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MODELING
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 ShockView
schematic
ShockView
plots A, B, C
Input data for
shock modeling
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7 ocillographic
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Necess.program
input data
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LDi Catalog Printable PDF28
Input Data for Shock Modeling
Please collect the following information to use in the selection of pipeline shock, surge, & hammer prevention equipment.
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Please first consider whether the addition of pressure vessels
to your piping system, can be avoided completely.
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A. Can the need for pump startup surge prevention be made unnecessary?
1.) To start a pump without a surge, start the pump slowly. If you specify a pressure that must not be exceeded Liquid Dynamics will quote for working out how slowly you must start your pumps, for you.
2.) Start as normal, but allow the flow to by-pass back to suction against a gradually increasing resistance of a slow closing valve in the bypass line. If you state the space available, and the pressure that must not be exceeded, - Liquid Dynamics will quote the by-pass system for you.
B. Can the need for valve closure shock prevention be made unnecessary?
1.) To close a valve without a shock, close the valve more slowly, when you specify a pressure that must not be exceeded, Liquid Dynamics will quote for working out how slowly you must close your valve, for you.
2.) Stop the flow going through the fast closing valve in the normal way, but first open another valve in a smaller line from a "T" immediately ahead of the fast closing valve, this line will be piped back to a point nearer to point of volume supply. State the space available and the pressure that must not be exceeded.
Liquid Dynamics will quote for determining the back-pass system dimensions for you.
C. Can the need for pump shutdown back-flow hammer prevention be made unnecessary?
1.) To stop a pump, without a back-flow hammer, slow the pump down gradually; or de-clutch the pump from its driver & allow the pump to spin down, while the inertia of the mass flowing away from the pump pulls liquid through the pump.
2.) If you can not decouple the pump drive, then provide a "suck-by" circuit, allowing the void that is sucked out behind the liquid that continues to travel away from the pump, to be filled by sucking past the pump. Liquid Dynamics will quote for establishing the dimensions of the "suck-by" circuit, for you.
**Additionally, Include pressure wave speed (acoustic velocity) m/s when available.
When neither 1 nor 2 of A, B, C, above, "preventive methods" are possible, we can provide a list of companies who can provide vessels suitable for the duties established by a ShockView model of the data that you provide to Ldi, as below.
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Both ASME vessel code and the EU Pressure Equipment Directive require your full disclosure of all use parameters.
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INFORMATION REQ.
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UNITS
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LIQUID Examples.
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Cust. Guestimates from past.
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Pls. mark:-
U=From Process Log.
V=Physical tables
W=Guestimation
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Liquid Density.
Specific Gravity
SG @ System Temp.
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Grams per milliliter
Grams per Cubic cm.
Kg/Liter or g/cm3
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Water
30% NaOH Solution
Ammonia NH3
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1.00
1.30
@ -30 C 0.68
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SG g/cm3
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Liquid Viscosity
@ System Temp.
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Centipoise, cP
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Water
w/ absorbed CO2 30% NaOH Solution
Ammonia NH3
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1.00
30.0
0.35
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Compressibility, reduction
in volume per unit change in pressure, @ system pressure & Temp.
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parts of a Liter
per Bar L/Bar
Liters/Kg cm2
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w/ absorbed air Water @ 10 Deg. C
Pentene & Pentane+HFacid Ammonia NH3
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50e-6
@ + 40 C 19.6e-5
11.389E-4
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A Dynamic (dt) equation must be resolved, accurate Time figure is essential
It has an exponential effect.
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Pump run up time or valve closure time or pump run down Sec.
("Instantaneous" shall mean 0.01 Sec. 10ms)
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1450 motor 6"x4" Centrif.
6" Air actuated butterfly
Diesel driven 24" x 20" Centrif.
Meter stop valve (depending on size)
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2.0 Sec.
1.0 Sec
5.0 Sec.
0.05 to 0.300 Sec.
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Bulk Modulus, Elasticity of pipe material
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Pacalles
Pa
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Steel
Concrete
Plastic PVC
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2e+11
4.2e+10
2.89e+9
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Pipe Wall thickness mm
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Millimeters (Dilation of pipe wall combined & liquid compressibility determines shock reduction & frequency) "effective softness"
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Pipe Internal Diameter Millimeters mm
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mm
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Force, Pressure at Pipe Inlet Bar or Kg/cm2
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Pipe Length Meters (Feet x 0.305)
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M
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Pressure that Shock must not exceed. Bar or Kg/cm2
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Theoretical mass flow
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Kilograms per second Kg/Sec.
US GPM x 3.8/60 x SG
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Kg/Sec
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Acceptable Materials of Construction
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Metals Plastics
Synthetic Rubbers
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Frequency of any current vibration Hertz, Hz.
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Vapor pressure at suction temperature for item C2 above.
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