HYDROSEAL PRO 150 —
peroxide-cured EPDM O-rings for hot water
HYDROSEAL PRO 150 is the peroxide-cured EPDM O-ring line for hot water, outdoor water fittings, HVAC service and common quick-connect garden hose systems. The article explains the chemistry only where the published evidence helps: compression set, elastic recovery and the limits of what M534 test data can predict in an installed joint.
Product status: this page is the technical reference for the working HYDROSEAL line and M534 compound. It is not proof that every shown size or assortment is stocked. Confirm current SKU, pack, lead time and compound documentation through B2B before ordering or specifying.
Documentation scope: Approval, compliance and certification references apply to the documented material grade, supplier certificate or listing, and stated test conditions unless a product-specific certificate says otherwise. A cut gasket size is not automatically certified as a separate product just because it is made from a documented material. For regulated applications, confirm the current certificate or listing scope, exact grade, medium, temperature, pressure and market requirement before specifying.
Selection rule: HYDROSEAL is selected when an EPDM O-ring must hold elastic recovery in hot water, outdoor exposure or long-term compression.
Use this when: hot water, HVAC, potable-water-adjacent fittings, quick-connect water fittings and outdoor EPDM O-ring applications within the compound data.
Do not use this when: do not use it for oil, fuel, mineral oil, aliphatic hydrocarbons or applications that require a different elastomer family.
Move to the next material when: hydrocarbon contact, aggressive chemical exposure or dynamic seal design moves the selection away from EPDM.
What HYDROSEAL is used for
HYDROSEAL PRO 150 is for O-ring positions where ordinary rubber selection is not enough: hot water fittings, outdoor connectors, HVAC water circuits, garden quick-connect couplings and service assortments where the same ring may sit compressed for long periods before it has to seal again.
The practical requirement is simple: the O-ring must remain elastic after time, temperature and compression. If it flattens permanently, it may look present in the groove but no longer press hard enough against the sealing surface.
What EPDM is — and what curing does to it
EPDM stands for Ethylene Propylene Diene Monomer — a synthetic rubber polymer. The base polymer is valued for its resistance to water, steam, ozone, UV radiation and weathering. It is widely used in plumbing, water supply, heating systems, outdoor installations and HVAC connections because it handles the conditions that other elastomers, particularly NBR, do not.
But EPDM as a raw polymer is not usable as a seal. It has to be vulcanised — cross-linked — to transform it from a soft, flowable material into an elastic solid that can hold a seal under compression. The curing agent used determines the type, density and thermal stability of those cross-links.
Two curing systems are common for EPDM: sulphur curing and peroxide curing. They can produce O-rings that look identical from the outside, but their behaviour under sustained heat and compression is different.
Sulphur curing — the standard approach
Sulphur curing is the older and more common process. Sulphur atoms form cross-links between polymer chains, creating a flexible network with good mechanical properties at moderate temperatures. Sulphur-cured EPDM is cost-effective, widely available and adequate for many standard sealing applications.
The limitation of sulphur cross-links is thermal stability. At elevated temperature, some sulphur-cured EPDM compounds can show greater permanent set than a suitably formulated peroxide-cured grade; the result depends on the complete formulation and test conditions. Permanent deformation remaining after the load is removed is called compression set. It is an important hot-water selection property, but installed failure also depends on the complete compound, gland design, squeeze, medium, temperature history and surface condition.
Compression set in plain terms: compress an O-ring into a groove, apply heat, leave it under load. When the system cools and pressure drops, how much of its original cross-section does the O-ring recover? A low compression set means it recovers well. A high compression set means it stays flattened — and a flattened O-ring no longer seals reliably.
Peroxide curing — what changes and why
Peroxide curing uses organic peroxide compounds as the cross-linking agent. Instead of sulphur bridges, peroxide curing creates direct carbon-to-carbon cross-links. These are chemically simpler, shorter and significantly more thermally stable than sulphur bridges.
The result is a cross-link network with better thermal stability. Under sustained heat and compressive load, a suitable peroxide-cured EPDM compound deforms less permanently than a comparable sulphur-cured grade. When load and temperature cycle, it can recover more of its cross-section and maintain sealing contact for longer.
Measured M534 results are shown in the table below. No generic sulphur-cured comparison curve is plotted because a fair comparison requires a named compound tested side by side under the same method, squeeze, medium, temperature and duration.
