# pressure relief valves for EV batteries, gears and motors

Topic radar · 44 documents · 2021-01-01–2026-09-12 · updated 2026-10-15

Canonical: https://slate.greyb.com/radar/pressure-relief-valves-for-ev-batteries-gears-and-motors/innovations

## In one minute

### The part now does three jobs
Eaton's 3-in-1 valve combines a battery-case leak check, passive venting and active venting in one unit, and the leak check can be run with the valve already in place [1]. Raval, Parker Prädifa, Nifco, Freudenberg and ITW reach the same functional set from different starting points. The part now carries a test function and a resealing requirement alongside its relief duty.

1. [eaton.com](https://www.eaton.com/us/en-us/company/news-insights/news-releases/2023/eaton-introduces-3-in-1-battery-pack.html)

### The performance numbers are the makers' own measurements
Every headline figure in this market traces back to the supplier's own bench. Gore's moisture result — under 20 mg per day at 22 °C and 50 percent relative humidity, described as less than one-tenth that of many commercially available dual vents — is attributed to Gore laboratory testing, and its durability claim to Gore testing after standard automotive aging. Freudenberg's 190 L/s at 300 mbar is a factor-of-2.5 gain measured against its own previous generation. Donaldson publishes a 115 mbar opening pressure, roughly 100 L/s at 100 mbar, IP67/68/69K and an operating range of −40 to 125 °C on a product datasheet. These are design and in-house test figures, and I found no independent measurement of a commercial pack vent's flow performance in the public record — which leaves the sizing question answered by supplier numbers alone.


### The buyers are taking the design in-house
The relief valve is being claimed by the organisations that write the specification. Cell and vehicle makers are filing their own pack-side designs — LG Energy Solution, Samsung SDI, CALB, Toyota, Ford, Maserati and SAIC Volkswagen among them — and the drive makers are filing on their own housings. A supplier selling into those accounts is competing against the customer's own design group. The venting standard's committee is chaired by a filtration supplier rather than an OEM, so the technical seat is held by a parts maker, but the OEMs are building their own claim to the part regardless.


### The valve opens for a test and closes again
Eaton's leak-check mechanism can be actuated on the assembly line, so the pack can be pressurised or put under vacuum for testing with the valve already fitted. Freudenberg's DIAvent maxFlow replaces the rubber umbrella of earlier designs with a profiled metal spring that snaps fully open at the trigger pressure and closes the opening again once pressure drops. It passes more than 190 L/s at 300 mbar, with the trigger pressure settable between 50 and 200 mbar. Because the mechanism reverses, a fully assembled pack can be tested non-destructively at end of line, which a one-shot burst disc cannot do. Gore's MultiVent opens its larger valve at 50 mbar, passes 50 L/s at 180 mbar and reseals.


### One supplier points to laboratories outside its own
PorVent is the exception I found. It states that its vents are tested by NABL-approved external laboratories for IP 66/68/69K, UL 94 V-0 flammability, temperature cycling, salt fog, mechanical impact and vibration, with an IPX7 immersion test run after the vibration test. It is still the supplier's account of the tests and no report is published, but it is the only public case I found where the testing body is named rather than the brand.


### The certification regime is the new barrier
A regulation with a date and a component standard turn the valve into a certified part. China's GB 38031-2025 requires no fire and no explosion and adds a bottom-impact test and a 300-cycle fast-charge safety test, and a Chinese group standard specifies the test method for a battery explosion-proof valve. The buyer's question stops being "can you make this" and becomes "can you prove it." Test evidence, certification and traceability become the qualification gate, a different barrier from manufacturing capacity, and they favour suppliers who have already run the tests. The leverage sits in the drafting: the Chinese standard's group was led by a Dongguan precision-electronics firm, so a supplier that helps write the test method knows what the test will be before its competitors do. Capacity is being added ahead of that gate — PUW's two new lines, against a top five that already held 58% of the market in 2024 — a bet on being one of the few suppliers who can pass it, placed against market estimates that disagree by an order of magnitude.


