Water hammer occurs in water supply lines and biphase systems that carry water in both liquid and gas states. It can damage system components through overstressing and cracking over time as it subjects the pipe to repeated shocks. The three main types of shocks are hydraulic, thermal, and differential. Hydraulic shock occurs when water moving at high speed is suddenly stopped, like closing a faucet quickly. Thermal shock happens when steam condenses rapidly, creating vacuum pressures. Differential shock is caused by velocity differences between steam and condensate that form pressure waves down the pipe. All three can weaken pipes over time through these damaging pressure fluctuations until rupture occurs.

1. Water Hammer
©2005 Armstrong International, Inc.

2. Where Water Hammer Occurs
• In any water supply line, hot or cold
• Will be more pronounced in biphase*
systems
• Examples of biphase applications are heat
exchangers, tracer lines, steam mains,
condensate return lines, and pump discharge
lines
*Systems that carry water in two states, as a liquid and as a gas
“Expect many enjoyable experiences !” 2
David M. Armstrong

3. Damaging Effects of Water Hammer
Thermostatic Elements
Overstress Gauges
Crack Trap Bodies
Rupture Fittings
Collapse Floats
Over time repeated stress on the pipe will weaken
to the point of rupture
“Expect many enjoyable experiences !” 3
David M. Armstrong

4. Conditions causing water hammer
• Hydraulic Shock
• Thermal Shock
• Differential Shock
“Expect many enjoyable experiences !” 4
David M. Armstrong

5. Hydraulic Shock
Visualize what happens at home when a faucet is open
• 100 Pounds of Water
• Moving 10 feet per second
• Equaling 7 miles per hour
• Shut Suddenly…. Equaling
• 100 Pound Hammer Stopping
• “Bang” “Bang” “Bang”
• 600 psi Shock Wave
• Reflecting Back to Forth until
energy is dissipated
“Expect many enjoyable experiences !” 5
David M. Armstrong

6. Thermal Shock
This Kind of Shock is Temperature Related
• Flash Steam Bubbles become
Trapped in Pools of Condensate
• Flooded Main, Tracer Line, Heat
Exchanger Tubing or Pumped
Condensate Return
• Condensate will be below
saturation causing immediately
collapse
• 1 pound of steam equals 1,600
times volume of water
• Causing a vacuum in all
directions
“Expect many enjoyable experiences !” 6
David M. Armstrong

7. Differential Shock
Steam flowing over condensate can create waves
• Velocity of Steam is 10-100 times greater than the velocity of liquid
• Steam moving over the condensate will start manufacturing waves
• Waves will grow until they block the pipe completely forming a “Slug”
• Steam cannot flow through the sealed condensate wall, thus causing
positive to negative pressure zone from the back to front of the
“Slug”
• Stopping only when suddenly impacted by equipment, tee, elbow,
valve, or any bend in the piping
“Expect many enjoyable experiences !” 7
David M. Armstrong