For such small, seemingly simple devices, with only one moving part and a spring inside, automotive PCV (positive crankcase ventilation) valves must meet surprisingly rigorous performance specifications in order to win automakers’ approval.

            Every valve design must document its ability to admit different amounts of airflow at a number of different vacuum levels.   For Novo Products, Inc., in Holland, Mich., satisfying these requirements went beyond learning new kinds of vacuum/flow test techniques.  When customers began requesting prototype flow-test data presented in graphical form, Novo had to find test capabilities that no known instrument could provide.  It ultimately met that challenge — and cut design testing time significantly — with a customized combination of mass-flow leak-tester and PC-based test-networking software. 

      No stranger to stringent auto-component specs, Novo has been serving that industry since 1973, building itself into a leading Tier-2 & 3 supplier of emission control devices, fuel delivery components and electronic engine controls, while earning ISO and QS 9000 certification along the way.  When the opportunity to solve one automaker’s PCV valve failure problem came along in 1999, the company sensed a long-term business opportunity as these inexpensive parts offered high volume potential.  Since then, Novo’s production of PCV valves has already risen above 4 million a year on only seven designs.

      Flow testing is vital because PCV valves must relieve engine crankcase pressure properly to prevent backfiring or blown gaskets and seals.  To do this, they regulate pressure outflow from the engine by means of a tapered poppet moving in and out of a tapered orifice.  The orifice outlet is connected by tubing to the engine’s air/fuel intake.  This allows the vacuum generated by the air/fuel intake to modulate the poppet.  Spring tension holds the poppet open when vacuum is low, but allows increasing vacuum to gradually pull the poppet closed.  When the poppet is open and engine gases are venting, the tubing and low vacuum channel those emissions back into the air/fuel intake so they can be reburned rather than vented to atmosphere as a pollutant.

      Each engine’s design presents a different relationship between the amount of vacuum and the amount of crankcase pressure allowed to vent.  That relationship in turn requires each PCV valve design to have a unique balance among the internal geometry of its poppet and orifice, the force of the spring and the level of vacuum. 

      Customer specs define the valve’s external size and shape, along with flow values desired at designated vacuum levels, termed Delta Points.  For PCV valves, vacuum typically ranges from 1 to 20 InHg (inches of mercury), while flow values might be anywhere between 0.2 and 8 cfm (cubic feet per minute).   Novo engineers are left to determine the internal design needed  to achieve the desired performance.

Largely trial and error "Largely trial and error"

      “We’ve never been able to develop any design formula for this”, says Novo Manufacturing Engineer Brent Veeneman.  “It’s largely trial and error, so the prototyping process can be very time consuming.  We start with a design that experience suggests should meet the requirements, test it against the customer’s specs, then make changes and test again, and keep repeating that process until we nail it.”

  He explains that while buyers will specify flow at three delta points for production QC testing, they’ll usually want to see design prototypes verified by a more definitive curve plotting flows at up to 20 points before authorizing production.

  “Meeting these kinds of specs was our first brush with flow testing”, he recalls.  “We have vast experience in using sophisticated leak-rate testing on fuel-system components, but that’s different.  There, it’s a matter of pressurizing the product and measuring the rate at which air leaks out.  Typically that’s a production-line QC test done to verify the leak-tight integrity of formed or assembled parts.  While PCV valves also get production-line QC flow testing, their design/prototype testing is critical because that’s what guides development of their internal geometry.  This up-front test procedure is far more intricate.”

      One complicating factor, he explains, is the time needed to let airflow stabilize at each vacuum point before the flow is measured.  Other complicating factors are the airflow’s absolute pressure (psia) and temperature, as these values will cause both vacuum pressure and air density to vary.  “Some buyers will base their vacuum and flow specs on standard atmospheric pressure of 14.7 psia (29.92 InHg) at 20°C,” he points out.  “Others prefer different ambient pressure and temperature baselines that they consider more representative of normal operating conditions.  Our flow-testing instruments must be able to report test data corrected to show flow as it would be under whatever standard conditions the buyer specifies.”

Homemade tester tried "Homemade tester tried"

      For its first foray into flow testing, Veeneman recalls, Novo followed its tradition of building equipment and fixtures in-house for economy.  “We tried combining a simple commercial flowmeter with our own valving system.  It worked, but manual data gathering was time consuming; we weren’t really sure about its accuracy, and felt we needed something better to double-check our method.”  For that, they called upon InterTech Development Co. (IDC), of Skokie, Ill., a firm that earlier provided several turnkey assembly systems with integrated leak-testing functions for Novo fuel-system products, plus leak-testing instruments and consultation for several other proprietary leak-test stands built by Novo engineers.  “Once we saw theirs,” he summarizes, “we scrapped ours.”

