AN ELECTRICALLY OPERATED HYDRAULIC CONTROL VALVE 721 



sections limit the flux and tend to reduce the pull for short gaps so that 

 the centering spring can be a simple linear member and still not lose 

 control when the armature is near the fixed pole face. The flat surfaces 

 on the neck permit the use of wrenches for assembly. Placing the necks 

 on the moving pole pieces further reduces the mass of the armature as- 

 sembly. 



To illustrate the saturation action, Fig. 9 shows the pull of one of the 

 magnets plotted against gap length for quiescent and maximum current. 

 The shim line and curves from a solenoid without a saturation neck also 



3600 



3400 



3200 



3000 



2800 



2600 



2400 



2200 „ 

 CO 



5 

 < 



2000 cc 

 O 



z 



1800 _i 



1600 



1400 



1200 



1000 



800 



600 



400 

 200 



3 

 Q. 



24 22 20 IB 16 14 12 10 8 



GAP IN LINEAR MILS 



Fig. 9 — Magnetic pull curves for a coil of the J-7 valve. 



