Allied Hy-Ram HR270, Safety, Operation And Maintenance Instructions, Page: 54 / 60

Allied Construction Products, LLC www.alliedcp.com
SOMM577202_14mar
43
14.0 Technical Information
14.1 Definition of Terms
For the purposes of this manual, Hydraulic Flow,
Operating Pressure, Dynamic Relief Pressure and
Static Relief Pressure 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. “Minimum flow” describes
the least amount required while permitting
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
attachment. Flow parameters for attachments
such as Breakers are represented by a minimum-
to-maximum range.

Operating Pressure – A measure of the
hydraulic oil pressure (values given in PSI / BAR)
taken in the breaker’s supply line during
operation. Pressure parameters for attachments
such as Breakers, are represented by a
minimum-to-maximum 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 (200 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