Pressure relief valve
|
DBD
9/12
RD 25710, edition: 2016-07,
Bosch Rexroth AG
Safety instructions:
Type-examination tested safety valves type DBD
1)
▶ Before ordering a type-examination tested safety valve,
it must be observed that for the desired
response
pressure
p
, the maximum admissible
flow
q
Vmax
of the
safety valve must be larger than the maximum possible
flow of the system/accumulator to be secured.
According to the
Pressure Equipment Directive
2014/68/EU
, the increase in the system pressure due to
the flow must not exceed 10% of the set response
pressure (see component marking on page 8).
▶ The maximum admissible flow
q
Vmax
stated in the
component marking must not be exceeded.
▶ Discharge lines of safety valves must end in a risk-free
manner. The accumulation of fluids in the discharge
system must
not
be possible (see data sheet
AD2000 A2).
It is imperative to observe the application notes!
▶ In the plant, the response pressure specified in the
component marking is set with a flow of 1 l/min.
▶ The maximum flow stated in the component marking
applies for applications without counter pressure in the
discharge line (port T).
▶ By removing the lead seal at the safety valve, the
approval according to the Pressure Equipment Directive
becomes void!
▶ Basically, the requirements of the Pressure Equipment
Directive and of data sheet AD2000 A2 have to be
observed!
▶ It is recommended to secure type-examination tested
safety valves against inadmissible disassembly by
means of wiring and sealing with the housing/block
(bore available in the adjustment type).
Notice:
The system pressure increases by the counter pressure
in the discharge line (port T) due to the increasing flow.
(Observe the data sheet AD 2000 A 2, point 6.3!)
To ensure that this increase in system pressure caused by
the flow does not exceed the value of 10% of the set
response pressure, the admissible flow has to be reduced
dependent on the counter pressure in the discharge line
(port T) (see diagrams on page 9 and 10).
1)
Component series 1X according to the Pressure Equipment
Directive 2014/68/EU
Characteristic curves:
Counter pressure in the discharge line
In principle, the valve should be operated without counter
pressure in the discharge line, if possible. In case of
counter pressure in the discharge line, the maximum flow
possible is reduced. There is a relationship between
maximum counter pressure
p
T
in the discharge line and
flow
q
V
, which can be seen from the following
characteristic curve. Characteristic curves for intermediate
values of the response pressure which are not listed must
be determined by means of interpolation.
When the flow approaches zero, the maximum counter
pressure
p
T
is in each case 10% of the response pressure.
With increasing flow, the maximum counter pressure
p
T
decreases.
Interpolation of intermediate values from the diagram
1. At the axis
p
T
, mark 1/10 of the value of
p
A
.
2. Determine the next lower and the next higher
characteristic curve for this point. The point marked at
p
T
divides the section between lower and higher
characteristic curve on the
p
T
axis with a certain
percentage.
3. At the
q
Vmax
axis, divide the section between next lower
and next higher characteristic curve in the same
percentage as the section at the
p
T
axis. From the zero-
crossing on the
q
Vmax
axis determined in that way, draw
a straight line to the value on the
p
T
axis marked before.
4. Mark the system flow to be secured at the
q
Vmax
axis.
5. Read off the maximum counter pressure for this value
using the line at the
p
T
axis drawn before.
