CAD-Integrated CFD Software Helps Design Innovative Flush Valve in Less Time

(August 17, 2006) -- EFD.Lab CAD-integrated computational fluid dynamics (CFD) software saved time in the design of an innovative flush valve by enabling Johnson Design engineers to solve design problems utilizing software rather than hardware prototypes. A unique feature in Johnson Design's Denali Flushometer flush valve is that it delivers a fixed volume of water independent of the position of the restriction on the rolling diaphragm which is randomly installed at various positions during the valve assembly. Johnson Design Engineering Manager Dustin Borg used EFD.Lab to evaluate the performance of the valve as the restriction was rotated 360 degrees in order to ensure that it delivered the right amount of water in each position. "EFD.Lab considerably reduced the amount of time required to optimize the design by enabling us to evaluate design concepts in software without having to build a prototype," Borg said.

Flush valves operate by taking advantage of pressure differentials between the inlet and control chambers. The pilot valve, when engaged by the handle, vents the control chamber lowering its pressure and allowing the rolling diaphragm to open which in turn begins the flush cycle. Rolling diaphragms offer the advantage of exposing only a very small area of unsupported diaphragm to pressure differentials, resulting in much lower forces compared to large diameter flat diaphragms. "But it's usually not possible to determine in advance where the restriction on the rolling diaphragm will end after the valve is assembled," Borg said. "As a result, a weakness of earlier diaphragm valve designs is that one valve of the same model may deliver 1.5 gallons while another will deliver 1.7 gallons. We decided to overcome this problem in designing the Denali Flushometer by evening out the pressure that the valve is exposed to around its entire circumference."

"This would have been a difficult task using physical prototyping because it would have been necessary to repeatedly assemble and disassemble the valve, each time slightly changing the position of the rolling diaphragm," Borg said. "We would have had no way to visualize the flow inside the valve so if we found a problem in a certain position we would have to rely on intuition and guesswork to try and solve it. With EFD.Lab we were able to move much more quickly to a solution. EFD.Lab automatically distinguished between the solid and empty spaces in our CAD model and meshed the empty regions to prepare for flow analysis. We measured the flow rate and pressure at the inlet and outlet of a similar existing valve and used those as boundary conditions. The analysis results showed flow rate and pressure at every section of the valve. The ability to visualize the flow within the valve made it easy to see what was causing pressure variations. We made a few design changes and soon had equalized the pressure around the valve. When we built and tested a prototype valve it worked exactly as we expected by providing consistent flow regardless of the position of the rolling diaphragm."

Interested readers can register for a free EFD software demo at:

Dr. Michael J. W. Reynell
81 Bridge Road, Hampton Court
Surrey KT8 9HH, England
Tel: +44 (0) 20 8487 3000

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