Mechanical Engineering Expert’s Opinion About the Clogged Float Valve Admitted
Posted on June 3, 2025 by Expert Witness Profiler
This is a product liability case involving Walmart’s sale of a pressure cooker that Plaintiff Vanessa Loftis claims injured her when the lid was able to be removed while the pressure cooker was—unbeknownst to her—still pressurized.
During the depressurization process, pressure cookers release steam; according to Loftis, the steam on that night “lasted forever,” around thirty to forty-five minutes. Loftis testified that she “kept checking on it, and then, when [the steam] finally did stop, that’s when [she] opened it and it kind of blew up.”
The contents of the cooker were ejected onto Loftis, causing burns to approximately 12% of her body, mostly on her abdomen, that later required debridement.
Walmart filed a motion to exclude Loftis’ expert, Dr. David Rondinone, arguing that his opinions are speculative, unreliable, and not tied to any applicable methodology.
Walmart appeared to make three specific challenges to Rondinone’s opinion: (1) that he proposed only “possible” causes of the incident with no basis in evidence; (2) that he did not physically test the subject cooker or an exemplar; and (3) that he did not rule out alternative causes.
Mechanical Engineering Expert Witness
David Rondinone holds an M.S. degree and a Ph.D. degree in Mechanical Engineering from the University of California, Berkeley, majoring in material behavior and design and minoring in structures and dynamics and electronic controls.
He also holds a B.S. degree in Engineering Physics and a B.A. degree in Astrophysics from the University of California, Berkeley. From 1993 to the present, he has worked as a Mechanical Engineering Consultant, and is a principal of Berkeley Engineering And Research, Inc. (referred to herein as “BEAR”).
He has worked for more than 30 years in the areas of failure analysis, design, and risk assessment of consumer and industrial equipment, including pressure cookers.
Discussion by the Court
Rondinone proposed three potential causes of the accident: (1) a float valve clog, resulting from an inadequately designed float valve, that caused the lid to remain unlocked while under pressure; (2) a boil-over event that was not properly warned against; or (3) a failure of the interlocking sliding mechanism.
Possible Causes
Walmart contended that Rondinone posits only “possible,” rather than “probable” causes of the accident and failed to ground these in facts.
However, Rondinone identified a float valve clog as the “most likely scenario” and “would say to a degree of reasonable engineering certainty it’s more likely a clogged or insufficient float valve interlock event” caused Loftis’ injuries “than . . . a boil-over event.”
Since Rondinone intended to testify that the incident was most likely caused by a clogged float valve, as supported by his expertise, prior testing of pressure cookers, examination of Instant Pots, and Loftis’ description of the incident, the Court refused to exclude his testimony on that basis.
Physical Testing
While Walmart conceded that it was not possible for Rondinone to test the subject pressure cooker in this case, as it was not available, it argued that his failure to conduct tests using an exemplar model is unjustified and rendered his testimony inadmissible.
However, Rondinone explained that in order to help him gain a more precise determination on probability as to whether this was a float valve incident, he would have had to run “an extensive statistical study, probably hundreds of tests,” and he has not “know[n] anybody who ever has” done that.
Further, he explained that it is “difficult to repeat” a clogged float valve, but his lab has “done tests for clogging on other models of pressure cooker” and shown that a user “can with a single use clog the vent,” which he reports “present[s] a risk of pressurization with the lid in an unlocked state.”
However, the Court held that Rondinone’s opinion that the float valve was clogged is supported by Loftis’ description of the incident and his prior testing of pressure cookers, not “unfounded assumptions.”
While Rondinone is “unable to recreate” the incident, the Court held that his opinion is “based on known facts and his expertise.”
Alternatives
Walmart challenged the admissibility of Rondinone’s opinion on the argument that he failed to rule out other possible causes.
In this case, Rondinone did engage with alternative explanations, including a boil-over event, a failed sliding mechanism, or some other accident like a spill. He then applied his expertise in the mechanics of pressure cookers to the facts in this case to deduce that a float valve clog was the most likely mechanical scenario here.
As for the possibility of a spill, he stated that “physically it’s probably possible,” but he would “have to disregard Loftis’ entire testimony, though, from start to finish for that to be true,” including “disbelieving her explanation of the removal of the lid and how the contents came out.”
Rondinone refused to say with absolute certainty that a float valve clog occurred here, but he did conclude the most likely cause within a “degree of reasonable engineering certainty.”
The Court held that Rondinone’s refusal to completely rule out other alternatives goes to the weight of his testimony, not its admissibility.
Held
The Court denied Walmart’s motion to exclude Dr. David Rondinone.
Key Takeaway:
Despite the fact that Rondinone did not test the subject pressure cooker or an exemplar model in this case, there is no single requirement for admissibility as long as the proffer indicates that the expert evidence is reliable and relevant.
The Court held that Rondinone’s conclusions are based on his experience and expertise [in pressure cooker cases], general engineering principles, information from Loftis about the accident, examination of an exemplar cooker, its design and specifications, competitors’ cookers, and photos of the accident, including of the subject pressure cooker and Loftis’ burns.
Case Details:
| Case Caption: | Loftis V. Walmart, Inc. |
| Docket Number: | 5:23cv5228 |
| Court Name: | United States District Court, Arkansas Western |
| Order Date: | June 02, 2025 |
