For flow rates of around 120 l/min, controlling the machines is relatively simple – a standard distributor (e.g., CETOP 05 ) with a suitably large solenoid coil is sufficient. But what if you're building a powerful press and the pump pumps 200, 500, or even 1,000 liters of oil per minute ?
With such dimensions, a standard coil becomes useless. The hydrodynamic forces pressing on the slider are so enormous that no electromagnet could move it. That's where electrohydraulic (pilot) control comes into play.
BRhydraulic experts explain how two-stage giants work in accordance with CETOP 07, 08 and 10 standards and how to avoid costly mistakes when setting them up.
1. How does a pilot valve (two-stage) work?
Manifolds such as CETOP 07 (NG16), CETOP 08 (NG25) or CETOP 10 (NG32) always consist of two elements, resembling a "sandwich":
-
At the bottom is the main valve: It's a massive cast iron block with a large working slide. It has no coils, but rather large side chambers.
-
At the top is the "pilot" (control valve): This is usually a standard, small CETOP 03 (NG6) size solenoid valve with two coils.
How it works: When you apply voltage to the coil of the small upper valve, it opens the flow to just a few liters of oil. This pressurized oil (called pilot oil) flows into the side chamber of the lower valve and moves the powerful main spool with enormous force. In other words, we use small pressure to control large pressure .
2. Internal or External Control? (The Mystery of Channels X and Y)
This is the most important design decision when purchasing pilot valves. On the manifold, in addition to the standard P, T, A, and B ports, you'll find additional X and Y ports.
-
Internal control: The pilot valve (top) "picks up" the pressure from the machine's main supply channel.
-
The catch: If the main valve is in the center position, open to the tank (relieving the pump), the pressure in the entire system drops to zero. Then the pilot has nothing to draw on, and the main valve won't move at all!
-
-
External Control (Recommended for heavy machinery): The small control valve (pilot) has its own independent oil supply through port X (e.g., from an additional, small gear pump). Used oil from the pilot flows through a separate port Y directly to the tank.
-
Why is this better? This completely isolates the valve from powerful impacts and pressure drops in the main cylinder circuit of a press or excavator.
-
3. Throttle Plate – How to avoid pipe explosions in the machine?
Imagine a forearm-sized slider shutting off 800 liters of oil per minute (in a CETOP 10 valve) in a fraction of a second. The shock wave (water hammer) would literally rupture the pipes, destroy the pump, and strip the threads.
To prevent this, a throttle plate (switch delay) is installed between the small pilot and the large main valve. This restricts the flow of pilot oil, allowing the powerful lower spool to move slowly and gracefully. The shift time can be smoothly adjusted from fractions of a second to several seconds, ensuring a smooth and safe start.
Summary
Operating at flow rates between 150 and 1100 l/min doesn't forgive amateur design errors. Selecting the NG16, NG25, or NG32 standard requires detailed knowledge of flow rates, external power supply (X/Y), and pressure surge suppression systems.
In the BRhydraulic store you will find professional standard solenoid valves CETOP 07 , CETOP 08 and CETOP 10 Fully configurable for control and flow. Are you running an industrial project? Our engineers will be happy to help you assemble the right valve block!