major markings are for reading to the nearest 100 psi.
On these gauges, the numeral reading must be
multiplied by 1,000 to obtain the actual pressure in psi.
On gauges designed for a range of 0 to 2,000 psi,
the dial is calibrated with two major markings, the
numerals 1,000 and 2,000, and four intermediate
graduations for reading to the nearest 200 psi. A gauge
of this type is shown in figure 12-38.
Figure 12-39.--Gauge and pressure transmitter snubber.
GAUGE AND PRESSURE TRANSMITTER
SNUBBERS
EMERGENCY SYSTEMS
A gauge and pressure transmitter snubber is a
According to the military specifications discussed
hydraulic component located upstream of pressure
earlier in this chapter, an aircraft may have a standby
gauges and pressure transmitters. Its purpose is to
hydraulic system for emergency operation of the flight
damper out system pressure surges that could cause
controls, a compressed air (pneumatic) system for
possible damage to gauges and pressure transmitters.
operating the brakes, and a mechanically operated
Snubbers also prevent cockpit hydraulic indicators
system for lowering the landing gear. Inspection and
from oscillating and fluctuating, which makes accurate
maintenance of these systems are also your
reading of the gauge not only difficult but often
responsibility.
impossible. Without the use of a snubber, pressure
oscillations and other sudden pressure changes
On aircraft using a standby hydraulic system, the
existing in hydraulic systems could affect the delicate
emergency power system components will usually
internal mechanism of both gauges and transmitters.
include a reservoir, a pump, and an emergency control
This may cause either complete destruction of the
in the cockpit for switching from NORMAL to
gauge or transmitter or, often worse, partial damage,
EMERGENCY. Additional components will vary
resulting in false readings.
from aircraft to aircraft, depending on the method used
for driving the emergency pump.
The basic components of a snubber are the
housing, fitting assembly with a fixed orifice diameter,
The emergency system pump may be
and the pin and plunger assembly, as shown in figure
electric-motor driven, ram-air turbine driven, or it may
12-39. The snubbing action is obtained by metering
be hand operated. All three methods are currently used
fluid through the snubber. The fitting assembly orifice
on naval aircraft.
restricts the amount of fluid that flows to the gauge or
Regardless of the method used in driving the
pressure transmitter, thereby snubbing the force of a
p u m p , t h e e m e rg e n cy p ow e r s y s t e m m u s t b e
pressure surge. The pin is pushed and pulled through
completely independent of the normal power system.
the orifice of the fitting assembly by the plunger,
The normal and emergency lines are usually separated
keeping it clear and at a uniform size.
as far apart from each other as practicable. This is done
to reduce to a minimum the possibility of both lines
being ruptured by a single projectile.
The emergency reservoir is usually located as
remotely as practicable from the normal reservoir, but
it is generally possible to fill both reservoirs through a
common filler port. Usually, the filler port is located
on the normal system reservoir.
Operation of Typical Motor-Driven System
A schematic diagram of a typical electric
motor-driven emergency power system is shown in
figure 12-40. Individual components included in the
Figure 12-38.--Hydraulic pressure gauge.
system are a reservoir, a motor-driven pump, an
12-38
