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MODELING
Pub 4 Main Menu


ShockView schematic

ShockView plots A, B, C

Input data for shock modeling

PulseView models relations

7 ocillographic plots

Necess. program input data

Equations& sources

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PLOTS
A. Potential Danger, B. Pressure drop,
C. Lack of dissipation


Generally, it is far less expensive to determine the peak pressure level and the frequency for the system piping, by running the system in a software model compiled in LDi ShockView for you, than to drill & tap holes for transducers, add an oscillograph, and/or data capture the problem.

ShockView

NOTE: Money is only saved by "modeling" when the input data is correct. Otherwise "garbage in - garbage out".
Some important facts that maybe overlooked are:

The elasticity of the pipe wall and the compressibility of the liquid govern the height of the pressure spike and the time taken for the wave to travel and return. Therefore these two figures - "elastic modulus of the pipe and the bulk modulus of the liquid" - are vital figures.
For a soft garden hose the speed of the wave will be down at about Mach 1, 700 mph, or for a very strong heavy wall iron pipe and the most incompressible liquid at low temperature, at 3250 mph.
Hot highly volatile hydrocarbons may have a bulk modulus of 300e - 5. Refrigerants and Ammonia can be even more compressible. Generally speaking the chemical engineer will be able to supply the right figure to you because he has it for calculating mass transfer and reactions.
The effective modulus controls the wave speed, which controls the frequency of reverberation.
Time: The time taken for a valve to close, or pump to start-up is ultra important; see the "Verification" plot.
Smaller pipes, higher flow velocity gives more dissipation so that the shock is reduced before it rebounds.
Accuracy of ShockView depends on data accuracy - p. 28



ShockViewExample LDi shock analysis software output plots A, B, & C show:
A.
In the time between i - ii and iii, which is 3.5 seconds for this long pipe, the pressure wave dissipation by rotary flow against the pipe wall, is only 2.5 psi. This warns of potential danger that this system could easily become an amplifier. The pipe is oversized for the flow rate.

B. A 2 second pump start up at 19 Bar (275 psi) 150# system makes +/- 39 psi shock at 2.43 Hertz. We also see first point "i" at 15.9 Bar. This means that the total pressure drop for the system is 3.1 Bar, or 45 psi.

C. The time chosen to run this model was a total of 21 seconds. At the end of this time, the peak has only degenerated down to 21 Bar (305 psi). The shock wave has traveled the length of the pipe and back 44 times (at 2.1 Hz.) and is resonating.

ShockView

ShockView Accuracy
13 psi in 39 feet of 1/2" pipe, 1/10th second valve closure, generates 180 psi shock. 1/2 second closure produces 24 psi shock.
LegendAccuracy

Other tests were performed on 3 diameters of 2 pipe materials in 10 lengths & 3 closure times.


Pressure at valve Valve closure time in seconds
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Liquid Dynamics International provides pipeline and pump user problem analysis, diagnostics, prediction by software, pulsation analysis, piping system analysis, and piping system simulation. For water hammer and shock solutions pulsation dampening and shock alleviating devices can be obtained from our associate websites.

PulseGuard Inc., and Ltd. for further information about pulsation dampeners / pulsation dampers.
PulseGuard. USA: Pulsation Dampeners | Pulsation-Dampeners.com: Pulsation Dampeners
PulseGuard Limited: Pulsation Dampers | PulseGuard für Deutschland: Pulsationsdämpfer

Large pressure vessels, jumbo bladders, float separator / big bellows type pipeline surge attenuators and
expansion / contraction volume compensators, surge alleviators, and shock alleviators.

Shock-Guard. USA: Surge Alleviators | Water-Hammer.com: Water Hammer
ShockGuard.co.uk: Shock Alleviators | Suction-Stabilizers: Suction Stabilizers

Information about energy saving in pumping systems, standby emergency power, safety shutdown systems,
hydraulic accumulators, and hydropneumatic accumulators.

Accumulators-Hyd: Hydraulic Accumulators
Accumulators.co.uk: Hydropneumatic Accumulators | HydroTrole: Hydraulic and Control Engineering

Protection against excess flow. Protect against toxic spills when pipes burst, guard against gushers and fluid
loss when hoses split. Flow-Guard against excess flow floods with flow fuses and breather bags.

FlowGuard: Flow-Guard - Flow Fuses and Breather Bags




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