What this looks like in numbers
Compression set is measured by compressing a test piece to a defined percentage of its original thickness, holding it at temperature for a set period, releasing it, and measuring how much thickness it has permanently lost. Lower is better. The following data are from compound M534 — peroxide-cured EPDM at 70 Shore A nominal hardness.
| Test condition | Standard | Compression set |
|---|---|---|
| 22h at 100°C | ISO 815-1 Met. A | 7% |
| 70h at 100°C | ISO 815-1 Met. A | 10% |
| 22h at 125°C | ISO 815-1 Met. A | 10% |
| 70h at 150°C | ISO 815-1 Met. A | 20% |
| 1000h at 110°C in water | DVGW W534 | 10.5% |
| 2000h at 110°C in water | DVGW W534 | 15.5% |
| 3000h at 110°C in water | DVGW W534 | 19.5% |
The DVGW W534 rows are the most relevant for water supply and plumbing applications. After 3000 hours at 110°C in water, the reported M534 compression set is 19.5%, compared with 10.5% at 1000 hours. These are compound-specific DVGW W534 results. They should not be used to quantify an advantage over a sulphur-cured compound unless both materials are tested side by side under the same method and conditions.
Peroxide vs sulphur — the practical differences
| Property | Peroxide cured | Sulphur cured |
|---|---|---|
| Compression set — short term | M534 data available | Use matched grade data |
| Compression set — long term heat | Compare matched test data | Compound-dependent |
| Thermal stability of cross-links | High — C–C bonds | Moderate — S bridges |
| Hot water resistance | Verify the M534 service envelope | Verify the exact sulphur-cured grade |
| Low temperature (static) | To -65°C | Typically to ~-40°C |
| Low temperature (dynamic) | To -45°C | Typically to ~-25°C |
| Ozone and UV resistance | Excellent | Excellent |
| Material cost | Higher | Lower |
The key distinction is long-term behaviour under heat. For short-duration, moderate-temperature applications, both perform adequately. For sustained hot water contact, elevated temperatures in plumbing and heating systems, or outdoor installations with thermal cycling, the difference in compression set behaviour becomes operationally significant.
Where peroxide curing is the correct specification
Peroxide-cured EPDM is usually the appropriate choice when one or more of the following apply:
- Sustained hot water contact above 100°C — heating systems, hot water circulation, DHW distribution
- The O-ring will be under continuous compressive load for extended periods — valve seats, pump housings, static seals in pressurised systems
- The installation is outdoor and will experience UV exposure, ozone and thermal cycling between cold and warm
- The system operates near the upper end of EPDM's temperature range — where sulphur cross-link degradation becomes measurable in service
- Long-term hot-water performance data or supporting water-service test data is required — DVGW W534 immersion results are relevant here
- Quick-connect outdoor water fittings and hose couplings — where the seal sits under repeated connection cycles, weather exposure and seasonal temperature change
The decision logic: if the application is water, heating, HVAC or outdoor and the O-ring will be under sustained load at elevated temperature, peroxide curing is generally the more appropriate specification. The cost difference per unit is small relative to the cost of a seal failure in a pressurised system.
Why peroxide EPDM matters in quick-connect garden fittings
Beyond hot-water and heating duty, peroxide-cured EPDM is also highly relevant for quick-connect outdoor water fittings, hose couplings and garden tap connectors — where the O-ring is exposed to water, UV, ozone, seasonal temperature swings and repeated connection cycles.
A quick-connect O-ring sits outdoors for months at a time. It sees cold starts in winter, warm tap water in summer, UV and ozone from sunlight, and repeated connect-disconnect cycles. It is a small seal, but failure is immediately visible as a leak at the coupling. Outdoor exposure, repeated cycling, contaminants and an unsuitable gland can age either compound. Cure system is one selection variable, not a one-season life predictor.
A suitably formulated peroxide-cured grade may retain recovery well through that cycle, but a dry connection still depends on correct size, squeeze, stretch, surface condition, lubricant compatibility and the actual exposure.
If the job is a leaking garden quick connector, outdoor tap fitting or hose coupling: the right answer is not a generic black O-ring. It is the correct peroxide-cured EPDM size or service assortment. Do not select a generic black ring by appearance. Compare compound documentation and use the correct size and gland condition; M534 has long-duration hot-water compression-set data, while another grade needs equivalent evidence for a fair comparison.
Where peroxide EPDM is not the right choice
EPDM — peroxide or sulphur — is not suitable for contact with oils, fuels, aliphatic hydrocarbons, mineral oils or chlorinated solvents. This is a property of the base polymer, not the curing system. The curing system affects thermal and compression behaviour, not chemical resistance to hydrocarbons.
For applications involving oil, fuel or solvent contact, NBR (nitrile rubber) is the standard specification. NBR has good oil and fuel resistance but poor ozone, UV and hot water resistance — the inverse of EPDM's profile.
