System Hydraulics and Valve Engineering

Copyright© 2008 Val-Matic Valve & Mfg. Corp1

System HydraulicsSystem Hydraulicsandand

Valve EngineeringValve Engineering

Copyright© 2008 Val-Matic Valve & Mfg. Corp 2

• Valve Definitions• System Hydraulics• Valve Flow Characteristics• Valve Construction• Valve Applications

OutlineOutline


A Valve is a mechanical device used to control flow or pressure in fluid systems.

A Valve consists of a closure member (plug or disc) that is positioned inside of the valve body and can be operated manually or with an actuator.

Valve DefinitionsValve Definitions


• On-Off• Flow Control• Pressure Control • Non-Return• Pressure Relief• Directional

Super Backflow Prevention Assembly

Valve TypesValve Types


FluidsFluids

• Liquid• Gas• Slurry• Solids


A uniformly distributed force which is exerted in all directions.

Pressure is measured in pounds per square inch (psig or psia).

Head is feet of water column (ft).

Differential Pressure is upstream pressure minus downstream pressure Delta P (psid). Also known as headloss.

PressurePressure


A moving volume of fluid at a velocity

Gas Flow: Compressible, SCFM

Liquid Flow: Incompressible, GPM

SCFM = Std (0 psig, 60ºF) cubic feet per minute

GPM = Gallons per minute

FPS = Feet per second

FPS = GPM x .4085 / D2

FlowFlow


Flow

Pressure

Pump CurvesPump Curves


A sudden change in pressure due to velocity changes. About 50 psi for every 1 fps change in velocity. The “hammer” is the pipe stretching and rebounding rapidly.

H = a v / g where:

H = pressure rise, ft a = wave velocity, ft/sec v = velocity change, ft/sec g = gravity, 32.2 ft/sec2

Surge (Water Hammer)Surge (Water Hammer)


The interval of time for a surge wave to travel the length of the system and return.

T = 2 L / a

where: T = critical time, sec L = length of pipe, ft. a = wave velocity, ft/sec

Critical TimeCritical Time


Any change in flow velocity Any change in flow velocity that occurs within the Critical that occurs within the Critical Time has the same effect as if Time has the same effect as if the change occurred the change occurred instantaneously!instantaneously!

Critical TimeCritical Time


• Air Valves can prevent air-related surges.• Vacuum Breakers can be used to create

cushions of air at pipeline high points.• Check Valves must close very fast or very

slow.• Fill pipelines slowly (i.e. 1 ft/sec).• Long pipelines need surge equipment or

control valves operating slowly with the pump.

Surge ControlSurge Control


OUCH!OUCH!

Surge ControlSurge Control


The difference between up and downstream pressures due to flow.

Q = Cv (ΔP )½

ΔP = (Q / Cv )2

where: ΔP= pressure drop, psi Cv = flow coefficient Q = flow rate, gpm

Pressure DropPressure Drop


Various TDCV Cv’s:

6” 1160

12” 5400

24” 25,500

48” 119,000

NOTE: A 6” Valve can handle 1600 GPM

TDCV

Pressure DropPressure Drop


Pressure drop expressed in feet of water column.

ΔH = K v2 / 2 gwhere:

ΔH = headloss, ft. of water column

K = flow coefficient v = flow velocity, ft/sec g = gravity, 32.2 ft/sec2

HeadlossHeadloss


Various K Values:90 Degree Elbow: 0.4Butterfly Valve: 0.4Tilted-Disc Check Valve: 0.5Plug Valve: 0.8Swing Flex Check Valve: 0.9Silent Check Valve: 3.01000 feet of pipe: 15.0

Silent Check Valve

HeadlossHeadloss


Competitor’s BFV 150B Flow Coefficients, K.

Size Val-Matic Pratt DeZurik

12” .43 .45 .56

24” .40 .30 .56

48” .36 .22 .40

72” .34 .23 .38

HeadlossHeadloss


Head Loss costs money in additional pumping costs:

GPM x ΔH x Sg x C/Kwh x 1.65

EC/Y = PE x ME

Where:EC/Y = energy cost per year, $/yearSg = specific gravity, water = 1.0C/Kwh = cost of electricity, $/Kw-hrPE = pump efficiency, (.85 typical)ME = motor efficiency, (.85 typical)

Energy CostsEnergy Costs


A 12” TDCV is used to replace a 12” control valve. The TDCV has a headloss of 0.7 ft. and the control valve, 2.9 ft. Based on an energy cost of $.08 per Kw-hr, what is the cost savings by using a TDCV for (6) 3200 gpm pumps operating 50% of the time?

3200 x (2.9-0.7) x 1 x .08 x 1.65

EC/Y = .85 x .85 = $1286

For (6) valves at 50% operation for 40 years:

Total cost savings = $1286 x 6 x .50 x 40 = $154,320

Energy ExampleEnergy Example


0

20

40

60

80

100

Quick-Open

Linear

EqualPercentage

CLOSED OPEN

Inherent Flow CharacteristicsInherent Flow Characteristics


% Cv

% Open

Inherent Flow CharacteristicsInherent Flow Characteristics


0

20

40

60

80

100

5000 ft.

500 ft.

12”Butterfly

CLOSED OPEN

Installed Flow CharacteristicsInstalled Flow Characteristics


0

20

40

60

80

100

12” BFV, 500 ft.

