A press fitting is only as good as the seal inside it. The steel holds the joint mechanically, but the ring seal is what keeps the fluid in, and different fluids need different rubbers. The Standard Press 316 stainless system uses a colour-coded set of three, so you can tell what a fitting is set up for by looking at the socket mouth.
The three seals at a glance
| Colour | Material | Service | Rated temperature | Sizes |
|---|---|---|---|---|
| Black | EPDM | Potable water (fitted as standard) | -20°C to +110°C | All fittings |
| Yellow | NBR | Natural gas | -20°C to +70°C | 15mm to 108mm |
| Green | FKM | Oils, fuels, high-temperature media | -20°C to +180°C | 15mm to 168.3mm |
There's also a green FKM flat gasket for the stainless press unions, 15mm to 54mm, for union joints carrying oils, fuels or high-temperature media.
Availability note: every stainless press fitting ships with the black EPDM seal. The replacement yellow NBR seals, green FKM seals and FKM union gaskets are listed in the range but not yet available to order online, so contact PSA if your job needs them.
Black EPDM: the default for water
EPDM handles hot and cold water, resists ageing and is what every stainless press fitting arrives with. Its -20°C to +110°C rating covers domestic and commercial hot water services, heating and chilled water.
Where EPDM is the wrong choice:
- Oils and fuels. EPDM swells and degrades in contact with petroleum products.
- Solar collector circuits and high-temperature hot water. Stagnation temperatures can exceed 110°C. In copper, the Standard Press solar range uses red FKM seals for exactly this reason. See EPDM vs FKM seals for solar and high-temp water.
- Compressed air carrying compressor oil. Oil-laden air can attack EPDM. Confirm the seal choice with PSA for air lines.
Green FKM: oils, fuels and heat
FKM (often called Viton) resists oils, diesel and fuels and holds up to +180°C. It's the seal for generator fuel lines, lubrication systems and high-temperature process lines. It isn't a drop-in upgrade for everything: use the seal the service calls for, not the one with the biggest temperature number.
Yellow NBR: gas, with a caveat
NBR is the seal for natural gas, and the yellow colour flags a gas fitting at a glance. Its rated range is narrower, -20°C to +70°C.
Be careful here. Gas work in Australia is done by a licensed gasfitter to AS/NZS 5601.1, and the fittings used have to be certified for gas. Swapping a black seal for a yellow one in the field isn't a substitute for using a fitting system certified for the gas service. Before specifying stainless press on a gas line, confirm the gas certification with PSA and your gas technical regulator. On copper, the same principle is why water and gas press fittings aren't interchangeable.
Good practice with seals
- Check the colour before you press, every time. A fitting from the wrong box is the most common seal mistake.
- Look for damage. A nicked or displaced seal fails. Deburr tube ends inside and out so the seal isn't cut on insertion.
- Don't lubricate with anything the seal isn't compatible with. Petroleum grease on EPDM is a classic error. Use water or a lubricant approved for the seal.
- Label the line where the service isn't water, so the next trade doesn't fit a black-seal fitting into a fuel line.
Pressing technique matters as much as the seal. See M-profile jaws for stainless press.
Frequently Asked Questions
What seal comes in Standard Press stainless fittings?
Black EPDM, for potable water, rated -20°C to +110°C. Yellow NBR and green FKM replacement seals are listed in the range for other services.
Which press seal is for oil or diesel?
Green FKM, rated -20°C to +180°C. EPDM should not be used with oils or fuels.
Can I use stainless press on gas by fitting a yellow seal?
Not on that basis alone. Gas installations need fittings certified for gas, installed by a licensed gasfitter to AS/NZS 5601.1. Confirm the gas certification with PSA and your gas regulator first.
Is the black EPDM seal OK for solar hot water?
Not for solar collector circuits, where stagnation temperatures can exceed its +110°C rating. Use a system with seals rated for the temperature, such as the copper solar press range with red FKM seals.