7.4 Mechanical Fundamentals - 7.4 Mechanical Fundamentals Flashcards
Three types of Piping
High Pressure/Temp.
Low Temp.
Seawater/Potable Water
Piping identification (>3/8”)
Measured by Inside Diameter (ID)
Designated by wall thickness
Tubing identification (< 3/8”)
Measured by Outside Diameter (OD)
Designated by wall thickness
Pipe Marking
Spaced not more than 15 feet apart; if concealed, not more than 5 feet apart
Name of the system (standard DC abbreviation may be used)
Specific service
Direction of flow
Pipe Marking classifications
Pipe hangars and supports
Designed to support weight of the piping, fluid, and insulation
Three types:
Rigid (fixed)
Spring
Resilient
Rigid (fixed)
Supports provide restraint in at least one direction; generally used in cold piping systems
Spring
Supports are used where necessary to permit pipe movements due to thermal expansion, contraction, or movement of the ship
Pictures
Resilient
Used to prevent noise radiated from shipboard equipment from interfering with ship sonar, and to prevent the noise from being radiated into the water
Insulation and Lagging
Used to prevent heat transfer from piping that is hotter or cooler than surrounding atmosphere
Valves
Control the flow of the contained fluid
Direct the flow of the contained fluid
Include several different types and sizes depending on application and controlling factors of the specific system
Globe valve
Used in steam, air, oil, and water lines
Common globe valve types:
Straight flow
Angle flow
Cross flow
Needle valve
Used to make relatively fine
adjustments in the flow of fluid;
allow more precise control of
flow than can be obtained with
an ordinary globe valve
Gate Valve
Acts like opening or closing a gate to
allow/stop flow and used when a
straight line flow of fluid or a
minimum flow restriction are required
Common gate valve types:
Rising Stem
Non-rising Stem
Ball Valve
Used in seawater, sanitary, trim and drain, air, hydraulic, and oil transfer systems
Uses a ball inside the valve to start and stop the flow of fluid
Common ball valve types:
Quick acting valve
Planetary gear valve
Butterfly Valves
Light weight, relatively small, and quick acting. Used in low pressure, low temp systems
-Valve seats are replaceable:
Lapping, grinding, or machine work not required
-Provide positive shut off
-Used in low pressure, low temperature systems
Check Valves
Prevents the fluid in a system from flowing in the wrong direction
-Operated by the flow of fluid in the piping
-Common types of check valves:
Swing check
Lift check
Ball check
-Stop check valves are used on drain lines, on discharge side of many pumps
Relief Valves
Protect piping system from excessive pressure
Designed to open when the preset lift pressure is reached and close when the pressure drops slightly below the lifting pressure
Can be lifted by hand for testing purposes
Sentinel Valves
Small relief valves installed in some systems to warn of impending over-pressurization
Actions must be taken quickly by watch standers to secure the piece of equipment or system and prevent damage from the increased pressure
Pumps
Devices which utilize an external source of power to apply a force to a fluid and transfer it from one place to another
Subject to cavitation
Positive displacement
Pumps displace a specific quantity of fluid regardless of resistance to flow (head)
Constant flow (given constant speed regardless of pressure/flow resistance)
Require a relief valve
Viscous fluids (lube oil, hydraulic oil, etc)
Non-positive displacement
Pumps displace a variable output of fluid depending on the resistance to flow
Variable flow
Non-Viscous fluids (usually water)
Not necessarily self priming
Vent and recirculation requirements
Positive displacement movement
Reciprocating
-Diesel fuel injectors
-Emergency feed
-HPACs
Rotary
-Air
-Oil
Moving Vane
Variable stroke
-Steering
Non-positive displacement movement
Propeller
-Gas turbine axial flow compressor
-Circulating water
-Main circulating water (on steam ships)
Jet
-Eductors (firemain driven)
-Air ejectors (steam driven)
Centrifugal
-Water
-Firemain
-Chill Water
-Potable Water
-Sea Water
