CETOP is a valve sizing and mounting standard for four-port hydraulic directional control valves, now defined by ISO 4401. The size number refers to the mounting interface, not the valve function, and it sets the maximum flow the valve can pass. CETOP 2 (NG4) handles up to 25 l/min, CETOP 3 (NG6) up to 80 l/min, CETOP 5 (NG10) up to 120 l/min as a single stage valve or 160 l/min as a two stage, CETOP 7 (NG16) up to 300 l/min, CETOP 8 (NG25) up to 700 l/min and CETOP 10 (NG32) up to 1000 l/min. Because the interface is standardised, any manufacturer’s valve of the same CETOP size will bolt onto the same subplate, which is what makes cross-brand replacement possible. Hydraulic & Engineering Services (HESL) carries directional control valves, flow and pressure controls and modular stack components ex-stock at its Strood trade counter. Check availability or ask us to identify your valve.
What is CETOP?
CETOP stands for Comité Européen des Transmissions Oléohydrauliques et Pneumatiques, the European fluid power committee that originally published the mounting standards for hydraulic valves. The naming stuck, and engineers still say “CETOP 3” every day even though the governing document is now ISO 4401:2005, which specifies the dimensions of the surfaces on which four-port directional control valves mount, specifically so that valves from different manufacturers are interchangeable.
The point that trips people up is this: a CETOP size does not tell you what the valve does. It tells you the footprint. It fixes where the P, T, A and B ports sit, where the mounting holes go and how big they are. Two valves can both be CETOP 3 and behave completely differently, one a three position solenoid valve, the other a manual lever valve, because the size describes the interface and nothing else.
That is exactly why the standard is useful. If you have a CETOP 3 subplate on your machine, you can fit a CETOP 3 valve from Rexroth, Duplomatic, Yuken, Atos or anyone else, and it will bolt down and line up.
What do CETOP, NG and ISO 4401 numbers mean?
Three naming systems describe the same thing, which is the main reason for the confusion:
- CETOP is the European committee designation, for example CETOP 3.
- NG comes from the German DIN 24340 standard and refers to the nominal port size in millimetres, for example NG6.
- ISO 4401 is the current international standard and uses the size in the code, for example ISO 4401-03.
So CETOP 3, NG6 and ISO 4401-03 are the same interface. A supplier quoting you an “NG6 solenoid valve” and one quoting a “CETOP 3 solenoid valve” are offering a valve with the same mounting pattern. Once you know that, most catalogue confusion disappears.
CETOP valve sizes and flow ratings compared
The size you need is driven by flow, not by pressure and not by cylinder size. Undersize the valve and you generate pressure drop, heat and sluggish actuators. Oversize it and you pay for capacity you never use and lose some control resolution.
| CETOP size | ISO 4401 code | NG equivalent | Max flow (l/min) | Typical application |
|---|---|---|---|---|
| CETOP 2 | ISO 4401-02 | NG4 | Up to 25 | Compact power packs, small actuators, test rigs |
| CETOP 3 | ISO 4401-03 | NG6 | Up to 80 | The common workhorse: most industrial and mobile circuits |
| CETOP 5 | ISO 4401-05 | NG10 | Up to 120 single stage, up to 160 two stage | Larger cylinders, grabs, heavier plant |
| CETOP 7 | ISO 4401-07 | NG16 | Up to 300 | Heavy industrial machinery, larger presses |
| CETOP 8 | ISO 4401-08 | NG25 | Up to 700 | Large presses, marine and heavy plant |
| CETOP 10 | ISO 4401-10 | NG32 | Up to 1000 | Very high flow systems |
Maximum flow figures are the industry standard ratings published for each interface size, as set out in this guide to CETOP valve sizes. Individual manufacturers state their own limits within these bands, and those limits often depend on the spool fitted and the pressure drop you are willing to accept, so always check the datasheet for the exact model rather than assuming the band maximum.
