FLUID POWER P&IDsDOE-HDBK-1016/1-93Engineering Fluid Diagrams and PrintsWith the basic function understood, a detailed study of the diagram can be accomplished usinga step-by-step analysis of each numbered local area in the diagram.LOCAL AREA NUMBER 1 Symbol for an open reservoir with a strainer. The strainer is used to clean the oil beforeit enters the system.LOCAL AREA NUMBER 2 Fixed displacement pump, electrically operated. This pump provides hydraulic pressureto the system.LOCAL AREA NUMBER 3Symbol for a relief valve with separate pressure gage. The relief valve is spring operatedand protects the system from over pressurization. It also acts as an unloader valve torelieve pressure when the cylinder is not in operation. When system pressure exceeds itssetpoint, the valve opens and returns the hydraulic fluid back to the reservoir. The gageprovides a reading of how much pressure is in the system.LOCAL AREA NUMBER 4Composite symbol for a 4-way, 2-position valve. Pushbutton PB-1 is used to activate thevalve by energizing the S-1 solenoid (note the valve is shown in the de-energizedposition). As shown, the high pressure hydraulic fluid is being routed from Port 1 to Port3 and then to the bottom chamber of the piston. This drives and holds the piston in localarea #5 in the retracted position. When the piston is fully retracted and hydraulic pressurebuilds, the unloader (relief) valve will lift and maintain the system's pressure at setpoint.When PB-1 is pushed and S-1 energized, the 1-2 ports are aligned and 3-4 ports arealigned. This allows hydraulic fluid to enter the top chamber of the piston and drive itdown. The fluid in the bottom chamber drains though the 3-4 ports back into thereservoir. The piston will continue to travel down until either PB-1 is released or fulltravel is reached, at which point the unloader (relief) valve will lift. LOCAL AREA NUMBER 5Actuating cylinder and piston. The cylinder is designed to receive fluid in either theupper or lower chambers. The system is designed so that when pressure is applied to thetop chamber, the bottom chamber is aligned to drain back to the reservoir. When pressureis applied to the bottom chamber, the top chamber is aligned so that it drains back to thereservoir. PR-02Rev. 0Page 32
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