Section 35 Chapter 1 - dmcpubs.com

1 Section 35 Chapter 1 8-94372 NHHow to Read symbols in a Hydraulic SchematicSECTION 35 - HOW TO READ symbols IN A HYDRAULIC SCHEMATIC - Chapter 135-2 TABLE OF CONTENTSHOW TO READ symbols IN A HYDRAULIC SCHEMATIC .. 35-3 Introduction .. 35-3 Circuit Diagrams .. 35-3 Symbol Systems .. 35-3 Using Schematic symbols .. 35-3 Reservoirs .. 35-3 Lines, Tubes and Hoses .. 35-4 Crossing or Joining Lines .. 35-5 Pump symbols .. 35-5 Hydraulic Motor symbols .. 35-6 Cylinder symbols .. 35-6 Pressure Control symbols .. 35-7 Normally Closed .. 35-7 Normally Open .. 35-7 Relief Valve .. 35-7 Pressure Reducing Valve .. 35-7 Sequence Valve .. 35-8 Directional Control symbols .. 35-8 Simplified symbols .. 35-8 One Way Valve .. 35-8By Pass Valve .. 35-8 Composite symbols .. 35-8 One Way Valves .. 35-8 Two Position Valves .. 35-8 Three Position Valves .. 35-9 Actuating Controls .. 35-9 Flow Control symbols .. 35-9 Restrictors .. 35-9 Accessories .. 35-10 SIMPLE SCHEMATIC.

2 35-12 COMMON symbols .. 35-14 Lines and Line Functions .. 35-14 Mechanical Devices .. 35-14 Pumps and Motors .. 35-14 Reservoirs .. 35-15 Cylinders .. 35-15 Valves .. 35-15 Valve Actuators .. 35-17 Accessories .. 35-17 Template Name: SM_2_colTemplate Date: 1994_04_05 Alt= to hide template informationAlt+ to display template informationSECTION 35 - HOW TO READ symbols IN A HYDRAULIC SCHEMATIC - Chapter 1 35-3 HOW TO READ symbols IN A HYDRAULIC SCHEMATICI ntroductionAccurate diagrams of hydraulic circuits are essential to theman who must repair them. The diagram shows how thecomponents will interact. It shows the field technician how itworks, what each component should be doing and where theoil should be going so that he can diagnose and repair purpose of this Section is to show you how to find yourway around schematic circuit DiagramsThere are two types of circuit Cutaway Circuit Diagrams show the internal constructionof the components as well as the flow paths.

3 By usingcolors, shades or various patterns in the lines andpassages, they are able to show many differentconditions of flow and pressure. Cutaway diagrams takeconsiderably longer to produce because of Schematic Circuit Diagrams the shorthand system ofthe industry, are usually preferred for troubleshooting. Aschematic diagram is made up of simple geometricsymbols for the components and their controls SystemsThere are several systems of symbols used when makingschematic diagrams. They are as follows:I. S. O. = International Standards OrganizationA. N. S. I. = American National Standards InstituteA. S. A. = American Standards AssociationJ. I. C. = Joint Industry ConferenceA combination of these symbols are shown in this are differences between the symbols but there isenough similarity so that if you understand the symbols in thissection you will be able to interpret other symbols as Schematic SymbolsReservoirsA rectangle with the top removed represents a ventedreservoir.

