Bosch Rexroth A2FM series - Counterbalance valve BVD; Function; Permissible inlet flow or pressure when using DBV and BVD

Bosch Rexroth AG, RE 91001-01-X-B2/01.2016
24 A2FM for explosive areas | Axial piston fixed motor
Counterbalance valve BVD
Counterbalance valve BVD
Function
Counterbalance valves for drives and winches should
reduce the danger of overspeed and cavitation in open
circuits of axial piston motors. Cavitation occurs if, during
braking, when going downhill or during the load‑lowering
process, the motor speed is greater than it should be for
the given inlet flow and thus the inlet pressure collapses.
If the difference between inlet pressure and outlet pressure
falls below the value “opening end of piston in counterholding
valve” (see data sheet 95522), the brake piston moves into
the closed position.
The cross‑sectional area of the counterbalance valve return
duct is then reduced, creating a bottleneck in the return
flow of the hydraulic fluid. The pressure increases and
brakes the motor until the rotational speed of the motor is
again as it should be for the given inlet flow.
Note
▶ BVD available in sizes 28 to 180,
▶ The counterbalance valve must be ordered additionally.
We recommend ordering the counterbalance valve and
the motor as a set.
Order example: A2FM90/61W–AAB188J‑S +
BVD20W27L/41B‑V01K00D0800S00
▶ The counterbalance valve does not replace the mechani‑
cal service brake and parking brake.
▶ Counterbalance valves must be optimized during proto‑
type commissioning to prevent unacceptable operating
conditions and compliance with the specification must
be verified.
▶ Observe the detailed notes on the BVD counterbalance
valve contained in data sheet 95522
▶ For the design of the brake release valve, we must know
the following data for the mechanical holding brake:
– the pressure at the start of opening
– the volume of the brake spool between minimum
stroke (brake closed) and maximum stroke (brake
released with 21bar)
– the required closing time for a warm device
(oil viscosity approx.15mm
2
/s)
Permissible inlet flow or pressure when using DBV and BVD
Without valve Limited values when using DBV and BVD
Motor DBV
1)
BVD
2)
NG
p
nom
/p
max
[bar]
q
V
[l/min]
NG
p
nom
/p
max
[bar]
q
V
[l/min]
NG
p
nom
/p
max
[bar]
q
V
[l/min]
Code
28 400/450 176 16 350/420 100 20 350/420 100 188
32 201
45 255
56 280 22 240 220
63 315
80 360
90 405
107 427 178
125 500
107 427 32 400 25 320 188
125 500
160 577
180 648
1) Pressure relief valve
2) Counterbalance valve, dual action