Choosing an actuator for a machine you're building seems simple – it needs to lift or push a specific weight. However, a key question arises at the point of purchase: should you choose a single-acting or double-acting version?
A poor choice isn't just a problem with installation. Connecting the actuator to the wrong hydraulic distributor can result in hose rupture, oil boiling, or even pump damage.
BRhydraulic experts explain how to recognize both types of actuators, how they work, and – most importantly – how to avoid the most expensive mistakes when connecting them.
1. Double-acting cylinder – Full control in both directions
This is the most popular and versatile type of actuator . You'll recognize it at first glance: it has two connections (ports) for hydraulic hoses .
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How does it work? Oil is pumped out of the pump alternately. When you apply pressure to the lower port, the cylinder extends (pushes). To retract it, you apply pressure to the upper port – then the oil pushes the piston rod back, and the lower chamber freely flows back into the reservoir.
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Application: Wherever force is needed in both directions: front loader arms (Tur), excavators, workshop presses or steering systems (power steering).
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Control: Requires standard hydraulic control valve (double acting section with ports A and B).
2. Single-acting actuator – Gravity (or spring) force
This type is structurally simpler. It typically has only one connection for a hydraulic hose. Inside, there's often no full piston, only a plunger.
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How does it work? Pressurized oil flows into the cylinder and forces the piston rod upward (e.g., when lifting a dump truck bed). When you want to lower the load, you simply open the valve (control lever) to allow the oil to flow freely. The oil returns to the reservoir under the influence of the load itself (gravity) or a return spring built into the cylinder.
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Application: Agricultural tippers (trailers), workshop lifts (frogs), forklifts (main mast).
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Control: Requires special distributor section (plunger/single acting).
3. The most expensive mistake: Single-sided actuator for a standard distributor
Imagine you have a standard double-acting distributor (two outlets: A and B) on your tractor. You want to connect a dump truck (single-acting cylinder with one hose) to it. You connect the hose to port A and leave port B unoccupied (or worse yet, plug it with a steel plug!).
What happens when you pull the lever to lower the dump truck? The valve connects port A to the return (the dump truck begins to lower), but it also forces full pressure oil from the pump into the plugged port B. The pump has nowhere to push the oil. The relief valve starts whining, the oil boils rapidly, and the pump is under tremendous strain.
How do I connect it correctly? You have two options:
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The ideal solution: Install a special single-acting (plunger) valve in the distributor or replace one section. At BRhydraulic, you'll find ready-made valves specifically designed for dump trucks.
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Workshop Solution: If you must use a standard section, connect the unused port in the distributor (B) directly to the free drain to the tank (T-line) with a special hose. Then, when the actuator is lowered, the pump will "grind" oil from port B directly into the tank, without resistance or risk of failure.
Summary
Choosing the right actuator is only half the battle – what you'll be controlling it with is crucial. If you're unsure whether your valve body will support the actuator in your machine, consult us. BRhydraulic offers both double-acting actuators and dedicated valve bodies , ensuring trouble-free operation of the entire system.