4 A rectangle with the top in place represents apressurized are other schematic diagrams that show a slightlydifferent version of a pressurized reservoir, but the symbolsare similar and easily recognized. An oval with a short line ontop or a rectangle with curved sides represents a reservoirthat is connected to the reservoir usually are drawn from thetop, regardless of where the actual connection the hydraulic line terminates below the fluid level, it is drawnall the way to the bottom of the RESERVOIRPRESSURIZED RESERVOIR710L8C710L8 APRESSURIZED RESERVOIRPRESSURIZED RESERVOIR710L8 ERETURN LINE ABOVETHE OIL LEVEL710L8 FSUCTION LINE OR RETURN LINE BELOW THE OIL LEVELT emplate Name: SM_2_colTemplate Date: 1994_04_05 Alt= to hide template informationAlt+ to display template informationSECTION 35 - HOW TO READ symbols IN A HYDRAULIC SCHEMATIC - Chapter 1 35-4A hydraulic line connected to the bottom of the reservoir maybe drawn from the bottom of the symbol if the bottomconnection is essential to the systems the pump inlet must be charged or flooded with a positivehead of oil above the inlet port, we would position thereservoir symbol above the pump symbol, and draw thesuction line out of the bottom of the reservoir vehicle or system reservoir has at least two hydrauliclines connected to it, and some may have many more.

5 Oftenthe components that are connected to the reservoir arespread all over the schematic. Rather than having a lot ofconfusing lines all over the schematic, it is customary to drawindividual reservoir symbols close to the components. Thereservoir is usually the only component symbol pictured morethan , Tubes and HosesA hydraulic line, tube, hose or any conductor that carries thefluid between components is shown as a working line, such as an inlet pressure or return, is shownas a solid lines with arrows show direction of or control lines are broken into long lines for leakage oil are broken into short flexible line is shown as an arc between two dots and isalways represented by a solid often you will see an enclosure outline that indicatesthat there are several symbols that make up a componentassembly such as a valve or a valve stack. The enclosureoutline appears like a box and is broken with dashes on WITH SUCTION LINE ATTACHED AT THE BOTTOM749L8 BPUMP710L8H710L8 JOIL FLOWS ONE WAY ONLY710L8 KOIL CAN FLOW EITHER WAY710L8K710L8B710L8C710L8 DTemplate Name: SM_2_colTemplate Date: 1994_04_05 Alt= to hide template informationAlt+ to display template informationSECTION 35 - HOW TO READ symbols IN A HYDRAULIC SCHEMATIC - Chapter 1 35-5 Crossing or Joining LinesThe shortest distance between two components that areconnect is a straight line.

6 There are lines that cross otherlines but are not connected. There are several ways to showcrossing that are connected are shown with a dot that representsthe connection or shown as a tee connection. The dotconnection is the most commonly used when drawingschematic SymbolsThere are many basic pump designs. A simple fixeddisplacement pump is shown as a circle with a black trianglethat is pointing outwards. The black triangle is like an arrowhead and points in the direction that the oil will flow. If thepump is reversible or designed to pump in either direction, itwill have two black triangles in it and they will be oppositeeach variable displacement pump is designated by drawing anarrow through the pump symbol at 45 degrees. To indicate avariable displacement pressure compensated pump, a smallbox with an arrow in it will be added to the side of the the pump is controlled by a lever or a pedal, it will be shownon the side of the drive shaft is shown as two short parallel lines extendingfrom the side of the pump.

7 If a curved arrow is shown on thedrive shaft, it will indicate the direction of THAT ARE NOT CONNECTED711L8H710L8P710L8 NDOT CONNECTIONTEE CONNECTIONLINES THAT ARE CONNECTED711L8J711L8 KINLETOUTLETFIXED DISPLACEMENTFIXED DISPLACEMENTREVERSIBLE710L8T710L8sVARIAB LE DISPLACEMENTVARIABLE DISPLACEMENTPRESSURE COMPENSATED710L8U710L8 VLEVER CONTROLLEDPEDAL OR TREADLECONTROLLED711L8L710L8 WPUMP WITH DRIVE SHAFTPUMP WITH DRIVE SHAFTAND DIRECTIONAL ARROWT emplate Name: SM_2_colTemplate Date: 1994_04_05 Alt= to hide template informationAlt+ to display template informationSECTION 35 - HOW TO READ symbols IN A HYDRAULIC SCHEMATIC - Chapter 1 35-6 Hydraulic Motor SymbolsHydraulic motor symbols are circles with black triangles, butopposite a pump the triangles point inward to show the motoris a receiver of oil. One triangle is used in a nonreversiblemotor and two triangles are used for a reversible simple schematic diagram is shown with a hydraulic motorconnected to a hydraulic SymbolsA cylinder symbol is a simple rectangle representing thebarrel.

