- (a) Describe, with the aid of a sketch, how a pressurised system sprinkler head is constructed.(5)
(b) Explain the operation of the sprinkler head and bulb assembly described in part (a), stating how the alarm is initiated.(5)
Contruction of a sprinkler head
let’s break down the construction of a typical sprinkler head, a critical component of fire protection systems on ships and in buildings.
Main Components:
- Frame:
- This is the body of the sprinkler head, typically made of brass or other corrosion-resistant metal. It provides structural support and houses the other internal components. 1. Fire Sprinkler Heads: Types, Parts & Differences [Guide] | RCI www.rcifire.com
- It also connects to the sprinkler piping system via a threaded or soldered joint.
- Deflector:
- This is the flower-shaped or dome-shaped component located just below the orifice (opening) of the sprinkler head. 1. Definition: Fire Sprinkler Head | Firewize firewize.com.au
- Its function is to distribute the water spray in a specific pattern, ensuring even coverage of the protected area. 1. Types of Sprinklers | NFPA www.nfpa.org
- Heat-Sensitive Element:
- This is the crucial component that triggers the sprinkler head in response to a fire. There are two main types:
- Fusible Link: A metal link that melts at a predetermined temperature, usually around 68°C (155°F). When the link melts, it releases the plug, allowing water to flow. 1. Did you know? Sprinkler Head Operation & Types www.firesecurity.co.uk
- Glass Bulb: A small glass bulb filled with a heat-sensitive liquid or a pressurized gas. The liquid expands or the gas pressure increases with rising temperature, causing the bulb to shatter at a specific temperature, typically between 57°C and 182°C (135°F and 360°F) depending on the hazard classification of the area. 1. What are the Differences Between Fusible Link vs Glass Bulb Sprinkler Heads? – Kinetix Fire kinetixfire.com2. How does a automatic fire sprinkler head work? – Firewize firewize.com.au
- Plug:
- This is a disc or cap that seals the orifice of the sprinkler head, preventing water flow until the heat-sensitive element is activated.
- Once the fusible link melts or the glass bulb shatters, the plug is released, allowing water to flow. 1. Sprinkler head – Designing Buildings Wiki www.designingbuildings.co.uk
- Orifice (Opening):
- This is the opening through which water is discharged once the sprinkler head is activated.
- The size of the orifice determines the flow rate and spray pattern of the water.
- Cap and/or Escutcheon:
- The cap or escutcheon is the decorative or protective cover that surrounds the sprinkler head. 1. What are Escutcheons and Are They Required for Fire Sprinklers? blog.koorsen.com
- It may also serve to deflect or direct the water spray pattern. 1. Sprinkler head – Designing Buildings Wiki www.designingbuildings.co.uk
Construction Process:
- The frame is manufactured using casting or machining processes, creating the body and internal structure to house the other components. 1. Fire Sprinkler Head Types: Pendents, Uprights, Sidewalls & Concealed – Blog | QRFS.com blog.qrfs.com
- The deflector is typically stamped or molded from metal and attached to the frame.
- The heat-sensitive element (fusible link or glass bulb) is assembled and installed within the frame.
- The plug is fitted into the orifice, sealing it securely.
- The cap or escutcheon is attached to the frame, completing the assembly. 1. Fire Sprinkler Heads: Types, Parts & Differences [Guide] | RCI www.rcifire.com
Types of Sprinkler Heads:
- Pendent Sprinkler: Hangs down from the ceiling and sprays water downwards.
- Upright Sprinkler: Points upwards and sprays water upwards towards the ceiling. 1. Types of Sprinklers | NFPA www.nfpa.org
- Sidewall Sprinkler: Mounted on a wall and sprays water horizontally. 1. Types of Sprinklers | NFPA www.nfpa.org
- Concealed Sprinkler: Hidden behind a decorative cover that releases upon activation.
Remember: The construction of sprinkler heads is strictly regulated to ensure their reliability and performance in fire emergencies. Different types and designs are available to suit various applications and hazard classifications.
Operation of the sprinkler head and bulb assembly
let’s break down the operation of a sprinkler head and bulb assembly, a common type of heat-sensitive trigger mechanism in fire sprinkler systems.
Key Components:
- Sprinkler Head Frame: This is the main body of the sprinkler, typically made of brass or other corrosion-resistant metal. It houses the other components and connects to the sprinkler piping. 1. Fire Sprinkler Heads: Types, Parts & Differences [Guide] | RCI www.rcifire.com
- Orifice: This is the opening in the sprinkler head through which water is discharged when activated.
- Plug: A small metal cap that seals the orifice, preventing water flow. 1. What are the Different Types of Fire Sprinkler Heads? – Blog – Koorsen Fire & Security blog.koorsen.com
- Glass Bulb: A small, sealed glass bulb filled with a heat-sensitive liquid (often a glycerin-based solution) or a pressurized gas. 1. FAQs on Fire Sprinkler Heads www.radfiresprinklers.com
- Deflector: This is the part below the orifice that shapes the water spray pattern for effective fire suppression. 1. Fire Sprinkler Heads: Types, Parts & Differences [Guide] | RCI www.rcifire.com
Normal Operation (No Fire):
- The plug is held tightly in place against the orifice by the intact glass bulb.
- Water pressure within the sprinkler piping is maintained, but no water flows as the orifice is sealed.
Operation During a Fire:
- Heat Detection:
- When a fire occurs, the air temperature in the vicinity of the sprinkler head rises rapidly. 1. How Fire Sprinklers Work: Thermal Sensitivity – Blog | QRFS.com blog.qrfs.com
- The heat is conducted to the glass bulb.
- Bulb Bursting:
- As the temperature rises, the liquid inside the glass bulb expands or the gas pressure increases. 1. What are the Different Types of Fire Sprinkler Heads? – Blog – Koorsen Fire & Security blog.koorsen.com
- When the temperature reaches the bulb’s design activation point (typically between 57°C and 182°C / 135°F and 360°F depending on the hazard classification), the pressure overcomes the bulb’s structural strength, causing it to shatter.
- Plug Release and Water Discharge:
- With the bulb broken, the plug is no longer held in place.
- Water pressure in the piping forces the plug out of the orifice.
- Water flows out of the sprinkler head, hitting the deflector and creating a controlled spray pattern to extinguish or control the fire. 1. How Fire Sprinklers Work: Thermal Sensitivity – Blog | QRFS.com blog.qrfs.com
Important Considerations:
- Each sprinkler head operates independently, only activating when the temperature in its immediate vicinity reaches its specific activation point. 1. What Causes a Fire Sprinkler to Activate? – Blog | QRFS.com blog.qrfs.com
- The glass bulb is color-coded to indicate its temperature rating, allowing for easy identification and proper placement in different hazard areas. 1. What do Fire Sprinkler Colors Mean? nfsa.org
- Sprinkler heads are designed to be tamper-proof, ensuring they remain functional until activated by a genuine fire.
In essence, the sprinkler head and bulb assembly act as a localized heat detector and automatic valve, releasing water only when needed to suppress a fire, thus minimizing water damage and providing efficient fire protection.