Q. Who has used the CRV®?” and “We do not want to be the first to use it."

A list of customers and applications can be seen on our partial customer list & case studies.

The CRV® and LAD® flow conditioners are over 20 years old and we have two patents on it in the United States, one in Australia, one in Europe, and one in Japan. We have sold over 3,000 CRV®s in sizes 2 inch to 72 inches (there is no limit to how small or large a CRV® can be made) in diameter, to the leading chemical, refining, and power companies of the world. 

Q. "What if one of those vanes in the CRV® comes loose? It could tear up a very expensive pump (or other downstream equipment)."

In all of our applications (of which 75% are with pumps) we have never had a vane come loose.  This is because of the vanes design. For the 2 inch through 12 inch diameter CRV®s the vane sets consist of three separate plates that are notched in the middle, fitted together, and then welded at their six intersections in the middle of the vane set. The vane sets are then welded (full penetration welds) on both sides of each vane to the inside of the CRV®s pipe body. It would be virtually impossible for a complete vane to come loose, and even if a whole vane did come loose, it couldn't geometrically make the 90 degree turn through the elbow. For the sizes larger than 12 inch in diameter we can make the CRV® vane sets as three individual plates or as six individual vanes. If the customer had a force in their piping system high enough to shear off half a vane (breaking four welds), then they would have greater problems in their piping system to worry about then a CRV® vane breaking loose. 



Q. What in-house capabilities does Cheng Fluid Systems have?

-Computational capabilities include:

-Static and dynamic structural including finite element analysis

- Fluid flow dynamic analysis

-Thermodynamics

-Combustion cycle analysis

-Heat transfer and system heat balance

-Economic modeling and financial analysis

-Professional Expertise based on over 30 years in the field.



Q. What sizes are available for the CRV® and LAD® Design?

Cheng fluid Systems has supplied 2” through 72” – but has designs up to any size. There is no size limitation for the CRV®s. We have quoted CRV®s up to 96 inches in diameter and as little as 3/4 inches in diameter. We regard the CRV® as a pressure containing part, we use certified materials for the CRV®s body, and all of the full penetration welds used in the construction of the CRV®s (6 inch diameter and above) are dye penetrant checked.  The CRV®s bodies are almost always made from seamless pipe.  The CRV®s are manufactured for us by outside vendors. The CRV®s vanes are cold formed using our vane bending molds and manufacturing techniques. The vane sets are welded together using ASME welding guidelines and procedures. The vane sets are welded into the CRV®s body following Cheng Fluid Systems recommended fabrication procedures.  

The LAD® follows the same criteria as the CRV®. The LAD® can be made in any size. The smallest LAD® we've made was for a 3 inch by 10 inch diameter expansion, and the largest we’ve made was for a 28 inch by 16 foot diameter expansion.  There is no set design for a LAD® and each LAD® is designed for its specific geometric application. Therefore the number of cones, length of cones, positioning of the cones, etc. will change for every LAD® application.

Q. What materials can the CRV® and LAD® be made of?

The CRV®s and LAD®s can be made from any material that the pipe or pressure vessel is made from.  This makes the welding of the CRV®s and LAD®s into the piping system or vessel easier. The CRV® Spool piece is made of the same material as used in the customer’s pipe. Vanes are usually 304SS, but can be made from standard material carbon steel – or any can be fabricated from any other commercial material.

Q. How many vanes are there?

Six vanes. For special applications multi-vane CRV®s may be designed.

Q. What is the length of a CRV®?

The length is normally the same as the diameter. Shortened CRV®s are offered if there are space constraints. The CRV®s length is also its weld end to weld end length.  Thus a 4 inch diameter weld end Cheng Rotation Vane (CRV®) is 4 inches long; a 12 inch diameter CRV® is 12 inches long; a 24 inch diameter CRV® is 24 inches long; etc.  The CRV®’s vanes are three quarters of the CRV®s length.  Depending on the type of flanges used, the flanged CRV®s will usually be longer in length then the weld end CRV®s.  CRV®s designed for specific applications can have more or less than six vanes and in these cases the CRV®’s body lengths will change.

Q. How is the CRV® manufactured and assembled?

A pattern is machined and the vanes formed to the pattern – the vanes are then welded at the center. The vane assembly is then inserted into the pipe stub and welded to the pipe wall.

Q. Are the commercial CRV® units made for any specific elbow, or will they work with fabricated mitered elbows?

The proper geometry of a CRV® is dependent on the geometry of the elbow.  They will work for mitered elbows if properly designed provided there are enough divisions to the miter to approximate an elbow.

