LOWLANDER HD MK2 & WIDEBODY MANURE SPREADER – INSTRUCTION & SPARES MANUAL
Page 78
The RELSV has several functions, one of which is load sensing. The service pressure may be modified by the RELSV
based upon the weight sensed by the valve, as the RELSV is connected to the suspension via a vertical linkage (rod)
and its operating arm.
With tandem axled trailers it is common to be connected between the two axles by either telescopic pole or an angle
iron, in order to give the RELSV an average spring deflection. The angle iron is usually mounted using rubber bobbings
which absorb the movement between the axles. (With tri-axled trailers there is no need for an angle iron, as the RESLV
is generally connected directly to the centre axle.)
As weight is removed from the trailer its chassis raises, causing the RELSV’s operating arm to lower (rotate clockwise).
This has the effect of increasing the ratio between input and output pressures, thus reducing the braking pressures.
This new, modified pressure exits the RELSV at port 2, and signals the ABS modulator valve at its port 4 (just below
where the ABS sensors plug in). The ABS modulator then delivers this same pressure to all of the brake chambers,
unless a “wheel locking tendency” is detected. (A full description of ABS function won’t be given as all our machines
do not have ABS installed).
For the machines that the design does not allow for the
automatic weight sensing relay emergency valve (REV) and
the manual load proportion (LP) valve are used in place of
the RELSV to modify the service pressure based upon the 3
distinct set weight points of UNLADEN, HALF-LADEN and
FULLY-LADEN. These pressure points are set up by the
manufacturer.
The load positions, which have corresponding pictorial on
the LP valve, must be manually selected, before driving off,
using the lever to match the trailer loading scenario.
The brakes are applied in a controlled manner, as the pressure
builds up behind a rubber diaphragm housed inside the brake
chambers (11), and the output forces act on the slack adjusters (or
levers) increasing the torque entering the foundation brakes via the
camshafts.
As the driver releases the brakes, the control pressure drops. This results in the air within the brake chambers
returning back up to the ABS modulator, where it exhausts to atmosphere. Therefore, no pressure should be evident
at the brake chambers whilst the service brakes are not being applied. This can be checked using the test points (12),
one of which should be found in one of the spare ports in the brake chambers. (A test procedure is given later).
Test points can be added to any spare ports, and they come in two standard port sizes
being M16x1.5 and M22x1.5. They can also be used to drain the air tanks, should no drain
valve be fitted.
The two-line air braking system contains an “emergency” function, which is designed to
apply full tank pressure into the brake chambers (irrespective of load condition) should
the red susie be removed or become ruptured.
This function is part of the RELSV, where the pressure in the red line and tank are “compared”, and tank pressure is
delivered into the brake chambers, via the ABS modulator, should the red line pressure fall below 2.5 bar. This
happens automatically when the trailer’s red susie is removed during uncoupling.
This emergency function is not a substitute for using the trailer’s mechanical parking brake, as any air leak would
cause the brakes to release, and the trailer would be left without any effective parking brake.
To Next Page
Loading...