### Opening happens in stages
Several designs open part of the flow path at a first pressure and the rest at a higher one. BYD claims a valve that opens part of its relief channel between a first and second preset pressure and the remainder above the second. EVE Power claims a three-stage valve with separate first and second opening pressures, and CPS Technology a burst vent with two valve portions releasing on incremented thresholds. BMW's battery housing valve opens reversibly at a first pressure for equalisation and irreversibly at a higher one to let hot gas out.


### The comparatives are aimed at rivals who are not named
Gore measures its moisture figure against "many commercially available dual vents" without naming one. Donaldson calls its degassing "the industry's fastest". Vernay calls VoltaVent an "unparalleled solution". The named benchmarks in this marketing are standards and regulations rather than competing products, which is a fair reading of where the buyer's attention is being directed.


## Overview


The pressure relief valve in an electric vehicle has been redefined by rules that took effect this year. China's GB 38031-2025 applies to new type approvals from 1 July 2026, with existing vehicles following in 2027, and it replaces the old five-minute warning with a requirement of no fire and no explosion, adding a bottom-impact test and a short-circuit test after 300 fast-charge cycles. SAE's three-document set adds the component-level rules: J3277/1 for non-destructive end-of-line leak testing of the pack and coolant system, J3325 for venting design and integration, and J3337, still in progress, for individual cells. A part that must survive a bottom impact and a fast-charge cycle, and that can be leak-tested in place without being destroyed, is a different component from the one-shot burst disc it replaced. Buyers now qualify on evidence of testing, which is a different gate from manufacturing capability.


## Research

### The gas path carries a filter stack
The opening carries a stack of filters behind it. LG Energy Solution's relief valve family uses a mesh plate that moves with the valve cover, with holes sized to block spark particles. ACS Industries claims an expanded-metal filter collar that acts as a heat sink and flame arrestor, with offset openings that turn the flow and shed particles. SVOLT adds a cleaning part that moves across the fire-filter mesh as gas flows, to stop the holes clogging. MANN+HUMMEL claims two separation screens in series, with a pressure relief valve that bypasses both when pressure is high.


### Breathing and emergency venting use separate paths
Normal pressure equalisation goes through a membrane; emergency venting goes through a valve. Freudenberg's element has a central coated ePTFE breathing membrane with a ring-shaped rubber valve around it, opening at about 40 mbar. Gore's MultiVent uses two valves and a membrane, with a protection zone between -30 and 50 mbar where no airflow passes, and holds moisture ingress under 20 mg per day. The membrane blocks water and dust while passing air; the valve handles the fast, large flow.


### Opening pressure falls as the cell heats
Measured activation pressures for the current interrupt device and the vent drop from about 2.2–2.36 MPa at ambient to 1.8–1.9 MPa at 100 °C. Burst pressure changes the runaway itself: at 1, 2 and 3 MPa the vent bursts at roughly 800, 1000 and 1300 seconds after heating begins, releasing 5.3, 6.1 and 6.5 litres of gas, with more hydrogen at higher burst pressures. An opening pressure quoted without the temperature at which it holds is an incomplete specification.


### Sizing needs a flow-versus-time curve
Steady-state permeability data cannot size a vent, because thermal runaway drives gas out far faster than any steady leak rate describes. The measured inputs are coming from cell tests. One study derived gas flow rates of 22.15 g/s for a high-power 18650 and 27.92 g/s for a high-energy one from the recoil of the venting jet; another measured release rates of 0.04–0.31 mol/s for NCM cells and 0.02–0.06 mol/s for LFP. Measured burst pressures of commercial 18650 vent caps came out below the value commonly quoted in the literature, at 2.158 and 1.906 MPa against 3.448 MPa, so venting occurs earlier than expected. What is still not published is a valve-level flow-versus-time curve.


### The same pressure problem appears in drive housings
The gear and motor half of the subject is a pressure-equalisation problem of the same kind. Valeo Siemens eAutomotive claims an electric machine with a venting channel and a pressure equalisation element at the housing opening. BMW claims a breather between the electric machine compartment and the transmission compartment, with a preloading element whose force on the valve body can be altered. Volkswagen's pressure compensation element opens a gap for a leak test and seals again in service. Konzelmann's element for e-axles operates at 70 mbar and uses a watertight membrane rated to 3 bar internal pressure.


