AN ELECTRICALLY OPERATED HYDRAULIC CONTROL VALVE 725 



type. The increase in working pressure is a great advantage for a guided 

 missile application because it results in lower weight, higher gain, and 

 faster response. For example, doubling the pressure permits actuating 

 cylinders of one half the size, an oil reservoir of one half the volume, and 

 an increase in both response and gain by a factor of about three. Such 

 features are sufficiently attractive to be worth a great deal of develop- 

 ment effort. However, reliable and stable operation can be achieved 

 under these high-gain conditions only if parasitic forces are kept ex- 

 tremely small. 



It was found that the relation between pressure drop and flow is not 

 so simple as one might expect from a sharp-edged, orifice-type control. 

 For large openings of the control orifice, the pressure losses in the fixed 

 orifices and passages of the valve body become an important factor. The 

 following law is an adequate representation of pressure-flow characteris- 

 tics : 



p = lOg + (^2 -f ^) q' (1) 



where 



p = pressure drop, psi 



q = rate of flow, cu in/sec 



X = valve opening, linear mils 



This equation was derived from test data from a model valve. These 

 data confirmed a computational analysis of the hydraulic circuit. Fig. 12 

 graphically illustrates the equation. It is a plot of flow against valve 

 position for various pressure drops. It will be noted that there is 0.001 

 inch difference between valve position and valve opening because of this 

 amount of overlap at the ports. 



Equation (1) provides the information necessary to compute the 

 maximum output power of the valve. If all the pressure drop were across 

 the control orifices, all the pressure would be utilized to accelerate the 

 oil at this point and only the square term of (1) would exist. If this were 

 the case, the maximum output power would occur when the pressure 

 drop across the valve was one-third of the supply pressure. The other 

 two-thirds of the pressure would be used to produce work in the C34inder. 

 If laminar flow existed throughout the valve the square term would drop 

 out, leaving a linear equation. If this were the case, maximum power 

 would occur with the total pressure equallv divided between valve and 

 load. \Vhen both the linear the square terms are present, maximum 

 power will occur when the pressure drop across the valve is somewhere 



