Hydraulic Quick-Release Coupling Types: ISO A, ISO B and Flat Face
Quick-release couplings let you connect and disconnect hydraulic lines without tools, but only if the two halves are the same type. Mixing incompatible standards is a common and frustrating mistake, because two couplings can be the same nominal size and still refuse to mate. This guide covers the three types you will meet most and how to specify the right one.
What are the main types of hydraulic quick-release couplings?
The short answer: the three most common are ISO 7241 Series A, ISO 7241 Series B, and ISO 16028 flat face. Series A and B are both poppet-style couplings that lock with a ball-and-sleeve mechanism and shut off automatically when disconnected, but they are dimensionally different and do not interchange. Flat-face (ISO 16028) couplings seal face-to-face before the internal valves open, giving a near-drip-free connection favoured on mobile equipment.
ISO 7241 Series A
Series A is a poppet-style coupling with male and female halves that lock together with a retractable sleeve and locking balls; internal shut-off valves stop leakage when disconnected. It is known for higher flow capacity and is common in Europe and in agricultural and forestry equipment.
- Choose it for: higher-flow general hydraulics, European and agricultural machinery.
ISO 7241 Series B
Series B works on the same poppet-and-ball principle but is more compact, suited to smaller equipment, and is common in North America and the chemical industry. Crucially, Series B is dimensionally different from Series A and the two cannot be connected, even at the same nominal size.
- Choose it for: more compact installations and equipment built to the Series B standard.
ISO 16028 flat face
Flat-face couplings are built to ISO 16028. Their flat faces mate and form a seal before the internal valves open, which minimises fluid loss and air inclusion during connect and disconnect, a near-drip-free action. That clean connection makes them the standard choice on skid steers and mobile equipment, and easier to keep contamination-free.
- Choose it for: clean, low-spill connection, mobile and construction equipment, contamination-sensitive circuits.
The interchangeability rule
Two rules cover almost every case:
- Different standards do not mix. ISO 7241 A, ISO 7241 B and ISO 16028 flat face are not interchangeable with each other. Both halves must be the same standard.
- Same standard usually does mix across brands. Couplings certified to the same ISO standard from different reputable brands will generally mate, because the standard fixes the critical dimensions.
When in doubt, confirm the standard on both halves before ordering rather than relying on nominal size.
Choosing the right coupling
| You need… | Choose |
|---|---|
| Higher flow, European / agricultural equipment | ISO 7241 Series A |
| Compact, Series B equipment | ISO 7241 Series B |
| Low-spill, clean connection on mobile equipment | ISO 16028 flat face |
Then confirm the body size, thread standard on the port end, pressure rating and material so the coupling suits the line, not just the mating profile.
The goal is a coupling that mates first time, whether you buy from us or not
We wrote this so you can match the standard on both halves and avoid the classic mismatch, wherever you source the coupling. Confirm the standard, not just the size, and you are most of the way there.
If you do want it sourced to spec, here is how we work: Velqor supplies ISO A and ISO B quick-disconnect couplings matched to your system size, thread standard and pressure requirement, confirmed against your requirement, tested and documented before dispatch. If a different standard would serve your equipment better, we will tell you rather than sell you the wrong one.
Frequently Asked Questions
Are ISO 7241 Series A and Series B interchangeable?
No. Although both are poppet-style couplings, Series A and Series B are dimensionally different and cannot be connected, even at the same nominal size. Both halves must be the same series.
What is the advantage of a flat-face (ISO 16028) coupling?
Flat-face couplings seal face-to-face before the valves open, so they connect and disconnect with minimal fluid loss and almost no air inclusion. That near-drip-free action keeps the system cleaner and is why they are standard on mobile equipment.
Will couplings from different brands work together?
Usually yes, if they are certified to the same ISO standard, because the standard fixes the critical mating dimensions. Couplings built to different standards will not mate regardless of brand.
Which coupling type is best for a skid steer?
ISO 16028 flat-face couplings are the common choice for skid steers and construction equipment because of their low-spill, contamination-resistant connection.
What else do I specify besides the coupling standard?
Confirm the body size, the thread standard on the port end, the pressure rating and the material, so the coupling fits the line and the port, not just the mating profile.