
2- NFPA 70 - 2017 edition (National Electric Code).
Anti-Vortex Plate According to NFPA 20 & 22
Muhammad Mosad June 04, 2019 NFPA 20, NFPA 22
Anti-Vortex Plate According to NFPA 20 & 22
Anti Vortex Plate According to NFPA 20 & 22
When to install "Anti-Vortex Plate"?:
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Where a tank is used as the suction source for a fire pump, the discharge outlet of the
tank shall be equipped with an assembly that controls vortex flow.
Purpose of using "Anti-Vortex Plate"?:
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Anti-Vortex plate is installed in the suction line of fire pumps to control the turbulence
in a flowing water, They are simple in design and very effectively controlling the
velocity of the fluid thus preventing cavitation to fire pumps and damage to impellers.
Dimensions of "Anti-Vortex Plate"?:
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The assembly shall consist of a horizontal steel plate that is at least twice the diameter of
the outlet on an elbow fitting.
Large, standard size anti-vortex plates [48 in. X 48 in. (1219 mm × 1219 mm)] are most
common and are desirable, as they are adequate for all sizes of fire protection pump
suction pipes normally used.
Installation dimensions:
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Mounted at the outlet a distance above the bottom of the tank equal to one-half the
diameter of the discharge pipe or 152mm whichever is greater.
Anti-Vortex Plate Inspection:
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Inspection of anti-vortex plate shall be after completion of the tank construction, and
before filling the tank with water.
The inspection shall verify that the horizontal steel plate and long radius elbow are
installed properly and meet the requirements of dimensions and installation height
mentioned above.
Below are illustration for installation of anti-vortex plate for various types of tanks
according to NFPA 22 (Standard for water tanks for private fire protection):
Anti-Vortex Plate
Anti-Vortex Plate
Anti-Vortex Plate
DISTANCE BELOW CEILING FOR STANDARD PENDANT & UPRIGHT
SPRINKLERS
Distance below ceiling for standard pendant & upright sprinklers
Distance below ceiling for standard pendant & upright sprinklers
For unobstructed construction:
The distance between sprinkler deflector and the ceiling shall be (1 in) minimum and (12 in)
maximum throughout the area of coverage of the sprinkler.
This requirements shall not apply for the followings:
1- For concealed, recessed, and flush types.
2- for light and ordinary hazard occupancies with ceilings of noncombustible or limitedcombustible construction where either (A) or (B) applies.
(A) Where a vertical change in ceiling elevation within the area of coverage of the sprinkler
creates a distance of more than 36 in. (900 mm) between the upper ceiling and the sprinkler
deflector, a vertical plane extending down from the ceiling at the change in elevation shall be
considered a wall for the purpose of sprinkler spacing as shown in Figure below.
Distance below ceiling for standard pendant & upright sprinklers
(B) Where the distance between the upper ceiling and the sprinkler deflector is less than or equal
to 36 in. (900 mm), the sprinklers shall be permitted to be spaced as though the ceiling was flat,
provided the obstruction rules are observed as shown in Figure below.
Distance below ceiling for standard pendant & upright sprinklers
Sprinkler distribution in Small rooms - NFPA 13
Sprinkler Distribution in Small Rooms According to NFPA 13
Sprinkler Distribution in Small Rooms According to NFPA 13
Definition of small room according to NFPA 13 - 2019 edition:
Small Room is defined according to NFPA 13 as a compartment of light hazard occupancy
classification having unobstructed construction and a floor area not exceeding 74 m2.
Unobstructed construction is defined according to NFPA 13 as a Construction where beams,
trusses, or other members do not impede heat flow or water distribution in a manner that
materially affects the ability of sprinklers to control or suppress a fire.
For more information about "Unobstructed Construction", please click here.
Light hazard occupancies are defined according to NFPA 13 as occupancies where fires with
low rate of heat release are expected as the quantity or combustibility of contents is low, below
are examples for light hazard occupancies:
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Office buildings
Museums
Restaurants seating areas
Hospitals
Educational buildings
Institutional building
Clubs
Church
Constraints for distribution of standard spray pendant & upright sprinklers in light hazard
occupancies:
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Maximum protection area per sprinkler for hydraulically calculated systems is 20m2, and
for pipe schedule method systems is 18m2
Maximum distance between sprinklers is 4.6m
Minimum distance between sprinklers is 1.8m
Maximum distance from sprinklers to walls is 2.3m
Minimum distance from sprinklers to walls is 100mm.
Constraints for distribution of standard spray pendant & upright sprinklers in small rooms:
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Sprinklers shall be permitted to be located not more than (2.7 m) from any single wall.
Other spacing limitation and maximum protection area of coverage per sprinkler
(mentioned above) shall not be exceeded.
Examples of sprinklers distribution in small rooms:
Sprinkler Distribution in Small Rooms According to NFPA 13
Sprinkler Distribution in Small Rooms According to NFPA 13
Sprinkler Distribution in Small Rooms According to NFPA 13