Video 7 C1: What is water hammer? Flashcards
NOT ON QUIZ 1
what does it mean when a liquid is incompressible?
it means no matter how much pressure you apply, their volume doesn’t change. (therefore, not “springy”)
what is water hammer also known as?
water transience
why can’t water “soften the blow” when valve is shut off?
b/c the water is incompressible. it isn’t springy
instead of being absorbed, that sudden change in momentum creates….
a spike in pressure that travels as a shockwave through the pipe
why is it called “water hammer”?
because, when you shut off the valve, you can sometimes hear the shockwave (change in momentum) banging in your walls, sounding like a hammer hitting the walls.
what does Grady compare the flow of water in a valve to (when valve is shut off)? (object)
trains
how can you reduce the effect of water hammer? (3 ways)
- reducing the velocity/speed of the fluid that’s moving through the pipe
- increasing the time over which the change in momentum occurs
- decrease the speed of sound through the fluid (wave celerity)
how can you reduce the velocity of the fluid that’s moving through the pipe? (V = Q/A)
increase the diameter or decrease the flow rate (Q)!
-> recall:
V is a function of Q/A:
- If you have a bigger D value, the denominator increases and reduces the fraction.
- If you have a smaller Q value, the nominator reduces along with the fraction
how can you increase the time at which the momentum change occurs? (2 ways)
- add in flywheels to pumps, so they spin down more slowly instead of stopping suddenly
- slowly close the valve
what is wave celerity?
how quickly a wave can propagate through the pipe
(how fast pressure changes travel through the fluid in the pipe)
how can you decrease wave celerity? (2 ways)
add flexibility to the pipe by: - increase elasticity: ability to move a little like moving it above ground or the material
- adding an anti-surge device (has an air-bladder that absorbs some of the shock)
what do water distribution systems for urban areas use with surge control?
water towers
how do water towers aid in surge control?
the free surface in the water tower moves up and down, absorbing sudden changes in pressure
how does water hammer cause damage?
Water hammer is like slamming a heavy object into the pipe walls. When fast-moving water suddenly stops, its momentum creates a huge pressure surge. This pressure can crack pipes, loosen fittings, or even cause bursts.
