LESSON 3
HYDRAULIC PRESSURE-LIMITING, CONTROLLING, AND SENSING DEVICES
STP Tasks: 552-758-1003
552-758-1006
552-758-1071
OVERVIEW
LESSON DESCRIPTION:
In this lesson you will learn the basic construction and operation of hydraulic pressure-limiting,
controlling, and sensing devices.
TERMINAL LEARNING OBJECTIVE:
ACTION:
After this lesson unit you will demonstrate knowledge of the basic construction and
operation of hydraulic controlling, pressure-limiting, and sensing devices.
CONDITIONS:
You will study the material in this lesson in a classroom environment or at home.
STANDARD:
You will correctly answer all the questions in the practice exercise before you
proceed to the subcourse examination.
REFERENCES: The material contained in this lesson was derived from the following publications.
AR 310-25, AR 310-50, FM 1-500, FM 1-509, TM 1-1500-204-23 Series, TM 55-
1510-Series, TM 55-1520-Series, and TM 4301A 05 0267 (Airforce).
INTRODUCTION
The hydraulic systems in modern Army aircraft operate at pressures up to 3,000 psi. These systems
must be protected against excessively high pressure that can cause seals and lines to fail. Pressure relief
valves are used to keep system pressure from exceeding a predetermined safe limit.
A complex hydraulic system can use any number of components: actuators, servos, irreversible valves,
selector valves, check valves, accumulators, hydraulic motors, etc. Each of these various components in
one hydraulic system can operate most efficiently at a different pressure. In systems having a single
hydraulic pump, pressure reducers are used to vary operating pressures to the different components.
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