4/16 Bosch Rexroth AG Hydraulics
B
Y
A
1
2
3
4
5
6
7
8
9
18
17
16
19 21
10
11
12
15
14
22
13
20
DRE(M); DRE(M)E RE 29276/03.11
Function, section
Type DREM…-6X/…YG24K4... (with check valve)
Valves of type DRE(M) are pilot controlled pressure reducing
valves. They are used for reducing an operating pressure.
These valves basically comprise of a pilot control valve (1)
with proportional solenoid (2), main valve (3) with main spool
insert (4), as well as an optional check valve (5).
Type DRE...
The pressure in channel A is set in a command value-depen-
dent form via the proportional solenoid (2).
In rest position - no pressure in channel B -, the spring (17) holds
the main spool (4) in its initial position. The connection from
channel B to A is closed. A start-up jump is thus suppressed.
Via the bore (6), the pressure in channel A acts on the sur-
face (7) of the main spool. The pilot oil is taken from channel
B and flows via the bore (8) to the constant flow controller (9)
keeping the pilot flow constant, independent of the pressure
drop between channel A and B. From the constant flow con-
troller (9), the pilot flow flows into the spring chamber (10),
through the bores (11) and (12) via the valve seat (13) into
the Y channel (14, 15, 16) and from there to the return.
The pressure required in channel A is preset at the related am-
plifier. The proportional solenoid moves the valve poppet (20)
in the direction of the valve seat (13) and limits the pressure
in the spring chamber (10) to the set value. If the pressure
in channel A is lower than the specified command value, the
higher pressure in the spring chamber (10) pushes the main
spool to the right. The connection from B to A is opened.
If the set pressure in A is achieved, the forces at the main
spool are balanced - the main spool is in control position.
PressureinchannelA•Spoolface(7)=
Pressureinthespringchamber(10)•Spoolface–Springforce(17)
If in a standing hydraulic fluid column (e.g. cylinder piston to
stop), the pressure in A is to be reduced, a lower command
value is (e.g.) specified at the control electronics and thus,
a lower pressure is pre-selected that is immediately applied
to the spring chamber (10). The higher pressure in A at the
face (7) of the main spool pushes the main spool against the
plug screw (18) to stop. The connection A to B is blocked and
A to Y is open. The force of spring (17) now acts against the
hydraulic force at the face (7) of the main spool. In this main
spool position, the hydraulic fluid can flow from channel A via
the control edge (19) to Y into the return.
If the pressure in A has been reduced to the pressure in the
spring chamber (10) plus ∆p from spring (17), the main spool
at the control edge A to Y closes the large control bores in
the socket.
The remaining differential pressure of approx. 10 bar to the
new command value pressure in A is only discharged via
the fine control bore (21). This results in a good transient re-
sponse without pressure undershoots.
For the free return flow from channel A to B, a check valve (5)
can optionally be installed. A part of this flow from channel
A simultaneously flows via the open control edge (19) of the
main spool from A to Y into the return.
Type DREM...
For hydraulic protection against an inadmissibly
high electric control current at the proportional
solenoid, which imperatively results in increased
pressures in port A, you can optionally install a
spring-loaded pressure relief valve as maximum
pressure limitation (22). The maximum pressure
limitation is pre-set referred to the relevant pres-
sure rating (table page 6).