Electrohydraulic Valves A Technical Look - Moog, Inc.

1 Electrohydraulic Technical LookMoog Inc. was the founded in 1951 by William C. Moog, inventor of the Electrohydraulic creation heralded a new era in precision control. Italso spurred the growth of Moog to become the world leaderin design and manufacture of Electrohydraulic control productsand systems. During the past decade the company has extendedits control expertise into Servo-Proportional Valves , ServoElectronics and Direct Drive products provide precise control of position, velocityand force so important to the proper operation of a widevariety of industrial example: Moog Inc. Servoactuators accurately control the thicknessof steel slabs in continuous casting operations. Moog Inc. ServoJet Servo-Proportional Valves control both velocity and pressure in plastic injection molding machinesand wall thickness in plastic blow molding machines.

2 Moog Inc. Direct Drive Valves control the thickness of paperon new state of the art paper of these applications involves precise control of a com-plex structure, which in most cases is subject to varying loadsthat can adversely affect performance. Moog products overcomethe structural and load variation effects through the principlesof feedback. Moog transducers measure the output, which couldbe position, velocity, pressure or acceleration and send signalsto the machine signals are compared with thedesired sensing and correcting on a continuous basisresults in optimum system ASSISTANCEThe information contained in this catalog presents typicalproducts offered by Moog; our true expertise is helping you solveyour motion control problems.

3 Our engineering staff is availableto assist you in your efforts to accurately and precisely controlposition, velocity or force in your specific application. Often timesthis results in designing a customized design and product, specifi-cally suited to your need. Moog s capabilities in this respect areunmatched in industry. So call us and let us know how we you will be glad you to our policy of continual research and improvement,we reserve the right to change specifications in this catalog without VALVE APPLICATIONS2 ApplicationsAPPLICATIONSI ndustrialBasic Metal ProcessingBlow/Injection Molding Earthquake SimulationEntertainment EquipmentFatigue TestingFlight SimulationGas, Steam & Hydro TurbinesMachine ToolsManufacturing SystemsMaterial TestingPaper MachinesRoboticsRubber ProcessingSaw & Veneer Mill MachinesSteel & Aluminum Mill EquipmentMobile/MarineActive SuspensionForestry MachinesMining MachineryRailroadsRemote ControlSeismic ExplorationShipsSubmersiblesVibration ReductionApplicationsApplicationsELECTRO HYDRAULIC VALVE SELECTION GUIDEFREQUENCY OF SERVOVALVE 90 PHASE LAG Hz(SMALL TO MEDIUM SIGNAL RESPONSE)FLOW WITH 1000 psi SERVOVALVE DROP - gpm 400 HRG761/D765 STDD765 SHR79-200 HR79-20079-100D68XD664G631 Moog offers the broadest line of Electrohydraulic Valves on the market today.

4 Our product line consists of Servovalves(Mechanical and Electric Feedback versions) and Servo-Proportional Valves (Direct Drive and Two Stage ServoJet versions). Servovalves typically utilize a ISO10372 mountingpattern and are nearly always zero lapped or axis cut (nomechanical deadband). Servo-Proportional Valves utilize anISO4401 mounting pattern and may have a mechanical of the proper valve involves understanding theperformance requirements of your chart belowattempts to categorize the more popular Moog valve series bytwo very important selection criteria flow and dynamic VALVESERVOJET SERVOVALVES electionSelectionSelection3 DETERMINE THE REQUIRED VALVE FLOW RATE ANDFREQUENCY RESPONSEa) In order to compensate for unknown forces, size the actuator area to produce a stall force 30% greater than the desired force to the supply pressure to the NFPA standard cylinder bore and rod sizes and select the area closest to the result of the above )

5 From the maximum required loaded velocity and the actuator area from the above calculation, determine the valve loaded flow and the load pressure ) Compute the no-load ) Determine the valve rated flow at 1,000 psi valve drop for Servovalves and 150 psi valve drop for Proportional by 10% for ) For open-loop control, a valve having a 90 phase lag at 3 Hzor higher, should be ) For closed loop control of systems utilizing electrical feedback,calculate the load natural frequency using the equations in thisbrochure under Load Resonant Frequency . The optimum perfor-mance will be achieved if the Servovalve 90 phase point exceedsthe load resonant frequency by a factor of three or ) With a calculated flow rate and frequency response, referencethe Valve Selection Table on page 3 for valve selection.