Q. How does a CRV® reduce or eliminate noise in a piping system?

The noise is generated in many cases by turbulence, such as large scale vortices shed along the boundary between separated flow and high speed core flow in elbows. The CRV® eliminates the turbulence.

Q. Will one CRV® design work equally well when flow velocity is increased (or reduced)?

Yes, except possibly in extreme cases, a change in flow rate velocity will not affect the CRV® effectiveness because the rotational velocity increases directly with an increase in flow velocity, so its effect is independent of velocity.

Q. What is the delivery time?

We quote 2-4 weeks A.R.O, but can offer expedited services.

Q. How many CRV®s have been sold?

Over 3,000 installations have been done.

Q. What is the life expectancy for a CRV®?

The life expectancy depends on details of the situation and is hard to predict, they can last for decades. Most of Our first installations are still in use after 20 years. We can also harden the CRV® if necessary to extend life further in abrasive situations.

Q. What are the benefits I will get when I install a CRV® upstream of an elbow? How much reduction in elbow pressure drop will I see?

Dependent on the local piping system design.

For elbows upstream of system components such as pumps, flow meters, or check valves, the main benefits come as a result of the uniform velocity profile and low level of turbulence of the flow downstream of the elbow. This means that:

-Pump performance is closer to design/test operating curve (discharge pressure vs. flow rate) and vibration is reduced, life is extended.

-Flow meters will give a more accurate measure of flow rate.

-Check valve oscillation and wear is reduced.

Reduction in elbow pressure drop is low, often even cancels elbow induced pressure drop, but velocity and other variable dependent. So far it is very rarely a problem and has been difficult to measure in laboratory test apparatus. For either air or water flow tests, using a given pumping capability, the problem in flow measurement is that when the CRV® is added and elbow pressure drop reduced, the flow rate increases until the pipe friction ∆p increases by the amount that the elbow ∆p decreases., This does result in an increase in flow rate. The problem is that the ∆p reduction cannot be measured as an isolated quantity. This is complicated by the fact that the measurement of the indicated base pressure drop through a plain elbow varies widely depending on the peripheral and axial location of the downstream static pressure taps.

Q. Do you need CRV®s in front of all elbows in a piping system?

Most critical are elbows just upstream of a system component such as a pump or flow meter that requires a uniform, non-turbulent inflow. If an elbow is experiencing erosion due to abrasive content or because of fluid flashing (cavitation due to localized pressure drops), a CRV® placed upstream of the elbow will yield ideal results.

Q. Will an elbow upstream of and adjacent to a CRV® reduce its capabilities?

Yes, we recommend 3 to 5 diameters of straight pipe upstream of the CRV® or install another CRV® proceeding each below.  Even in cases where this is not possible a CRV placed before the last elbow will help to correct turbulence caused by that last elbow.

Q. Can the CRV® be used with close coupled or out of plane elbows.

Yes, the CRV®s can be used ahead of close coupled and/or out of plane elbows.  We would have to see a piping drawing of the elbows to determine the type and placement of the CRV®s.  

Q. If two elbows are together, can one CRV® suffice for both?

Yes, however, the vane angle will have to be different. The CRV® will even out the flow going through an elbow so that it exits the elbow as if it had exited a length of straight pipe.  If there is an elbow immediately preceding the last elbow and in the same plane, we treat that as a 180 degree bend and design the CRV® vanes appropriately for that situation.  If there is sufficient length of straight pipe between the last two elbows however, then only one CRV® is required before the last elbow.

Some situations, have a very short piece of straight pipe between the two elbows, too short to establish smooth flow and also insufficient to have room for a second CRV®.  In this case we will treat it as an approximation to a 180 degree bend and provide just one CRV®, but with the vane angles designed for this configuration.

Q. Does the positioning or location of the CRV® upstream of an elbow influence the downstream flow quality?

Yes, however, in most applications it is positioned immediately upstream of the elbow entrance.

Q. What are pressure limitations for the CRV®s and LAD®s?

The CRV® and LAD®s designs are largely independent of the flowing pressure; flowing media; temperature; velocity; Reynolds number; etc...  The CRV® can be used on a gas or a liquid, high flow or low flow.  

Q. What is the pressure drop through the CRV®?

The pressure drop through a CRV® is the same the same order as the pressure drop that you would have through an equivalent sized elbow.  But, because the CRV® eliminates the flow turbulence created by the elbow, the elbow is turned into the equivalent of a straight length of pipe, and instead of two pressure drops the elbows pressure drop is eliminated. Thus there is no little gain or loss of pressure when a CRV® is used in combination with an elbow.  In fact in some of the tests that we ran in our lab, we found that a CRV® elbow combination had a slightly lower pressure drop then just the elbow.  Not much, but this can be considered as a side benefit of using a CRV®.

