C2 CRH Hydraulics (4G) 6/25/00 8:15 PM Page 1
Hydraulic System
Hydraulic System
Citation; CI; CII; CII-627
RH CROSSOVER BUS LH MAIN EXT BUS
LH ENGINE RH ENGINE
FIRE RELIEF AND FIRE
PUSH BLEED VALVE PUSH
HYD LOW
LEVEL
LEFT RIGHT
HYD LEVEL
ENGINE LO ENGINE
PUMP PUMP
FIREWALL RESERVOIR FIREWALL
SHUTOFF HYD FLOW SHUTOFF
LOW
BOOT STRAP LH RH
PRESSURE LINE
FLOW SWITCH
L HYD R HYD AND CHECK
PRESS LO PRESS LO VALVE
FILTER FILTER
1
PRESSURE
BYPASS SWITCH BYPASS
HYD PRESS
PRESSURE
ON RETURN
LANDING GEAR
DRAIN
HYD
PRESS ON
GROUND
SERVICE
CONNECTIONS
THRUST
REVERSERS CHECK
VALVE
SYSTEM
BYPASS RELIEF
VALVE VALVE
(NORMALLY 1,350 TO 1,500 PSI FILTER
SPEEDBRAKES OPEN)
L HYD R HYD
PRESS LO PRESS LO
SUPPLY
FLOW
RETURN DETECTOR
PRESSURE
1 UNITS 002 THROUGH 049 W/O SB550-29-5
Citation I/II/SII For training only 4G-1
May 1998
C2 CRH Hydraulics (4G) 6/25/00 8:15 PM Page 2
Hydraulic System
Citation SII
RH CROSSOVER BUS LH MAIN EXT BUS
LH ENGINE RH ENGINE
FIRE FIRE
PUSH PUSH
RELIEF AND
BLEED VALVE
HYD LOW
LEFT LEVEL RIGHT
ENGINE ENGINE
PUMP PUMP
FIREWALL RESERVOIR FIREWALL
SHUTOFF SHUTOFF
BOOT STRAP
PRESSURE LINE HYD FLOW FLOW SWITCH
LOW AND CHECK
VALVE
LH RH
FILTER
FILTER
BYPASS
BYPASS
CHECK PRESSURE
VALVE
PRESSURE RETURN
LANDING GEAR SWITCH DRAIN
HYD GROUND
PRESS ON SERVICE
THRUST CONNECTIONS
REVERSERS
CHECK
VALVE
SPEEDBRAKES
SYSTEM
BYPASS RELIEF VALVE
FLAPS 1,350 TO 1,500 PSI FILTER
VALVE
(NORMALLY
OPEN)
SUPPLY
RETURN
PRESSURE
4G-2 For training only Citation I/II/SII
May 1998
Hydraulic Systems
Hydraulic System
An open-center hydraulic system supplies 1,500 PSI pressure
for operation of the:
■ landing gear
■ thrust reversers (if installed)
■ speedbrakes
■ flaps (SII only).
With the engines running, each constant-displacement engine-
driven hydraulic pump draws fluid from the self-pressurizing
reservoir through an electrically operated firewall shutoff valve. If
reservoir fluid level drops to approximately the REFILL (0.2 gals)
mark, the reservoir’s low fluid level warning switch illuminates the
HYD LEVEL LO (C0; CI) or HYD LOW LEVEL annunciator.
From each pump, pressurized fluid flows through a filter before
reaching the check valve flow detector or flow switch check
valve. If a filter begins clogging, its bypass valve opens when a
pressure differential of 100 PSID is sensed between the input
and output side of the filter to route fluid around the filter.
On Citation/Citation I units 001 to 470 without SB 500-29-06
and Citation II units 002 to 049 and 064 without SB 550-29-
05, the check valve flow detector measures the differential pres-
sure between the two engine-driven pump outputs. If one pump
loses pressure or fails, pressure from the operating pump shifts
the flow detector switch to illuminate the HYD FLOW LOW or
HYD PRESS LO (C0; CI) annunciator. Actuating differential
pressure linearly varies with hydraulic system pressure. At 60
PSI, a differential pressure of 25 PSID illuminates the annunci-
ator. At 1,500 PSI, 170 PSID illuminates the annunciator. Check
valves prevent reverse flow from an operating pump to an inop-
erative pump.
Citation I/II/SII For training only 4G-3
June 1997
On Citation/Citation I units 471 and subsequent and previ-
ous aircraft with SB 500-29-6, Citation II units 002 to 049 and
064 with SB 550-29-05, and Citation II units 050 and subse-
quent, two flow switch check valves replace the check valve flow
detector. If a pump’s output drops to 1.33 GPM, the flow switch
closes to illuminate the HYD PRESS LO (C0; CI) or HYD FLOW
LOW annunciator. Check valves prevents reverse flow from an
operating pump to an inoperative pump.
After flowing through the check valve flow detector or flow switch
check valve, the two hydraulic pressure flows combine. During
no load conditions, the electrically operated bypass valve opens
so fluid flows continuously through the system. In this condition,
fluid returns to the hydraulic reservoir through a filter and check
valve.
During landing gear, thrust reverser (if installed), speedbrake, or
flap (SII only) operation, the bypass valve closes to provide pres-
sure to the using system. As system pressure builds, a relief
valve in-line with the bypass valve begins opening at 1,350 PSI
and fully opens at 1,500 PSI to maintain system pressure at
1,500 PSI. A pressure switch also closes with an increasing pres-
sure of 125 to 165 PSI to illuminate the HYD PRESS ON annun-
ciator to indicate normal system operation.
4G-4 For training only Citation I/II/SII
June 1997
Hydraulic System
Hydraulic System
Power Source L/R engine-driven hydraulic pumps
Distribution Hydraulic reservoir
L/R engine-driven hydraulic pumps
Hydraulic bypass valve
Hydraulic manifolds
Control LH/RH ENG FIRE PUSH switchlights
Landing gear handle
Speedbrake switch
Thrust reverser lever (optional)
Flap lever (SII)
Monitor LH/RH ENG FIRE PUSH switchlights
Annunciators
HYD PRESS ON
L/R HYD FLOW LO (CII 550 and sub; SII)
L/R HYD PRESS LO (CII 002 to 549)
SPEED BRAKE EXTEND
HYD LOW LEVEL
ARM/UNLOCK/DEPLOY T/R lights
Flap position indicator (SII)
Landing gear annunciators
Protection Circuit breakers
Pressure relief valve in reservoir low pressure
area opens to drain excess fluid when reservoir
fills to capacity
If one hydraulic pump fails, either pump can
operate the system (at a reduced rate)
Pushing the ENG FIRE PUSH switchlight closes
the corresponding hydraulic and fuel firewall
shutoff valves and TR isolation valve to stop
flammable liquid flow to the affected engine.
Flaps (blow up protection)
Refer to appropriate system section for protec-
tion in a specific aircraft system.
Citation I/II/SII For training only 4G-5
June 1997
4G-6 For training only Citation I/II/SII
June 1997
