jcb JS200 Service Manual page 275

Section E
31 - 7
Operation (continued)
* Load Holding Valve
* 1. Boom Section (refer to fig. 5, 6, 14) .
When the boom is lowered (Fig 6), the spool moves to the right as shown. At the same time, when P
holding valve piston D pushes the poppet B, connecting Dr port. The oil in the load holding valve poppet (P) spring cavity C is
released to the Dr port and poppet (P) opens.
2. Dipper Section (refer to fig. 9, 10, 15) .
*
During dipper crowd, the spool moves to the left as shown and the passage W from the load holding valve is connected to the
tank passage. The oil in the load holding valve poppet spring cavity A side creates differential pressure between the ram port B
and is released, opening the poppet. (Fig 10)
During dipper dumping, the spool moves to the left as shown (Fig. 9) and when oil flows to passage V (Fig. 15-2) it resists the
*
force of the spring D of the load holding valve poppet (U), pushes open the poppet and flows to A
When the spool is in neutral, the pressure from the cylinder port B is fed through hole C, goes around the poppet spring cavity
side A and, by the spring D force, seats the poppet.
Regenerative Circuit (Refer to Fig. 10, 16)
For this valve, a regenerative circuit is built into the dipper I spool.
During dipper crowd, (Fig. 10, 16), with the ram extending, the bottom side oil is insufficient and the pressure of passage U
becomes lower than that of passage V. The pressure of passage V overcomes the spring C force and part of the oil which flows
from the cylinder port D through the spool neck to the tank pushes open the poppet (Y) and by flowing through the constriction
(Z), raises the pressure of passage U and prevents cavitation.
9803/6400
Hydraulics
Control Valve JS200/JS240
Section E
31 - 7
is pressurised, the load
LC
port.
L4
Issue 2*