Q. Does the CRV® slow down the velocity of my fluid?

The CRV® does not slow down the velocity of the fluid.  On the inlet side of the CRV® the attack angle of the CRV®s vanes is zero as the vanes at this point are parallel to the flow.  As the fluid flow goes through the CRV® and its vanes, the vanes turn the flow slightly to create the swirl.  This swirl has an absolute minimal effect on the flows velocity.  A single elbow has a significant effect on the fluids velocity.  The CRV® eliminates the elbows “slow down” velocity effect.    

Q. Will a CRV® in a pump suction line reduce the NPSH available?

The differential pressure across a CRV® is very small if any.

Q. What if my flows (velocities, pressures, temperatures, etc.) change, do I have to get a different CRV®?

The great thing about the CRV®s design is that it is independent of all of these conditions.  The CRV® solves the problem of flow turbulence caused by the 90 degree turn in piping elbows and tees.  The CRV®s design is independent of the flowing media (gas or liquid), pressure, flow rate, Reynolds number, etc.  No matter what fluid is flowing in the piping system, the CRV® solves the turbulence problem caused by the 90 degree elbow.  If a customer knows that his flow rate (or pressure) might double or triple in the future, we would like to know this only from the stand point of selling them a thicker walled pipe and vane Cheng Rotation Vane (CRV®) for the higher flows.  We would not be changing the CRV®s basic design for the increased flow rates.  The only thing that we have to know is if the CRV® will be used with a long radius or short radius elbow.  This will not change the price or delivery of the CRV®, but the type elbow used does determine what the CRV®s vane angle should be.

Q. Can you estimate pump flow increase for a CRV® placed just upstream of an elbow adjacent to a pump.

The change in pump flow varies with the piping, but an estimate can sometimes be made.

Q. What information do you require to analyze our system?

You may submit information through our online quote form or by email info@chengfluid.com

-Isometric of system with dimensions

-Flows properties such as flow rate, pressure and temperature

-Statement of problem

-Elbow radius i.e. short, long, sharp miter and angle of turn (typically 45⁰, 90⁰, 180⁰)

-Line size, schedule, and material

-Nature of fluid being transmitted i.e. air, water, etc.

Q. How can the CRV® influence flow meter accuracy?

By assuring that the flow approaching the meter has a known uniform velocity distribution.

Q. How can the CRV® eliminate check valve chatter?

By eliminating the flow separation in an elbow upstream of the check valve and the large scale turbulence that the separated flow develops. 

Q. CRV® be used with other products besides pumps?

Because most pump applications have an elbow on their suction inlet, 75% of the CRV®s we sell are for pump problems (cavitation, vibration, seal leaking, bearing wear, etc.).  But the CRV®s can also be used with control valves and pressureregulators (which will hunt when they receive a turbulent flow from an elbow); flow meters (which lose accuracy when they receive a turbulent flow from an elbow); check valves (which slam and oscillate when they receive a turbulent flow from an elbow); and compressors (which lose efficiency when they receive a turbulent flow from an elbow). 

Q. Why do you have to know if the CRV® will be used with a long radius or a short radius elbow?”

Long radius and short radius elbows are common standard elbow fittings in the piping industry.  They refer to 90 degree turns.  A short radius elbow has its center line radius equal to its pipe diameter.  Thus a 4 inch diameter short radius elbow has a center line radius of 4 inches.  A 4 inch diameter long radius elbow has its center line radius at 1.5 times its diameter.  Therefore a 4 inch diameter long radius elbow will have a center line radius of 6 inches (1.5 x 4 = 6. We match the CRV® to the elbows radius.  The short radius CRV® and the long radius CRV® have two different vane angles.  A long radius elbow should be used with a long radius CRV® and a short radius elbow should be used with a short radius CRV®.  There is no extra cost for a short radius or long radius CRV®. If the angle of the pipe bend is less or more than 90 degrees (120 degrees, 70 degrees, 45 degrees, etc.) we have to design a special vane angle CRV® for that specific application.  The same CRV® principal and design can also be used on piping tees, Y-branches, laterals, and U-bends. 

Q. Why do your CRV®s have a right angle (clockwise) swirl?

The CRV® produces a right hand swirl which counteracts the flow turbulence caused by an elbow.  It doesn’t matter how the elbow is orientated (horizontal or vertical), where it is located, the size, the flowing media, etc.  A CRV® with a left hand swirl would have the same results as a right hand swirl CRV®, the result would be the same at the exit of the elbow.  On one measurement application, the customer wanted to place their meter right on the outlet side of the elbow.  They stated that if there was any residual swirl at the exit of the elbow, they wanted it to be left handed because their meter turned in that direction.  So we supplied them with a left hand swirl CRV®.