      Collaborating with InterTech, Novo initially built a two-station machine with each station having two test fixtures, one for valves operating in the 0.2 to 2 cfm flow range, the other for valves operating in the 2 to 6 cfm range.  Low-flow and high-flow fixtures of both stations were connected alternately to a pair of InterTech M-1035 mass-flow instruments.  One M-1035 was equipped with a mass-flow transducer covering the lower range, while the other’s transducer covered the higher range.  Both instruments were equipped with programmable vacuum regulators covering the full 1-20 InHg range.

      In the typical production QC test, the PCV valve remains in the same fixture while the M-1035 sequences through three programs, one for each of the specified vacuum Delta Points.  Arriving at each Point, the instrument pauses for the prescribed stabilization time, then measures the rate of airflow through the valve.  Each Delta Point test typically takes about 12 seconds, for a total part-to-part test cycle of 36 seconds.  

  In each test, air drawn through the valve by the vacuum is channeled across the M-1035’s transducer,  producing an output voltage proportional to its mass flow, which the instrument electronically translates and displays as an almost instantaneous single-point flow-rate measurement.  It also displays vacuum pressures during the test, compares both pressure and flow against pre-set limits, and signals either accept or reject.  No operator judgment or external calculations are needed.

      The dual-fixture, dual-station, dual-instrument setup devised by Novo enables one fixture in each station to be testing while its counterpart in the other station is manually unloaded and reloaded. The second fixture in each station allowed a different part with a different set of programs to be tested simultaneously.  

      By using stationary fixtures, with each test instrument switched back and forth between stations by PLC-controlled valves, Novo avoided the higher cost of automatic moving fixtures along with the cost of safety devices that moving fixtures would require.   Whenever a valve fails its test, the M-1035 prevents the PLC from switching to the alternate fixture until the operator acknowledges the reject.

Records kept automatically "Records kept automatically"

      The production tester’s M-1035s, programmed to treat each Delta-Point measurement as a separate test, automatically save vacuum, flow and pass/fail records for their last 1000 tests (333 valves), which Veeneman can print out for R&R studies or to evaluate any anomaly in reject rates.  They also have on-board memory to store 100 programs, so each instrument can accept enough three-program sequences for up to 33 valve designs.  This accommodates Novo’s seven-valve family with room to spare for future product-line growth.  Programs are easily recalled for product changeover through the M-1035 keypads.  

      With the InterTech instruments’ ability to program precise vacuum points and flow limits, and recall test data, the production tester became the instrument-of-choice for prototype testing as well, Veeneman continues.  “When new valve designs began calling for full 20-point curves spanning both low and high flow ranges, we would test the low-flow and high-flow delta points on whichever M-1035 had the appropriate transducer, then collect the data from both and manually plot the curve by patching the segments together.  That wasn’t the best way to do it,” he admits, “because it puts a void in the curve wherever the data jump from one instrument to the other.  In addition, it was always possible that the combined data didn’t reflect identical  calibration in both instruments.   Still,  it was better than anything else we had at the time.”

      Six months after start-up, Veeneman recalls, Novo’s high-flow valve production ended temporarily, so the high-flow production instrument was refitted with a low-flow transducer to provide more testing capacity for the increasing volume of valves in that range.  “With that,” he says, “the only way we could do full-curve prototype testing was to fill in the missing-range points with our old home-made tester, which made the task more difficult and less reliable.”

      “It became obvious that in order to seriously pursue this business, we needed a full-range tester and a better way to analyze and visualize the data,” he points out.   “The problem was, it didn’t exist.”

      Wanting to take a fresh look at where to start, Veeneman called in several test instrument suppliers.  “We found most were cautious about the wide range and high level of accuracy we wanted, and were oriented more toward mechanical than electronic technology in modulating flows, so once again we felt more comfortable dropping this challenge on InterTech.”

Customized  lab tester created "Customized  lab tester created"

      Building upon the vacuum-regulated M-1035 platform already familiar to Novo in their production test stand, InterTech proposed a customized version of that instrument.  Its mass-flow transducer would be replaced with an external laminar flow element having a master lab calibration accuracy of ± 0.6%-of-reading across the desired flow range of 0.2 to 8 cfm.  This would be coupled with a high-accuracy differential-pressure transducer certified at 0.15%-of-reading and a high-accuracy absolute-pressure transducer certified for 0.3%-of-reading, along with an airflow temperature sensor. 

