What is impulse circuit? Explain

the main valve using the impulse of an impulse valve. As shown in fig. in circuit has two valves ; main valve and impulse valve. Main valve is a single pilot operated spring return type 4/2 direction control valve. Impulse valve is palm button operated spring return type 3/2 direction control valve. In normal position of valves, the double acting cylinder is in retracted position. When the palm button of impulsive valve is pressed manually, compressed air flows to the pilot port of main valve. Hence the speed of main valve will be shifted to the second position. Double acting cylinder is extends.