Q. Are there any spare parts needed for the CRV®s or LADs?

There are no moving parts in a CRV® or LAD® and no spare parts are required for startup and/or maintenance.

Q. Are there special installation procedures for the installation of the CRV®?

The CRV® is welded (flanged) into the piping system, right at but no further than one pipe diameter away from, the inlet side of an elbow or tee.  The CRV® should be positioned in the piping system so that the flow arrow on the CRV®s name tag is pointing in the same direction as the flow in the piping system.  Standard ASME welding guidelines and procedures should be followed when welding a CRV® into a piping system.

Q. What is the proper length of pipe I would need after an elbow so I wouldn’t have to use a CRV®?

Any fluid dynamics text book will tell you that after a fluid (gas or liquid) makes a 90 degree turn through a piping elbow or tee, it becomes turbulent.  The fluid will have separated, accelerated and reverse flows; and this flow turbulence can cause noise, vibration, erosion, and cavitation.  If any equipment such as pumps, compressors, meters, control valves, pressure and temperature regulators; etc. are used immediately downstream of these elbows or tees they will be negatively affected by this flow turbulence.  The pumps will cavitate and vibrate; compressors will lose efficiency; meters will not measure accurately; control valves, pressure and temperature regulators will hunt; etc.  The flow turbulence caused by the elbows and tees does not settle down until it is at least ten pipe diameters downstream from the elbow or tee.  The flow turbulence will be completely settled down within fifteen to twenty pipe diameters downstream of the elbow or tee (varies with fluid, i.e. gas or liquid, high or low viscosity).

Q. Who is the biggest competitor of the CRV®?

The only real competitor of the CRV® is good piping design.  If there are ten to twenty pipe diameters between the outlet and downstream side of the elbow and the pump’s, meters, control valve’s, etc., inlet there would be no need to install a CRV®. After ten pipe diameters the flow turbulence starts to settle down so that equipment can be installed and it won’t be affected by the flow turbulence caused by the elbow or tee.  But unfortunately (especially on larger diameters) there isn’t enough room to design the piping system correctly. 

There are products on the market that are installed on the downstream side of the elbow to control the flow turbulence created by the elbow.  These products will slow the velocity of the fluid down and then try to control it.  These products take up space where there generally isn’t room and they create a big pressure drop.  The CRV® is the only product in the world that goes on the upstream side of the elbow; the CRV® prevents the flow turbulence problem from happening; and the CRV® accomplishes this without significant additional pressure drop.    

Q. What is the relative cost of the CRV® and LAD®?

The CRV®s and LAD®s cost depend on the quantities, diameters, and materials of construction our customers will require.  Therefore we do not have any inventory of our CRV® and LAD® product lines. The CRV® is treated as a pressure containing part and comes with material certificates for the CRV®s body and vane material; the CRV®s body is seamless pipe (for most sizes); all full penetration welds used in the fabrication.  The CRV®s are made using any specified ASME codes and the welds are dye penetrant checked.

The customer should understand that when they are purchasing CRV®s and LAD®s, they are paying for the technology not just the metal the products are manufactured from.  When you buy the Microsoft Windows software you get the box, the CD, and the instructions.  You are buying the “Windows” technology that is in the CD, not just the CD.

Once the CRV®s and LAD®s are in the piping system they will begin to pay for themselves in a matter of months by eliminating cavitation, vibration, noise, etc.  The system (pump, meter, reacting vessel, etc.) will operate more efficiently, consume less energy, and will have more throughput.  Increased safety, preventing product spills, eliminating unscheduled down times, and eliminating environmental cleanup are side benefits of using our products.  There are no spare parts required and problems such as premature system shutdown will be prevented. 

Q. Can the CRV® have different end connections other than weld ends?

Because there are no moving parts in a CRV® and no spare parts are required for startup or maintenance, 90% of the CRV®s we sell are weld end by weld end.  If a customer wants flanged ends (weld neck, slip on, etc.) or any other fitting connection they are available at an added cost.

Q. Can the CRV® or LAD® have different coatings?

The CRV® and LAD® can be had with any kind of internal or external coating that any pipe or vessel can have. The coatings are optional and there is an extra charge for them. (All of our CRV®s and LAD®s are shipped with no coatings or paint on them.)