8 The piston and rod are represented by a tee that isinserted into the rectangle. The symbol can be drawn in the cylinder is single acting there is only one port shown onthe symbol. The port is shown on the end of the cylinder thatreceives pressurized fluid and the opposite end of thecylinder is left open. A double acting cylinder symbol has bothends closed and has two ports on the double rod end cylinder has a rod extending from each endof the cylinders have cushions built into them. The cushionslows down the movement of the piston as it nears the end ofits stroke. Cylinder cushions are shown as a smallerrectangle on the piston. If the cushion has an adjustableorifice, a slanted arrow is drawn at 45 degrees across MOTORREVERSIBLE MOTOR711L8 FPUMPMOTOR711L8 QTEERECTANGLE711L8Q711L8 PPORTSINGLE ACTING CYLINDERPORTSDOUBLE ACTING CYLINDER712L8 ADOUBLE ROD END CYLINDER749L8E730L8 ESINGLE ROD ENDFIXED CUSHION BOTH ENDSSINGLE ROD END ADJUSTABLECUSHION ROD END ONLYT emplate Name: SM_2_colTemplate Date: 1994_04_05 Alt= to hide template informationAlt+ to display template informationSECTION 35 - HOW TO READ symbols IN A HYDRAULIC SCHEMATIC - Chapter 1 35-7 Pressure Control SymbolsThe basic symbol is a square (which is called an envelope)with external port connections and an arrow inside to showthe oil passage and direction of flow.

9 Usually this type ofvalve operates by balancing the oil pressure against a spring,so a spring is shown on one side of the symbol and a pilotpressure line on the other ClosedA normally closed valve, such as a relief or sequence valve, isshown with the arrow offset from the ports and toward thepilot pressure line side of the square. The spring holds thevalve closed until the pilot line oil pressure is greater than thespring pressure. Mentally visualize a build up of pressure inthe pilot line and the square moving over, compressing thespring. The oil can now flow through the OpenA normally open valve is shown with the arrow connecting thetwo ports. It closes when pressure overcomes spring visualize a build up of pressure in the pilot line andthe square moving over, compressing the spring. The oil flowthrough the valve is now ValveA relief valve is shown as a normally closed symbolconnected between the pressure line and the reservoir. Theflow direction arrow points away from the pressure line portand toward the reservoir.

10 This shows very graphically how arelief valve operates. When pressure in the systemovercomes the valve spring, flow is from the pressure linethrough the relief valve to the Reducing ValveA pressure reducing valve is shown as a normally opensymbol in a pressure line. This valve works opposite of arelief valve, since it senses outlet pressure versus inletpressure. As the outlet pressure builds, it works against apredetermined spring force. As the spring force is overcome,flow through the valve is modulated or shut OFFSETFROM PORTSSPRINGOUTLETPILOTLINEARROW ALIGNEDWITH PORTSNORMALLY CLOSEDMENTALLY VISUALIZE SQUAREMOVING TOWARD SPRINGINLET712L8E712L8 DSPRINGOUTLETPILOTLINEMENTALLY VISUALIZE SQUAREMOVING TOWARD SPRINGNORMALLY OPENINLET712L8 FPRESSURE LINEPUMPRELIEF VALVE712L8 HHIGH PRESSURE INLETPILOTLINEREDUCED OUTLET PRESSUREDRAIN LINE TORESERVOIRT emplate Name: SM_2_colTemplate Date: 1994_04_05 Alt= to hide template informationAlt+ to display template informationSECTION 35 - HOW TO READ symbols IN A HYDRAULIC SCHEMATIC - Chapter 1 35-8 Sequence ValveThe normally closed symbol is also used for a sequencevalve.