The Humble Check Valve
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The Humble Check Valve

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The selection of check valves for puped systems

The selection of check valves for puped systems

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  • Geoff can be contacted at geoffrey.stone@yahoo.co.uk or 0402 35 2313
  • This book comes highly recommended for further study of check valve performance in a pumped system. The publisher is Wiley.
  • These graphs show typical losses for various types of check valves. Reference should be made to the valve manufacturers for more precise data however these data can be used for preliminary designs. This is often necessary as the valve supplier has not been selected when the design is underway.These graphs have been taken from Fluid Transients in Pipeline Systems By ARD Thorley published by Wiley
  • Waterhammer software is readily available from a number of sources. The more common products in Australia are Hytran, AFT’s Impulse, Bentley’s Hammer, Watham and Flowmaster.
  • Delft laboratories undertake dynamic testing of check valves. A search of their website will reveal a selection of technical research papers that provide insight into the dynamic performance of check valves.
  • This graph has been taken from Fluid Transients in Pipeline Systems By ARD Thorley published by Wiley. It illustrates the different values of maximum reverse velocity versus deceleration for common check valves. These values represent actual results of a valve of a particular size. To compare the systems and their check valves dimensionless characteristics are used.
  • This graph shows typical non dimensional maximum reverse velocity versus deceleration for various types of check valves. Reference should be made to the valve manufacturers for more precise data however these data can be used for preliminary designs. This is often necessary as the valve supplier has not been selected when the design is underway.The graphs illustrate the benefits of using the nozzle type check valves where the system exhibits high deceleration.This graph has been taken from Fluid Transients in Pipeline Systems By ARD Thorley published by Wiley
  • These graphs have been taken from Fluid Transients in Pipeline Systems By ARD Thorley published by Wiley. The graphs illustrate the transient response for the same system when different check valves are used. Each system is different and should be independently analysed for transient response.
  • Illustrations from Crane Energy Flow Solutions - High Performance Check Valves
  • Swing check valves come ina variety of forms to meet temperature and pressure conditions. This illustration is one used in the petro-chem industry
  • The valve illustrated here is commonly used in the water industry for transmission pipelines. It is a legacy design that is challenged these days by non slam varieties.
  • The valve illustrated here is commonly used in the water industry for transmission pipelines. It is a legacy design that is challenged these days by non slam varieties.
  • A low cost valve that is commonly used in all industries from nuclear through process to building services. It is manufactured by many companies. Some are better than others in providing technical information required for dynamic analysis.
  • These valves provide a solution for potential surge situations where the fluid contains solids such as in sewage and slurries. For corrosive situations the inserted probes and overrides are usually not specified. Also these valves are available with rubber or epoxy lining. They have found a market in the highly corrosive desalination pipe work market where sea water is highly corrosive..
  • This valve type of valve is manufactured by Mokveld, Noreva, Crane and Ventomat. The valve is the premium valve as far as check valves are concerned. It has the low head loss and very good quick closing characteristics.
  • The hydraulic check valve opens and closes at controlled, adjustable speeds to provide for smoothoperation and reduce pressure surges associated with conventional check valves.When the upstream (inlet) pressure is greater than the downstream (outlet)pressure, the valve moves to the open position at a controlled speed by exhaustingcontrol water from above the diaphragm to the downstream side through an adjustable needlevalve.When the upstream pressure becomes less than the downstream pressure, the valve closes toprevent reverse flow at a controlled speed by introducing control water above the diaphragmfrom the downstream side through a second needle valve.
  • The hydraulic check valve opens and closes at controlled, adjustable speeds to provide for smoothoperation and reduce pressure surges associated with conventional check valves.When the upstream (inlet) pressure is greater than the downstream (outlet)pressure, the valve moves to the open position at a controlled speed by exhaustingcontrol water from above the diaphragm to the downstream side through an adjustable needlevalve.When the upstream pressure becomes less than the downstream pressure, the valve closes toprevent reverse flow at a controlled speed by introducing control water above the diaphragmfrom the downstream side through a second needle valve.
  • A simple check valve used in the building services industry
  • A type of valve used primarily for solids bearing and tidal flow of low pressure corrosive fluids. Valves up to DN2000 are manufactured by red valve. The valves are manufactured by mainly by hand lay up techniques. Head losses is quite high. The valve needs to be orientated as shown in the vertical in order to close on rising head in free service applications. The valve will close around sticks and twigs.
  • This type of valve provides a loss cost unit suitable for large diameters. The design allows for construction in corrosion resistant materials.
  • Where would we be without these check valves? With modern materials there have been several attempts to introduce the design into industrial applications. The closest clone is the duckbill check valve.
  • Although mainly concerned with pumps ANSI/HI 9.8 standard can be used for pipe lengths design to avoid the effects of vortexing on check valve internals.