Q. Can the CRV® or LAD® have a before and after Computational Flow Analysis (CFD) done before an order is placed?

Cheng Fluid Systems works with a number of outside computer flow analysis people.  If a customer wants a computer flow analysis of their application, before and after the CRV®s and LAD®s are installed, we can offer this at an optional extra charge.  A CFD analysis generally takes three to four weeks to complete. 

Q. Can the Cheng Rotation Vane (CRV®) be hydro tested?

Yes, the CRV®s can be hydro tested. The CRV®s bodies are usually made out of seamless pipe, so all a hydro test will prove is that the seal between the test flanges is holding.   If seamless pipe has to be used, a hydro test can optionally be done after manufacture.  There is an extra charge for this. 

Q. Can the CRV® welds be X-rayed?

Dependent on size, because the CRV®s welds are so close together and the angles are so tight, we cannot get the film and camera into the CRV® and take an x-ray.  (If the CRV® has weld neck flanged ends, those welds can be x-rayed.)  If the welds are a concern all of the full penetration welds on the CRV® can be dye penetrant checked.   

Q. Can the CRV® be made for specific applications?

All our CRVs are made specific for each customer’s application.  Certain common situations occur repeatedly, but we have often had unique cases which required a unique CRV design.  We have sold special vane angle designed CRV®s to specific customers for their applications.  A major chemical company contracted Cheng Fluid Systems for 24 inch diameter special vane angle CRV®s.  These CRV®s were put at the inlet of their reacting vessels, to give the entering gases a specific swirl angle.

Q. What data do I need to have in order to quote a LAD®?

-The customer’s name, contact information, etc. 

-A description of what the expansion problem is, or what expansion problem are they trying to solve.

-A drawing (it can be a hand sketch) of the expansion (reacting vessel) showing diameters, distances, dimensions, and other equipment in the piping system.  We also need to have the drawings of the upstream and downstream piping to the expansion.

-What is the piping and expansions material, diameter, schedule, and wall thickness?

-What are the flow conditions?  (Velocity, pressure, temperature, type of fluid, etc.).

-Has the expansion already been built or is it still in the design stage?  (We can advise on expansion design in conjunction with LAD).

Q. What is the history of the CRV® and the LAD®?

While Dr. Cheng was teaching Physics at Santa Clara University, he received a grant from NASA to study the flow around ninety degree turns in large wind tunnels.  This is how he got started on the CRV®.  Dr. Cheng spent over three years in the laboratory doing countless experiments and collecting data before he came up with the final design of the CRV® that he patented.  The CRV® may look simple but the angle and shape of curvature of the vanes, the number of the vanes, the length of the vanes, and their relationship to each other all have to be correct for the CRV® to work properly. The LAD® also was developed after studying the sudden expansion problems in thewind tunnels.

Q. How does the Large Angle Diffuser (LAD®) work?

The patented Large Angle Diffuser (LAD®) is a series of truncated cones all with a common focal point.  The LAD®s are welded to the inside of a concentric expansion in a vessel or piping system.  A LAD® placed in an expansion, will ensure a uniform flow of fluid (liquid or gas) across the entire cross sectional area of the expansion.  All of the expansion induced flow turbulence which also causes accelerated and reverse flows, noise, separation, and vibration will be virtually eliminated, and this will be accomplished with a minimum amount of pressure drop.  After the LAD® is installed it will produce a uniform flow of fluid across the entire expansion area allowing for a complete non turbulent reaction (heat transfer, etc.) while allowing the vessel to operate at its maximum efficiency.



Q. What is the pressure drop through the LAD®?

The LAD® is also an obstruction in the flow stream.  When a fluid hits a sudden expansion it separates and has reverse flows and an accelerated central flow.  With this “expansion turbulence” there is an accompanying pressure drop.  The LAD® controls the expansion and reduces the pressure drop.  Some of our customers have told us that with the use of a LAD®, they have recovered up to 60% of the pressure drop that they experienced without the LAD®.  Again it is hard to predict, but our customers can expect to have less of a pressure drop when they use a LAD®, then without it.

The value and effectiveness of the Cheng Fluid's products have been proven in over 3,000 installations with over 1500 being used by Fortune 500 chemical, refining, nuclear and power companies all over the world.

Cheng Fluid Systems, Inc. Is Dedicated To Solving Our Customer's Fluid Flow Problems By Using Our Technology & Experience, Along With Our Patented Products, The CRV® & LAD®. Our CRV® products are custom made to specifically address each piping issue offering the greatest achievable flow correction.

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Our flow conditioners are custom made to specifically address each piping issue offering the greatest achievable flow correction.