THE HUMBLE CHECK VALVE Selection of Check Valves for Pumped Systems By Geoffrey D Stone C.Eng FIMechE; CP Eng FIEAust Design Detail & Development Geoff can be contacted at 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 This book comes highly recommended for further study of check valve performance in a pumped system. The publisher is Wiley.

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 Valves A common way of selecting a valve 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

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 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 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. 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.

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 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.

Using Dimensionless Criteria This 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 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

Comparison Swing vs. Nozzle Check Valve Swing Check Valve Nozzle Check Valve 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.

Types of Check Valves Swing Hydraulic Tilt Ball Dual Plate Piston Flexible Flap Lift Nozzle (Disc) Duckbill Nozzle (Ring) Wafer Plate Diaphragm Heart Type

Different Principles of Operation Swing Check Duo Check Illustrations from Crane Energy Flow Solutions - High Performance Check Valves

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 valves come ina variety of forms to meet temperature and pressure conditions. This illustration is one used in the petro-chem industry

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 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.

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 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.

Dual Plate Economic Wafer bodied Variety of spring stiffness's Corrosion resistant materials 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.

Flexible Flap Economic Use in water, sewage & mining industries Coatings for corrosion resistance Full bodied type 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..

Nozzle (Disc) Universal application for clean fluids Original design of non slam valve Low head loss Used for gas and liquids 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.

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 The hydraulic check valve opens and closes at controlled, adjustable speeds to provide for smooth operation 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 exhausting control water from above the diaphragm to the downstream side through an adjustable needle valve. When the upstream pressure becomes less than the downstream pressure, the valve closes to prevent reverse flow at a controlled speed by introducing control water above the diaphragm from the downstream side through a second needle valve.

Ball Type Economic Simple construction Balls easily damaged The hydraulic check valve opens and closes at controlled, adjustable speeds to provide for smooth operation 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 exhausting control water from above the diaphragm to the downstream side through an adjustable needle valve. When the upstream pressure becomes less than the downstream pressure, the valve closes to prevent reverse flow at a controlled speed by introducing control water above the diaphragm from the downstream side through a second needle valve.

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 A simple check valve used in the building services industry

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 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.

Wafer Plate Type Economic Large diameter High head loss Low pressure applications Corrosion resistant materials This type of valve provides a loss cost unit suitable for large diameters. The design allows for construction in 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 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.

Installation Criteria Pipe Fittings Two Elbows Pumps

Instability at Pipe Fitttings 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.

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