Not suitable for oils and fuels. Contact with hydrocarbons causes rapid swelling and loss of mechanical properties regardless of curing system. An EPDM O-ring in a fuel application will fail. Specify NBR for oil and fuel contact.
Peroxide EPDM vs NBR — where each fits
| Property | Peroxide EPDM | NBR |
|---|---|---|
| Hot water / air service | To +150°C where supported by the compound data; steam requires separate verification | Not recommended |
| Cold temperature (static) | To -65°C | To -30°C typically |
| Ozone resistance | Excellent | Poor — cracks |
| UV resistance | Excellent | Limited |
| Outdoor long-term use | Well suited | Not recommended |
| Mineral oils & fuels | Not suitable | Good resistance |
| Potable water systems | Appropriate where compound documentation and listing scope match | Not appropriate |
| Compression set — sustained heat | Low | Moderate |
A note on compound data
When evaluating an EPDM compound, the compression set data at multiple time and temperature points tells you more than any single hardness or tensile strength value. Hardness and tensile are easy to match between compounds. Long-term compression set under sustained heat is harder to optimise — it reflects the quality of the cross-link network directly.
If a compound datasheet shows compression set only at short duration and low temperature, that does not give you the information needed to specify for a hot water or heating application with confidence. Look for data at 1000 hours or longer at 100°C or above. That is where the difference between curing systems becomes visible in numbers.
Size range
The working Kinetics Line size reference for compound M534 is shown below. Current availability, pack quantity, exact compound documentation and any custom size must be confirmed through B2B before ordering or specifying.
| Dimensions (d1 × d2) | SKU 25 pcs | SKU 100 pcs |
|---|---|---|
| 2.60 × 1.90 mm | B-2014ORG01-25 | B-2014ORG01-100 |
| 3.40 × 1.90 mm | B-2014ORG02-25 | B-2014ORG02-100 |
| 4.20 × 1.90 mm | B-2014ORG03-25 | B-2014ORG03-100 |
| 4.90 × 1.90 mm | B-2014ORG04-25 | B-2014ORG04-100 |
| 5.70 × 1.90 mm | B-2014ORG05-25 | B-2014ORG05-100 |
| 6.40 × 1.90 mm | B-2014ORG06-25 | B-2014ORG06-100 |
| 6.75 × 1.78 mm | B-2014ORG54-25 | B-2014ORG54-100 |
| 7.20 × 1.90 mm | B-2014ORG07-25 | B-2014ORG07-100 |
| 8.00 × 1.90 mm | B-2014ORG08-25 | B-2014ORG08-100 |
| 8.90 × 1.90 mm | B-2014ORG09-25 | B-2014ORG09-100 |
| 8.90 × 2.70 mm | B-2014ORG10-25 | B-2014ORG10-100 |
| 10.50 × 2.70 mm | B-2014ORG11-25 | B-2014ORG11-100 |
| 12.00 × 2.00 mm | B-2014ORG41A-25 | B-2014ORG41A-100 |
| 12.10 × 2.70 mm | B-2014ORG12-25 | B-2014ORG12-100 |
| 12.37 × 2.62 mm | B-2014ORG53-25 | B-2014ORG53-100 |
| 13.00 × 2.00 mm | B-2014ORG42-25 | B-2014ORG42-100 |
| 13.00 × 2.50 mm | B-2014ORG37A-25 | B-2014ORG37A-100 |
| 13.60 × 2.70 mm | B-2014ORG13-25 | B-2014ORG13-100 |
| 14.00 × 1.78 mm | B-2014ORG50-25 | B-2014ORG50-100 |
| 14.00 × 2.00 mm | B-2014ORG45-25 | B-2014ORG45-100 |
| 15.00 × 2.00 mm | B-2014ORG46-25 | B-2014ORG46-100 |
| 15.10 × 2.70 mm | B-2014ORG14-25 | B-2014ORG14-100 |
| 16.00 × 2.50 mm | B-2014ORG37-25 | B-2014ORG37-100 |
| 16.90 × 2.70 mm | B-2014ORG15-25 | B-2014ORG15-100 |
| 17.17 × 1.78 mm | B-2014ORG51-25 | B-2014ORG51-100 |
| 18.00 × 1.00 mm | B-2014ORG56-25 | B-2014ORG56-100 |
| 18.00 × 2.00 mm | B-2014ORG41-25 | B-2014ORG41-100 |
| 18.30 × 3.60 mm | B-2014ORG17-25 | B-2014ORG17-100 |
| 18.40 × 2.70 mm | B-2014ORG16-25 | B-2014ORG16-100 |
| 18.77 × 1.78 mm | B-2014ORG52-25 | B-2014ORG52-100 |