The Humble Check Valve The Humble Check Valve Presentation Transcript

  • THE HUMBLE CHECK VALVE
    Selection of Check Valves for Pumped Systems
    By Geoffrey D Stone C.Eng FIMechE; CP Eng FIEAust RPEQ
    Design Detail & Development
    http://waterhammer.hopout.com.au/                 Skype address geoffrey.stone@yahoo.co.uk
  • Why do we need check valves?
    To prevent reverse flow
    To stop a pipe or tank emptying when a pump stops
    To prevent pressure transients damaging the pump
    To prevent parallel pumps rotating in reverse
    To prevent contamination in complex networks or in the home
    To hold pressure in the line
    For positive displacement pump operation
    To provide waterhammer mitigation
    To prevent flooding
  • Avoiding Check Valve Slam
    “ Check valves are sometimes selected without proper thought to their response under transient flow conditions.”
    “In reality , check valve slam is caused by valves that are not matched to the system of which they are an integral part.”
    Fluid Transients in Pipeline Systems Prof. ARD Thorley
  • A Check Valve’s Selection and Performance
    Most check valves are selected based on industry practice & lowest cost
    A low level of engineering effort is made in selecting a check valve
    Unless a surge analysis is done little is known of the behaviour of a check valve in a pumped system
    A check valve can be as important as a safety relief valve if it mitigates surge
    Many manufacturers cannot provide technical data such as:-
    Head loss vs. flow
    Reverse velocity vs. deceleration
    Closing time
    Velocity to close
    Pressure to fully re-open after closure
  • Loss Coefficients for Different ValvesA common way of selecting a valve
  • Systems Most at Risk of Check Valve Slam
    Parallel pump systems
    A pump trip in a rising main protected by an air vessel
    Systems with an initial vertical lift followed by a long horizontal pipeline
    Networks with varying conditions
    High head systems
    Systems fitted with check valves with long travel distance and a high mass of component parts
    Systems that have not had a dynamic analysis. (Murphy’s Law)
    NB A resilient seated valve can make as much noise in check valve slam as a metal seated one!
  • Why avoid check valve slam?
    Reduce damage to seats, discs and springs
    Eliminate vibration in adjacent piping
    Reduce damage to pipe supports and trust blocks
    Eliminate noise
    Reduce fear amongst operators and asset owners
  • How should we select a check valve?
    Undertake system dynamic modelling to determine:
    Reverse velocity
    Fluid deceleration on pump stop
    Establish the acceptable head rise based upon the pipe rating, design code and/or thrust block design criteria.
    Determine the maximum allowable reverse velocity using the Joukowsky equation below
    H = c x ∆V
    g
    where c =celerity m/s; ∆V =change in velocity m/s & g = acceleration due to gravity m/s2
    Establish which valves have data available
  • Delft Laboratories Studies
    Studies at Delft Labs concluded that valve geometry affected the magnitude of pressure surges and reverse velocities.
    The conclusions were:-
    Reverse velocities and pressure surges are greater for valves with a larger mass of valve components.
    (2) Reverse velocities are greater for valves with larger strokes or travel of components to close.
    (3) Reverse velocities are less for valves that were spring assisted to close.
    These conclusions are justified because of the increased time necessary to accelerate and overcome the inertia of valve internals and the distance they must travel.
  • Compare Maximum Reverse Velocity & Deceleration for Different Valves
    Draw a line from the left of the graph of the computed maximum reverse velocity from the acceptable head rise
    Draw a line up from the computed deceleration
    Select any valve who’s plot falls below the intersection of these two lines.
    A reverse velocity of 0.15 to 0.3m/s will unlikely result in check valve slam
