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 TM 55-1925-273-10-1
0039 00
When the P1/P2/P1&P2 switch (figure 4, item 7) is in the P2 position, the switch is CLOSED between terminals 3
and 4 and OPEN between all other terminals. This supplies power to the pump 2 control relay (figure 4, item 13).
When the pump 2 control relay is powered, it CLOSES between terminals 9 and 5 and OPENS between terminals 9
and 1. This powers the pump 2 starter (figure 4, item 14) and the pump 2 RUNNING light (figure 4, item 15). When the
pump 2 control relay is not powered, it CLOSES between terminals 9 and 1 and OPENS between terminals 9 and 5. This
illuminates the number 2 pump READY light (figure 4, item 16) and secures power to the motor by opening the pump 2
starter.
When the P1/P2/P1&P2 switch (figure 4, item 7) is in the BOTH position, the switch is CLOSED between terminals 3, 4, 5,
and 6, and OPEN between terminals 1 and 2. This supplies power to both control relays (figure 4, items 9 and 13) and both
starters and lights are powered as described in the two preceding paragraphs.
The low level switch (figure 4, item 4) has both NO and NC contacts. The NO contacts supply power to the LOW OIL
LEVEL light (figure 4, item 17) while the NC contacts supply power to the high temperature cutoff switch (figure 4, item 7).
When the hydraulic fluid level in the reservoir drops below 98 gallons (371 liters), the NO contacts CLOSE, illuminating the
LOW OIL LEVEL light, and the NC contacts OPEN, securing power to the pump motors (figure 4, item 18).
TOWING MACHINE HYDRAULIC SYSTEM
The towing machine hydraulic system provides the primary power for the towing machines. In emergency situations, the
towing machine hydraulic system can also be aligned to supply hydraulic power to the central hydraulic system. The towing
machine hydraulic system is comprised of a diesel engine, a hydraulic pump, relief valves, a reservoir, a heat exchanger,
suction and return filters, and gauges and indicators. Each of these components, except the diesel engine, is described in the
paragraphs below. The diesel engine has its own technical manual (TM 55-1925-211-24). Following the description of the
components, the operation of the towing machine hydraulic system is described.
HYDRAULIC PUMP
A diesel engine-driven, dual vane, hydraulic pump (figure 5, sheet 1, item 1) provides the hydraulic power for the towing
machine hydraulic system. The hydraulic pump is actually two hydraulic pumps in one housing. One hydraulic pump
section is rated at 69 gal/min (261 L/min) at 1800 r/min while the other hydraulic pump section is rated at 38 gal/min (144
L/min) at 1800 r/min. This dual vane hydraulic pump arrangement permits the towing machine hydraulic system, when
properly configured, to supply the central hydraulic system and the towing machine hydraulic system simultaneously. Each
dual vane section is provided with its own check valve (figure 5, sheet 1, item 2). The check valves prevent one vane section
from backfeeding into the other during hydraulic pump operation.
0039 00-6
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