Hydraulic fluid: functions, systems & application

Hydraulic systems

The components which make up a hydraulic system are essentially the same, regardless ofScreen Shot 2017-03-02 at 10.59.02
the application. There is a hydraulic fluid reservoir, a pump to force the fluid through the system, an electric motor or other power source to drive the pump and valves that control the direction of flow, pressure and flow rate. Then, actuators are employed to convert the energy of the fluid into mechanical force or torque to do the useful work. Actuators can be either cylinders to provide linear motion or motors for rotary motion. Finally, all the components are connected by pipes and hoses to convey the fluid from one location to another.

Hydraulic fluid main functions and applications

The primary function of any hydraulic uid is to transfer power throughout a hydraulic system.

The hydraulic fluid also acts as the lubricant of all moving parts (e.g. cylinders and pumps) of the system and protects it against corrosion. Compatibility with seals and hoses is also a major issue with hydraulic fluids, as different systems have completely different requirements.

Hydraulic systems that can be found in a vehicle include (amongst others) certain power steering systems, stability control, traction control, hydraulic clutches, hydraulic systems on convertibles and some central locking mechanisms however, different applications make completely different demands on the fluids. Fluids for hydraulic systems are selected per several operating conditions such as load, speed, temperature, as well as any special requirements for the type of end use application of the specific hydraulic system.

What is hydraulic fluid made of?

Hydraulic uid formulations vary greatly with speci cation however, a typical formulation includes a base oil (mineral or synthetic based) and an additive package. The additive package typically includes anti-oxidants, anti-wear and anti-foam agents, emulsifiers/demulsifiers, corrosion inhibitors and viscosity-index improvers that are used to enhance properties such as resistance to oxidation, air release, thermal stability, anti-corrosion, extreme pressure, anti-wear and ltration performance.

Comma LDS Fluid

Following a strategy of vehicle parc coverage increase for hydraulic applications, the new Comma LDS Fluid has been introduced. This product is currently suitable for approximately 1.3M vehicles in the UK.

This fully synthetic formulated product is recommended for all applications requiring the PSA S71 2710 specification. Originally developed for use in the Citroën C5 Hydractive 3+ suspension system, it is also specified for use in power steering, stability control, hydraulic clutches, hydraulic systems on convertibles and some central locking mechanisms of PSA group vehicles (Peugeot, Citroën and DS) and vehicles using PSA Group components such as certain SsangYong and Toyota models.

Comma LHM +

Comma LHM + is an advanced mineral based product which has been used in the combined hydraulic systems of Citroens for years. It meets ISO 7308 and Citroen B71 2710 and is compatible with other LHM and LHM Plus uids meeting Citroen B712710. It is also suitable for certain Peugeot, Rolls Royce & Bentley models.


Comma MVCHF is a special synthetic oil based hydraulic fluid suitable for power steering, central hydraulic and suspension level control systems which require CHF11S* and CHF202*.

It is also suitable for certain stability and traction control systems, hydrostatically driven fans, generators and air conditioning units, control of convertible car top covers and central locking systems requiring any of the specifications listed below:

VW/Audi G 002 000/TL52146; BMW; Opel B040.0070; MB 345.00; Porsche; MAN 3623/93 CHF11S; ISO 7308; DIN 51 524T2

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