Actuator control system

In a fluid control system for use in controlling the position of a follower such as a valve or the like comprising:

• a closed fluid manifold containing a fixed volume of fluid;
• a variable volume actuator connected in fluid communication to said manifold;
• means operably connected to said actuator for resiliently biasing said actuator;
• means coupling the follower to said actuator to selectively and precisely move said follower in response to changes in volume in said actuator whereby said follower is moved precisely as the fluid is added to or removed from said manifold;
• and
• a first fluid pump for selectively adding a set volume of fluid to said manifold thereby to move said follower a predetermined distance in one direction;
• a second fluid pump for selectively removing a set volume of fluid from said manifold thereby to move said follower a predetermined distance in the opposite direction;
• said first and second pumps each comprising a pump body defining a fixed volume chamber including a reciprocable plunger disposed therein, supply-discharge means for supplying fluid to said chamber and for discharging fluid from said chamber, reciprocating means for selectively reciprocating said plunger in said chamber to discharge a set volume of fluid from said pump body;
• and
• coupling means including said supply-discharge means coupling said first and second pumps to said manifold and for maintaining the set volume added to or removed from said manifold by first and second pumps respectively independent of the fluid pressure in said manifold.