JUNE-JULY 2018 JAN-FEB 2018 | Page 58

BOOK IN SERIES
“ This article has been excerpted from the textbook “ Electro-Hydraulic Components and Systems ”
ISBN : 978-0-9977634-2-3
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Hydraulics Versus Electrical Systems - CHAPTER 1

Author Dr . Medhat Khalil
1.1.2.5- Energy Storage Elements ( Capacitive Elements )
Each of the two systems has Capacitive Elements of different sizes to store energy . As shown in Fig . 1.14 , Capacitors ( 1 ) or Batteries ( 2 ) are used to store electrical energy . Accumulators ( 3 ) are used to store hydraulic energy . The amount of stored energy and the charge time is proportional to the size of the capacitive element in both systems . It is known for fact that electrical capacitive elements have larger Energy Density than hydraulic accumulators . effort variable across the element in order for flow to pass through the element in the forward direction . Minimum Cracking Pressure is required to open a check valve . Barrier Voltage is required to open the diode .
1 2
1
Figure 1.15 - Non Return Elements
Figure 1.14 - Energy Storage Elements
1.1.2.6- Non-Return Elements
3
Each of the two systems has a Non-Return Element of different sizes to prevent flow in the reverse direction . As shown in Fig . 1.15 , Diodes ( 1 ) are used in electrical systems and Check Valves ( 2 ) are used in hydraulic systems . Both diodes and check valves require a minimum value of the
2
1.1.2.7- Electrical versus Hydraulic Power Control Elements
From what has been previously discussed , electrical control elements have the following advantages over the hydromechanical valves :
• Controllability : because of the digital control capabilities , electrical control elements perform expanded , reprogrammable and smarter control functions than hydro-mechanical valves .
• Closed-Loop Control : hydro-mechanical components can ’ t be used to build closed loop control system with electrical feedback . They can perform limited closed control with mechanical feedback such as in pressure compensated , power limited and load sense pumps .
• Size : electrical control elements are smaller in size for the same power .
• Material : electrical control elements are produced from less amount of material .
• Production Process : electrical control elements require less physical production process . Hydraulic valves require casting , machining , forging , heat treatment , etc .
58 Global MDA Journal may 2018