COMPONENT OPERATION / Swing Device Relief Valve During starting or stopping swing operation, pressure in the swing circuit becomes high. The relief valve prevents the circuit pressure from rising higher than the set-pressure. Low Pressure Relief Operation (Shockless Function): 1. Pressure at port HP (swing circuit) is routed into oil chamber C (9) through orifice (2) in poppet (1). 2. When pressure oil in chamber C (9) flows to oil chamber A (8) through passage A (4) and to oil chamber B (7) through passage B (5). 3. As the receiving area in oil chamber B (7) is lar- ger than that in oil chamber A (8), piston (6) moves to the left. 4.
As long as piston (6) keeps moving, a pressure difference is developed between the front and the rear of poppet (1). When this pressure difference is increased more than the spring (3) force, pop- pet (1) is unseated and pressure oil flows to port LP from port HP. 5. When piston (6) is moved to full stroke, the pres- sure difference between the front and the rear of poppet (1) disappears and poppet (1) is seated. High Pressure Relief Operation (Overload Preven- tion): 1. After piston (6) is moved to full stroke, spring (3) is compressed and the circuit pressure becomes the relief set-pressure. 2.
If pressure at port HP increases more than the spring (3) set-pressure, poppet (1) is unseated and pressure oil flows to port LP from port HP. 3. When pressure at port HP is reduced to the specified level, poppet (1) is seated by the spring (3) force. 6 5 2 3 4 1 HP LP 8 9 7 T178-03-02-005 1 - Poppet 4 - Passage A 6 - Piston 8 - Oil Chamber A 2 - Orifice 5 - Passage B 7 - Oil Chamber B 9 - Oil Chamber C 3 - Spring T3-2-7