FLUID POWER P&IDs
Engineering Fluid Diagrams and Prints
With the basic function understood, a detailed study of the diagram can be accomplished using
a 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 before
it enters the system.
LOCAL AREA NUMBER 2
Fixed displacement pump, electrically operated. This pump provides hydraulic pressure
to the system.
LOCAL AREA NUMBER 3
Symbol for a relief valve with separate pressure gage. The relief valve is spring operated
and protects the system from over pressurization. It also acts as an unloader valve to
relieve pressure when the cylinder is not in operation. When system pressure exceeds its
setpoint, the valve opens and returns the hydraulic fluid back to the reservoir. The gage
provides a reading of how much pressure is in the system.
LOCAL AREA NUMBER 4
Composite symbol for a 4-way, 2-position valve. Pushbutton PB-1 is used to activate the
valve by energizing the S-1 solenoid (note the valve is shown in the de-energized
position). As shown, the high pressure hydraulic fluid is being routed from Port 1 to Port
3 and then to the bottom chamber of the piston. This drives and holds the piston in local
area #5 in the retracted position. When the piston is fully retracted and hydraulic pressure
builds, 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 are
aligned. This allows hydraulic fluid to enter the top chamber of the piston and drive it
down. The fluid in the bottom chamber drains though the 3-4 ports back into the
reservoir. The piston will continue to travel down until either PB-1 is released or full
travel is reached, at which point the unloader (relief) valve will lift.
LOCAL AREA NUMBER 5
Actuating cylinder and piston. The cylinder is designed to receive fluid in either the
upper or lower chambers. The system is designed so that when pressure is applied to the
top chamber, the bottom chamber is aligned to drain back to the reservoir. When pressure
is applied to the bottom chamber, the top chamber is aligned so that it drains back to the