Terex TA30 - Air Pressure Protection Valve

Section 250-0290
SM 1938 4-00
1
BRAKING SYSTEM - Air Pressure Protection Valve
Fig. 1 - Pressure Protection Valve Installation
1 - Pressure Protection Valve
2 - Mounting Bracket
3 - Lockwasher
4 - Nut
5 - Elbow - 90°
6 - Adaptor
7 - Tee Piece
8 - Pressure Switch
9 - Adaptor
10 - Elbow - 90°
11 - Adaptor
12 - Tee Piece
13 - Pressure Switch
SM - 2447
DESCRIPTION
The 4 way pressure protection valve can be identified
as item 9 in Section 250-0000, AIR BRAKING
SYSTEM SCHEMATIC.
Mounted off the front left hand side of the tractor
frame, adjacent to the primary air tank, the pressure
protection valve is located in the air compressor and
air drier delivery line, immediately prior to the air tanks.
The pressure protection valve supplies air to all three
tanks for the service brakes, secondary braking and
accessory air devices. If a pressure drop or failure is
experienced in one circuit of the air system, the valve
closes, isolating the circuit, enabling the compressor to
continue to recharge the unfailed circuits.
The pressure protection valve also has a built in safety
function which does not allow the spring brakes to be
released, unless there is sufficient pressure in the
service brake system to at least provide the prescribed
residual braking performance of the laden vehicle by
application of the service brakes.
Fig. 2 - Pressure Protection Valve Schematic
SM - 2448
OPERATION
Numbers in parenthesis refer to Fig. 2.
The pressure protection valve takes air from the
compressor and supplies it to the separate circuits of
the vehicle's brake and auxiliary systems.
The valve has elements which feed circuits '21' and
'22' which, when the vehicle system is being charged,
are designed to remain closed until the supply
pressure to them reaches 6.0 to 6.3 bar, after which
they open to supply the appropriate circuit and then
remain in the open state allowing air to flow back
through the element ('Feedback') thereby equalising
the pressures in circuits '21' and '22'.
This feedback will continue unless the supply pressure
falls to 4 bar minimum at which point the valve element
will close preventing any further feedback ('Limited
Feedback').
Air flows from circuits '21' and '22' through non-return
valves to the elements feeding circuits '23' and '24',
both designed to open at 6.0 to 6.3 bar. Circuit '24' is
fed through a feedback element the same as circuits
13
16
17
18
14
15
10
11,12
9
8
7
6
1
2
4
3
5
22
1
24 23
21
Rear
Tank
Primary
Tank
Auxiliary
Front
Tank
Park/Emergency
Brake Control
Primary
Tank
Front
Brake
Tank
Rear
Brake
Tank and
Treadle
Valve
Courtesy of Machine.Market