Working pressure is a separate specification. Most CETOP 3 and CETOP 5 valves are rated somewhere between 250 and 350 bar depending on the manufacturer and the port. Size and pressure rating are independent decisions.
CETOP 3 vs CETOP 5: which do you need?
This is the decision most people are actually making, because between them these two sizes cover the large majority of industrial circuits.
Choose CETOP 3 (NG6) when your circuit flow is comfortably under 80 l/min. It is the most widely stocked size in the world, the cheapest to buy, the smallest to package and the one with the deepest range of spools, solenoid options and modular stack components available off the shelf. If you are near the top of its range, look closely at the pressure drop curves before committing.
Choose CETOP 5 (NG10) when flow exceeds what a CETOP 3 will pass without excessive pressure drop, typically above 70 to 80 l/min. A single stage CETOP 5 covers up to 120 l/min. If you need more, a two stage (pilot operated) CETOP 5 will take you to around 160 l/min, which is often cheaper and more compact than jumping up to a CETOP 7.
The practical test is simple. Calculate your actual maximum flow through the valve, add a margin, then pick the smallest size that passes it without a pressure drop your circuit cannot absorb. Guessing from the size of the machine is how systems end up running hot.
For reference, a CETOP 3 valve mounts on an interface with four M5 threaded holes on a 31.75 mm by 31.75 mm bolt pattern, which is why a CETOP 3 valve is unmistakable once you have seen one.
Are CETOP valves from different manufacturers interchangeable?
Mechanically, yes, and that is the whole purpose of the standard. A CETOP 3 valve from one manufacturer will bolt to a CETOP 3 subplate designed for another. This is what lets you replace an obsolete valve without re-machining a manifold.
Functionally, you still have to match four things:
- Spool configuration. The centre condition and the flow paths must match your circuit. Manufacturers use different letter codes for the same spool, so never assume that a code carries across brands.
- Actuation and voltage. Solenoid operated, lever, hydraulic pilot or air pilot, and if solenoid, the correct voltage: 12V DC, 24V DC, 110V AC or 230V AC.
- Flow and pressure rating. Confirm the replacement is rated for your working pressure and passes your flow.
- Port pattern variant. ISO 4401 codes include a port pattern element as well as a size, covering options such as drain ports or pilot ports. A CETOP 5 with a drain port is not identical to one without.
Get all four right and the swap is straightforward. Get the spool wrong and the machine will move, just not the way you expect. This is the single most common mistake we see across the trade counter, and it is why we ask for the full part number or a photograph of the valve nameplate rather than just the size.
What are the spool centre options and why do they matter?
For a 4/3 valve (four ports, three positions), the centre condition determines what happens when the valve is at rest. That behaviour is a design decision, not a detail:
- Closed centre. P, T, A and B are all blocked. The actuator is hydraulically locked and pump pressure is maintained. Standard choice where a load must be held.
- Tandem centre. P is connected to T while A and B are blocked. The actuator holds position while the pump is unloaded back to tank, which saves energy and reduces heat on fixed displacement systems.
- Open centre. All ports are connected. Pump flow circulates freely to tank and no pressure builds.
- Float centre. A, B and T are connected while P is blocked. The actuator can move freely under external force, which is what lets equipment follow ground contours.
If a machine will not hold its load in neutral, or if the system is running hot for no obvious reason, the spool centre condition is worth checking before anything gets stripped. It is a common cause of a fault that gets misdiagnosed as a worn cylinder. Our guide to hydraulic cylinder failure causes and warning signs covers how to tell the difference between a drifting load caused by valve bypass and one caused by a failed piston seal.
How do you identify a CETOP valve you already have?
If you are trying to replace a valve on an existing machine, work through this in order:
- Read the nameplate. The manufacturer’s part number is the fastest route. A Rexroth 4WE6 is a CETOP 3, a 4WE10 is a CETOP 5, and the model number encodes the spool and voltage.
- Count and measure the bolts. Four M5 bolts on a roughly 32 mm square pattern means CETOP 3. Larger patterns with M6 or bigger step you up the range.
