Allied AR110C, Safety, Operation And Maintenance, Page: 50 / 60

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14.0 Technical Information
14.1 Definition of Terms
Work tools, such as Breakers, are designed to
operate within prescribed limits. For the purposes of
this manual, terms are defined as follows:

Range – A range is represented by two values
'V1 – V2' and generally means the lowest-to-
highest limit of a device that will allow it to
adequately respond. The term “minimum flow”
describes the least amount required that permits
continuous operation that is both satisfactory and
efficient.

Hydraulic Flow – A measure of the volume of oil
(values given in GPM / LPM) necessary for the
safe and efficient operation of the Allied
equipment. Breakers are designed to operate
within the prescribed minimum and maximum
flow range.

Operating Pressure – A measure of the
hydraulic oil pressure (values given in PSI / BAR)
taken while the work tool is in operation. Work
tools, such as Breakers, are designed to operate
within the prescribed minimum and maximum
pressure range.

Relief Valve – An adjustable, spring-loaded
valve that opens when a preset pressure value is
reached. A relief valve is safety device, used to
protect the circuit against hydraulic overload.
Relief valves vary in design. Pilot controlled
pressure relief valves are designed so that the
relief pressure increases very little as the flow
through the valve increases. For Breaker
applications, they are recommended over direct
acting type relief valves.

Dynamic Relief Pressure – Also referred to as
“Cracking Pressure”. The pressure measured at
the moment the oil pressure exceeds the preset
value of the relief valve and the spool “cracks”
open.

Static Relief Pressure – Also referred to as “Full
Relief Pressure”. The pressure measured at the
moment the relief valve has opened fully and all
oil is by-passed.

Opening Curve – The opening curve is the rise
of pressure between dynamic (first open) and
static (all of the oil flow is bypassed). The
dynamic pressure is always less than the static
pressure. A relief valve adjusted to a dynamic
pressure of 3000 psi (207 Bar) will crack open
when the preset point is reached, but fully opens
at a higher pressure.
Fig. 14-1: Flow-Pressure Diagram
FLOW
PRESSURE
Hydraulic
Flow Range
Operating
Pressure
Range
Static Relief Pressure
(No flow to attachment)
Dynamic Relief Pressure
(Relief valve cracks open)
Attachment
Operational
Range
Operating Pressure
Opening
Curve