| 19.80 × 3.60 mm | B-2014ORG18-25 | B-2014ORG18-100 |
| 20.00 × 3.00 mm | B-2014ORG44-25 | B-2014ORG44-100 |
| 21.00 × 2.00 mm | B-2014ORG47-25 | B-2014ORG47-100 |
| 21.30 × 3.60 mm | B-2014ORG19-25 | B-2014ORG19-100 |
| 23.00 × 3.60 mm | B-2014ORG20-25 | B-2014ORG20-100 |
| 24.60 × 3.60 mm | B-2014ORG21-25 | B-2014ORG21-100 |
| 25.00 × 3.00 mm | B-2014ORG43-25 | B-2014ORG43-100 |
| 26.20 × 3.60 mm | B-2014ORG22-25 | B-2014ORG22-100 |
| 27.00 × 3.00 mm | B-2014ORG38-25 | B-2014ORG38-100 |
| 27.80 × 3.60 mm | B-2014ORG23-25 | B-2014ORG23-100 |
| 28.00 × 3.00 mm | B-2014ORG38A-25 | B-2014ORG38A-100 |
| 29.00 × 2.00 mm | B-2014ORG48-25 | B-2014ORG48-100 |
| 29.00 × 3.00 mm | B-2014ORG38B-25 | B-2014ORG38B-100 |
| 29.30 × 3.60 mm | B-2014ORG24-25 | B-2014ORG24-100 |
| 30.00 × 3.00 mm | B-2014ORG39-25 | B-2014ORG39-100 |
| 30.80 × 3.60 mm | B-2014ORG25-25 | B-2014ORG25-100 |
| 31.00 × 3.00 mm | B-2014ORG39A-25 | B-2014ORG39A-100 |
| 32.50 × 3.60 mm | B-2014ORG26-25 | B-2014ORG26-100 |
| 33.00 × 3.00 mm | B-2014ORG40-25 | B-2014ORG40-100 |
| 34.00 × 3.00 mm | B-2014ORG40A-25 | B-2014ORG40A-100 |
| 34.10 × 3.60 mm | B-2014ORG27-25 | B-2014ORG27-100 |
| 35.60 × 3.60 mm | B-2014ORG28-25 | B-2014ORG28-100 |
| 37.30 × 3.60 mm | B-2014ORG29-25 | B-2014ORG29-100 |
| 38.00 × 2.00 mm | B-2014ORG55-25 | B-2014ORG55-100 |
| 40.00 × 3.00 mm | B-2014ORG49-25 | B-2014ORG49-100 |
| 43.82 × 5.34 mm | B-2014ORG31-25 | B-2014ORG31-100 |
| 59.69 × 5.34 mm | B-2014ORG32-25 | B-2014ORG32-100 |
Do not assume that every listed dimension is currently available in NBR. Ask B2B to confirm the compound, size, pack and lead time before substituting.
If the application calls for peroxide EPDM
Where the specification leads
When the application requires peroxide-cured EPDM rather than standard sulphur-cured EPDM, the next step is the correct compound in the correct size or service assortment — not a generic EPDM O-ring. If the job is a leaking garden quick connector, outdoor tap fitting or hose coupling — or a hot water system or HVAC connection — the specification leads to the same compound. Kinetics Line EPDM Peroxide O-Rings are based on compound M534 — a peroxide-cured EPDM at 70 Shore A with documented hot-water compression-set performance. Supporting references for M534 include WRAS BS 6920, KTW D2, W270, EN 681.1, DVGW W534 and current French water-contact documentation as stated in the compound file, as well as USP Class VI and 3-A Sanitary Standard. These references apply to the compound documentation and stated test scope; for applications where compound-specific documentation is required, current M534 technical data is available on request.
Peroxide curing is not a premium label. It is a specific technical property that matters in specific conditions.
For moderate temperature, short-duration or non-critical applications, sulphur-cured EPDM is adequate. For sustained hot-water or elevated-temperature duty, M534's long-duration compression-set results provide useful evidence. They do not by themselves predict installed service life or prove superiority over an untested comparison compound. Outdoor UV and ozone resistance come from the EPDM base polymer, not from the curing system.
The decision is straightforward once the operating conditions are defined. For sustained heat, long service intervals or hot-water contact, compare the exact compound's long-duration data with the real gland and medium. The 1000, 2000 and 3000 hour M534 results are useful inputs, not the whole specification.