- Check the subplate, not just the valve. The interface belongs to the manifold. That is what your replacement has to match.
- Note the coil voltage. It is usually printed on the coil body or the DIN connector.
- Photograph the hydraulic symbol. Most valves carry the ISO 1219 symbol on the nameplate, which tells you the spool configuration directly.
If the plate is unreadable, which is common on plant that has been in service for twenty years, bring it in. Identifying obsolete and unmarked valves from the hardware itself is routine work for our team, and if the original is genuinely unavailable we can specify a current equivalent or design the circuit change around it through our hydraulic design service.
Keeping the right CETOP valves on the shelf
The reason CETOP 3 dominates is availability. When a machine goes down, the difference between a two hour fix and a two week wait is usually whether the valve is in stock somewhere nearby. For plant that cannot afford downtime, holding a spare directional control valve and coil for your critical circuits is one of the cheapest pieces of insurance available, and it is standard practice on the energy from waste and rail sites we support.
The same logic applies to the attachments those valves control. Grab circuits in particular run hard, and a valve fault on a grab is often mistaken for a mechanical problem with the attachment itself, which is why our Kinshofer grab repair work usually starts with checking the control side before anything is stripped. Equally, if a cylinder is drifting, it is worth deciding whether the valve or the cylinder is at fault before booking work in, and our guide to hydraulic cylinder repair vs replacement sets out how that decision is made.
HESL holds directional control valves, flow and pressure controls, pumps, motors, filtration, hoses and fittings on an ex-stock basis at the trade counter in Strood. Bosch Rexroth is our primary partner, so we have direct access to the full Rexroth valve range including the 4WE6 (CETOP 3) and 4WE10 (CETOP 5) families, alongside stock from Atos, Staffa and Kawasaki, backed by next day supply. Whether you are replacing a single CETOP 3 solenoid valve or specifying a full modular stack for a new power pack, we can identify the part and confirm availability the same day.
Working to ISO 9001:2015 and Achilles accreditation, our team supports industrial, mobile, marine, rail and utilities customers across England from the Medway workshop.
Need a CETOP valve identified, matched or supplied? Talk to our team or call 01634 295 650. Send us the part number or a photo of the nameplate and we will tell you what it is and what we can get.
FAQ
What does CETOP mean on a hydraulic valve? CETOP is a European standard for the mounting interface of four-port hydraulic directional control valves, now defined internationally by ISO 4401. The CETOP number identifies the size of the mounting surface and the maximum flow the valve can pass. It does not describe the valve’s function.
Is CETOP 3 the same as NG6? Yes. CETOP 3, NG6 and ISO 4401-03 all describe the same mounting interface. CETOP is the European committee designation, NG comes from the German DIN 24340 standard, and ISO 4401 is the current international standard.
What flow can a CETOP 3 valve handle? A CETOP 3 (NG6) valve handles a maximum flow of up to 80 litres per minute. The exact limit depends on the spool fitted and the acceptable pressure drop, so check the manufacturer’s datasheet for your specific model.
What is the difference between CETOP 3 and CETOP 5? CETOP 3 (NG6) passes up to 80 l/min and CETOP 5 (NG10) passes up to 120 l/min as a single stage valve or up to 160 l/min as a two stage valve. CETOP 5 has a larger mounting interface and larger ports. Choose CETOP 5 when your flow exceeds roughly 70 to 80 l/min.
Are CETOP valves interchangeable between manufacturers? Mechanically yes, which is the purpose of the standard. Any CETOP 3 valve will bolt to a CETOP 3 subplate. You must still match the spool configuration, the actuation type and coil voltage, the pressure and flow rating, and the ISO 4401 port pattern variant.
What is the biggest CETOP valve size? CETOP 10 (NG32) is the largest common size and handles a maximum flow of up to 1000 litres per minute. The range runs CETOP 2, 3, 5, 7, 8 and 10.