SERVICE VALVE CIRCUIT IN A HYDRAULIC EXCAVATOR.

摘要

The service valve circuit has a predetermined actuator operation valve and is connected for operating a special attachment. A confluence valve (17) which effects electromagnetic proportional flow-rate control is provided in a confluence circuit (16) that makes communication between the inflow circuits (3F,3R) of two variable pumps (2F,2R). There are further provided an electric switch (21) which turns on or off the confluence valve depending upon a required flow rate, and a volume (22) which adjusts the flow rate after passing the confluence valve over a range of a maximum of 1 to 2 pumps depending upon the required flow rate. The necessity of confluence for the flow rate required by the special attachment (e) or the confluent flow rate is set in advance to eliminate excess or lack of confluent flow rate. Therefore, there is no need of adjusting the flow rate depending on the number of revolutions of the engine.