AN ELECTRICALLY OPERATED HYDRAULIC CONTROL VALVE 727 



Therefore 



W = Pq - lOr/ - 7.i)q^ 



This expression can be differentiated and equated to zero to find the 

 point of maximum power. 



-^ = P - 20q - 22.8r/ =0 .,. 



dq (4) 



q = V'O.192 + 0.0439P - 0.439 



Substituting for q in ecjuation (2) we find that for maximum power 



p = 0.333 P + V2.15 + 0.49P - 1.46 (5) 



The normal supply pressure for the J-7 valve is 2,000 psi. Substituting 

 this value for P in (4) and (5) 



q = 8.95 cu in/sec 

 and 



p = 696 psi 



When these values are substituted in (3), we find 



TFmax = 11,700 in lb/sec 



= 1.77 horsepower 



Examination of the above equations will show that if the valve is 

 used with a very low supply pressure, the linear term in (1) is dominant. 

 In this case the maximum power output occurs when the pressure drop 

 is nearly one-half the supply pressure. In the case of a veiy high supply 

 pressure, the squared term is dominant and maximum power occurs 

 when the pressure drop across the valve approaches one-third the 

 supply pressure. 



The ratio between the electrical (juiescent input power to the coils 

 and the maximum hydraulic out power is about 1,600, or a power gain of 

 32 db. Based on maximum signal the gain is 29 db. All forces must be 

 precisely balanced and tolerances on parts be carefully controlled in 

 order to realize this amount of gain in a single stage mechanical device. 



DYNAMIC HYDRAULIC EFFECTS 



Examination of the illustrations of the valve will show that it is 

 statically balanced; i.e., pressure on any of the ports does not tend to 

 translate the plunger. However, the flow of oil through a valve of this 

 t,vpe produces a force on the plunger which tends to close the ports or 