6 AnyServovalve that has equal or higher flow capacity andresponse will be an acceptable choice. However, it is prefer-able not to oversize the Servovalve flow capacity as this willneedlessly reduce system ) Consult individual data sheets for complete valve performance PARAMETERS FOR SERVO OR PROPORTIONALVALVE SELECTIONS upply PressureServovalve and ServoJet Valves are intended to operate withconstant supply pressure and require continuous pilot flow tomaintain the hydraulic bridge supply pressure shouldbe set so that the pressure drop across the valve is equal to one-third of the supply flow capacity should include thecontinuous pilot flow to maintain the hydraulic bridge Drive Valve performance is constant no matter what thesupply , they are good in systems with fluctuatingsupply Moog Inc.

7 Valves will operate at supply pressuresfrom 200 to 3,000 psi. Optional Valves for 50 to 5,000 psioperation are available. Refer to individual valve of FluidMoog Inc. Valves operate most effectively with fluids that exhibita viscosity of 60 to 450 SUS at 100 F. Due to the Servovalve oper-ating range of -40 F to 275 F, care should be taken to assure fluidviscosity does not exceed 6,000 SUS. In addition, fluid cleanliness isof prime importance and should be maintained at ISO DIS 4406 Code 16/13 max, 14/11 recommended. Consult the Moog and Valve Series catalogs for compatibility with material used in the constructionof Valves must be considered. Contact the factory for RequirementsIn most applications, a portion of the available supply pressuremust be used to overcome some force.

8 Since valve flow ratings aregiven as a function of pressure drop across the valve, total forcerequirements must be known in order to determine what portionof the supply pressure is available to be dropped across the force is the summation of all individual forces that occur dueto the static or dynamic configuration of the Due to a LoadForce due to a load FLcan be an aiding or resistive component,depending upon the load s orientation and direction of has to be taken when computing FLto ensure theproper external friction coefficients and resolved forces are FRA =PSwhere:A = actuator area (in2)FR= force required to movethe load (lb) at maximumvelocity, ref. key parametersPS= supply pressure (psi)QL= AXLwhere:QL= loaded flow (in3/sec)XL= maximum required loaded velocity (in/sec)FRPL=Awhere:PL= load pressure drop (psi)PSQNL= QLPS-PLwhere:QNL= no-load flow (in2/sec)QNLQR= ( ) to gpm conversionwhere:QR= Servovalve rated flow (gpm) at 1,000 psi drop or Proportional Valve rated flow at 150 psi drop10% padFR= FL+ FA+ FE+ FSwhere.

9 FR= total required force (lb)FL= force due to load (lb)FA= force due to acceleration (lb)FE= force due to external disturbance (lb)FS= force due to seal friction (lb)HOW TO SELECT A SERVO OR PROPORTIONAL VALVEWLRESISTIVELOADPISTONEXTENDINGWLAID INGLOADPISTONRETRACTING4 Force Due to AccelerationThe forces required to overcome inertia become very largein high speed applications and are critical to valve MaVMAXa =TaWL+WPM = gForce Due to External DisturbancesThese forces can be generated by constant or Due to Seal FrictionMost Valves are used on applications which employ some sortof motion motion devices usually utilize elastomerseals to separate the various pressure frictionbetween these seals and the moving parts acts as opposing practice involves setting seal friction at 10% ofthe maximum force available, unless absolute values are = mWLcos (lb)

10 WLFL WLFLFL = mWLWL = weight of load (lb)m = coefficient of frictionFECONSTANTEXTERNALCOMPRESSIONOR TENSILEFORCEPRESSINTERMITTENTDEFORMATION FORCEFE where:M = mass (lb - sec2/in)a = acceleration (in/sec2)WP= weight of piston (lb)VMAX= maximum velocity (in/sec)Ta= time period foracceleration (sec)WL= weight of loadFS= FMAX where:FMAX= stall force (lb)Dynamic ResponseA valve s dynamic response can be easily determined by measuringthe frequency at which the phase lag between the input currentand output flow reaches 90 (90 phase lag point).The frequencyresponse will vary with input signal amplitude, supply pressure,and fluid , comparisons must use consis-tent recommended peak-to-peak signal amplitude is 80%of the valve rated current.