      While the M-1035s in production testing provide mass-flow transducer accuracy of ± 0.5%-of-range, which satisfies Novo’s high-accuracy requirements over their relatively short cfm ranges,  percent-of-reading capabilities are essential in their lab counterpart to assure consistently high accuracy at all points along its extended cfm range.  Adding the high-accuracy transducers and temperature sensor, along with custom programming, enables the lab’s M-1035 to measure flow values at ambient temperature and pressure, but display and record them as corrected to  buyer-specified standard conditions.

      Test program and data storage, usually resident inside a standard M-1035 when serving more conventional applications, was shifted to an external PC (laptop) running a customized version of InterTech’s S-3085 Monitor Software. 

      Normally used to network up to 34 IDC leak-testing instruments for supervision by remote host computer, the S-3085 software was conceived for better management of multi-station testing operations, QC/SPC programs and traceability documentation.  Adapting it for Novo’s lab testing requirements, IDC modified this package to let the PC accept and store test parameters for up to 20 Delta Points for each PCV valve design, including calculations for correcting atmospheric pressure and temperature to buyer specifications.  Additional software customization allows the PC to display real-time results for all Delta-Point tests combined into a single continuous graph, depicting changes in both vacuum level and airflow over time against each Point’s upper and lower (accept/reject) limits.   Using a PC for this task allows complete full-range curves to be seen on a single screen, exported to MS EXCEL format, printed out, even e-mailed directly to customers.

PC increases capacity "PC increases capacity"

      Adding the PC served other essential purposes as well.  While a standard M-1035 can store and recall enough test programs for up to 33 three-point production tests, the lab tester needed greater storage capacity.  As each Delta-Point test requires a separate test program, 20-point tests for each of 7 PCV valve models tallies 140 programs…and that total is certain to grow as more valve models come into Novo’s product mix.  

      Although a standard M-1035 automatically stores data from its last 1000 tests, the S-3085 software enables the lab tester’s PC to store much larger amounts of test data, by date, in Microsoft Access database format, at 2 million test records per 100 MB of available space.  It also allows the PC to recall stored test data either in total or using selection filters such as date, accept/reject results, or causes of rejects (e.g. high or low pressure).  Exported to MS EXCEL format, test data for multiple samples of the same prototype can be merged for presentation as screens combining both the data table and full-range curves comparing average flow performance vs. high/low extremes across the sample population.

      The lab unit’s test functions are controlled by the M-1035, in which custom programming enables that instrument to receive the multi-point program for a specific PCV valve design as downloaded from the PC, then sequence through the test for each Delta Point while sending real-time test data back to the PC for display and storage.   Each Delta-Point’s test program starts by ramping the M-1035’s programmable vacuum regulator to approximate target level, followed by closed-loop adjustment to reach precise level, pausing for the prescribed stabilization time, reading the transducers, measuring the flow, correcting the measurement per the customer’s standard conditions, comparing that with specified limits, concluding accept or reject, and advancing to the next Delta-Point test program.

Speeds design, "Speeds design, "boosts productivity "boosts productivity"

      The IDC system has greatly speeded the task of prototype testing, Veeneman says.  “We see it cutting our actual testing time by 40-50 percent, largely because it’s a dedicated lab instrument.  We no longer need to wait for a break in production — or worse, interrupt it.  Using the production testers for design work wasted time with tooling and program changeovers for the test parts, then changing everything back to resume the production testing afterward.  It also required a much more extensive calibration procedure.”

      With the new testing equipment, he estimates the total time needed to design a new PCV valve is typically reduced by about 20 percent.  “That’s because we have more accurate flow data plus presentation in curves that make the data easier to interpret.  Real-time graphic display lets us see and document in greater detail exactly how a design is behaving at all times during its cycle.  We no longer have to plot curves manually or patch curves together.  This in turn gives us better direction and helps us respond more quickly with design, tooling and equipment adjustments.”

      “Manufacturing PCV valves is not difficult,” Veeneman sums up.  “The hard part is the design and  prototyping stage, and there, the quality of the testing is what separates the premium product from the commodity.  Our new system makes it easier to meet the differing standards of automotive customers precisely.”   

      The benefit of better design testing also trickles down to productivity, he adds.  “Customers don’t specify stabilization time, so while we’re tweaking a new design’s internal geometry to achieve the flow spec, we also can try alternatives in springs and poppet designs to shorten the stabilizing time as well.  Shorter stabilizing time allows faster part-to-part cycles in QC testing later, when the part is in production.”  

      The customized IDC system also gives Novo a better tool for studying any abnormal failure rate appearing in production valves, and for evaluating the design of competitive products, he notes.  In addition, the S3085 software enables the PC to reprocess the stored data into histogram or trend charts for statistical evaluations when needed. 

      “Our industry has historically struggled with PCV valve flow measurement, but I think our new IDC lab tester finally brought us a solution to that problem.”