AN ELECTRICALLY OPERATED HYDRAULIC CONTROL VALVE 731 



in the plunger is reduced and a curved surface added to direct the flow 

 parallel to the valve axis. This configuration reduces the dynamic force 

 for two reasons. First, the amount of radial surface exposed to the low 

 pressure is greatly reduced. Second, the cur\'ed surface acts much like a 

 turbine blade in deflecting the oil stream and developing a reaction thrust 

 that opposes the Bernoulli force. The reaction thrust increases as the 

 longitudinal component of the high-velocity jet is increased. If the jet 

 can be turned to become parallel with the longitudinal axis without 

 appreciable loss in velocity, the maximum reaction thrust is obtained. In 

 this case, the force is equal to the increase in the longitudinal component 

 of momentum over the conditions of the free jet as shown in Fig. 1.']. 



F = ^ (1 - cos 69°) (8) 



where 



F = force, lb 



p = fluid density, Ib/cu in 



q = flow rate, cu in/sec 



V = fluid \'elocity, ft/sec 



g = acceleration of gravity, ft/sec* 



Calculations of the dynamic forces in accordance with the above reason- 

 ing yield only approximate results because the local velocities and 

 their gradients are functions of passage shape as well as pressure drops. 

 The contour of the plunger grooves were computed for use in the first 

 experimental model, whose design was intended to alleviate this problem. 

 Refinements to the initial model were made by cut-and-try methods. 

 Since the forces involved are relatively small, and their magnitude 

 changes so rapidly with plunger position, specialized measuring instru- 

 ments had to be developed whose sensitivity was high and compliance 

 very low. 



A certain amount of contradiction was apparent in the force measure- 

 ments made. To better understand the action of the oil within the valve, 

 a transparent replica of the cross section of a yaXxe port was used under 

 a microscope. Figs. 15, 16, and 17 are illustrations of typical tests. Fig. 15 

 is two views of an early type valve with rectangular ports at different 

 openings and pressure drops. The arrows indicate a portion of the 

 cylindrical sliding surface separating the plunger and body. The lower 

 left shadow is the sharp corner at the edge of the annulus in the plunger. 



