Hydraulic distributors – closed-loop vs open-loop systems

Published : 12/29/2017 20:46:54
Categories : Hydraulic valves

Hydraulic distributorsclosed-loop vs open-loop systems

It is really hard to imagine functioning of many fields of economy without hydraulic distributors nowadays. These devices are very widely used e.g. in mining, building, road building or agriculture machines. Hydraulic distributors regulate directions of flow of fluids in hydraulic systems and work in open-loop and closed-loop systems (circuits).

The article constitutes an attempt of short explanation of principles of operation, advantages and disadvantages of both hydraulic systems.

Hydraulic systems

Hydraulic systems are used for pressurising hydraulic fluids (usually vegetable or mineral oils) and controlling their flow directions. Fluids under pressure are used for transmitting power from one location to another. They move different parts of machines and facilitate manual or automatic steering making it quick and very precise. As fluids are only slightly compressible they do not require using much force to pressurise them. However, pressurised fluids have intense power and can do a lot of very effective work. To put it simply, fluid motions are forced by pumps and then fluid energy is being picked up by hydraulic cylinders changing energy of fluid streams into linear motion, or by hydraulic motors, which convert energy of fluid streams into circular motion.

Open-loop hydraulic systems

In open-loop hydraulic systems (or: open-loop circuits), a pump sucks fluid from a tank and forces it into a receiver. Fluid does the work and comes back to the tank, is sucked again by the pump and the whole cycle is repeated.

Additional tank or tanks enable better cooling and purification of hydraulic fluids. Due to these reasons, open-loop hydraulic systems are more resistant to overheating and possible damage. Their failure frequency is usually lower, so costs of operation and maintain are lower as well.

However, as open-loop systems are usually bigger, they rather cannot be used in tight spaces. Farther, they require greater amounts of hydraulic fluid, which is usually highly flammable. For that reason, it is not recommended using open-loop systems in areas especially threatened with fire or explosion.

Closed-loop hydraulic systems

In closed-loop hydraulic systems (also named: closed-loop circuits) hydraulic fluid circulates directly between the pump and the receiver. It gives its energy to the receiver, comes back to the pump and the whole cycle starts anew.

As there is no additional outer tanks with fluids in closed-loop circuits, they are usually more compact and more suitable to use in smaller machines and tight spaces.

On the other hand, closed-loop systems are much more complicated as they require additional steering elements and systems to complement occurring fluid leakage. For this reason, they are more subjected to overheating and more damageable. In the result, the whole machinery is more prone to contamination with e.g. dust and consequently more expensive to operation, maintain and repair.


To sum up, when choosing a hydraulic distributor one should take into consideration conditions of work environment. In vast areas, high temperatures, intense dustiness open-loop systems will be more suitable. Using closed-loop circuits is recommended mainly in tight spaces and moderate temperatures.



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