DRESSTA TD-25M EXTRA, Service Manual

Page: 402 / 595

SECTION 10B
VALVES
Page 12
TD-25M EXTRA DRESSTA
PILOT PRESSURE VALVE
12. SPECIFICATIONS (Refer to Fig.’s. 10B.10 and 10B.11)
Spring Data
Adjusting Spool Spring (18):
Free Length .................................................................................................................. 57 [mm]
Test Length ............................................................................................................... 33.9 [mm]
Test Load .............................................................................................................. 356
±
18 [N]
Number of Coils ....................................................................................................................... 9
Controlling Spool Spring (3):
Free Length .................................................................................................................. 54 [mm]
Test Length ............................................................................................................... 28.6 [mm]
Test Load .................................................................................................................. 66
±
6 [N]
Number of Coils .................................................................................................................... 14
Relief Valve Spring (13):
Free Length ............................................................................................................... 21.7 [mm]
Test Length .................................................................................................................. 15 [mm]
Test Load .................................................................................................................. 67
±
3 [N]
Number of Coils .................................................................................................................... 10
13. DESCRIPTION (Refer to Fig.’s. 10B.10 and 10B.11)
The pilot pressure valve serves two basic function. The first is to supply a controlled pressurized oil
for blade and ripper pilot control valves. The second is to supply pilot pressure, to allow the blade
and/or ripper to be lowered in a dead engine situation.
When the engine is running, pilot pump flow enters port P . Spool (10) is a pressure regulator spool
set to regulate P pressure. P pressure enters the right end of the spool (10) through the pilot
orifice. This pressure moves spool to the left into the regulating spring (18). When sufficient
pressure is reached the spool moves to the left and allows oil to flow to tank through the
T port. In
the event of cold oil, a cold oil relief ball (12) is provided located in the center left end of the spool
(10). The cold oil relief limits pressure spikes at start up.
As P pressure builds it also pushes against the right end of the pilot supply spool (5). The right
hand spool diameter is less than the spool bore allowing pilot oil to flow past this clearance and
push the spool (5) to the left. The pilot supply spool (5) shifts to the left against its spring (3).
P
pressure is now open to PP . PP supplies pressure to the pilot valves for blade and ripper controls.
When the engine is off, both spools (5 and 10) shift to the right. In this condition the pilot supply
spool (5) directs oil from port
AI to PP . AI is connected to the shuttle network from the blade and
ripper cylinders. If a blade or ripper cylinder is off of the ground or the equipment is powered into
the ground then the trapped cylinder pressure is used through the shuttle network as pilot supply
pressure. The stored pressure from the cylinders enters port
AI and passes out PP to the pilot
valves.
Legend for Fig.’s. 10B.10 and 10B.11
1. Plug
2. O-Ring
3. Pilot Supply Spool Spring
4. Body
5. Pilot Supply Spool
6. O-Ring
7. Plug 8. Plug
9. O-Ring
10. Pressure Regulating Spool
11. Pin
12. Ball
13. Relief Valve Spring
14. Plug 15. O-Ring
16. Sleeve
17. Shim(s)
18. Regulating Spool Spring
19. O-Ring
20. Plug