CAP AS 3907628 - Caterpillar

Illustration 1 g03820515
Main control valve
(1) Inlet manifold
(2) Outlet manifold
(3) Unload valve (margin relief) Unload Valve (Margin Relief Valve - Closed)
Illustration 2 g02290560
Inlet manifold
(1) Inlet manifold
(3) Unload valve (margin relief)
(9) Pump supply
(12) Spring
(13) Orifice
(14) Load signal to pump control
(15) Spool
(16) Load sense from resolvers
(17) Passage Unload valve (margin relief) (3) is located in inlet manifold (1). Unload valve (3) allows hydraulic pump oil to be returned to the hydraulic tank when no hydraulic operation is being performed. Unload valve (margin relief) (3) also acts to maintain a maximum differential pressure between load signal from resolvers (16) and pump supply pressure (9).When a control valve is shifted from the NEUTRAL position, signal pressure works on the right end of spool (15). Spring (12) and load sense signal from resolvers (16) works against supply pressure (9).Unload Valve (Margin Relief Valve - Open)
Illustration 3 g02290673
Inlet manifold
(1) Inlet manifold
(3) Unload valve (margin relief)
(9) Pump supply
(12) Spring
(13) Orifice
(14) Load signal to pump control
(15) Spool
(16) Load sense from resolvers
(17) Passage When a control valve returns to the NEUTRAL position rapidly, load sense from resolvers (16) drops and supply pressure (9) moves spool (15) to the left to dump flow quickly to unload the pump.When all circuits are in the NEUTRAL position, the unload valve (margin relief) will cause the pump to be upstroked slightly to make up for the flow losses across unload valve (margin relief) (3).This action should improve system response when a control valve is first shifted.