You want to add an additional function to your machine - e.g., bale grab control in a loader. So you buy a second, smaller control valve, connectors, and hoses. You look at the old control valve: power from the pump (P) and return to the tank (T). You come up with a brilliant, simple idea: "I'll unscrew the return hose (T) from the first control valve and connect it to the power supply (P) of the second one!"
You start the tractor, pull the lever, and suddenly hear a loud CRACK. The cast iron casing of the first control valve breaks in half, and oil floods the entire workshop. What went wrong?
BRhydraulic experts explain why connecting control valves "in series" is the shortest path to system destruction and how one inconspicuous sleeve saves the day.
1. Fatal mistake: Connecting port T (Tank) to port P (Pump)
Why did the control valve housing break? The problem lies in the design of the internal channels.
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Port P (Pressure): It is designed to withstand powerful pressure surges of 250-300 bar. The thick cast iron casing handles this force without problems.
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Port T (Return): This is the outlet channel. The walls around it are very thin, as the oil is supposed to flow freely from here, without any resistance, straight to the tank (pressure close to 0 bar).
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What happens when you connect T to P of the second control valve? When you block the flow on the second control valve (or try to lift a heavy load with it), enormous pressure (e.g., 160 bar) builds up in the line between them. This pressure "reverses" to the thin-walled T port in the first control valve. The housing cannot withstand it and simply bursts.
2. Pressure sleeve (Carry-Over / Power Beyond) – Your savior
To correctly and safely connect two control valves, you need a pressure sleeve (often referred to as a Carry-Over sleeve). This is a special, threaded nipple with an extension and an O-ring at the end.
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How does it work? The sleeve is screwed into a specially prepared port in the first control valve (most often marked with the letter N). Its long "nose" with a seal goes deep into the control valve body and physically separates the high-pressure channel from the tank channel inside.
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Effect: Oil not used by the first control valve flows through the sleeve under full pressure directly to the second control valve, bypassing the delicate return channel (T).
3. How to correctly connect a series system?
No more guessing. Here is the only 100% correct and safe diagram for connecting two control valves in an open hydraulic system:
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Main supply: The pump delivers oil to port P in Control Valve No. 1.
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Power Beyond (Carry-Over): From port N (with the pressure sleeve screwed in) in Control Valve No. 1, you run a hose to port P (supply) in Control Valve No. 2.
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Returns (Critical point!): From both control valves, ports T (return) must be connected to each other (e.g., using a tee) and routed loosely, directly to the oil tank. No valves along the way!
Summary
Never skimp on the correct connection diagram. The cost of a pressure sleeve is usually a few dozen zlotys, while a new control valve and cleaning dozens of liters of oil from the floor can cost thousands. If you plan to expand the hydraulics in your tractor - write to us, we will gladly draw a safe diagram for you!
