Constant pressure - Hydraulic system 1

[tomm0005]

Goodmorning, I have a question related to the aircraft's hydraulic system. Specifically, while I was studying I've run into this concept: "A hydraulic system works at constant pressure", what does it mean? Could you give me an exemple of a plant that works at constant flowrate?

 

[LittleInch]

It means exactly what it says.

The hydraulic pressure is maintained at a fixed pressure regardless of flowrate.

Many plants work at a constant flowrate e.g.. an oil refinery or chemical plant.

Vague question so vague answer....

 

[rb1957]

Not really my specialty but here goes ...

draw a systematic drawing of a hydraulic system. the key features are tubing (doh), an actuator, a return line (to a sump or reservoir [we have a technical name, just not coming to mind]), and a pump.

Pump supplies pressurised fluid to the line (from the reservior) to the actuator. A valve will open for the actuator to do work, causing some fluid to flow, and be discharged back into the sump/reservoir.

I really can't think of any other types of hydraulic system; maybe plants (ground-based refineries) use constant flow rate.

 

[3DDave]

Where exactly did this come from and what was the rest of the paragraph talking about?

 

[Compositepro]

I believe the question is regarding hydraulic power systems. Constant pressure means that the supply pressure is kept constant, whatever the flow. This requires a variable displacement pump, which is relatively more expensive and complex to control. Most systems are constant flow because they use a less expensive constant speed gear pump. When the load requires less than full flow, the excess is returned to the tank through a relief valve that sets the system operating pressure. If no flow is needed, the pump's flow is returned to the tank through an open valve so there is little pressure. Thus the pump uses little power. When there is any work to do, the valve to tank closes and the pressure increases to relief valve pressure. Thus the system consumes full power whenever any load is applied. It is not energy efficient but it is cheap, simple, and robust.