### The standards set what the part must pass
SAE J3325, published as a Technical Information Report in March 2025, covers vent design for pressure equalisation and emergency degassing, spark arrestors and hot particle filters, pack integration and validation procedures. J3277/1 sets non-destructive end-of-line leak testing for the pack assembly and the coolant system. China's GB 38031-2025 requires no fire and no explosion and adds a bottom-impact test and a 300-cycle fast-charge safety test.


### Vents sometimes do not open
Two case studies of cylindrical cells found vents that failed to operate as intended, with the casing rupturing in one and the side wall in the other. The process side documents moulding problems, a plunger sticking under high gas pressure and a structurally weak centre. Both failures are settled by how the part is made and validated.


## Market

### Design wins arrive as nominations and unnamed projects
ITW's battery safety valve was "nominated by one of the premium OEMs in Europe for their next generation BEV platform" — a nomination, not a production award, with the customer unnamed; the performance claim attached to it is leakage below 1 mL/min during valve operation and operation without external power. KACO says its new pressure compensation element is "already successfully in use in a first series project" without naming the drive maker or the vehicle. For two of the more visible recent entries, the public evidence of a design win is a supplier sentence rather than a named platform.


### The drive side sells a different failure mode
The gear and motor half is marketed on contamination and water rather than on gas flow. KACO's launch is framed around oil mist clogging the membrane of conventional elements, and around IP6K4, IP6K7 and IP6K9 protection. Donaldson's electric-drive-module vent pairs an ePTFE membrane with a prefilter whose stated job is to keep oil off it. Konzelmann sells its element for wading, quoting a valve that operates at 70 mbar and a membrane rated to 3 bar internal pressure. A battery vent is sold on litres per second; a drive housing vent is sold on surviving the oil and the puddle.


### What counts as public varies by supplier
Shenzhen Milvent's battery-pack vents are published as distributor datasheets — MIV-32, MIV-32MAEX and a bayonet-mount variant — quoting IP66/67/68, an operating range of −40 to +125 °C, and in one listing "low cost Vent instead of traditional breather plug". Bontaz makes its case in a trade-press feature rather than a launch release, describing a piston-based resealable valve with an adjustable threshold from 50 mbar and an IP6K9K rating. NOK's public record for its pressure relief valve series is exhibition announcements, with a snap-fit variant shown in May 2026 and no published performance figures. A buyer comparing these suppliers is comparing documents of very different kinds.


### The marketing itself alleges the specifications do not hold
One supplier's buyer-facing content claims that while some products specify a burst-pressure tolerance of ±10 percent, batch-to-batch deviation can reach ±30 percent, and that standard stainless-steel membranes lose strength above 500 °C, so the membrane may not rupture when it should. This is a competitor's promotional argument rather than a measurement, and the figures should be read as an allegation. It is worth noting because the field's own marketing is where the complaint about specification quality is made in public.


## Strategy

### Design effort has moved into filings
Public engineering writing on vent sizing is thin, and the answer visible in filings is to make the opening threshold a sequence rather than a single number. BYD, EVE Power, CPS Technology, Rivian, Donaldson, Cummins, Nifco and A Tech all claim staged or multi-threshold relief. That is where the design work has gone, and the public literature has not caught up.


### The drive-housing half is a parallel track
The same pressure problem appears on the drive side, and the same kind of suppliers serve it. KACO has started series production of pressure compensation elements for electric drive units, Donaldson and Lee Co sell venting and relief valves for electric drive modules, and ITW's balance plug is listed for battery, transmission and motor. The filings put the OEMs inside this half too, with BMW, Valeo and Volkswagen claiming their own housing elements. The market estimates are built around battery vents, so this half is being worked without a public number attached to it.


### The field is splitting between integration and commoditization
One direction integrates upward: the valve carries sensing and diagnostics and becomes a small module rather than a moulded fitting, and the valve location is treated as a sensing point. The other simplifies downward: a low-cost, high-tolerance commodity, with slit valve plates aimed at cutting cost and process complexity, sealing that tolerates the opening's inner diameter, and dual-stage vents claimed to replace most of the vents in a pack. Which wins depends on whether vehicle makers write diagnostics into the vent scope. The evidence for the instrumented module rests on one supplier page and one laboratory study, so I would treat it as a direction rather than a settled trend.


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