Week 16 – Fluid Power – Part 2 (Fluid Power Components)Telehandler

What components make up a Fluid Power System?

As presented in our earlier Article 1 : Introduction to the amazing world of Fluid Power – Part 1, we discussed and described Fluid Power as the use of fluid under certain conditions to generate, transmit & control flow and pressure – which enables a work function to be completed.

The focus of this article is to look at the components that drive a fluid power system. The uniqueness for incorporating  Fluid  for transmitting power, requires an understanding of  six core levels of components that make up a fluid power system, these are:

  1. Input Prime mover power source (Electrical/Combustion type Engine)
  2. Fluid Reservoir
  3. Fluid Power – Pump System
  4. Pressure Control Valves
  5. Directional Control Valves
  6. Actuator Linear/Rotary

The Danfoss company (www.powersolutions.danfoss.com) has produced some fantastic application posters that illustrate very clearly how these components integrate the internal workings of a fluid power circuit. In fact one of their company tag lines, Said’s it best “What really matters is inside”

For this article we are introducing the key principals of these elements, as we delve deeper into this world of fluid power applications we will explore in more detail the many considerations  that will need to be considered when bringing a host of components together to build an efficient fluid power circuit. As a starting point  the following provides an outline of these key elements:

1. Fluid Reservoir

Tank/Hydraulic reservoir this is a fabricated container that holds oil required for the system. There are other parts in the tank like strainers/ filters and calculating reservoir sizes for a particular operation will be discussed later in the chapter.

2. Input Prime mover power source

Prime mover: – This is the main source of power. This can be an electrical motor, Engine etc:-

3. Fluid Power – The Pump System (Heart)

Fluid Power pumps:  The heart of Fluid Power system is the Pump, it’s  purpose is to transfer fluid from the reservoir through the maze of conduits of piping and fittings through to the actual actuator. At this point of the discussion it’s about understanding a pump creates flow, there are many forms of a pump designs and configurations, starting with the basic classifications options like,

1. Manual – Hand/foot pump

2. Power driven pumps

3. Fixed displacement

4. Variable displacement

5. Double pumps/ Tandem pumps Pressure compensated pumps:

Each of these elements will be presented in more detail later in this series of Introduction to wonderful world of fluid power systems.  However there is a very important principal that needs to be mentioned here because it forms the underlying thought process that must go into designing a Fluid Power System and that is the efficiency question.

There are two types of efficiency referred to in a fluid power system:

1) Volumetric efficiency

2) Hydraulic efficiency

Volumetric efficiency: Theoretical swept volume in Cubic centimetres (CC) per revolution of shaft/ Actual volume of liquid discharged in CC per revolution of shaft.

Hydraulic Efficiency:-. This is the ratio of input power to input power

Efficiency = Output power/ Input power.

This value varies from type of pumps, Manufacturers design & properties of oil used. Performance curves of hydraulic pumps: – Manufacturers’ Test hydraulic pumps after it is assembled & it is tested for its performance. The values are plotted in relation to discharge, pressure, volumetric efficiency, RPM, Power transmitted. These are called performance curves. A specific future article will be prepared on this very topic as it becomes a very interesting and important basis for being able to design efficient hydraulic systems.

4.Control Valves

Pressure control valves, Flow control valves & Direction control valves.

The principle of a Fluid System is to transform mechanical energy into a fluid power energy to complete a work function. So far we have discuss the principle of using a fluid power pump to generate flow to move an actuator to complete this work function, now we need to control this flow and this is achieved by using a range of control valves, there are six basic levels of control valves:

1. Directional Control Valve (DCV) – used to divert the flow of fluid from one port to another, most commonly used to control direction of a work function.

2. Pressure Valves – used most commonly as a safety function of the Fluid Power circuit, for example as a relief valve – design to allow the circuit not over pressurise.

3. Flow Control Valves – used to meter the amount of flow that flows into a specific function of the fluid power circuit.

4. Holding/Sequence Type Valves – used for specific functions to can occur in a Fluid power circuit.

5. Flow Dividers

Again each one of these elements will be explored in more detail as the impact of selecting an incorrectly sized valve will cause major efficiencies in this circuit design.

 5. Actuators

Actuators is the term used to describe the actual elements that used to perform the work function of the Fluid Power circuit.

Actuators have:

• Linear functions • Rotary Functions

Each of these will again be described in details as to sizing and selecting an actuator to complete a work function.


Next Article is about describing the fundamental purpose of what Fluid Power Systems is about – “Work” Fluid Power Circuits.com.au