10
2.5
The risks of not complying with the start-up and shut-down procedures
A liquid in motion in a pipe system represents a lot of energy, and it must be very carefully dealt with.
When the liquid flow is stopped it is imperative that this is done smoothly.
Note!
For this reason fast-closing valves should not be used unless the pipes of the system are very short.
Valves must be operated gradually. The longer the pipes and the higher the flow rate, the more important this
becomes.
Note!
WATER HAMMER is the name given to short-lasting pressure peaks, travelling along the pipe as a wave at the
speed of sound, and resulting from a sudden deceleration of the motion of the liquid in a closed system.
Thus, it is usually related to shutting down of a system. However, when starting up a system with open valves and
empty pipes, the fluid may encounter an obstacle, like a fine-mesh strainer, a flow meter or heat exchanger, causing
a sudden reduction of flow velocity – if not a complete halt – , and so we may have the condition of a Water
Hammer.
In the worst case, the pressure surge caused by such a sudden stop of the motion of a fluid can be several times the
normal pressure of the system.
Therefore it is very important for the protection of the whole installation that start-ups and shut-downs are carried
out with great care.
