Servovalves with integrated Electronics D791 and D792 Series

D791 and D792 SeriesThree stage servovalvesThe flow control servovalves D791and D792 Series are throttle valvesfor 3-way and preferably 4-wayapplications. These three stageservovalves have been especiallydeveloped for such demandingapplications where high flow ratesand at the same time extremedynamic performance requirementsmust be met. The design ofthese valves is based on the wellknown D079 Series. The integratedelectronics has beenreplaced by a new design applyingSMD technology. The valves areoffered with pilot valves of D761or D765 Series, optional standardresponse or high response versionsare available. Series D791 can deliverrated flow up to 250 l/min,Series D792 is available with ratedflow up to 1000 l/min.These valves are suitable for pressureor force control, position andvelocity control systems with highdynamic response requirements.Principle of operationAn electrical command signal (setpoint, input signal) is applied tothe integrated control amplifierwhich drives a current throughthe pilot valve coils. The pilot valveproduces differential pressure inits control ports. This pressuredifference results in a pilot flowwhich causes main spool displacement.The position transducer which isexcited via an oscillator measuresthe position of the main spool(actual value, position voltage).This signal then is demodulatedand fed back to the controlamplifier where it is comparedwith the command signal. Thecontrol amplifier drives the pilotvalve until the error betweencommand signal and feedbacksignal is zero. Thus, the position ofthe main spool is proportional tothe electrical command signal.Operational featuresr Electrical position feedback with pressure isolated positiontransducer (LVDT), no wearr Integrated SMD electronics with false polarity protectionr Optional external pilot supply and return connections via fifthand sixth port in valve bodyr Low threshold and hysteresis, excellent null stabilityr Preadjusted at factoryThe valves D791 and D792 Seriesdescribed in this catalogue havesuccessfully passed EMC testsrequired by EC Directive. Pleasetake notice of the respectivereferences in the electronicssection.The actual flow depends on theelectrical command signal andthe valve pressure drop, and maybe calculated using the squareroot function for a sharp-edgedorifice.The flow value Q calculated inthis way should not exceed anaverage flow velocity of 30 m/s inports P, A, B and T.Q = QNQ [l/min] = calculated flowQ N[l/min] = rated flowDp [bar] = actual valve pressuredropDp N[bar] = rated valve pressuredrop∆pIf large flow rates with high valvepressure drops are required, an∆p-2 QNappropriate higher pilot pressure p X ≥ 2,5⋅10⋅ ∆pAKhas to be chosen to overcome theflow forces. An approximate valuecan be calculated as follows:Q [l/min] = max. flowDp [bar] = valve pressure dropwith QA K[cm 2 ] = spool drive area[bar] = pilot pressurep XThe pilot pressure p Xhas to be atleast 15 bar above the returnpressure of the pilot stage.Our quality management systemis certified in accordance withDIN EN ISO 9001.This catalogue is for users withtechnical knowledge. To ensurethat all necessary characteristicsfor function and safety of thesystem are given, the user has tocheck the suitability of theproducts described here.In case of doubt please contactMOOG.2