8” BFV, 500 ft.

CLOSED OPEN

Installed Flow CharacteristicsInstalled Flow Characteristics


0

20

40

60

80

100

Worm Gear

Traveling Nut

CLOSED

OPEN

VALVE

POSITION

ACTUATOR STROKE

Actuator Operating StatisticsActuator Operating Statistics


• Cavitation is the vaporization and subsequent violent condensation of a liquid due to localized low pressure areas in a piping system.

• Cavitation sounds like rocks flowing through the valve.

• Continuous Cavitation will shorten the life of the valve and piping system.

CavitationCavitation


A Cavitation Index can be calculated to predict whether cavitation will occur as follows:

σ = (Pu – Pv) / (Pu – Pd)where:

σ = cavitation index, dimensionless Pd= downstream pressure, psig Pv= vapor pressure (-14.2 psig at

60ºF) Pu = upstream pressure, psig

The lower the index, more likely Cavitation



For Example, an 8” plug valve is used in a backwash system to limit flow rate with an upstream pressure of 11 psig and a downstream pressure of 5 psig and a throttled position of 22 degrees open.

σ = (Pu – Pv) / (Pu – Pd)

σ = (11 – (-14.2)) / (11 – 5)

σ = 4.2



Valve Constant Cavitation Data

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Valve Opening, Degrees Open

Ca

vit

ati

on

Co

eff

icie

nt

BUTTERFLY VALVE

PLUG VALVE

Cavitation

Free

Zone

Cavitation



Pressure Class does not a Pressure Rating Make!AWWA Class 150A: 150

psig, 8 fpsAWWA Class 250B: 250 psig, 16 fps

ANSI Class 125 Gray Iron: 150 psigANSI Class 250 Gray Iron: 300 psig

ANSI Class 150 Ductile Iron: 250 psigANSI Class 300 Ductile Iron: 640 psig

ANSI Class 150 Steel: 285 psigANSI Class 300 Steel: 740 psig

Pressure ClassesPressure Classes


• Flanged: ANSI, ISO, DIN, AS, BS• Mechanical Joint: AWWA C111• Push-On (i.e. Tyton)• Threaded: NPT, BSPT• Grooved, Shouldered, Victaulic

Valve End TypesValve End Types


Ductile Iron ASTM A536 Grade 65-45-12

American Society of Testing and Materials (ASTM)Tensile Strength: 65,000 psiYield Strength: 45,000 psiElongation: 12% (Ductile)Hardness: 170 BHNShrinkage: 1/16” per footChemistry: Iron, Silicon, Carbon, Sulfur, Magnesium

Material PropertiesMaterial Properties


Ductile IronGray Iron

Material PropertiesMaterial Properties


Gray Iron: ASTM A126 Class BDuctile Iron: ASTM A536 Gr. 65-45-12Cast Steel: ASTM A216 Gr. WCBCast SS: ASTM A351 Gr. CF8M (316

SS)

Body and Disc MaterialsBody and Disc Materials


• Cast SS: ASTM A216 Gr. CF8M (316 SS)• SS Bar: ASTM A276, Type 316• 17-4 Bar: ASTM A564, Gr. 630, Cd

H1150• Bronze: ASTM B584 C83600 (85-5-

5-5)• Alum. Brz: ASTM B271 C95400

Trim MaterialsTrim Materials


• Buna-N (NBR, Nitrile, Hycar) 200ºF• Viton (FKM, Fluorocarbon) 400ºF• Natural Rub (NR, Poly-Isoprene) 200ºF• Neoprene (CR, Chloroprene) 250ºF• EPDM (Ethylene Propylene) 250ºF• Hypalon (Chlorosulfonated PE) 250ºF

Temperature, Durometer, Compatibility

Seal MaterialsSeal Materials


Seal MaterialsSeal Materials


• Water should be in the 6.5-10 PH range

• Chlorine content should be less than 2 ppm

• Brackish or salt water is corrosive to irons

• All SS or DI/FBE for salt and mine water

CorrosionCorrosion


• Corrosion Inhibitor (Fernox), 0 mils• Universal metal primer, 3 mils• Black Asphaltic, 3 mils• Polyamide 2-part epoxy, 6 mils• Fusion Bonded Epoxy (FBE), 10 mils• Linings of Natural Rubber or Teflon,

1/8”

Coatings and LiningsCoatings and Linings


1. Upstream disturbances affect valve performance.

2. Pressures and flows must be within ratings.

3. Unusual fluids can cause corrosion or safety issues.

4. Pressure direction affects actuator sizing and performance.

5. Vertical flow changes the operation of check valves.

6. DDCV Series 8900 is the only check valve for air service.

7. Air valves freeze.

8. Discs and stems can interfere with the adjacent valves.

Installation MattersInstallation Matters


ASTM: Properties of MaterialsAWWA: Water Industry RequirementsUL / FM: Fire Protection RequirementsISO: Metric Flanges and ValvesANSI/NSF 61: Drinking Water MaterialsSSPC: Painting Council Sand BlastingMSS: Valve, Fittings, and ActuatorsMIL: Military Specifications

Industry StandardsIndustry Standards

System Hydraulics and Valve Engineering

Documents

Transcript of System Hydraulics and Valve Engineering