Massey Ferguson 5400 - Issue 1.b
09D01.9
Trailer braking - Open centre
C . Operation, trailer brakes released
and partial braking
Trailer brakes released (Fig. 5)
The control channel Y is not under pressure (no action
on brake pedals).
Port B (supply to the trailer brake connector) is linked
to return channel R via the drilled hole f of the control
spool (2).
Flow QP from the pump flows via port P to the flow
control valve (1).
Flow QP - QX is directed towards port N (continuity
towards auxiliary spool valve and lift spool valve).
Partial flow QX (approximately 0.6 l/min) from port P is
directed towards the diaphragm (11), the reducer (9),
the drilled hole (10) and the control spool (2) to join
channel R.
Consequently, the pressure drop produced by the
reducer (9) maintains the flow control valve (1) in open
position a, the position in which it does not ensure a
regulating function.
Partial trailer braking
Start of the braking process (Fig. 6)
The piston (6) of the pilot flow housing (5) is pressure
fed by the tractor braking system (action on the brake
pedals).
The pressure arrives via port Y, the control spool
assembly (2) is then pushed to the left, obstructing the
drilled hole f and cutting off the communication of port
B (towards the trailer brake connector) with the return
channel R, then the link with the drilled hole (10).
The control spool (2) moves from position c to position
e. The QX control flow is cut and the flow control valve
(1) moves to position b (regulating position).
A constant flow QK flows from port P to port B
(towards the trailer brake connector) via the diaphragm
(11), the drilled hole (12), the channel (13) and the
non-return valve (3). The diaphragm (11) has a surface
area calculated in relation to the constant flow rate QK.
The residual flow QR goes via the flow control valve (1)
and is directed to port N (continuity with the auxiliary
spool valve and the lift spool valve).
The channel of port B (towards the trailer brake
connector) is placed under pressure and acts upon the
surface (14) of the control spool (2) against the pres-
sure on piston (6) by the tractor braking system.
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