  • Using Dimensionless CriteriaThis is used when data is only available for one size of valve from the manufacturer and another is used in the design
    MRV = Dimensionless maximum reverse velocity
    Decln= Dimensionless deceleration
  • Dimensionless Criteria for Different Valves
  • Comparison Swing vs. Nozzle Check Valve
    Swing Check Valve
    Nozzle Check Valve
  • Types of Check Valves
    Swing
    Tilt
    Dual Plate
    Flexible Flap
    Nozzle (Disc)
    Nozzle (Ring)
    Diaphragm
    Hydraulic
    Ball
    Piston
    Lift
    Duckbill
    Wafer Plate
    Heart Type
  • Different Principles of Operation
    Swing Check
    Duo Check
  • Swing Check
    Economic
    Corrosion resistant materials or or coated for same
    The most common type
    Metal or Soft Seated
    Full Bodied or Wafer
    Gravity or Spring
    Hinged flap
    Extended Spindle for:-
    Counterweight
    Hydraulic dampener
    Limit switches
    Position indicator
  • Swing Check (Counterweight)
    Complicated swing check
    Fitted with Counterweight
    Fitted with pneumatic or hydraulic dampener
    High maintenance to remain effective
    High mass & inertia
    Long travel distance to close
    Counterweights increase head loss
    High cost
  • Tilt Type
    Common in the water industry
    Large Diameter
    Full bodied type
    Soft or metal seats
    Coated for corrosion resistance
    High mass
    Extended spindle for :-
    Counterweight
    Hydraulic dampener
    Limit switches
    Position indicator
  • Dual Plate
    Economic
    Wafer bodied
    Variety of spring stiffness's
    Corrosion resistant materials
  • Flexible Flap
    Economic
    Use in water, sewage & mining industries
    Coatings for corrosion resistance
    Full bodied type
  • Nozzle (Disc)
    Universal application for clean fluids
    Original design of non slam valve
    Low head loss
    Used for gas and liquids
  • Nozzle (Ring)
    Universal application for clean fluids
    Modern design for surge mitigation
    Low mass
    Short travel
    Tight shut off
    Low head loss
    Available in corrosion resistant materials
  • Diaphragm Type
    Solids bearing fluids
    Positive displacement pump operations
    Corrosion resistant materials
    Limited life
  • Hydraulic
    Economic
    Used in the water and aviation industry
    Combination valve with functions such as:-
    Flow control
    Altitude control
    Pressure Control
    Surge anticipation
  • Ball Type
    Economic
    Simple construction
    Balls easily damaged
  • Piston Type
    Use in steam and petro-chem service
  • Lift Type
    Simple
    Generally small bore
    Gravity or spring operation
    Used in steam or water systems
  • Duckbill Type
    Used for solids bearing fluids
    Large diameters
    Corrosion resistant materials
    In line or connected to end of pipe
    High head loss
    Closes against solids
  • Wafer Plate Type
    Economic
    Large diameter
    High head loss
    Low pressure applications
    Corrosion resistant materials
  • Heart Valve
    We all have them
    Considered the most important of check valves
    Artificial heart valves developed in Australia
    These check valves allow the positive displacement heart pump to function with pressure transients
    Maintains pressure in the system
  • Installation Criteria
    • Pipe Fittings
    • Two Elbows
    • Pumps
  • Instability at Pipe Fitttings
  • Instability Near Elbows
  • Instability at Pump Discharge
  • Questions
    Is data available from check valve suppliers?
    Yes & No, The more technically proficient have undertaken tests
    Can I assume that there will not be check valve slam?
    If the system is very similar to an existing system this is possible.
  • The End
    Thanks are extended to Prof ARD Thorley for his very informative book Fluid Transients in Pipeline Systems for the valuable graphs & insights in dynamic behaviour of check valves.
    Also I would like to thank those check valve suppliers who publish data on the internet or provide such to engineers.
    These include but are not limited to:-
    Noreva, Mokveld, Tyco, Crane, Red Valve, AVK, Apco, Valmatic, Cla-Val & Valmatic